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• QSqlQuery UPDATE/INSERT DateTime with server's time (eg CURRENT_TIMESTAMP)

  - by Skinniest Man

  I am using QSqlQuery to insert data into a MySQL database. Currently all I care about is getting this to work with MySQL, but ideally I'd like to keep this as platform-independent as possible. What I'm after, in the context of MySQL, is to end up with code that effectively executes something like the following query: UPDATE table SET time_field=CURRENT_TIMESTAMP() WHERE id='5' The following code is what I have attempted, but it fails: QSqlQuery query; query.prepare("INSERT INTO table SET time_field=? WHERE id=?"); query.addBindValue("CURRENT_TIMESTAMP()"); query.addBindValue(5); query.exec(); The error I get is: Incorrect datetime value: 'CURRENT_TIMESTAMP()' for column 'time_field' at row 1 QMYSQL3: Unable to execute statement. I am not surprised as I assume Qt is doing some type checking when it binds values. I have dug through the Qt documentation as well as I know how, but I can't find anything in the API designed specifically for supporting MySQL's CURRENT_TIMESTAMP() function, or that of any other DBMS. Any suggestions?

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• Error in connection in ruby.

  - by piemesons

  require 'rubygems' require 'mysql' db = Mysql.connect('localhost', 'root', '', 'mohit') //db.rb:4: undefined method `connect' for Mysql:Class (NoMethodError) //undefined method `real_connect' for Mysql:Class (NoMethodError) db.query("CREATE TABLE people ( id integer primary key, name varchar(50), age integer)") db.query("INSERT INTO people (name, age) VALUES('Chris', 25)") begin query = db.query('SELECT * FROM people') puts "There were #{query.num_rows} rows returned" query.each_hash do |h| puts h.inspect end rescue puts db.errno puts db.error end error i am geting is: undefined method `connect' for Mysql:Class (NoMethodError) OR undefined method `real_connect' for Mysql:Class (NoMethodError) EDIT return value of Mysql.methods ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "object_id", "__send__", "method_defined?", "instance_variable_defined?", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "instance_method", "hash", "autoload?", "dup", "to_enum", "instance_methods", "public_method_defined?", "instance_variables", "class_variable_defined?", "eql?", "constants", "id", "instance_eval", "singleton_methods", "module_exec", "const_missing", "taint", "instance_variable_get", "frozen?", "enum_for", "private_method_defined?", "public_instance_methods", "display", "instance_of?", "superclass", "method", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "public_class_method", "to_s", "<=", "const_set", "allocate", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "autoload", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"] return value of Mysql.methods(false) is []... blank array

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• JPA/Hibernate Parent/Child relationship

  - by NubieJ

  Hi I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this): I have two entities: Parent and Child (naming changed). Parent contains a list of Children and Children refers back to parent. e.g. @Entity public class Parent { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "PARENT_ID", insertable = false, updatable = false) private int id; /* ..... */ @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true) private Set<child> children; /* ..... */ } @Entity public class Child { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "CHILD_ID", insertable = false, updatable = false) private int id; /* ..... */ @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID") private Parent parent; /* ..... */ } I want to be able to do the following: Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY. Retrieve a Child entity which would contain an instance of the Parent entity. Using the code above (or similar) results in two exceptions: Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML... Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id") Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId); return (Parent) query.getSingleResult(); } Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?

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• Best practice accessing an array set within a class

  - by user350599

  I have created a basic class for a customer. I haven't done this before and want to know the best way to access the data. Should I have a get() method for every field in the customer array or should I simply pass the customer array back and access with the page. i.e. Just return the array class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); $this->customer = mysql_fetch_row($query); } public function get_customer() { return $this->customer; } } versus create a method for each item in the array class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); $this->customer = mysql_fetch_row($query); } public function get_customer_name() { return $this->customer->customer_name; } ... ... } versus option 3 based on Tobias' feedback: (not sure if syntax is correct) class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; return $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); return mysql_fetch_row($query); } }

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• The question about the basics of LINQ to SQL working

  - by Alex

  I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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• Linq. Help me tune this!

