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  • What's the difference between instance and server process in Oracle database.

    - by Summer_More_More_Tea
    Hi folks: I'm now getting familiar with Oracle database. Unfortunately, I'm puzzled by the concept instance and server process. My question is what's the difference between instance and server process. What's more, what's the life cycle of instance and server process respectively? My textbook at hand is about Oracle 9i, which doesn't give me a clear explanation. Any reply will be appreciated. Thanks in advance. Kind regards!

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  • Type Casting variables in PHP: Is there a practical example?

    - by Stephen
    PHP, as most of us know, has weak typing. For those who don't, PHP.net says: PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which the variable is used. Love it or hate it, PHP re-casts variables on-the-fly. So, the following code is valid: $var = "10"; $value = 10 + $var; var_dump($value); // int(20) PHP also alows you to explicitly cast a variable, like so: $var = "10"; $value = 10 + $var; $value = (string)$value; var_dump($value); // string(2) "20" That's all cool... but, for the life of me, I cannot conceive of a practical reason for doing this. I don't have a problem with strong typing in languages that support it, like Java. That's fine, and I completely understand it. Also, I'm aware of—and fully understand the usefulness of—type hinting in function parameters. The problem I have with type casting is explained by the above quote. If PHP can swap types at-will, it can do so even after you force cast a type; and it can do so on-the-fly when you need a certain type in an operation. That makes the following valid: $var = "10"; $value = (int)$var; $value = $value . ' TaDa!'; var_dump($value); // string(8) "10 TaDa!" So what's the point? Can anyone show me a practical application or example of type casting—one that would fail if type casting were not involved? I ask this here instead of SO because I figure practicality is too subjective. Edit in response to Chris' comment Take this theoretical example of a world where user-defined type casting makes sense in PHP: You force cast variable $foo as int -- (int)$foo. You attempt to store a string value in the variable $foo. PHP throws an exception!! <--- That would make sense. Suddenly the reason for user defined type casting exists! The fact that PHP will switch things around as needed makes the point of user defined type casting vague. For example, the following two code samples are equivalent: // example 1 $foo = 0; $foo = (string)$foo; $foo = '# of Reasons for the programmer to type cast $foo as a string: ' . $foo; // example 2 $foo = 0; $foo = (int)$foo; $foo = '# of Reasons for the programmer to type cast $foo as a string: ' . $foo;

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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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  • Type Casting variables in PHP: Is there a practical example?

    - by Stephen
    PHP, as most of us know, has weak typing. For those who don't, PHP.net says: PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which the variable is used. Love it or hate it, PHP re-casts variables on-the-fly. So, the following code is valid: $var = "10"; $value = 10 + $var; var_dump($value); // int(20) PHP also alows you to explicitly cast a variable, like so: $var = "10"; $value = 10 + $var; $value = (string)$value; var_dump($value); // string(2) "20" That's all cool... but, for the life of me, I cannot conceive of a practical reason for doing this. I don't have a problem with strong typing in languages that support it, like Java. That's fine, and I completely understand it. Also, I'm aware of—and fully understand the usefulness of—type hinting in function parameters. The problem I have with type casting is explained by the above quote. If PHP can swap types at-will, it can do so even after you force cast a type; and it can do so on-the-fly when you need a certain type in an operation. That makes the following valid: $var = "10"; $value = (int)$var; $value = $value . ' TaDa!'; var_dump($value); // string(8) "10 TaDa!" So what's the point? Can anyone show me a practical application or example of type casting—one that would fail if type casting were not involved? I ask this here instead of SO because I figure practicality is too subjective. Edit in response to Chris' comment Take this theoretical example of a world where user-defined type casting makes sense in PHP: You force cast variable $foo as int -- (int)$foo. You attempt to store a string value in the variable $foo. PHP throws an exception!! <--- That would make sense. Suddenly the reason for user defined type casting exists! The fact that PHP will switch things around as needed makes the point of user defined type casting vague. For example, the following two code samples are equivalent: // example 1 $foo = 0; $foo = (string)$foo; $foo = '# of Reasons for the programmer to type cast $foo as a string: ' . $foo; // example 2 $foo = 0; $foo = (int)$foo; $foo = '# of Reasons for the programmer to type cast $foo as a string: ' . $foo; UPDATE Guess who found himself using typecasting in a practical environment? Yours Truly. The requirement was to display money values on a website for a restaurant menu. The design of the site required that trailing zeros be trimmed, so that the display looked something like the following: Menu Item 1 .............. $ 4 Menu Item 2 .............. $ 7.5 Menu Item 3 .............. $ 3 The best way I found to do that wast to cast the variable as a float: $price = '7.50'; // a string from the database layer. echo 'Menu Item 2 .............. $ ' . (float)$price; PHP trims the float's trailing zeros, and then recasts the float as a string for concatenation.

