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• Writing more efficient xquery code (avoiding redundant iteration)

  - by Coquelicot

  Here's a simplified version of a problem I'm working on: I have a bunch of xml data that encodes information about people. Each person is uniquely identified by an 'id' attribute, but they may go by many names. For example, in one document, I might find <person id=1>Paul Mcartney</person> <person id=2>Ringo Starr</person> And in another I might find: <person id=1>Sir Paul McCartney</person> <person id=2>Richard Starkey</person> I want to use xquery to produce a new document that lists every name associated with a given id. i.e.: <person id=1> <name>Paul McCartney</name> <name>Sir Paul McCartney</name> <name>James Paul McCartney</name> </person> <person id=2> ... </person> The way I'm doing this now in xquery is something like this (pseudocode-esque): let $ids := distinct-terms( [all the id attributes on people] ) for $id in $ids return <person id={$id}> { for $unique-name in distinct-values ( for $name in ( [all names] ) where $name/@id=$id return $name ) return <name>{$unique-name}</name> } </person> The problem is that this is really slow. I imagine the bottleneck is the innermost loop, which executes once for every id (of which there are about 1200). I'm dealing with a fair bit of data (300 MB, spread over about 800 xml files), so even a single execution of the query in the inner loop takes about 12 seconds, which means that repeating it 1200 times will take about 4 hours (which might be optimistic - the process has been running for 3 hours so far). Not only is it slow, it's using a whole lot of virtual memory. I'm using Saxon, and I had to set java's maximum heap size to 10 GB (!) to avoid getting out of memory errors, and it's currently using 6 GB of physical memory. So here's how I'd really like to do this (in Pythonic pseudocode): persons = {} for id in ids: person[id] = set() for person in all_the_people_in_my_xml_document: persons[person.id].add(person.name) There, I just did it in linear time, with only one sweep of the xml document. Now, is there some way to do something similar in xquery? Surely if I can imagine it, a reasonable programming language should be able to do it (he said quixotically). The problem, I suppose, is that unlike Python, xquery doesn't (as far as I know) have anything like an associative array. Is there some clever way around this? Failing that, is there something better than xquery that I might use to accomplish my goal? Because really, the computational resources I'm throwing at this relatively simple problem are kind of ridiculous.

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• "Row not found or changed" Problem

  - by winston schröder

  Hi there, I'm working on a SQL CE Database and get into the "Row nor found or changed" exception. The exception only occurs when I try to update. On the first Run after the insert it shows up a MemberChangeConflict which says, that my Column Created_at has in all three values (current, original, database) the same. But in a second attempt it doesn't appear anymore. The DataContext is instanciated on Startup and freed on Exit of my Local(!) Application. I use a sqlmetal generated mapping and code file. In the map I added some Associations and set the timemstamp columns UpdateCheck property to Always while all other have the setting never. The Timestamp Column is marked as isVersion="true", the Id Column as Primary Key. Since I don't dispose the datacontext I expected to be using implicit transaction. When I run the SubmitChanges Method within a TransactionScope. Can anyone tell me how I can update the timestamp within the code ? I know about the Problems one has to deal with if you dispose the datacontext. So I decided not to do this since I use a Single User Local DB Cache File. (I did already use a version where I disposed the datacontext after every usage, but this version had a real bad performance and error rate, so I decided to choose the other variant.) LibDB.Client.Vehicles tmp = null; try { tmp = e.Parameter as LibDB.Client.Vehicles; if (tmp == null) return; if (!this._dc.Vehicles.Contains(tmp)) { this._dc.Vehicles.Attach(tmp); } this.ShowChangesReport(this._dc.GetChangeSet()); using (TransactionScope ts = new TransactionScope()) { try { this._dc.SubmitChanges(); ts.Complete(); } catch (ChangeConflictException cce) { Console.WriteLine("Optimistic concurrency error."); Console.WriteLine(cce.Message); Console.ReadLine(); foreach (ObjectChangeConflict occ in this._dc.ChangeConflicts) { MetaTable metatable = this._dc.Mapping.GetTable(occ.Object.GetType()); LibDB.Client.Vehicles entityInConflict = (LibDB.Client.Vehicles)occ.Object; Console.WriteLine("Table name: {0}", metatable.TableName); Console.Write("Vin: "); Console.WriteLine(entityInConflict.Vin); foreach (MemberChangeConflict mcc in occ.MemberConflicts) { object currVal = mcc.CurrentValue; object origVal = mcc.OriginalValue; object databaseVal = mcc.DatabaseValue; MemberInfo mi = mcc.Member; Console.WriteLine("Member: {0}", mi.Name); Console.WriteLine("current value: {0}", currVal); Console.WriteLine("original value: {0}", origVal); Console.WriteLine("database value: {0}", databaseVal); } throw cce; } } catch (Exception ex) { this.ShowChangeConflicts(this._dc.ChangeConflicts); Console.WriteLine(ex.Message); } } this.ShowChangesReport(this._dc.GetChangeSet());

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• Forms bound to updateable ADO recordsets are not updateable when the source includes a JOIN

  - by Art

  I'm developing an application in Access 2007. It uses an .accdb front end connecting to an SQL Server 2005 backend. I use forms that are bound to ADO recordsets at runtime. For the sake of efficiency, the recordsets usually contain only one record, and are queried out on the server: Public Sub SetUpFormRecordset(cn As ADODB.Connection, rstIn As ADODB.Recordset, rstSource As String) Dim cmd As ADODB.Command Dim I As Long Set cmd = New ADODB.Command cn.Errors.Clear ' Recordsets based on command object Execute method are Read Only! With cmd Set .ActiveConnection = cn .CommandType = adCmdText .CommandText = rstSource End With With rstIn .CursorType = adOpenKeyset .LockType = adLockPessimistic 'Check the locktype after opening; optimistic locking is worthless on a bound End With ' form, and ADO might open optimistically without firing an error! rstIn.Open cmd, , adOpenKeyset, adLockPessimistic 'This should run the query on the server and return an updatable recordset With cn If .Errors.Count <> 0 Then For Each errADO In .Errors Call HandleADOErrors(.Errors(I)) I = I + 1 Next errADO End If End With End Sub rstSource (the string containg the TSQL on which the recordset is based) is assembled by the calling routine, in this case from the Open event of the form being bound: Private Sub Form_Open(Cancel As Integer) Dim rst As ADODB.Recordset Dim strSource As String, DefaultSource as String Dim lngID As Long lngID = Forms!MyParent.CurrentID strSource = "SELECT TOP (100) PERCENT dbo.Customers.CustomerID, dbo.Customers.LegacyID, dbo.Customers.Active, dbo.Customers.TypeID, dbo.Customers.Category, " & _ "dbo.Customers.Source, dbo.Customers.CustomerName, dbo.Customers.CustAddrID, dbo.Customers.Email, dbo.Customers.TaxExempt, dbo.Customers.SalesTaxCode, " & _ "dbo.Customers.SalesTax2Code, dbo.Customers.CreditLimit, dbo.Customers.CreationDate, dbo.Customers.FirstOrder, dbo.Customers.LastOrder, " & _ "dbo.Customers.nOrders, dbo.Customers.Concurrency, dbo.Customers.LegacyLN, dbo.Addresses.AddrType, dbo.Addresses.AddrLine1, dbo.Addresses.AddrLine2, " & _ "dbo.Addresses.City, dbo.Addresses.State, dbo.Addresses.Country, dbo.Addresses.PostalCode, dbo.Addresses.PhoneLandline, dbo.Addresses.Concurrency " & _ "FROM dbo.Customers INNER JOIN " & _ "dbo.Addresses ON dbo.Customers.CustAddrID = dbo.Addresses.AddrID " strSource = strSource & "WHERE dbo.Customers.CustomerID= " & lngID With Me 'Default is Set up for editing one record If Not Nz(.RecordSource, vbNullString) = vbNullString Then If .Dirty Then .Dirty = False 'Save any changes on the form .RecordSource = vbNullString End If If rst Is Nothing Then 'Might not be first time through DefaultSource = .RecordSource Else rst.Close Set rst = Nothing End If End With Set rst = New ADODB.Recordset Call setupformrecordset(dbconn, rst, strSource) 'dbconn is a global variable With Me Set .Recordset = rst End With End Sub The recordset that is returned from setupformrecordset is fully updateable, and its .Supports property shows this. It can be edited and updated in code. The entire form, however, is read only, even though it's .AllowEdits and .AllowAdditions properties are both true. Even the fields from the right hand side (the 'many' side) cannot be edited. Removing the INNER JOIN clause from the TSQL (restricting strSource to one table) makes the form fully editable. I've verified that the TSQL includes priimary key fields from both tables, and each table includes a timestamp field for concurrency. I tried changing the .CursorType and .CursorLocation properties of the recordset to no avail. What am I doing wrong?

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• Evidence-Based-Scheduling - are estimations only as accurate as the work-plan they're based on?

  - by Assaf Lavie

  I've been using FogBugz's Evidence Based Scheduling (for the uninitiated, Joel explains) for a while now and there's an inherent problem I can't seem to work around. The system is good at telling me the probability that a given project will be delivered at some date, given the detailed list of tasks that comprise the project. However, it does not take into account the fact that during development additional tasks always pop up. Now, there's the garbage-can approach of creating a generic task/scheduled-item for "last minute hacks" or "integration tasks", or what have you, but that clearly goes against the idea of aggregating the estimates of many small cases. It's often the case that during the development stage of a project you realize that there's a whole area your planning didn't cover, because, well, that's the nature of developing stuff that hasn't been developed before. So now your ~3 month project may very well turn into a 6 month project, but not because your estimations were off (you could be the best estimator in the world, for those task the comprised your initial work plan); rather because you ended up adding a whole bunch of new tasks that weren't there to begin with. EBS doesn't help you with that. It could, theoretically (I guess). It could, perhaps, measure the amount of work you add to a project over time and take that into consideration when estimating the time remaining on a given project. Just a thought. In other words, EBS works on a task basis, but not on a project/release basis - but the latter is what's important. It's what your boss typically cares about - delivery date, not the time it takes to finish each task along the way, and not the time it would have taken, if your planning was perfect. So the question is (yes, there's a question here, don't close it): What's your methodology when it comes to using EBS in FogBugz and how do you solve the problem above, which seems to be a main cause of schedule delays and mispredictions? Edit Some more thoughts after reading a few answers: If it comes down to having to choose which delivery date you're comfortable presenting to your higher-ups by squinting at the delivery-probability graph and choosing 80%, or 95%, or 60% (based on what, exactly?) then we've resorted to plain old buffering/factoring of our estimates. In which case, couldn't we have skipped the meticulous case by case hour-sized estimation effort step? By forcing ourselves to break down tasks that take more than a day into smaller chunks of work haven't we just deluded ourselves into thinking our planning is as tight and thorough as it could be? People may be consistently bad estimators that do not even learn from their past mistakes. In that respect, having an EBS system is certainly better than not having one. But what can we do about the fact that we're not that good in planning as well? I'm not sure it's a problem that can be solved by a similar system. Our estimates are wrong because of tendencies to be overly optimistic/pessimistic about certain tasks, and because of neglect to account for systematic delays (e.g. sick days, major bug crisis) - and usually not because we lack knowledge about the work that needs to be done. Our planning, on the other hand, is often incomplete because we simply don't have enough knowledge in this early stage; and I don't see how an EBS-like system could fill that gap. So we're back to methodology. We need to find a way to accommodate bad or incomplete work plans that's better than voodoo-multiplication.