  - by dtrick

  I have a linq query that is causing some timeout issues. Basically, I have a query that is returning the top 100 results from a table that has approximately 500,000 records. Here is the query: using (var dc = CreateContext()) { var accounts = string.IsNullOrEmpty(searchText) ? dc.Genealogy_Accounts .Where(a => a.Genealogy_AccountClass.Searchable) .OrderByDescending(a => a.ID) .Take(100) : dc.Genealogy_Accounts .Where(a => (a.Code.StartsWith(searchText) || a.Name.StartsWith(searchText)) && a.Genealogy_AccountClass.Searchable) .OrderBy(a => a.Code) .Take(100); return accounts.Select(a => } } Oddly enough it is the first linq query that is causing the timeout. I thought that by doing a 'Take' we wouldn't need to scan all 500k of records. However, that must be what is happening. I'm guessing that the join to find what is 'searchable' is causing the issue. I'm not able to denormalize the tables... so I'm wondering if there is a way to rewrite the linq query to get it to return quicker... or if I should just write this query as a Stored Procedure (and if so, what might it look like). Thanks.

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• Paginating requests to an API

  - by user332912

  I'm consuming (via urllib/urllib2) an API that returns XML results. The API always returns the total_hit_count for my query, but only allows me to retrieve results in batches of, say, 100 or 1000. The API stipulates I need to specify a start_pos and end_pos for offsetting this, in order to walk through the results. Say the urllib request looks like "http://someservice?query='test'&start_pos=X&end_pos=Y". If I send an initial 'taster' query with lowest data transfer such as http://someservice?query='test'&start_pos=1&end_pos=1 in order to get back a result of, for conjecture, total_hits = 1234, I'd like to work out an approach to most cleanly request those 1234 results in batches of, again say, 100 or 1000 or... This is what I came up with so far, and it seems to work, but I'd like to know if you would have done things differently or if I could improve upon this: hits_per_page=1000 # or 1000 or 200 or whatever, adjustable total_hits = 1234 # retreived with BSoup from 'taster query' base_url = "http://someservice?query='test'" startdoc_positions = [n for n in range(1, total_hits, hits_per_page)] enddoc_positions = [startdoc_position + hits_per_page - 1 for startdoc_position in startdoc_positions] for start, end in zip(startdoc_positions, enddoc_positions): if end total_hits: end = total_hits print "url to request is:\n ", print "%s&start_pos=%s&end_pos=%s" % (base_url, start, end) p.s. I'm a long time consumer of StackOverflow, especially the Python questions, but this is my first question posted. You guys are just brilliant.

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• Dividing numbers between rows in MySQL + PHP

  - by André Figueira

  Hi I am working on a kind of raffle system which divides 1 million random numbers into an x amount of tickets, e.g. 1 million random numbers to 10,000 tickets. Each ticket is a row in a database, we then have another table ticket numbers in which i need to give 100 numbers to each ticket they are related by the ticket id. So at the moment this is my code: //Amount of the 1 million tickets divided to the tickets $numbersPerTickets = $_POST['numbersPerTicket']; //The total cost of the property $propertyPrice = $_POST['propertyPrice']; //The total amount of tickets $totalTickets = NUMBER_CIELING / $numbersPerTickets; //The ticket price $ticketPrice = $propertyPrice / $totalTickets; //Generate array with random numbers up to 999,999 $randomTicketNumbers = createTicketNumbers(); //Creation loop counter $ticketCreationCount = 1; //Loop and create each ticket while($ticketCreationCount <= $totalTickets) { //Create a padded ticket number $ticketNumber = str_pad($ticketCreationCount, 6, 0, STR_PAD_LEFT); $query = ' INSERT INTO tickets( propertyID, ticketNumber, price ) VALUES( "'.$propertyID.'", "'.$ticketNumber.'", "'.$ticketPrice.'" ) '; $db->query($query); //Get the ID of the inserted ticket to use to insert the ticket numbers $ticketID = $db->insert_id; $loopBreak = $numbersPerTickets; $addedNumberCount = 1; foreach($randomTicketNumbers as $key => $value) { $query = ' INSERT INTO ticketNumbers( ticketID, number ) VALUES( "'.$ticketID.'", "'.$value.'" ) '; $db->query($query); unset($randomTicketNumbers[$key]); if($addedNumberCount == $loopBreak){ break; }else{ $addedNumberCount++; } } $ticketCreationCount++; } But this isn't working it adds the right amount of tickets, which in the case for testing is 10,000 but then adds far too many ticket numbers, it ends up exceeding the million numbers in the random tickets array, The random tickets array is just a simple 1 tier array with 1 million numbers sorted randomly.