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  • Running TeamCity from Amazon EC2 - Cloud based scalable build and continuous Integration

    - by RoyOsherove
    I’ve been having fun playing with the amazon EC2 cloud service. I set up a server running TeamCity, and an image of a server that just runs a TeamCity agent. I also setup TeamCity  to automatically instantiate agents on EC2 and shut them down based upon availability of free agents. Here’s how I did it: The first step was setting up the teamcity server. Create an account on amazon EC2 (BTW, amazon’s sites works better in IE than it does in chrome.. who knew!?) Open the EC2 dashboard, and click “Launch Instance” . From the “Quick Start” tab I selected from the list: “Getting Started on Microsoft Windows Server 2008 (AMI Id: ami-c5e40dac)” .  it’s good enough to just run teamcity. In the instance details, I used the default (Small instance, 1.7 GB mem). You might want to choose a close availability zone based on where you are. We want to “Launch instances” so click continue. Select the default kernel, RAM disk and all. No need to enable monitoring for now (you can do that later). click continue. If you don’t have a key pair, you will be prompted to create one. Once you do, select it in the list. Now you’ll be prompted to create a security group. I named mine “TC” as in “TeamCity”. each group is a bunch of settings on which ports can be let through into and out of a hosted machine.  keep it as the default settings. We will change them later. Click continue,  review and then click “Launch”. Now you’ll be able to see the new instance in the running instances list on your site. Now, you need to install stuff on that instance (TeamCity!) . To do that, you’ll need to Remote desktop into that instance. To do that, we’ll get the admin password for that instance: Check it on the list, and click “Instance Actions” - “Get Windows Admin Password”. You might have to wait about 10 minutes or so for the password to be generated for you. Once you have the password, you will remote desktop (start-run-‘mstsc’) into the instance. It’s address is a dns address shown below the list under “Public DNS”. it looks something like: ec2-256-226-194-91.compute-1.amazonaws.com Once you’re inside the instance – you’ll need to open IE (it is in hardened mode so you’ll have to relax its security settings to download stuff). I first downloaded chrome and using chrome I downloaded TeamCity. Note that the download speed is FAST. several MBs per second. To be able to see TeamCity from the outside, you will need to open the advanced firewall settings inside the remote machine, and add incoming and outgoing rules for port 80 (HTTP). Once you do that, you should be able to see the machine from the outside. If you still can’t, see the next step. I also enabled ports 9090 since I will use this machine to create an agent image later as well. Now configure the security group (TC) to enable talking to agents: IN the EC2 dashboard click on “Security Groups” and select your group. To add a rule, click on the empty list under the ‘protocol’ header. select TCP. from and ‘to’ ports are 9090. source ip is 0.0.0.0/0 (every ip is allowed). click “Save.  Also make sure you can see “HTTP” tcp 80 in that list. if you can’t see it, add it or you won’t be able to browse to the machine’s teamcity server home page. I also set an elastic IP for the machine: so I always have the same IP for the machine instance. Allocate and set one through the”Elastic IP” link on the EC2 dashboard.   you should now have a working instance of teamcity.   Now let’s create an agent image. Repeat steps 1-9, but this time, make sure you select a machine that fits what an agent might do. I selected Instance type – Hihg-CPU medium machine,  that is much faster. On that machine, I installed what I needed (VS 2010, PostSharp etc..). downloading VS 2010 from MSDN (2 GB took less than 10 min!) Now, instead of installing teamcity, browse using the browser to the teamcity homepage (from within the remote machine). go to the Administration page, and click the upper right link “Install agents”. Install the agent on he local machine – set it to the IP or DNS of the running TeamCity server. That way you’ll be able to check their connectivity live before making this machine your official agent image to reuse. Once the agent is installed, see that the TC server can see it and use it. see steps 13-14 above if they can’t. Once it works, you can take steps to make this image your agent image to be reused. next, here is a copy-paste of several steps to take from http://confluence.jetbrains.net/display/TCD5/Setting+Up+TeamCity+for+Amazon+EC2 Configure system so that agent it is started on machine boot (and make sure TeamCity server is accessible on machine boot). Test the setup by rebooting machine and checking that the agent connects normally to the server. Prepare the Image for bundling: Remove any temporary/history information in the system. Stop the agent (under Windows stop the service but leave it in Automatic startup type) Delete content agent logs and temp directories (not necessary) Delete "<Agent Home>/conf/amazon-*" file (not necessary) Change config/buildAgent.properties to remove properties: name, serverAddress, authToken (not necessary)   Now, we need to: Make AMI from the running instance. Configure TeamCity EC2 support on TeamCity server. Making an AMI: Check the instance of the agent in the EC2 dashboard instance list, and select instance actions->Create Image (EBS AMI) you’ll see the image pending in the APIs list in the EC2 dashboard. this could take 30 minutes or more. meanwhile we can configure the could support in the teamcity server. COPY THE AMI ID to the clipboard (looks like ami-a88aa4ce) Configuring TeamCity for Cloud: In TeamCity, click on “Agents” and then on “Cloud” tab. this is where you will control your cloud agents. to configure new cloud agents based on APIs, click on the right link to the “configuration page” Create a new profile and select AMazon EC2 as cloud type. Use your AMI ID that you copied to the clipboard into the “Images” field. Select an availability zone that is the same as the one your instance is running on for best communication perf between them make sure you select the ‘TC’ security group hopefully, that should be it, and teamcity will try to instantiate new instances on demand. Note that it may take around 10 minutes for an agent to become available to teamcity from the time it’s started.