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• C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

  - by James Michael Hare

  So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton, the basic Design Pattern is that a Singleton class is one where there is only ever one instance of the class created.  This means that constructors must be private to avoid users creating their own instances, and a static property (or method in languages without properties) is defined that returns a single static instance. 1: public class Singleton 2: { 3: // the single instance is defined in a static field 4: private static readonly Singleton _instance = new Singleton(); 5:  6: // constructor private so users can't instantiate on their own 7: private Singleton() 8: { 9: } 10:  11: // read-only property that returns the static field 12: public static Singleton Instance 13: { 14: get 15: { 16: return _instance; 17: } 18: } 19: } This is the most basic singleton, notice the key features: Static readonly field that contains the one and only instance. Constructor is private so it can only be called by the class itself. Static property that returns the single instance. Looks like it satisfies, right?  There's just one (potential) problem.  C# gives you no guarantee of when the static field _instance will be created.  This is because the C# standard simply states that classes (which are marked in the IL as BeforeFieldInit) can have their static fields initialized any time before the field is accessed.  This means that they may be initialized on first use, they may be initialized at some other time before, you can't be sure when. So what if you want to guarantee your instance is truly lazy.  That is, that it is only created on first call to Instance?  Well, there's a few ways to do this.  First we'll show the old ways, and then talk about how .Net 4.0's new System.Lazy<T> type can help make the lazy-Singleton cleaner. Obviously, we could take on the lazy construction ourselves, but being that our Singleton may be accessed by many different threads, we'd need to lock it down. 1: public class LazySingleton1 2: { 3: // lock for thread-safety laziness 4: private static readonly object _mutex = new object(); 5:  6: // static field to hold single instance 7: private static LazySingleton1 _instance = null; 8:  9: // property that does some locking and then creates on first call 10: public static LazySingleton1 Instance 11: { 12: get 13: { 14: if (_instance == null) 15: { 16: lock (_mutex) 17: { 18: if (_instance == null) 19: { 20: _instance = new LazySingleton1(); 21: } 22: } 23: } 24:  25: return _instance; 26: } 27: } 28:  29: private LazySingleton1() 30: { 31: } 32: } This is a standard double-check algorithm so that you don't lock if the instance has already been created.  However, because it's possible two threads can go through the first if at the same time the first time back in, you need to check again after the lock is acquired to avoid creating two instances. Pretty straightforward, but ugly as all heck.  Well, you could also take advantage of the C# standard's BeforeFieldInit and define your class with a static constructor.  It need not have a body, just the presence of the static constructor will remove the BeforeFieldInit attribute on the class and guarantee that no fields are initialized until the first static field, property, or method is called.   1: public class LazySingleton2 2: { 3: // because of the static constructor, this won't get created until first use 4: private static readonly LazySingleton2 _instance = new LazySingleton2(); 5:  6: // Returns the singleton instance using lazy-instantiation 7: public static LazySingleton2 Instance 8: { 9: get { return _instance; } 10: } 11:  12: // private to prevent direct instantiation 13: private LazySingleton2() 14: { 15: } 16:  17: // removes BeforeFieldInit on class so static fields not 18: // initialized before they are used 19: static LazySingleton2() 20: { 21: } 22: } Now, while this works perfectly, I hate it.  Why?  Because it's relying on a non-obvious trick of the IL to guarantee laziness.  Just looking at this code, you'd have no idea that it's doing what it's doing.  Worse yet, you may decide that the empty static constructor serves no purpose and delete it (which removes your lazy guarantee).  Worse-worse yet, they may alter the rules around BeforeFieldInit in the future which could change this. So, what do I propose instead?  .Net 4.0 adds the System.Lazy type which guarantees thread-safe lazy-construction.  Using System.Lazy<T>, we get: 1: public class LazySingleton3 2: { 3: // static holder for instance, need to use lambda to construct since constructor private 4: private static readonly Lazy<LazySingleton3> _instance 5: = new Lazy<LazySingleton3>(() => new LazySingleton3()); 6:  7: // private to prevent direct instantiation. 8: private LazySingleton3() 9: { 10: } 11:  12: // accessor for instance 13: public static LazySingleton3 Instance 14: { 15: get 16: { 17: return _instance.Value; 18: } 19: } 20: } Note, you need your lambda to call the private constructor as Lazy's default constructor can only call public constructors of the type passed in (which we can't have by definition of a Singleton).  But, because the lambda is defined inside our type, it has access to the private members so it's perfect. Note how the Lazy<T> makes it obvious what you're doing (lazy construction), instead of relying on an IL generation side-effect.  This way, it's more maintainable.  Lazy<T> has many other uses as well, obviously, but I really love how elegant and readable it makes the lazy Singleton.

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• mysql not starting

  - by Eiriks

  I have a server running on rackspace.com, it been running for about a year (collecting data for a project) and no problems. Now it seems mysql froze (could not connect either through ssh command line, remote app (sequel pro) or web (pages using the db just froze). I got a bit eager to fix this quick and rebooted the virtual server, running ubuntu 10.10. It is a small virtual LAMP server (10gig storage - I'm only using 1, 256mb ram -has not been a problem). Now after the reboot, I cannot get mysql to start again. service mysql status mysql stop/waiting I believe this just means mysql is not running. How do I get this running again? service mysql start start: Job failed to start No. Just typing 'mysql' gives: mysql ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111) There is a .sock file in this folder, 'ls -l' gives: srwxrwxrwx 1 mysql mysql 0 2012-12-01 17:20 mysqld.sock From googleing this for a while now, I see that many talk about the logfile and my.cnf. Logs Not sure witch ones I should look at. This log-file is empty: 'var/log/mysql/error.log', so is the 'var/log/mysql.err' and 'var/log/mysql.log'. my.cnf is located in '/etc/mysql' and looks like this. Can't see anything clearly wrong with it either. # # The MySQL database server configuration file. # # You can copy this to one of: # - "/etc/mysql/my.cnf" to set global options, # - "~/.my.cnf" to set user-specific options. # # One can use all long options that the program supports. # Run program with --help to get a list of available options and with # --print-defaults to see which it would actually understand and use. # # For explanations see # http://dev.mysql.com/doc/mysql/en/server-system-variables.html # This will be passed to all mysql clients # It has been reported that passwords should be enclosed with ticks/quotes # escpecially if they contain "#" chars... # Remember to edit /etc/mysql/debian.cnf when changing the socket location. [client] port = 3306 socket = /var/run/mysqld/mysqld.sock # Here is entries for some specific programs # The following values assume you have at least 32M ram # This was formally known as [safe_mysqld]. Both versions are currently parsed. [mysqld_safe] socket = /var/run/mysqld/mysqld.sock nice = 0 [mysqld] # # * Basic Settings # # # * IMPORTANT # If you make changes to these settings and your system uses apparmor, you may # also need to also adjust /etc/apparmor.d/usr.sbin.mysqld. # user = mysql socket = /var/run/mysqld/mysqld.sock port = 3306 basedir = /usr datadir = /var/lib/mysql tmpdir = /tmp skip-external-locking # # Instead of skip-networking the default is now to listen only on # localhost which is more compatible and is not less secure. bind-address = 127.0.0.1 # # * Fine Tuning # key_buffer = 16M max_allowed_packet = 16M thread_stack = 192K thread_cache_size = 8 # This replaces the startup script and checks MyISAM tables if needed # the first time they are touched myisam-recover = BACKUP #max_connections = 100 #table_cache = 64 #thread_concurrency = 10 # # * Query Cache Configuration # query_cache_limit = 1M query_cache_size = 16M # # * Logging and Replication # # Both location gets rotated by the cronjob. # Be aware that this log type is a performance killer. # As of 5.1 you can enable the log at runtime! #general_log_file = /var/log/mysql/mysql.log #general_log = 1 log_error = /var/log/mysql/error.log # Here you can see queries with especially long duration #log_slow_queries = /var/log/mysql/mysql-slow.log #long_query_time = 2 #log-queries-not-using-indexes # # The following can be used as easy to replay backup logs or for replication. # note: if you are setting up a replication slave, see README.Debian about # other settings you may need to change. #server-id = 1 #log_bin = /var/log/mysql/mysql-bin.log expire_logs_days = 10 max_binlog_size = 100M #binlog_do_db = include_database_name #binlog_ignore_db = include_database_name # # * InnoDB # # InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/. # Read the manual for more InnoDB related options. There are many! # # * Security Features # # Read the manual, too, if you want chroot! # chroot = /var/lib/mysql/ # # For generating SSL certificates I recommend the OpenSSL GUI "tinyca". # # ssl-ca=/etc/mysql/cacert.pem # ssl-cert=/etc/mysql/server-cert.pem # ssl-key=/etc/mysql/server-key.pem [mysqldump] quick quote-names max_allowed_packet = 16M [mysql] #no-auto-rehash # faster start of mysql but no tab completition [isamchk] key_buffer = 16M # # * IMPORTANT: Additional settings that can override those from this file! # The files must end with '.cnf', otherwise they'll be ignored. # !includedir /etc/mysql/conf.d/ I need the data in the database (so i'd like to avoid reinstalling), and I need it back up running again. All hint, tips and solutions are welcomed and appreciated.

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• Computer Networks UNISA - Chap 12 &ndash; Networking Security