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• Qt XQuery into a QStringList

  - by Stewart

  Hi, I'm trying to use QtXmlQuery to extract some data from XML. I'd like to put this into a QStringList. I try the following: QByteArray in = "this is where my xml lives"; QBuffer received; received.setData(in); received.open(QIODevice::ReadOnly); QXmlQuery query; query.bindVariable("data", &received); query.setQuery(NAMESPACE //contains definition of the t namespace "doc($data)//t:service/t:serviceID/text()"); QBuffer outb; outb.open(QIODevice::ReadWrite); QXmlSerializer s(query, &outb); query.evaluateTo(&s); qDebug() << "buffer" << outb.data(); //This works perfectly! QStringList * queryResult = new QStringList(); query.evaluateTo(queryResult); qDebug() << "string list" << *queryResult; //This gives me no output! As you can see, everything works fine when I send the output into a QBuffer via a QXmlSerializer... but I get nothing when I try to use a QStringList.

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• Why is only 2 of my querys working? (PHP/Mysql)

  - by ggfan

  When I remove a posting, I want it to remove the posting itself, any comments related to it, and like/dislike of the comments, and favorites that people added. So there are 4 queries that do this, but somehow only 2 of the 4 are working. When I switch say query 2 for query 3, then query 2 works and query 3 doesn't... The table names are correct and it is getting the data via $_GET. // Grab the data from the GET $posting_id = $_GET['posting_id']; // Delete the posting from the database $query = "DELETE FROM posting WHERE posting_id=$posting_id LIMIT 1"; mysqli_query($dbc, $query) or die(mysql_error()); // Delete the comments $query2 = "DELETE FROM comments WHERE posting_id=$posting_id "; mysqli_query($dbc, $query2) or die(mysql_error()); // Delete the like/dislike $query3 = "DELETE FROM comment_likedislike WHERE posting_id=$posting_id "; mysqli_query($dbc, $query3) or die(mysql_error()); // Delete the favorites $query4 = "DELETE FROM favorite WHERE posting_id=$posting_id "; mysqli_query($dbc, $query4) or die(mysql_error());

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• Passing arguments and conditions to model in codeigniter

  - by stormdrain

  I'm adding some models to a project, and was wondering if there is a "best practice" kind of approach to creating models: Does it make sense to create a function for each specific query? I was starting to do this, then had the idea of creating a generic function that I could pass parameters to. e.g: Instead of function getClients(){ return $this->db->query('SELECT client_id,last FROM Names ORDER BY id DESC'); } function getClientNames($clid){ return $this->db->query('SELECT * FROM Names WHERE client_id = '.$clid); } function getClientName($nameID){ return $this->db->query('SELECT * FROM Names WHERE id ='.$nameID); } } Something like function getNameData($args,$cond){ if($cond==''){ $q=$this->db->query('SELECT '.$args.' FROM Names'); return $q; }else{ $q=$this->db->query('SELECT '.$args.' FROM Names WHERE '.$cond); return $q; } } where I can pass the fields and conditions (if applicable) to the model. Is there a reason the latter example would be a bad idea? Thanks!

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• Java program will read from database, but not write to it

  - by ck1221

  I have a Java program that successfully connects to a mysql database that is hosted on godaddy's server. I can read from that db with out issue, however, when I try to write to it with INSERT or UPDATE for example, the query does not execute. I am using the 'admin' account that I set up through godaddy, I realize this is not the root account. I have checked and verified that the connection is not read only, and have logged out of phpmyadmin while the query ran. I'm not sure what else I can try or if anyone has experienced this issue. Maybe a setting to the connection I have failed to set? Or maybe its not possible since the db is hosted on godaddy's servers? Any help is great! Thanks. Here is some relevant code: Connection to db: Connection con; public DBconnection(String url, String user, String pass) { try { Class.forName("com.mysql.jdbc.Driver").newInstance(); con = DriverManager.getConnection (url,user,pass); if(!con.isClosed()) System.out.println("connecton open"); } catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();} } Send Query: public ResultSet executeQuery(String query) { ResultSet rs = null; try { Statement stmt = (Statement) con.createStatement(); rs = stmt.executeQuery(query); //while(rs.next()) //System.out.println(rs.getString("ticket_num")); } catch (SQLException e) {} return rs; } Insert Query (works in phpmyadmin): conn.executeQuery("INSERT INTO tickets VALUES(55555,'12/01/2012','me','reports','test','','','0','Nope')");

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• Need a design approach or suggestion for a simple structure using Servlet.