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  • SOA & BPM Best of Oracle OpenWorld 2011

    - by JuergenKress
    Oracle OpenWorld 2011 is over – what important updates did you miss? Keynotes: Best of Oracle OpenWorld keynotes and general session is available on-demand: " + __flash__argumentsToXML(arguments,0) + "")); }' s_getswfurl='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getcharset='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getversion='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getmovieid='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getpageurl='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getpagename='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getaccount='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_gettrackclickmap='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' s_getdomindex='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' onomnitureunload='function () { return eval(instance.CallFunction("" + __flash__argumentsToXML(arguments,0) + "")); }' We recommend to watch: Oracle Cloud Computing Larry Ellison, CEO, Oracle Watch full-length keynote   Middleware General Session Hasan Rizvi, SVP, Oracle Watch full-length general session Presentations: All presentations are available online at the OpenWorld Content Catalog Product highlight: Was to launch of BPM Suite 11.1.1.5 Feature Pack Released and the Oracle Process Accelerators. For details please visit the Oracle BPM team blog and the Oracle SOA team blog.

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  • Why "object reference not set to an instance of an object" doesn't tell us which object?

    - by Saeed Neamati
    We're launching a system, and we sometimes get the famous exception NullReferenceException with the message Object reference not set to an instance of an object. However, in a method where we have almost 20 objects, having a log which says an object is null, is really of no use at all. It's like telling you, when you are the security agent of a seminar, that a man among 100 attendees is a terrorist. That's really of no use to you at all. You should get more information, if you want to detect which man is the threatening man. Likewise, if we want to remove the bug, we do need to know which object is null. Now, something has obsessed my mind for several months, and that is: Why .NET doesn't give us the name, or at least the type of the object reference, which is null?. Can't it understand the type from reflection or any other source? Also, what are the best practices to understand which object is null? Should we always test nullability of objects in these contexts manually and log the result? Is there a better way?