  - by MarkPearl

  After reading this section you should be able to Identify security risks in LANs and WANs and design security policies that minimize risks Explain how physical security contributes to network security Discuss hardware and design based security techniques Understand methods of encryption such as SSL and IPSec, that can secure data in storage and in transit Describe how popular authentication protocols such as RADIUS< TACACS,Kerberos, PAP, CHAP, and MS-CHAP function Use network operating system techniques to provide basic security Understand wireless security protocols such as WEP, WPA and 802.11i Security Audits Before spending time and money on network security, examine your networks security risks – rate and prioritize risks. Different organizations have different levels of network security requirements. Security Risks Not all security breaches result from a manipulation of network technology – there are human factors that can play a role as well. The following categories are areas of considerations… Risks associated with People Risks associated with Transmission and Hardware Risks associated with Protocols and Software Risks associated with Internet Access An effective security policy A security policy identifies your security goals, risks, levels of authority, designated security coordinator and team members, responsibilities for each team member, and responsibilities for each employee. In addition it specifies how to address security breaches. It should not state exactly which hardware, software, architecture, or protocols will be used to ensure security, nor how hardware or software will be installed and configured. A security policy must address an organizations specific risks. to understand your risks, you should conduct a security audit that identifies vulnerabilities and rates both the severity of each threat and its likelihood of occurring. Security Policy Content Security policy content should… Policies for each category of security Explain to users what they can and cannot do and how these measures protect the networks security Should define what confidential means to the organization Response Policy A security policy should provide for a planned response in the event of a security breach. The response policy should identify the members of a response team, all of whom should clearly understand the the security policy, risks, and measures in place. Some of the roles concerned could include… Dispatcher – the person on call who first notices the breach Manager – the person who coordinates the resources necessary to solve the problem Technical Support Specialist – the person who focuses on solving the problem Public relations specialist – the person who acts as the official spokesperson for the organization Physical Security An important element in network security is restricting physical access to its components. There are various techniques for this including locking doors, security people at access points etc. You should identify the following… Which rooms contain critical systems or data and must be secured Through what means might intruders gain access to these rooms How and to what extent are authorized personnel granted access to these rooms Are authentication methods such as ID cards easy to forge etc. Security in Network Design The optimal way to prevent external security breaches from affecting you LAN is not to connect your LAN to the outside world at all. The next best protection is to restrict access at every point where your LAN connects to the rest of the world. Router Access List – can be used to filter or decline access to a portion of a network for certain devices. Intrusion Detection and Prevention While denying someone access to a section of the network is good, it is better to be able to detect when an attempt has been made and notify security personnel. This can be done using IDS (intrusion detection system) software. One drawback of IDS software is it can detect false positives – i.e. an authorized person who has forgotten his password attempts to logon. Firewalls A firewall is a specialized device, or a computer installed with specialized software, that selectively filters or blocks traffic between networks. A firewall typically involves a combination of hardware and software and may reside between two interconnected private networks. The simplest form of a firewall is a packet filtering firewall, which is a router that examines the header of every packet of data it receives to determine whether that type of packet is authorized to continue to its destination or not. Firewalls can block traffic in and out of a LAN. NOS (Network Operating System) Security Regardless of the operating system, generally every network administrator can implement basic security by restricting what users are authorized to do on a network. Some of the restrictions include things related to Logons – place, time of day, total time logged in, etc Passwords – length, characters used, etc Encryption Encryption is the use of an algorithm to scramble data into a format that can be read only by reversing the algorithm. The purpose of encryption is to keep information private. Many forms of encryption exist and new ways of cracking encryption are continually being invented. The following are some categories of encryption… Key Encryption PGP (Pretty Good Privacy) SSL (Secure Sockets Layer) SSH (Secure Shell) SCP (Secure CoPy) SFTP (Secure File Transfer Protocol) IPSec (Internet Protocol Security) For a detailed explanation on each section refer to pages 596 to 604 of textbook Authentication Protocols Authentication protocols are the rules that computers follow to accomplish authentication. Several types exist and the following are some of the common authentication protocols… RADIUS and TACACS PAP (Password Authentication Protocol) CHAP and MS-CHAP EAP (Extensible Authentication Protocol) 802.1x (EAPoL) Kerberos Wireless Network Security Wireless transmissions are particularly susceptible to eavesdropping. The following are two wireless network security protocols WEP WPA

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• SQL SERVER – LCK_M_XXX – Wait Type – Day 15 of 28

  - by pinaldave

  Locking is a mechanism used by the SQL Server Database Engine to synchronize access by multiple users to the same piece of data, at the same time. In simpler words, it maintains the integrity of data by protecting (or preventing) access to the database object. From Book On-Line: LCK_M_BU Occurs when a task is waiting to acquire a Bulk Update (BU) lock. LCK_M_IS Occurs when a task is waiting to acquire an Intent Shared (IS) lock. LCK_M_IU Occurs when a task is waiting to acquire an Intent Update (IU) lock. LCK_M_IX Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock. LCK_M_S Occurs when a task is waiting to acquire a Shared lock. LCK_M_SCH_M Occurs when a task is waiting to acquire a Schema Modify lock. LCK_M_SCH_S Occurs when a task is waiting to acquire a Schema Share lock. LCK_M_SIU Occurs when a task is waiting to acquire a Shared With Intent Update lock. LCK_M_SIX Occurs when a task is waiting to acquire a Shared With Intent Exclusive lock. LCK_M_U Occurs when a task is waiting to acquire an Update lock. LCK_M_UIX Occurs when a task is waiting to acquire an Update With Intent Exclusive lock. LCK_M_X Occurs when a task is waiting to acquire an Exclusive lock. LCK_M_XXX Explanation: I think the explanation of this wait type is the simplest. When any task is waiting to acquire lock on any resource, this particular wait type occurs. The common reason for the task to be waiting to put lock on the resource is that the resource is already locked and some other operations may be going on within it. This wait also indicates that resources are not available or are occupied at the moment due to some reasons. There is a good chance that the waiting queries start to time out if this wait type is very high. Client application may degrade the performance as well. You can use various methods to find blocking queries: EXEC sp_who2 SQL SERVER – Quickest Way to Identify Blocking Query and Resolution – Dirty Solution DMV – sys.dm_tran_locks DMV – sys.dm_os_waiting_tasks Reducing LCK_M_XXX wait: Check the Explicit Transactions. If transactions are very long, this wait type can start building up because of other waiting transactions. Keep the transactions small. Serialization Isolation can build up this wait type. If that is an acceptable isolation for your business, this wait type may be natural. The default isolation of SQL Server is ‘Read Committed’. One of my clients has changed their isolation to “Read Uncommitted”. I strongly discourage the use of this because this will probably lead to having lots of dirty data in the database. Identify blocking queries mentioned using various methods described above, and then optimize them. Partition can be one of the options to consider because this will allow transactions to execute concurrently on different partitions. If there are runaway queries, use timeout. (Please discuss this solution with your database architect first as timeout can work against you). Check if there is no memory and IO-related issue using the following counters: Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Read all the post in the Wait Types and Queue series. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• SQL SERVER – Beginning of SQL Server Architecture – Terminology – Guest Post

  - by pinaldave

  SQL Server Architecture is a very deep subject. Covering it in a single post is an almost impossible task. However, this subject is very popular topic among beginners and advanced users.  I have requested my friend Anil Kumar who is expert in SQL Domain to help me write  a simple post about Beginning SQL Server Architecture. As stated earlier this subject is very deep subject and in this first article series he has covered basic terminologies. In future article he will explore the subject further down. Anil Kumar Yadav is Trainer, SQL Domain, Koenig Solutions. Koenig is a premier IT training firm that provides several IT certifications, such as Oracle 11g, Server+, RHCA, SQL Server Training, Prince2 Foundation etc. In this Article we will discuss about MS SQL Server architecture. The major components of SQL Server are: Relational Engine Storage Engine SQL OS Now we will discuss and understand each one of them. 1) Relational Engine: Also called as the query processor, Relational Engine includes the components of SQL Server that determine what your query exactly needs to do and the best way to do it. It manages the execution of queries as it requests data from the storage engine and processes the results returned. Different Tasks of Relational Engine: Query Processing Memory Management Thread and Task Management Buffer Management Distributed Query Processing 2) Storage Engine: Storage Engine is responsible for storage and retrieval of the data on to the storage system (Disk, SAN etc.). to understand more, let’s focus on the following diagram. When we talk about any database in SQL server, there are 2 types of files that are created at the disk level – Data file and Log file. Data file physically stores the data in data pages. Log files that are also known as write ahead logs, are used for storing transactions performed on the database. Let’s understand data file and log file in more details: Data File: Data File stores data in the form of Data Page (8KB) and these data pages are logically organized in extents. Extents: Extents are logical units in the database. They are a combination of 8 data pages i.e. 64 KB forms an extent. Extents can be of two types, Mixed and Uniform. Mixed extents hold different types of pages like index, System, Object data etc. On the other hand, Uniform extents are dedicated to only one type. Pages: As we should know what type of data pages can be stored in SQL Server, below mentioned are some of them: Data Page: It holds the data entered by the user but not the data which is of type text, ntext, nvarchar(max), varchar(max), varbinary(max), image and xml data. Index: It stores the index entries. Text/Image: It stores LOB ( Large Object data) like text, ntext, varchar(max), nvarchar(max),  varbinary(max), image and xml data. GAM & SGAM (Global Allocation Map & Shared Global Allocation Map): They are used for saving information related to the allocation of extents. PFS (Page Free Space): Information related to page allocation and unused space available on pages. IAM (Index Allocation Map): Information pertaining to extents that are used by a table or index per allocation unit. BCM (Bulk Changed Map): Keeps information about the extents changed in a Bulk Operation. DCM (Differential Change Map): This is the information of extents that have modified since the last BACKUP DATABASE statement as per allocation unit. Log File: It also known as write ahead log. It stores modification to the database (DML and DDL). Sufficient information is logged to be able to: Roll back transactions if requested Recover the database in case of failure Write Ahead Logging is used to create log entries Transaction logs are written in chronological order in a circular way Truncation policy for logs is based on the recovery model SQL OS: This lies between the host machine (Windows OS) and SQL Server. All the activities performed on database engine are taken care of by SQL OS. It is a highly configurable operating system with powerful API (application programming interface), enabling automatic locality and advanced parallelism. SQL OS provides various operating system services, such as memory management deals with buffer pool, log buffer and deadlock detection using the blocking and locking structure. Other services include exception handling, hosting for external components like Common Language Runtime, CLR etc. I guess this brief article gives you an idea about the various terminologies used related to SQL Server Architecture. In future articles we will explore them further. Guest Author  The author of the article is Anil Kumar Yadav is Trainer, SQL Domain, Koenig Solutions. Koenig is a premier IT training firm that provides several IT certifications, such as Oracle 11g, Server+, RHCA, SQL Server Training, Prince2 Foundation etc. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Security, SQL Server, SQL Tips and Tricks, SQL Training, T SQL, Technology

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• MySQL Connector/Net 6.4.6 Maintenance Release has been released