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  • What is the list of special variables available when writing a shell command for a context menu

    - by giovanni.pellicciotta
    When extending the Windows' shell context menu (e.g. for adding an 'Open command here' prompt on directories), a 'command' key needs to be created in the registry. The value of this 'command' key apparently can be any valid command line. I want to know which 'special variables' are available for use inside this command line. For example, I use following command for opening and cmd window from within a directory's context menu (*): cmd.exe /e:on /f:on /s /k pushd "%V" I cannot find any reference to what %V actually means or what the full list of such variables is. (*) Following registry keys are created for this: [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Directory\shell\cmdshell] @=Open Command Prompt Here" HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Directory\shell\cmdshell\command] @="cmd.exe /e:on /f:on /s /k pushd \"%V\""

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  • fglrx: No matching Device section for instance... found how to fix it?

    - by Lejo
    I have HD 4850 card, Ubuntu 12.10 and installed legacy drivers using makson96 ppa. The issue is, that FGLRX can not detect my device and loads vesa bios. I had the same problem on ubuntu 11.10, 12.04 versions. I want to manually help fglrx find a matching device to load as it shoudld do. It is interesting, why does fglrx search for a device in a PCI:0@1:0:1 Bus? in xorg.cof different bus is indicated: Section "Device" Identifier "aticonfig-Device[0]-0" Driver "fglrx" BusID "PCI:1:0:0" EndSection fglrxinfo display: :0.0 screen: 0 OpenGL vendor string: Advanced Micro Devices, Inc. OpenGL renderer string: ATI Radeon HD 4800 Series OpenGL version string: 3.3.11653 Compatibility Profile Context Here is a part of my xorg log: [ 3.846] (II) VESA: driver for VESA chipsets: vesa [ 3.846] (II) FBDEV: driver for framebuffer: fbdev [ 3.846] (++) using VT number 7 [ 3.846] (WW) Falling back to old probe method for fglrx [ 3.883] (II) Loading PCS database from /etc/ati/amdpcsdb [ 3.883] (--) Assigning device section with no busID to primary device [ 3.883] (--) Chipset Supported AMD Graphics Processor (0x9442) found [ 3.884] (WW) fglrx: No matching Device section for instance (BusID PCI:0@1:0:1) found [ 3.884] (II) AMD Video driver is running on a device belonging to a group targeted for this release [ 3.884] (II) AMD Video driver is signed [ 3.884] (II) fglrx(0): pEnt->device->identifier=0xb7791d8f [ 3.884] (WW) Falling back to old probe method for vesa [ 3.884] (WW) Falling back to old probe method for fbdev from lispci i foud out finally, that my video card is in 01:00.0 slot. logically, if fglrx searches for a vdeo card device in a wrong place, it will not find it. 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI RV770 [Radeon HD 4850] Thanks in advance.

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  • Generating/managing config files for hosted application