  - by fernando

  MySQL Connector/Net 6.4.6, a new version of the all-managed .NET driver for MySQL has been released.  This is a maintenance release and is recommended for use in production environments. It is appropriate for use with MySQL server versions 5.0-5.6. This is intended to be the final release for Connector/NET 6.4. It is now available in source and binary form from http://dev.mysql.com/downloads/connector/net/#downloads and mirror sites (note that not all mirror sites may be up to date at this point-if you can't find this version on some mirror, please try again later or choose another download site.) The 6.4.6 version of MySQL Connector/Net brings the following fixes: - Fix for List.Contains generates a bunch of ORs instead of more efficient IN clause in   LINQ to Entities (Oracle bug #14016344, MySql bug #64934). - Fix for error when trying to change the name of an Index on the Indexes/Keys editor; along with this fix now users can change the Index type of a new Index which could not be done   in previous versions, and when changing the Index name the change is reflected on the list view at the left side of the Index/Keys editor (Oracle bug #13613801). - Fix for stored procedure call using only its name with EF code first (MySql bug #64999, Oracle bug #14008699). - Fix for performance issue in generated EF query: .NET StartsWith/Contains/EndsWith produces MySql's locate instead of Like (MySql bug #64935, Oracle bug #14009363). - Fix for script generated for code first contains wrong alter table and wrong declaration for byte[] (MySql bug #64216, Oracle bug #13900091). - Fix for Exception thrown when using cascade delete in an EDM Model-First in Entity Framework (Oracle bug #14008752, MySql bug #64779). - Fix for Session locking issue with MySqlSessionStateStore (MySql bug #63997, Oracble bug #13733054). - Fixed deleting a user profile using Profile provider (MySQL bug #64409, Oracle bug #13790123). - Fix for bug Cannot Create an Entity with a Key of Type String (MySQL bug #65289, Oracle bug #14540202). This fix checks if the type has a FixedLength facet set in order to create a char otherwise should create varchar, mediumtext or longtext types when using a String CLR type in Code First or Model First also tested in Database First. Unit tests added for Code First and ProviderManifest. - Fix for bug "CacheServerProperties can cause 'Packet too large' error" (MySQL Bug #66578 Orabug #14593547). - Fix for handling unnamed parameter in MySQLCommand. This fix allows the mysqlcommand to handle parameters without requiring naming (e.g. INSERT INTO Test (id,name) VALUES (?, ?) ) (MySQL Bug #66060, Oracle bug #14499549). - Fixed inheritance on Entity Framework Code First scenarios. Discriminator column is created using its correct type as varchar(128) (MySql bug #63920 and Oracle bug #13582335). - Fixed "Trying to customize column precision in Code First does not work" (MySql bug #65001, Oracle bug #14469048). - Fixed bug ASP.NET Membership database fails on MySql database UTF32 (MySQL bug #65144, Oracle bug #14495292). - Fix for MySqlCommand.LastInsertedId holding only 32 bit values (MySql bug #65452, Oracle bug #14171960) by changing   several internal declaration of lastinsertid from int to long. - Fixed "Decimal type should have digits at right of decimal point", now default is 2, but user's changes in   EDM designer are recognized (MySql bug #65127, Oracle bug #14474342). - Fix for NullReferenceException when saving an uninitialized row in Entity Framework (MySql bug #66066, Oracle bug #14479715). - Fix for error when calling RoleProvider.RemoveUserFromRole(): causes an exception due to a wrong table being used (MySql bug #65805, Oracle bug #14405338). - Fix for "Memory Leak on MySql.Data.MySqlClient.MySqlCommand", too many MemoryStream's instances created (MySql bug #65696, Oracle bug #14468204). - Small improvement on MySqlPoolManager CleanIdleConnections for better mysqlpoolmanager idlecleanuptimer at startup (MySql bug #66472 and Oracle bug #14652624). - Fix for bug TIMESTAMP values are mistakenly represented as DateTime with Kind = Local (Mysql bug #66964, Oracle bug #14740705). - Fix for bug Keyword not supported. Parameter name: AttachDbFilename (Mysql bug #66880, Oracle bug #14733472). - Added support to MySql script file to retrieve data when using "SHOW" statements. - Fix for Package Load Failure in Visual Studio 2005 (MySql bug #63073, Oracle bug #13491674). - Fix for bug "Unable to connect using IPv6 connections" (MySQL bug #67253, Oracle bug #14835718). - Added auto-generated values for Guid identity columns (MySql bug #67450, Oracle bug #15834176). - Fix for method FirstOrDefault not supported in some LINQ to Entities queries (MySql bug #67377, Oracle bug #15856964). The release is available to download at http://dev.mysql.com/downloads/connector/net/6.4.html Documentation ------------------------------------- You can view current Connector/Net documentation at http://dev.mysql.com/doc/refman/5.5/en/connector-net.html You can find our team blog at http://blogs.oracle.com/MySQLOnWindows. You can also post questions on our forums at http://forums.mysql.com/. Enjoy and thanks for the support!

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• Prevent Changing the Screen Saver and Wallpaper in Windows 7

  - by Mysticgeek

  Sometimes you might not want users to have the ability to change Screen Savers and Wallpaper on Windows 7 workstations. Today we look at how to prevent them from changing either one or both. You might administer computers in your home or small office and find it annoying when users continuously change the wallpaper and Screen Savers to something obnoxious. A lot of times they might be inexperienced users and download these so-called “wonderful and free” Screen Saver/Wallpaper packages from shady sites that include loads of Spyware. Preventing users from changing them is another helpful tool to avoid wasteful time spent switching things back. Prevent Changing Screensavers & Wallpaper Using Group Policy Editor  Note: This method uses Group Policy which is not available in Home versions on Windows 7. Open the Start Menu and enter gpedit.msc into the Search box and hit Enter. When Local Group Policy Editor opens, navigate to User Configuration \ Administrative Templates \ Control Panel \ Personalization. Then in the right column double-click on Prevent changing desktop background. Now check the radio button next to Enabled, then click OK. Back on the Group Policy Screen, double-click on Prevent changing screen saver. In the next screen select the radio button next to Enable, click OK, then close out of Group Policy Editor. Now when a user goes into the Personalization section, the Desktop Background hyperlink is now grayed out and inactive. Notice the message One or more of the settings on this page has been disabled by the system administrator at the bottom of the section. If they click to change the Screen Saver, an error message will pop up letting them know the function is disabled. Prevent Changing Screensavers & Wallpaper Using a Registry Hack You can also make a couple Registry changes to prevent users from changing the Wallpaper & Screen Saver…which will work on Home versions of Windows 7. Before making any Registry changes make sure you back it up first. Open the Registry by typing regedit into the Search box in the Start menu and hit Enter. First we’ll start with the Wallpaper. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System and create a new String Value and name it Wallpaper. Then modify the Value data to point to the location of the Wallpaper you want it to always be. Where in this example it’s our main wallpaper on our local drive…then click OK. Now let’s make sure they can’t change the Screen Saver. In the same Registry location, we need to make a new DWORD (32-bit) Value. Give it the Value name of NoDispScrSavPage and the value data of “1” and click OK. Close out of the Registry and restart the machine or simply log off then back on again for the changes to take effect. Results For the Wallpapers, a user can still go in and see the selections, however if they try to change it to something else… It will just go back to the Personalization screen and no changes will be made, as we set the value to only be the background we specified. If the user tries to make a change to the Screen Saver, the hyperlink will be grayed out and inactive, and the message One or more of the settings on this page has been disabled by the system administrator will be displayed at the bottom of the section. Conclusion If you’re tired of users changing the Wallpaper and Screen Saver, and want another way to help avoid Malware, locking down these settings can help a lot. Again, before making any changes to the Registry, make sure to back it up. These settings should work in Vista and XP as well. Similar Articles Productive Geek Tips Save 1-4% More Battery Life With Windows Vista Battery SaverCustomize Your Windows Vista Logon ScreenEnable "Ubuntu Style" Logons in Windows VistaManage the Delete Confirmation Dialog box in Windows 7Dual Monitors: Use a Different Wallpaper on Each Desktop TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips Acronis Online Backup DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows Fun with 47 charts and graphs Tomorrow is Mother’s Day Check the Average Speed of YouTube Videos You’ve Watched OutlookStatView Scans and Displays General Usage Statistics How to Add Exceptions to the Windows Firewall Office 2010 reviewed in depth by Ed Bott

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• CLR via C# 3rd Edition is out

  - by Abhijeet Patel

  Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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• MySQL Connector/Net 6.5.5 Maintenance Release has been released

  - by fernando

  MySQL Connector/Net 6.5.5, a new maintenance release of our 6.5 series, has been released.  This release is GA quality and is appropriate for use in production environments.  Please note that 6.6 is our latest driver series and is the recommended product for development. It is now available in source and binary form from http://dev.mysql.com/downloads/connector/net/#downloads and mirror sites (note that not all mirror sites may be up to date at this point-if you can't find this version on some mirror, please try again later or choose another download site.) The 6.5.5 version of MySQL Connector/Net brings the following fixes: - Fix for ArgumentNull exception when using Take().Count() in a LINQ to Entities query (bug MySql #64749, Oracle bug #13913047). - Fix for type varchar changed to bit when saving in Table Designer (Oracle bug #13916560). - Fix for error when trying to change the name of an Index on the Indexes/Keys editor; along with this fix now users can change the Index type of a new Index which could not be done   in previous versions, and when changing the Index name the change is reflected on the list view at the left side of the Index/Keys editor (Oracle bug #13613801). - Fix for stored procedure call using only its name with EF code first (MySql bug #64999, Oracle bug #14008699). - Fix for List.Contains generates a bunch of ORs instead of more efficient IN clause in   LINQ to Entities (Oracle bug #14016344, MySql bug #64934). - Fix for performance issue in generated EF query: .NET StartsWith/Contains/EndsWith produces MySql's locate instead of Like (MySql bug #64935, Oracle bug #14009363). - Fix for script generated for code first contains wrong alter table and wrong declaration for byte[] (MySql bug #64216, Oracle bug #13900091). - Fix and code contribution for bug Timed out sessions are removed without notification which allow to enable the Expired CallBack when Session Provider times out any session (bug MySql #62266 Oracle bug # 13354935) - Fix for Exception thrown when using cascade delete in an EDM Model-First in Entity Framework (Oracle bug #14008752, MySql bug #64779). - Fix for Session locking issue with MySqlSessionStateStore (MySql bug #63997, Oracble bug #13733054). - Fixed deleting a user profile using Profile provider (MySQL bug #64470, Oracle bug #13790123) - Fix for bug Cannot Create an Entity with a Key of Type String (MySQL bug #65289, Oracle bug #14540202). This fix checks if the type has a FixedLength facet set in order to create a char otherwise should create varchar, mediumtext or longtext types when using a String CLR type in Code First or Model First also tested in Database First. Unit tests added for Code First and ProviderManifest. - Fix for bug "CacheServerProperties can cause 'Packet too large' error". The issue was due to a missing reading of Max_allowed_packet server property when CacheServerProperties is in true, since the value was read only in the first connection but the following pooled connections had a wrong value causing a Packet too large error. Including also a unit test for this scenario. All unit test passed. MySQL Bug #66578 Orabug #14593547. - Fix for handling unnamed parameter in MySQLCommand. This fix allows the mysqlcommand to handle parameters without requiring naming (e.g. INSERT INTO Test (id,name) VALUES (?, ?) ) (MySQL Bug #66060, Oracle bug #14499549). - Fixed inheritance on Entity Framework Code First scenarios. Discriminator column is created using its correct type as varchar(128) (MySql bug #63920 and Oracle bug #13582335). - Fixed "Trying to customize column precision in Code First does not work" (MySql bug #65001, Oracle bug #14469048). - Fixed bug ASP.NET Membership database fails on MySql database UTF32 (MySQL bug #65144, Oracle bug #14495292). - Fix for MySqlCommand.LastInsertedId holding only 32 bit values (MySql bug #65452, Oracle bug #14171960) by changing   several internal declaration of lastinsertid from int to long. - Fixed "Decimal type should have digits at right of decimal point", now default is 2, but user's changes in   EDM designer are recognized (MySql bug #65127, Oracle bug #14474342). - Fix for NullReferenceException when saving an uninitialized row in Entity Framework (MySql bug #66066, Oracle bug #14479715). - Fix for error when calling RoleProvider.RemoveUserFromRole(): causes an exception due to a wrong table being used (MySql bug #65805, Oracle bug #14405338). - Fix for "Memory Leak on MySql.Data.MySqlClient.MySqlCommand", too many MemoryStream's instances created (MySql bug #65696, Oracle bug #14468204). - Added ANTLR attribution notice (Oracle bug #14379162). - Fixed Entity Framework + mysql connector/net in partial trust throws exceptions (MySql bug #65036, Oracle bug #14668820). - Added support in Parser for Datetime and Time types with precision when using Server 5.6 (No bug Number). - Small improvement on MySqlPoolManager CleanIdleConnections for better mysqlpoolmanager idlecleanuptimer at startup (MySql bug #66472 and Oracle bug #14652624). - Fix for bug TIMESTAMP values are mistakenly represented as DateTime with Kind = Local (Mysql bug #66964, Oracle bug #14740705). - Fix for bug Keyword not supported. Parameter name: AttachDbFilename (Mysql bug #66880, Oracle bug #14733472). - Added support to MySql script file to retrieve data when using "SHOW" statements. - Fix for Package Load Failure in Visual Studio 2005 (MySql bug #63073, Oracle bug #13491674). - Fix for bug "Unable to connect using IPv6 connections" (MySQL bug #67253, Oracle bug #14835718). - Added auto-generated values for Guid identity columns (MySql bug #67450, Oracle bug #15834176). - Fix for method FirstOrDefault not supported in some LINQ to Entities queries (MySql bug #67377, Oracle bug #15856964). The release is available to download at http://dev.mysql.com/downloads/connector/net/6.5.html Documentation ------------------------------------- You can view current Connector/Net documentation at http://dev.mysql.com/doc/refman/5.5/en/connector-net.html You can find our team blog at http://blogs.oracle.com/MySQLOnWindows. You can also post questions on our forums at http://forums.mysql.com/. Enjoy and thanks for the support! 