    - by mfinni
    I asked a question about config management, and haven't seen a reply. It's possible my question was too vague, so let's get down to brass tacks. Here's the process we follow when onboarding a new customer instance into our hosted application : how would you manage this? I'm leaning towards a Perl script to populate templates to generate shell scripts, config files, XML config files, etc. Looking briefly at CFengine and Chef, it seems like they're not going to reduce the amount of work, because I'd still have to manually specify all of the changes/edits within the tool. Doesn't seem to be much of a gain over touching the config files directly. We add a stanza to the main config file for the core (3rd-party) application. This stanza has values that defines the instance (customer) name the TCP listener port for this instance (not one currently used) the DB2 database name (serial numeric identifier, already exists, they get prestaged for us by the DBAs) three sub-config files, by name - they need to be created from 3 templates and be named after the instance The sub-config files define: The filepath for the DB2 volumes The filepath for the storage of objects The filepath for just one of the DB2 volumes (yes, redundant to the first item. We run some application commands, start the instance We do some LDAP thingies (make an OU for the instance, etc.) We add a stanza to the config file for our security listener that acts as a passthrough to LDAP instance name LDAP OU TCP port for instance DB2 database name We restart the security listener (off-hours), change the main config file from item 1, stop and restart the instance. It is now authenticating via LDAP. We add the stop and start commands for this instance to the HA failover scripts. We import an XML config file into the instance that defines things for the actual application for the customer - user names, groups, permissions, and business rules. The XML is supplied by the implementation team. Now, we configure the dataloading application We add a stanza to the existing top-level config file that points to a new customer-level config file. The new customer-level config file includes: the instance (customer) name the DB2 database name arbitrary number of sub-config files, by name Each of the sub-config files defines: filepaths to the directories for ingestion, feedback, backup, and failure those filepaths have a common path to a customer-specific folder, and then one folder for each sub-config file Each of those filepaths needs to be created We need to add this customer instance to our monitoring scripts that confirm the proper processes are running and can be logged into. Of course, those monitoring config files include the instance name, the TCP port, the DB2 database name, etc. There's also a reporting application that needs to be configured for the new instance. You get the idea. There's also XML that is loaded into WAS by the middleware team. We give them the values for them to plug into the XML - they could very easily hand us the template and we could give them back completed XML.

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  • What Are All the Variables Necessary to Create Blackbox Logs for Nginx?

    - by Alan Gutierrez
    There's an article out there, Profiling LAMP Applications with Apache's Blackbox Logs, that describes how to create a log that records a lot of detailed information missing in the common and combined log formats. This information is supposed to help you resolve performance issues. As the author notes "While the common log-file format (and the combined format) are great for hit tracking, they aren't suitable for getting hardcore performance data." The article describes a "blackbox" log format, like a blackbox flight recorder on an aircraft, that gathers information used to profile server performance, missing from the hit tracking log formats: Keep alive status, remote port, child processes, bytes sent, etc. LogFormat "%a/%S %X %t \"%r\" %s/%>s %{pid}P/%{tid}P %T/%D %I/%O/%B" blackbox I'm trying to recreate as much of the format for Nginx, and would like help filling in the blanks. Here's what Nginx blackbox format would look like, the unmapped Apache directives have question marks after their names. access_log blackbox '$remote_addr/$remote_port X? [$time_local] "$request"' 's?/$status $pid/0 T?/D? I?/O?/B?' Here's a table of the variables I've been able to map from the Nginx documentation. %a = $remote_addr - The IP address of the remote client. %S = $remote_port - The port of the remote client. %X = ? - Keep alive status. %t = $time_local - The start time of the request. %r = $request - The first line of request containing method verb, path and protocol. %s = ? - Status before any redirections. %>s = $status - Status after any redirections. %{pid}P = $pid - The process id. %{tid}P = N/A - The thread id, which is non-applicable to Nignx. %T = ? - The time in seconds to handle the request. %D = ? - The time in milliseconds to handle the request. %I = ? - The count of bytes received including headers. %O = ? - The count of bytes sent including headers. %B = ? - The count of bytes sent excluding headers, but with a 0 for none instead of '-'. Looking for help filling in the missing variables, or confirmation that the missing variables are in fact, unavailable in Nginx.

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  • Multiple MySQL instances via mysqlmanager under Debian

    - by Karolis T.
    Has anyone got multiple MySQL instances running on Debian with mysqlmanager? Problem is, Debian doesn't ship with init.d script that takes mysqlmanager into account. Oh, and it doesn't work for me. I'm trying to run 3 instances, here's what I get after starting mysqlmanager # mysqlmanager --defaults-file=/etc/mysql/my.cnf ... 090614 0:42:10 starting instance 'mysqld2'... 090614 0:42:10 guardian: starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld3'... 090614 0:42:10 guardian: starting instance 'mysqld3'... 090614 0:42:10 guardian: starting instance 'mysqld2'... 090614 0:42:10 starting instance 'mysqld2'... 090614 0:42:10 guardian: starting instance 'mysqld1'... 090614 0:42:10 starting instance 'mysqld1'... ... It just keeps "starting" and "restarting", but no MySQL instance ever starts up.