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• Why lock-free data structures just aren't lock-free enough

  - by Alex.Davies

  Today's post will explore why the current ways to communicate between threads don't scale, and show you a possible way to build scalable parallel programming on top of shared memory. The problem with shared memory Soon, we will have dozens, hundreds and then millions of cores in our computers. It's inevitable, because individual cores just can't get much faster. At some point, that's going to mean that we have to rethink our architecture entirely, as millions of cores can't all access a shared memory space efficiently. But millions of cores are still a long way off, and in the meantime we'll see machines with dozens of cores, struggling with shared memory. Alex's tip: The best way for an application to make use of that increasing parallel power is to use a concurrency model like actors, that deals with synchronisation issues for you. Then, the maintainer of the actors framework can find the most efficient way to coordinate access to shared memory to allow your actors to pass messages to each other efficiently. At the moment, NAct uses the .NET thread pool and a few locks to marshal messages. It works well on dual and quad core machines, but it won't scale to more cores. Every time we use a lock, our core performs an atomic memory operation (eg. CAS) on a cell of memory representing the lock, so it's sure that no other core can possibly have that lock. This is very fast when the lock isn't contended, but we need to notify all the other cores, in case they held the cell of memory in a cache. As the number of cores increases, the total cost of a lock increases linearly. A lot of work has been done on "lock-free" data structures, which avoid locks by using atomic memory operations directly. These give fairly dramatic performance improvements, particularly on systems with a few (2 to 4) cores. The .NET 4 concurrent collections in System.Collections.Concurrent are mostly lock-free. However, lock-free data structures still don't scale indefinitely, because any use of an atomic memory operation still involves every core in the system. A sync-free data structure Some concurrent data structures are possible to write in a completely synchronization-free way, without using any atomic memory operations. One useful example is a single producer, single consumer (SPSC) queue. It's easy to write a sync-free fixed size SPSC queue using a circular buffer*. Slightly trickier is a queue that grows as needed. You can use a linked list to represent the queue, but if you leave the nodes to be garbage collected once you're done with them, the GC will need to involve all the cores in collecting the finished nodes. Instead, I've implemented a proof of concept inspired by this intel article which reuses the nodes by putting them in a second queue to send back to the producer. * In all these cases, you need to use memory barriers correctly, but these are local to a core, so don't have the same scalability problems as atomic memory operations. Performance tests I tried benchmarking my SPSC queue against the .NET ConcurrentQueue, and against a standard Queue protected by locks. In some ways, this isn't a fair comparison, because both of these support multiple producers and multiple consumers, but I'll come to that later. I started on my dual-core laptop, running a simple test that had one thread producing 64 bit integers, and another consuming them, to measure the pure overhead of the queue. So, nothing very interesting here. Both concurrent collections perform better than the lock-based one as expected, but there's not a lot to choose between the ConcurrentQueue and my SPSC queue. I was a little disappointed, but then, the .NET Framework team spent a lot longer optimising it than I did. So I dug out a more powerful machine that Red Gate's DBA tools team had been using for testing. It is a 6 core Intel i7 machine with hyperthreading, adding up to 12 logical cores. Now the results get more interesting. As I increased the number of producer-consumer pairs to 6 (to saturate all 12 logical cores), the locking approach was slow, and got even slower, as you'd expect. What I didn't expect to be so clear was the drop-off in performance of the lock-free ConcurrentQueue. I could see the machine only using about 20% of available CPU cycles when it should have been saturated. My interpretation is that as all the cores used atomic memory operations to safely access the queue, they ended up spending most of the time notifying each other about cache lines that need invalidating. The sync-free approach scaled perfectly, despite still working via shared memory, which after all, should still be a bottleneck. I can't quite believe that the results are so clear, so if you can think of any other effects that might cause them, please comment! Obviously, this benchmark isn't realistic because we're only measuring the overhead of the queue. Any real workload, even on a machine with 12 cores, would dwarf the overhead, and there'd be no point worrying about this effect. But would that be true on a machine with 100 cores? Still to be solved. The trouble is, you can't build many concurrent algorithms using only an SPSC queue to communicate. In particular, I can't see a way to build something as general purpose as actors on top of just SPSC queues. Fundamentally, an actor needs to be able to receive messages from multiple other actors, which seems to need an MPSC queue. I've been thinking about ways to build a sync-free MPSC queue out of multiple SPSC queues and some kind of sign-up mechanism. Hopefully I'll have something to tell you about soon, but leave a comment if you have any ideas.

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• MySQL Connect Only 10 Days Away - Focus on InnoDB Sessions

  - by Bertrand Matthelié

  Time flies and MySQL Connect is only 10 days away! You can check out the full program here as well as in the September edition of the MySQL newsletter. Mat recently blogged about the MySQL Cluster sessions you’ll have the opportunity to attend, and below are those focused on InnoDB. Remember you can plan your schedule with Schedule Builder. Saturday, 1.00 pm, Room Golden Gate 3: 10 Things You Should Know About InnoDB—Calvin Sun, Oracle InnoDB is the default storage engine for Oracle’s MySQL as of MySQL Release 5.5. It provides the standard ACID-compliant transactions, row-level locking, multiversion concurrency control, and referential integrity. InnoDB also implements several innovative technologies to improve its performance and reliability. This presentation gives a brief history of InnoDB; its main features; and some recent enhancements for better performance, scalability, and availability. Saturday, 5.30 pm, Room Golden Gate 4: Demystified MySQL/InnoDB Performance Tuning—Dimitri Kravtchuk, Oracle This session covers performance tuning with MySQL and the InnoDB storage engine for MySQL and explains the main improvements made in MySQL Release 5.5 and Release 5.6. Which setting for which workload? Which value will be better for my system? How can I avoid potential bottlenecks from the beginning? Do I need a purge thread? Is it true that InnoDB doesn't need thread concurrency anymore? These and many other questions are asked by DBAs and developers. Things are changing quickly and constantly, and there is no “silver bullet.” But understanding the configuration setting’s impact is already a huge step in performance improvement. Bring your ideas and problems to share them with others—the discussion is open, just moderated by a speaker. Sunday, 10.15 am, Room Golden Gate 4: Better Availability with InnoDB Online Operations—Calvin Sun, Oracle Many top Web properties rely on Oracle’s MySQL as a critical piece of infrastructure for serving millions of users. Database availability has become increasingly important. One way to enhance availability is to give users full access to the database during data definition language (DDL) operations. The online DDL operations in recent MySQL releases offer users the flexibility to perform schema changes while having full access to the database—that is, with minimal delay of operations on a table and without rebuilding the entire table. These enhancements provide better responsiveness and availability in busy production environments. This session covers these improvements in the InnoDB storage engine for MySQL for online DDL operations such as add index, drop foreign key, and rename column. Sunday, 11.45 am, Room Golden Gate 7: Developing High-Throughput Services with NoSQL APIs to InnoDB and MySQL Cluster—Andrew Morgan and John Duncan, Oracle Ever-increasing performance demands of Web-based services have generated significant interest in providing NoSQL access methods to MySQL (MySQL Cluster and the InnoDB storage engine of MySQL), enabling users to maintain all the advantages of their existing relational databases while providing blazing-fast performance for simple queries. Get the best of both worlds: persistence; consistency; rich SQL queries; high availability; scalability; and simple, flexible APIs and schemas for agile development. This session describes the memcached connectors and examines some use cases for how MySQL and memcached fit together in application architectures. It does the same for the newest MySQL Cluster native connector, an easy-to-use, fully asynchronous connector for Node.js. Sunday, 1.15 pm, Room Golden Gate 4: InnoDB Performance Tuning—Inaam Rana, Oracle The InnoDB storage engine has always been highly efficient and includes many unique architectural elements to ensure high performance and scalability. In MySQL 5.5 and MySQL 5.6, InnoDB includes many new features that take better advantage of recent advances in operating systems and hardware platforms than previous releases did. This session describes unique InnoDB architectural elements for performance, new features, and how to tune InnoDB to achieve better performance. Sunday, 4.15 pm, Room Golden Gate 3: InnoDB Compression for OLTP—Nizameddin Ordulu, Facebook and Inaam Rana, Oracle Data compression is an important capability of the InnoDB storage engine for Oracle’s MySQL. Compressed tables reduce the size of the database on disk, resulting in fewer reads and writes and better throughput by reducing the I/O workload. Facebook pushes the limit of InnoDB compression and has made several enhancements to InnoDB, making this technology ready for online transaction processing (OLTP). In this session, you will learn the fundamentals of InnoDB compression. You will also learn the enhancements the Facebook team has made to improve InnoDB compression, such as reducing compression failures, not logging compressed page images, and allowing changes of compression level. Not registered yet? You can still save US$ 300 over the on-site fee – Register Now!

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• What's New In 11.1.2.1 (Talleyrand SP1)

  - by russ.bishop

  This release is primarily about bug fixes and that's what we spent the most time on, but we also addressed a number of other things: 1. Performance improvements We've done a lot of work to improve the performance of page load and execution times. For example, the View Compare page is about half the size it was previously! We've also done a lot of work on the server to improve performance of queries, exports, action scripts, etc. We implemented some finer-grained locking so fewer operations will block other users while they are in progress. We made some optimizations to improve performance when you have a lot of network or database latency as well. Just a few examples: An Import that previously took 8 GB of memory and hours to complete now runs in about 30 minutes and never takes more than 1 GB of RAM. Searching by exact Node Name now completes within 2 seconds even for a hierarchy with millions of nodes. Another search that was taking 30 seconds to run now completes in less than 5 seconds. 2. Upgrade support This release supports automatic upgrade from previous releases, built right into the console. 3. Console Improvements The Console has been reorganized and made easier to use. It is also much more multi-threaded so it responds quicker without freezing up when you save changes or when it needs to get status. 4. Property Namespaces Properties now have a concept called a Namespace. This is tied into the Application Templates to prevent conflicts with duplicate property names. Right now, if you have an AccountType and you pull in the HFM template, it also has AccountType so you end up creating properties with decorations on the name like "Account Type (HFM)". This is no longer necessary. In addition, properties within a namespace must have unique labels but they can be duplicated across namespaces. So in the Property Grid when you click on the HFM category, you just see "AccountType". When you click on MyCategory, you see "AccountType", but they are different properties with different values. Within formulas, the names are still unique (eg: Custom.AccountType vs HFM.AccountType). I'll write more about this one later. 5. Single Sign On DRM now supports Single Sign-On via HSS. For example, if you are using Oracle's OAM as your SSO solution then you configure HSS to use OAM just like you would before. You also configure DRM to use HSS, again just like before. Then you configure OAM to protect the DRM web app, like you would any other website. However once you do those things, users are no longer prompted to enter their username/password. They simply get redirected to OAM if they don't already have a login token, otherwise they pick their application and sail right into DRM. You can also avoid having to pick an application (see the next item) 6. URL-based navigation You can now specify the application you want to log into via the URL. Combined with SSO and your Intranet, it becomes easy to provide links on our intranet portal that take users directly into a specific DRM application. We also support specifying the Version, Hierarchy, and Node. Again, this can be used on your internal portal, but the scenarios get even more interesting when you are using workflow like Oracle BPEL you can automatically generate links within emails that will take users directly to a specific node in the UI. 7. Job status and cancellation A lot of the jobs now report their status and support true cancellation. Action Scripts also report a progress complete percentage since the amount of work is known ahead of time. 8. Action Script Options Action scripts support Option declarations at the top of the file so a script can self-describe (when specified in the file, the corresponding item in the file is ignored). For example: Option|DetectDelimiter Option|UsePropertyNames|true This will tell DRM to automatically detect the delimiter (a pipe symbol in this case) and that all references to properties are by Name, not by Label. Note that when you load a script in the UI, if you use Labels we automatically try to match them up if they are unique. Any duplicates are indicated and you are presented with a choice to pick which property you actually referred to. This is somewhat similar to Version substitution, but tailored for properties. There are other more minor changes and like I said earlier a lot of bug fixes and performance improvements. Hopefully I will get a chance to dig into some of these things in future blog posts.

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• Oracle CRM On Demand Release 24 is Generally Available

  - by Richard Lefebvre

  Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 We are pleased to announce that Oracle CRM On Demand Release 24 is Generally Available as of October 25, 2013 Get smarter, more productive and the best value with Oracle CRM On Demand Release 24. Oracle CRM On Demand continues to be the most complete Software-as-a-Service (SaaS) CRM solution available. Now, with Release 24, organizations of all types and sizes benefit from actionable insight anywhere, anytime, as well as key enhancements in mobility, embedded social, analytics, integration and extensibility, and ease of use.Next Generation Mobile and Desktop Solutions : Oracle CRM On Demand Release 24 offers a complete set of mobile and desktop solutions that improve productivity by enabling reps to access and update information anywhere, anytime. Capabilities include: Oracle CRM On Demand Disconnected Mobile Sales (DMS) – A disconnected native iPad solution, DMS has been further streamlined mobile sales process by adding Structured Product Messaging to record brand specific call objectives, enhancements in HTML5 eDetailing including message response tracking and improvements in administration and configuration such as more field management options for read only fields, role management and enhanced logging. Oracle CRM On Demand Connected Mobile Sales. This add-on mobile service provides a configurable mobile solution on iOS, BlackBerry and now Android devices. You can access data from CRM On Demand in real time with a rich, native user experience, that is comfortable and familiar to current iOS, BlackBerry and Android users. New features also include Single Sign On to enhance security for mobile users.  Oracle CRM On Demand Desktop: This application centralizes essential CRM information in the familiar Microsoft Outlook environment,increasing user adoption and decreasing training costs. Users can manage CRM data while disconnected, then synchronize bi-directionally when they are back on the network. New in Oracle CRM On Demand Desktop Version 3 is the ability to synchronize by Books of Business, and improved Online Lookup. Mobile Browser Support: The following mobile device browsers are now supported: Apple iPhone, Apple iPad, Windows 8 Tablets, and Google Android. Leverage the Social Enterprise Engaging customers via social channels is rapidly becoming a significant key to enhanced customer experience as it provides proactive customer service, targeted messaging and greater intimacy throughout the entire customer lifecycle. Listening to customers on the social channels can identify a customers’ sphere of influence and the real value they bring to their organization, or the impact they can have on the opportunity. Servicing the customer’s need is the first step towards loyalty to a brand, integrating with social channels allows us to maximize brand affinity and virally expand customer engagements thus increasing revenue. Oracle CRM On Demand is leveraging the Social Enterprise through its integration with Oracle’s Social Relationship Management (SRM) product suite by providing out-of-the-box integration with Social Engagement and Monitoring (SEM), Social Marketing (SM) and Oracle Social Network (OSN). With Oracle CRM On Demand Release 24, users are able to create a service request from a social post via SEM and have leads entered on a SM lead form automatically entered into Oracle CRM On Demand along with the campaign, streamlining the lead qualification process. Get Smarter with Actionable Insight The difference between making good decisions and great decisions depends heavily upon the quality, structure, and availability of information at hand. Oracle CRM On Demand Release 24 expands upon its industry-leading analytics capabilities to provide greater business insight than ever before. New capabilities include flexible permissions on analytics reports folders, allowing for read only access to reports, and additional field and object coverage. Get More Productive with Powerful Tools Oracle CRM On Demand Release 24 introduces a new set of powerful capabilities designed to maximize productivity. A significant new feature for customizing Oracle CRM On Demand is a JavaScript API. The JS API allows customers to add new buttons, suppress existing buttons and even change what happens when a user clicks an existing button. Other usability enhancements, such as personalized related information applets, extended case insensitive search provide users with better, more intuitive, experience. Additional privileges for viewing private activities and notes allow administrators to reassign records as needed, and Custom Object management. Workflow has been added to the Order Item object; and now tasks can be assigned to a relative user, such as an Account Owner, allowing more complex business processes to be automated and adhered to. Get the Best Value Oracle CRM On Demand delivers unprecedented value with the broadest set of capabilities from a single-provider solution, the industry’s lowest total cost of ownership, the most on-demand deployment options, the deepest CRM expertise and experience of any CRM provider, and the most secure CRM in the cloud. With Release 24, Oracle CRM On Demand now includes even more enterprise-grade security, integration, and extensibility features, along with enhanced industry editions to save you time and money. New features include: Business Process Administration: A new privilege has been added that allows administrators to override a Business Process Administration rule.This privilege permits users to edit a locked record, or unlock a record, in the event of a material change that needs to be reflected per corporatepolicy. Additionally, the Products Detailed object has been added to Business Process Administration, enabling record locking and logic to be applied. Expanded Integration: Oracle continues to improve Web Services each release, by adding more object coverage enabling customers and partners to easily integrate with CRM On Demand. Bottom Line Oracle CRM On Demand Release 24 enables organizations to get smarter, get more productive, and get the best value, period. For more information on Oracle CRM On Demand Release 24, please visit oracle.com/crmondemand

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• Using Transaction Logging to Recover Post-Archived Essbase data

  - by Keith Rosenthal

  Data recovery is typically performed by restoring data from an archive.  Data added or removed since the last archive took place can also be recovered by enabling transaction logging in Essbase.  Transaction logging works by writing transactions to a log store.  The information in the log store can then be recovered by replaying the log store entries in sequence since the last archive took place.  The following information is recorded within a transaction log entry: Sequence ID Username Start Time End Time Request Type A request type can be one of the following categories: Calculations, including the default calculation as well as both server and client side calculations Data loads, including data imports as well as data loaded using a load rule Data clears as well as outline resets Locking and sending data from SmartView and the Spreadsheet Add-In.  Changes from Planning web forms are also tracked since a lock and send operation occurs during this process. You can use the Display Transactions command in the EAS console or the query database MAXL command to view the transaction log entries. Enabling Transaction Logging Transaction logging can be enabled at the Essbase server, application or database level by adding the TRANSACTIONLOGLOCATION essbase.cfg setting.  The following is the TRANSACTIONLOGLOCATION syntax: TRANSACTIONLOGLOCATION [appname [dbname]] LOGLOCATION NATIVE ENABLE | DISABLE Note that you can have multiple TRANSACTIONLOGLOCATION entries in the essbase.cfg file.  For example: TRANSACTIONLOGLOCATION Hyperion/trlog NATIVE ENABLE TRANSACTIONLOGLOCATION Sample Hyperion/trlog NATIVE DISABLE The first statement will enable transaction logging for all Essbase applications, and the second statement will disable transaction logging for the Sample application.  As a result, transaction logging will be enabled for all applications except the Sample application. A location on a physical disk other than the disk where ARBORPATH or the disk files reside is recommended to optimize overall Essbase performance. Configuring Transaction Log Replay Although transaction log entries are stored based on the LOGLOCATION parameter of the TRANSACTIONLOGLOCATION essbase.cfg setting, copies of data load and rules files are stored in the ARBORPATH/app/appname/dbname/Replay directory to optimize the performance of replaying logged transactions.  The default is to archive client data loads, but this configuration setting can be used to archive server data loads (including SQL server data loads) or both client and server data loads. To change the type of data to be archived, add the TRANSACTIONLOGDATALOADARCHIVE configuration setting to the essbase.cfg file.  Note that you can have multiple TRANSACTIONLOGDATALOADARCHIVE entries in the essbase.cfg file to adjust settings for individual applications and databases. Replaying the Transaction Log and Transaction Log Security Considerations To replay the transactions, use either the Replay Transactions command in the EAS console or the alter database MAXL command using the replay transactions grammar.  Transactions can be replayed either after a specified log time or using a range of transaction sequence IDs. The default when replaying transactions is to use the security settings of the user who originally performed the transaction.  However, if that user no longer exists or that user's username was changed, the replay operation will fail. Instead of using the default security setting, add the REPLAYSECURITYOPTION essbase.cfg setting to use the security settings of the administrator who performs the replay operation.  REPLAYSECURITYOPTION 2 will explicitly use the security settings of the administrator performing the replay operation.  REPLAYSECURITYOPTION 3 will use the administrator security settings if the original user’s security settings cannot be used. Removing Transaction Logs and Archived Replay Data Load and Rules Files Transaction logs and archived replay data load and rules files are not automatically removed and are only removed manually.  Since these files can consume a considerable amount of space, the files should be removed on a periodic basis. The transaction logs should be removed one database at a time instead of all databases simultaneously.  The data load and rules files associated with the replayed transactions should be removed in chronological order from earliest to latest.  In addition, do not remove any data load and rules files with a timestamp later than the timestamp of the most recent archive file. Partitioned Database Considerations For partitioned databases, partition commands such as synchronization commands cannot be replayed.  When recovering data, the partition changes must be replayed manually and logged transactions must be replayed in the correct chronological order. If the partitioned database includes any @XREF commands in the calc script, the logged transactions must be selectively replayed in the correct chronological order between the source and target databases. References For additional information, please see the Oracle EPM System Backup and Recovery Guide.  For EPM 11.1.2.2, the link is http://docs.oracle.com/cd/E17236_01/epm.1112/epm_backup_recovery_1112200.pdf

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• Documentation Changes in Solaris 11.1