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  • Storing user info in Session using an Object vs. normal variables

    - by justinl
    I'm in the process of implementing a user authentication system for my website. I'm using an open source library that maintains user information by creating a User object and storing that object inside my php SESSION variable. Is this the best way to store and access that information? I find it a bit of a hassle to access the user variables because I have to create an object to access them first: $userObj = $_SESSION['userObject']; $userObj->userId; instead of just accessing the user id like this how I would usually store the user ID: $_SESSION['userId']; Is there an advantage to storing a bunch of user data as an object instead of just storing them as individual SESSION variables? ps - The library also seems to store a handful of variables inside the user object (id, username, date joined, email, last user db query) but I really don't care to have all that information stored in my session. I only really want to keep the user id and username.

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  • How can I access variables outside of current scope in javascript?

    - by sekmet64
    I'm writing some application in javascript and cannot figure it out how to access the variables declared in my function, inside this jquery parse. Inside I can access global variables, but I don't really want to create global vars for these values. Basically I want to extract file names from an xml document in the simulationFiles variable. I check if the node attribute is equal with the simName and extract the two strings inside the xml elements, that part I think it's working. How can I extract those xml elements and append them to local variables? function CsvReader(simName) { this.initFileName = "somepath"; this.eventsFileName = "somepath"; $(simulationFiles).find('simulation').each(function() { if ($(this).attr("name") == simName) { initFileName += $(this).find("init").text(); eventsFileName += $(this).find("events").text(); } }); }

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  • Should I use curly brackets or concatenate variables within strings?

    - by mririgo
    Straight forward question: Is there an advantage or disadvantage to concatenating variables within strings or using curly braces instead? Concatenated: $greeting = "Welcome, ".$name."!"; Curly braces: $greeting = "Welcome, {$name}!"; Personally, I've always concatenated my strings because I use UEStudio and it highlights PHP variables a different color when concatenated. However, when the variable is not broken out, it does not. It just makes it easier for my eyes to find PHP variables in long strings, etc. EDIT: People are confusing this about being about SQL. This is not what this question is about. I've updated my examples to avoid confusion.

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  • How is this statement making sense? (Sun's naming convention for Java variables)

    - by polygenelubricants
    I've been quoting this segment from Sun's document for the past few days, and only now do I stop and think about what it's saying, and I can't make sense out of it. Please keep in mind that English is not my first language. Naming conventions Variables: Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. How is this making sense? Isn't this saying that class names are in mixed case with a lowercase first letter? Like I should name it class myClass? And class constants are also in mixed case with a lowercase first letter? Like I should name it Integer.maxValue? And is it really saying anything about how variables themselves should be named? Am I not parsing this properly or is this actually a blatant error?

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  • How to open a pdf or a djvu on an specific instance of a document viewer?

    - by ciro
    I want using any free Linux document viewer that does both pdf and djvu (Okular, Evince, etc.) to do the following: magic_command('document-viewer','./11.pdf','instance1') magic_command('document-viewer','./21.djvu','instance2') two instances (windows) of document-viewer are opened one with 11.pdf and the other with 21.djvu then: magic_command('document-viewer','./12.djvu','instance1') magic_command('document-viewer','./22.pdf','instance2') the first instance (window) of document-viewer loads 12.djvu the second instance (window) of document-viewer loads 22.pdf

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  • Small website on Amazon EC2 Linux: a single large instance or more small instances in load balancing?