  - by alanc

  One of the first places you can see Solaris 11.1 changes are in the docs, which have now been posted in the Solaris 11.1 Library on docs.oracle.com. I spent a good deal of time reviewing documentation for this release, and thought some would be interesting to blog about, but didn't review all the changes (not by a long shot), and am not going to cover all the changes here, so there's plenty left for you to discover on your own. Just comparing the Solaris 11.1 Library list of docs against the Solaris 11 list will show a lot of reorganization and refactoring of the doc set, especially in the system administration guides. Hopefully the new break down will make it easier to get straight to the sections you need when a task is at hand. Packaging System Unfortunately, the excellent in-depth guide for how to build packages for the new Image Packaging System (IPS) in Solaris 11 wasn't done in time to make the initial Solaris 11 doc set. An interim version was published shortly after release, in PDF form on the OTN IPS page. For Solaris 11.1 it was included in the doc set, as Packaging and Delivering Software With the Image Packaging System in Oracle Solaris 11.1, so should be easier to find, and easier to share links to specific pages the HTML version. Beyond just how to build a package, it includes details on how Solaris is packaged, and how package updates work, which may be useful to all system administrators who deal with Solaris 11 upgrades & installations. The Adding and Updating Oracle Solaris 11.1 Software Packages was also extended, including new sections on Relaxing Version Constraints Specified by Incorporations and Locking Packages to a Specified Version that may be of interest to those who want to keep the Solaris 11 versions of certain packages when they upgrade, such as the couple of packages that had functionality removed by an (unusual for an update release) End of Feature process in the 11.1 release. Also added in this release is a document containing the lists of all the packages in each of the major package groups in Solaris 11.1 (solaris-desktop, solaris-large-server, and solaris-small-server). While you can simply get the contents of those groups from the package repository, either via the web interface or the pkg command line, the documentation puts them in handy tables for easier side-by-side comparison, or viewing the lists before you've installed the system to pick which one you want to initially install. X Window System We've not had good X11 coverage in the online Solaris docs in a while, mostly relying on the man pages, and upstream X.Org docs. In this release, we've integrated some X coverage into the Solaris 11.1 Desktop Adminstrator's Guide, including sections on installing fonts for fontconfig or legacy X11 clients, X server configuration, and setting up remote access via X11 or VNC. Of course we continue to work on improving the docs, including a lot of contributions to the upstream docs all OS'es share (more about that another time). Security One of the things Oracle likes to do for its products is to publish security guides for administrators & developers to know how to build systems that meet their security needs. For Solaris, we started this with Solaris 11, providing a guide for sysadmins to find where the security relevant configuration options were documented. The Solaris 11.1 Security Guidelines extend this to cover new security features, such as Address Space Layout Randomization (ASLR) and Read-Only Zones, as well as adding additional guidelines for existing features, such as how to limit the size of tmpfs filesystems, to avoid users driving the system into swap thrashing situations. For developers, the corresponding document is the Developer's Guide to Oracle Solaris 11 Security, which has been the source for years for documentation of security-relevant Solaris API's such as PAM, GSS-API, and the Solaris Cryptographic Framework. For Solaris 11.1, a new appendix was added to start providing Secure Coding Guidelines for Developers, leveraging the CERT Secure Coding Standards and OWASP guidelines to provide the base recommendations for common programming languages and their standard API's. Solaris specific secure programming guidance was added via links to other documentation in the product doc set. In parallel, we updated the Solaris C Libary Functions security considerations list with details of Solaris 11 enhancements such as FD_CLOEXEC flags, additional *at() functions, and new stdio functions such as asprintf() and getline(). A number of code examples throughout the Solaris 11.1 doc set were updated to follow these recommendations, changing unbounded strcpy() calls to strlcpy(), sprintf() to snprintf(), etc. so that developers following our examples start out with safer code. The Writing Device Drivers guide even had the appendix updated to list which of these utility functions, like snprintf() and strlcpy(), are now available via the Kernel DDI. Little Things Of course all the big new features got documented, and some major efforts were put into refactoring and renovation, but there were also a lot of smaller things that got fixed as well in the nearly a year between the Solaris 11 and 11.1 doc releases - again too many to list here, but a random sampling of the ones I know about & found interesting or useful: The Privileges section of the DTrace Guide now gives users a pointer to find out how to set up DTrace privileges for non-global zones and what limitations are in place there. A new section on Recommended iSCSI Configuration Practices was added to the iSCSI configuration section when it moved into the SAN Configuration and Multipathing administration guide. The Managing System Power Services section contains an expanded explanation of the various tunables for power management in Solaris 11.1. The sample dcmd sources in /usr/demo/mdb were updated to include ::help output, so that developers like myself who follow the examples don't forget to include it (until a helpful code reviewer pointed it out while reviewing the mdb module changes for Xorg 1.12). The README file in that directory was updated to show the correct paths for installing both kernel & userspace modules, including the 64-bit variants.

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• Differences Between NHibernate and Entity Framework

  - by Ricardo Peres

  Introduction NHibernate and Entity Framework are two of the most popular O/RM frameworks on the .NET world. Although they share some functionality, there are some aspects on which they are quite different. This post will describe this differences and will hopefully help you get started with the one you know less. Mind you, this is a personal selection of features to compare, it is by no way an exhaustive list. History First, a bit of history. NHibernate is an open-source project that was first ported from Java’s venerable Hibernate framework, one of the first O/RM frameworks, but nowadays it is not tied to it, for example, it has .NET specific features, and has evolved in different ways from those of its Java counterpart. Current version is 3.3, with 3.4 on the horizon. It currently targets .NET 3.5, but can be used as well in .NET 4, it only makes no use of any of its specific functionality. You can find its home page at NHForge. Entity Framework 1 came out with .NET 3.5 and is now on its second major version, despite being version 4. Code First sits on top of it and but came separately and will also continue to be released out of line with major .NET distributions. It is currently on version 4.3.1 and version 5 will be released together with .NET Framework 4.5. All versions will target the current version of .NET, at the time of their release. Its home location is located at MSDN. Architecture In NHibernate, there is a separation between the Unit of Work and the configuration and model instances. You start off by creating a Configuration object, where you specify all global NHibernate settings such as the database and dialect to use, the batch sizes, the mappings, etc, then you build an ISessionFactory from it. The ISessionFactory holds model and metadata that is tied to a particular database and to the settings that came from the Configuration object, and, there will typically be only one instance of each in a process. Finally, you create instances of ISession from the ISessionFactory, which is the NHibernate representation of the Unit of Work and Identity Map. This is a lightweight object, it basically opens and closes a database connection as required and keeps track of the entities associated with it. ISession objects are cheap to create and dispose, because all of the model complexity is stored in the ISessionFactory and Configuration objects. As for Entity Framework, the ObjectContext/DbContext holds the configuration, model and acts as the Unit of Work, holding references to all of the known entity instances. This class is therefore not lightweight as its NHibernate counterpart and it is not uncommon to see examples where an instance is cached on a field. Mappings Both NHibernate and Entity Framework (Code First) support the use of POCOs to represent entities, no base classes are required (or even possible, in the case of NHibernate). As for mapping to and from the database, NHibernate supports three types of mappings: XML-based, which have the advantage of not tying the entity classes to a particular O/RM; the XML files can be deployed as files on the file system or as embedded resources in an assembly; Attribute-based, for keeping both the entities and database details on the same place at the expense of polluting the entity classes with NHibernate-specific attributes; Strongly-typed code-based, which allows dynamic creation of the model and strongly typing it, so that if, for example, a property name changes, the mapping will also be updated. Entity Framework can use: Attribute-based (although attributes cannot express all of the available possibilities – for example, cascading); Strongly-typed code mappings. Database Support With NHibernate you can use mostly any database you want, including: SQL Server; SQL Server Compact; SQL Server Azure; Oracle; DB2; PostgreSQL; MySQL; Sybase Adaptive Server/SQL Anywhere; Firebird; SQLLite; Informix; Any through OLE DB; Any through ODBC. Out of the box, Entity Framework only supports SQL Server, but a number of providers exist, both free and commercial, for some of the most used databases, such as Oracle and MySQL. See a list here. Inheritance Strategies Both NHibernate and Entity Framework support the three canonical inheritance strategies: Table Per Type Hierarchy (Single Table Inheritance), Table Per Type (Class Table Inheritance) and Table Per Concrete Type (Concrete Table Inheritance). Associations Regarding associations, both support one to one, one to many and many to many. However, NHibernate offers far more collection types: Bags of entities or values: unordered, possibly with duplicates; Lists of entities or values: ordered, indexed by a number column; Maps of entities or values: indexed by either an entity or any value; Sets of entities or values: unordered, no duplicates; Arrays of entities or values: indexed, immutable. Querying NHibernate exposes several querying APIs: LINQ is probably the most used nowadays, and really does not need to be introduced; Hibernate Query Language (HQL) is a database-agnostic, object-oriented SQL-alike language that exists since NHibernate’s creation and still offers the most advanced querying possibilities; well suited for dynamic queries, even if using string concatenation; Criteria API is an implementation of the Query Object pattern where you create a semi-abstract conceptual representation of the query you wish to execute by means of a class model; also a good choice for dynamic querying; Query Over offers a similar API to Criteria, but using strongly-typed LINQ expressions instead of strings; for this, although more refactor-friendlier that Criteria, it is also less suited for dynamic queries; SQL, including stored procedures, can also be used; Integration with Lucene.NET indexer is available. As for Entity Framework: LINQ to Entities is fully supported, and its implementation is considered very complete; it is the API of choice for most developers; Entity-SQL, HQL’s counterpart, is also an object-oriented, database-independent querying language that can be used for dynamic queries; SQL, of course, is also supported. Caching Both NHibernate and Entity Framework, of course, feature first-level cache. NHibernate also supports a second-level cache, that can be used among multiple ISessionFactorys, even in different processes/machines: Hashtable (in-memory); SysCache (uses ASP.NET as the cache provider); SysCache2 (same as above but with support for SQL Server SQL Dependencies); Prevalence; SharedCache; Memcached; Redis; NCache; Appfabric Caching. Out of the box, Entity Framework does not have any second-level cache mechanism, however, there are some public samples that show how we can add this. ID Generators NHibernate supports different ID generation strategies, coming from the database and otherwise: Identity (for SQL Server, MySQL, and databases who support identity columns); Sequence (for Oracle, PostgreSQL, and others who support sequences); Trigger-based; HiLo; Sequence HiLo (for databases that support sequences); Several GUID flavors, both in GUID as well as in string format; Increment (for single-user uses); Assigned (must know what you’re doing); Sequence-style (either uses an actual sequence or a single-column table); Table of ids; Pooled (similar to HiLo but stores high values in a table); Native (uses whatever mechanism the current database supports, identity or sequence). Entity Framework only supports: Identity generation; GUIDs; Assigned values. Properties NHibernate supports properties of entity types (one to one or many to one), collections (one to many or many to many) as well as scalars and enumerations. It offers a mechanism for having complex property types generated from the database, which even include support for querying. It also supports properties originated from SQL formulas. Entity Framework only supports scalars, entity types and collections. Enumerations support will come in the next version. Events and Interception NHibernate has a very rich event model, that exposes more than 20 events, either for synchronous pre-execution or asynchronous post-execution, including: Pre/Post-Load; Pre/Post-Delete; Pre/Post-Insert; Pre/Post-Update; Pre/Post-Flush. It also features interception of class instancing and SQL generation. As for Entity Framework, only two events exist: ObjectMaterialized (after loading an entity from the database); SavingChanges (before saving changes, which include deleting, inserting and updating). Tracking Changes For NHibernate as well as Entity Framework, all changes are tracked by their respective Unit of Work implementation. Entities can be attached and detached to it, Entity Framework does, however, also support self-tracking entities. Optimistic Concurrency Control NHibernate supports all of the imaginable scenarios: SQL Server’s ROWVERSION; Oracle’s ORA_ROWSCN; A column containing date and time; A column containing a version number; All/dirty columns comparison. Entity Framework is more focused on Entity Framework, so it only supports: SQL Server’s ROWVERSION; Comparing all/some columns. Batching NHibernate has full support for insertion batching, but only if the ID generator in use is not database-based (for example, it cannot be used with Identity), whereas Entity Framework has no batching at all. Cascading Both support cascading for collections and associations: when an entity is deleted, their conceptual children are also deleted. NHibernate also offers the possibility to set the foreign key column on children to NULL instead of removing them. Flushing Changes NHibernate’s ISession has a FlushMode property that can have the following values: Auto: changes are sent to the database when necessary, for example, if there are dirty instances of an entity type, and a query is performed against this entity type, or if the ISession is being disposed; Commit: changes are sent when committing the current transaction; Never: changes are only sent when explicitly calling Flush(). As for Entity Framework, changes have to be explicitly sent through a call to AcceptAllChanges()/SaveChanges(). Lazy Loading NHibernate supports lazy loading for Associated entities (one to one, many to one); Collections (one to many, many to many); Scalar properties (thing of BLOBs or CLOBs). Entity Framework only supports lazy loading for: Associated entities; Collections. Generating and Updating the Database Both NHibernate and Entity Framework Code First (with the Migrations API) allow creating the database model from the mapping and updating it if the mapping changes. Extensibility As you can guess, NHibernate is far more extensible than Entity Framework. Basically, everything can be extended, from ID generation, to LINQ to SQL transformation, HQL native SQL support, custom column types, custom association collections, SQL generation, supported databases, etc. With Entity Framework your options are more limited, at least, because practically no information exists as to what can be extended/changed. It features a provider model that can be extended to support any database. Integration With Other Microsoft APIs and Tools When it comes to integration with Microsoft technologies, it will come as no surprise that Entity Framework offers the best support. For example, the following technologies are fully supported: ASP.NET (through the EntityDataSource); ASP.NET Dynamic Data; WCF Data Services; WCF RIA Services; Visual Studio (through the integrated designer). Documentation This is another point where Entity Framework is superior: NHibernate lacks, for starters, an up to date API reference synchronized with its current version. It does have a community mailing list, blogs and wikis, although not much used. Entity Framework has a number of resources on MSDN and, of course, several forums and discussion groups exist. Conclusion Like I said, this is a personal list. I may come as a surprise to some that Entity Framework is so behind NHibernate in so many aspects, but it is true that NHibernate is much older and, due to its open-source nature, is not tied to product-specific timeframes and can thus evolve much more rapidly. I do like both, and I chose whichever is best for the job I have at hands. I am looking forward to the changes in EF5 which will add significant value to an already interesting product. So, what do you think? Did I forget anything important or is there anything else worth talking about? Looking forward for your comments!

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• Intermittent PolicyException: Execution permission cannot be acquired.

  - by Aaron Maenpaa

  We are intermittently seeing the following exception shortly after an App Pool recycle in an ASP.NET application: System.Configuration.ConfigurationErrorsException: Could not load file or assembly 'Microsoft.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418) ---> System.IO.FileLoadException: Could not load file or assembly 'Microsoft.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418) File name: 'Microsoft.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' ---> System.Security.Policy.PolicyException: Execution permission cannot be acquired. at System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Boolean checkExecutionPermission) at System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Int32& securitySpecialFlags, Boolean checkExecutionPermission) at System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) at System.Reflection.Assembly.Load(String assemblyString) at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) The specific DLL that fails to load varies from incident to incident, but is always one referenced by the main assembly. We're running on ASP.NET 3.5 on Windows Server 2008. This seems to happen in batches affecting some but not all of sites on the same App Pool. We have a large number of sites all running the same code. Once a site has failed to load a DLL it throws up a Yellow Screen of Death until the next App Pool recycle. We haven't been able to reproduce this behavior and the sites seem to work fine for days or weeks at a time (and many App Pool recycles) before failing. Has anybody else seen similar behavior? Update: We've tried reproducing the failure by setting up a few hundred sites and writing a script to hit them repeatedly while recycling the App Pool once every couple of minutes and were unable to accomplish much other than loading down the server's CPU for a few days straight. We then tried messing (locking one of the DLLs, changing the file permissions) with the copies of the DLLs that ASP.NET makes and managed to reproduce similar behavior but not the same exception. Does anybody have any ideas on how to adjust the security policy to get it to throw a System.Security.Policy.PolicyException: Execution permission cannot be acquired. when loading a specific DLL?

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• Java ReentrantReadWriteLocks - how to safely acquire write lock?

  - by Andrzej Doyle

  I am using in my code at the moment a ReentrantReadWriteLock to synchronize access over a tree-like structure. This structure is large, and read by many threads at once with occasional modifications to small parts of it - so it seems to fit the read-write idiom well. I understand that with this particular class, one cannot elevate a read lock to a write lock, so as per the Javadocs one must release the read lock before obtaining the write lock. I've used this pattern successfully in non-reentrant contexts before. What I'm finding however is that I cannot reliably acquire the write lock without blocking forever. Since the read lock is reentrant and I am actually using it as such, the simple code lock.getReadLock().unlock(); lock.getWriteLock().lock() can block if I have acquired the readlock reentrantly. Each call to unlock just reduces the hold count, and the lock is only actually released when the hold count hits zero. EDIT to clarify this, as I don't think I explained it too well initially - I am aware that there is no built-in lock escalation in this class, and that I have to simply release the read lock and obtain the write lock. My problem is/was that regardless of what other threads are doing, calling getReadLock().unlock() may not actually release this thread's hold on the lock if it acquired it reentrantly, in which case the call to getWriteLock().lock() will block forever as this thread still has a hold on the read lock and thus blocks itself. For example, this code snippet will never reach the println statement, even when run singlethreaded with no other threads accessing the lock: final ReadWriteLock lock = new ReentrantReadWriteLock(); lock.getReadLock().lock(); // In real code we would go call other methods that end up calling back and // thus locking again lock.getReadLock().lock(); // Now we do some stuff and realise we need to write so try to escalate the // lock as per the Javadocs and the above description lock.getReadLock().unlock(); // Does not actually release the lock lock.getWriteLock().lock(); // Blocks as some thread (this one!) holds read lock System.out.println("Will never get here"); So I ask, is there a nice idiom to handle this situation? Specifically, when a thread that holds a read lock (possibly reentrantly) discovers that it needs to do some writing, and thus wants to "suspend" its own read lock in order to pick up the write lock (blocking as required on other threads to release their holds on the read lock), and then "pick up" its hold on the read lock in the same state afterwards? Since this ReadWriteLock implementation was specifically designed to be reentrant, surely there is some sensible way to elevate a read lock to a write lock when the locks may be acquired reentrantly? This is the critical part that means the naive approach does not work.

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• What are the reasons why the CPU usage doesn’t go 100% with C# and APM?

  - by Martin

  I have an application which is CPU intensive. When the data is processed on a single thread, the CPU usage goes to 100% for many minutes. So the performance of the application appears to be bound by the CPU. I have multithreaded the logic of the application, which result in an increase of the overall performance. However, the CPU usage hardly goes above 30%-50%. I would expect the CPU (and the many cores) to go to 100% since I process many set of data at the same time. Below is a simplified example of the logic I use to start the threads. When I run this example, the CPU goes to 100% (on an 8/16 cores machine). However, my application which uses the same pattern doesn’t. public class DataExecutionContext { public int Counter { get; set; } // Arrays of data } static void Main(string[] args) { // Load data from the database into the context var contexts = new List<DataExecutionContext>(100); for (int i = 0; i < 100; i++) { contexts.Add(new DataExecutionContext()); } // Data loaded. Start to process. var latch = new CountdownEvent(contexts.Count); var processData = new Action<DataExecutionContext>(c => { // The thread doesn't access data from a DB, file, // network, etc. It reads and write data in RAM only // (in its context). for (int i = 0; i < 100000000; i++) c.Counter++; }); foreach (var context in contexts) { processData.BeginInvoke(context, new AsyncCallback(ar => { latch.Signal(); }), null); } latch.Wait(); } I have reduced the number of locks to the strict minimum (only the latch is locking). The best way I found was to create a context in which a thread can read/write in memory. Contexts are not shared among other threads. The threads can’t access the database, files or network. In other words, I profiled my application and I didn’t find any bottleneck. Why the CPU usage of my application doesn’t go about 50%? Is it the pattern I use? Should I create my own thread instead of using the .Net thread pool? Is there any gotchas? Is there any tool that you could recommend me to find my issue? Thanks!

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• Asynchronous callback for network in Objective-C Iphone

  - by vodkhang

  I am working with network request - response in Objective-C. There is something with asynchronous model that I don't understand. In summary, I have a view that will show my statuses from 2 social networks: Twitter and Facebook. When I clicked refresh, it will call a model manager. That model manager will call 2 service helpers to request for latest items. When 2 service helpers receive data, it will pass back to model manager and this model will add all data into a sorted array. What I don't understand here is that : when response from social networks come back, how many threads will handle the response. From my understanding about multithreading and networking (in Java), there must have 2 threads handle 2 responses and those 2 threads will execute the code to add the responses to the array. So, it can have race condition and the program can go wrong right? Is it the correct working model of iphone objective-C? Or they do it in a different way that it will never have race condition and we don't have to care about locking, synchronize? Here is my example code: ModelManager.m - (void)updateMyItems:(NSArray *)items { self.helpers = [self authenticatedHelpersForAction:NCHelperActionGetMyItems]; for (id<NCHelper> helper in self.helpers) { [helper updateMyItems:items]; // NETWORK request here } } - (void)helper:(id <NCHelper>)helper didReturnItems:(NSArray *)items { [self helperDidFinishGettingMyItems:items callback:@selector(model:didGetMyItems:)]; break; } } // some private attributes int *_currentSocialNetworkItemsCount = 0; // to count the number of items of a social network - (void)helperDidFinishGettingMyItems:(NSArray *)items { for (Item *item in items) { _currentSocialNetworkItemsCount ++; } NSLog(@"count: %d", _currentSocialNetworkItemsCount); _currentSocialNetworkItemsCount = 0; } I want to ask if there is a case that the method helperDidFinishGettingMyItems is called concurrently. That means, for example, faceboook returns 10 items, twitter returns 10 items, will the output of count will ever be larger than 10? And if there is only one single thread, how can the thread finishes parsing 1 response and jump to the other response because, IMO, thread is only executed sequently, block of code by block of code

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