    - by Enrico Detoma
    I need to run a small website with a JSON webservice on Amazon EC2 Linux. The largest number of requests come from the JSON webservice, which provides some load in terms of MySQL queries. I'm trying to decide between two choices: A single large instance (Ubuntu 12.04 64-bit) with full LAMP stack or One or two small instances (Ubuntu 12.04 64-bit) with Apache/PHP only One small instance dedicated to MySQL (or RDS) Which setup would you consider to be more performant?

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  • What's the easiest way to auto-backup an EC2 instance?

    - by ripper234
    I have an EBS-backed Amazon EC2 instance. I would like to create a daily backup schedule, and keep, say, a week's worth of daily backups, plus a few older images (from 2,3,4 weeks ago). I don't mind creating the backups on the fly, with the snapshot mechanism, but I would like an easy wrapper to manage it for me. What is the simplest way to set this up? How much would this cost me, for a micro instance?

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  • Ruby on Rails ActiveRecord/Include/Associations can't get my query to work

    - by Cypher
    I just started learning Rails and I'm just trying to set up query via associations. All the queries I try to write seem to be doing bizzare things and end up trying to query two tables parsed together with an '_' as one table. I have no clue why this would ever happen My tables are as follows: schools: id name variables: id name type var_entries: id variable_id entry school_entries: id school_id var_entry_id my rails association tables are $local = { :adapter => "mysql", :host => "localhost", :port => "3306".to_i, :database => "spy_2", :username =>"root", :password => "vertrigo" } class School < ActiveRecord::Base establish_connection $local has_many :school_entries has_many :var_entries, :through => school_entries end class Variable < ActiveRecord::Base establish_connection $local has_many :var_entries has_many :school_entries, :through => :var_entries end class VarEntry < ActiveRecord::Base establish_connection $local has_many_and_belongs_to :school_entries belongs_to :variables end class SchoolEntry < ActiveRecord::Base establish_connection $local belongs_to :school has_many :var_entries end I want to do this sql query: SELECT school_id, variable_id,rank FROM school_entries, variables, var_entries, schools WHERE var_entries.variable_id = variables.id AND school_entries.var_entry_id = var_entries.id AND schools.id = school_entries.school_id AND variables.type = 'number'; and put it into Rails notation: here is one of my many failed attempts schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "variables.type = 'number'") the error: 'const_missing': uninitialized constant VarEntry::Variables (NameError) if i remove variables schools = VarEntry.all(:include => [:school_entries, :variables], :conditions => "type = 'number'") the error is: Mysql::Error: Unkown column 'type' in 'where clause': SELECT * FROM 'var_entries' WHERE (type=number) (ActiveRecord::StatementInvalid) Can anyone tell me where I'm going horribly wrong?

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  • List of Django model instance foreign keys losing consistency during state changes.

    - by Joshua
    I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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  • How can I make a Maybe-Transformer MaybeT into an instance of MonadWriter?

    - by martingw
    I am trying to build a MaybeT-Transformer Monad, based on the example in the Real World Haskell, Chapter Monad Transformers: data MaybeT m a = MaybeT { runMT :: m (Maybe a) } instance (Monad m) => Monad (MaybeT m) where m >>= f = MaybeT $ do a <- runMT m case a of Just x -> runMT (f x) Nothing -> return Nothing return a = MaybeT $ return (Just a) instance MonadTrans MaybeT where lift m = MaybeT $ do a <- m return (Just a) This works fine, but now I want to make MaybeT an instance of MonadWriter: instance (MonadWriter w m) => MonadWriter w (MaybeT m) where tell = lift . tell listen m = MaybeT $ do unwrapped <- listen (runMT m) return (Just unwrapped) The tell is ok, but I can't get the listen function right. The best I could come up with after 1 1/2 days of constructor origami is the one you see above: unwrapped is supposed to be a tuple of (Maybe a, w), and that I want to wrap up in a Maybe-Type and put the whole thing in an empty MonadWriter. But the compiler complains with: Occurs check: cannot construct the infinite type: a = Maybe a When generalising the type(s) for `listen' In the instance declaration for `MonadWriter w (MaybeT m)' What am I missing?

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