  - by akshay

  Hi I have to design such that whenever user pass a query I process it using servlet and then call the js page to draw the chart 1 user writes a query on a page 2 the page call the servelt class public class MyServlet extends Httpservlet implements DataSourceServlet {..... return data The user see a beautiful string like this.. google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); 3 when the user hits on different html page myhtml.js it draws the chart. I want the Myservlet class itself call the myhtml.js page and draw the chart directly. and want to eliminate the beautiful string google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); from coming on user's browser What should i do? I tried using functions to call another page like request dispatcher(), redirect() calling myhtml.js page directly after myservlet process the query results. But i get the result like this google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); and the entire myhtml.js code page below it on the browsers that to without the chart been draw. Is there anyway to element the beautiful string from coming on clients browser and only show them the chart been drawn ? :) This is the small tutorial i am following http://code.google.com/apis/visualization/documentation/dev/dsl_get_started.html

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• Applying iterative algorithm to a set of rows from database

  - by Corvin

  Hello, this question may seem too basic to some, but please bear with be, it's been a while since I dealt with decent database programming. I have an algorithm that I need to program in PHP/MySQL to work on a website. It performs some computations iteratively on an array of objects (it ranks the objects based on their properties). In each iteration the algorithm runs through all collection a couple of times, accessing various data from different places of the whole collection. The algorithm needs several hundred iterations to complete. The array comes from a database. The straightforward solution that I see is to take the results of a database query and create an object for each row of the query, put the objects to an array and pass the array to my algorithm. However, I'm concerned with efficacy of such solution when I have to work with an array of several thousand of items because what I do is essentially mirror the results of a query to memory. On the other hand, making database query a couple of times on each iteration of the algorithm also seems wrong. So, my question is - what is the correct architectural solution for a problem like this? Is it OK to mirror the query results to memory? If not, which is the best way to work with query results in such an algorithm? Thanks!

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• Composable FLinq expressions

  - by Daniel

  When doing linq-to-sql in c#, you could do something like this: var data = context.MyTable.Where(x => x.Parameter > 10); var q1 = data.Take(10); var q2 = data.Take(3); q1.ToArray(); q2.ToArray(); This would generate 2 separate SQL queries, one with TOP 10, and the other with TOP 3. In playing around with Flinq, I see that: let data = query <@ seq { for i in context.MyTable do if x.Parameter > 10 then yield i } @> data |> Seq.take 10 |> Seq.toList data |> Seq.take 3 |> Seq.toList is not doing the same thing. Here it seems to do one full query, and then do the "take" calls on the client side. An alternative that I see used is: let q1 = query <@ for i in context.MyTable do if x.Param > 10 then yield i } |> Seq.take 10 @> let q2 = query <@ for i in context.MyTable do if x.Param > 10 then yield i } |> Seq.take 3 @> These 2 generate the SQL with the appropriate TOP N filter. My problem with this is that it doesn't seem composable. I'm basically having to duplicate the "where" clause, and potentially would have to duplicate other other subqueries that I might want to run on a base query. Is there a way to have F# give me something more composable? (I originally posted this question to hubfs, where I have gotten a few answers, dealing with the fact that C# performs the query transformation "at the end", i.e. when the data is needed, where F# is doing that transformation eagerly.)

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• Efficient way to call .Sum() on multiple properties

  - by SherCoder

  I have a function that uses Linq to get data from the database and then I call that function in another function to sum all the individual properties using .Sum on each individual property. I was wondering if there is an efficient way to sum all the properties at once rather than calling .Sum() on each individual property. I think the way I am doing as of right now, is very slow (although untested). public OminitureStats GetAvgOmnitureData(int? fnsId, int dateRange) { IQueryable<OminitureStats> query = GetOmnitureDataAsQueryable(fnsId, dateRange); int pageViews = query.Sum(q => q.PageViews); int monthlyUniqueVisitors = query.Sum(q => q.MonthlyUniqueVisitors); int visits = query.Sum(q => q.Visits); double pagesPerVisit = (double)query.Sum(q => q.PagesPerVisit); double bounceRate = (double)query.Sum(q => q.BounceRate); return new OminitureStats(pageViews, monthlyUniqueVisitors, visits, bounceRate, pagesPerVisit); }

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• SelectQuery eating up 100% CPU

  - by modernzombie

  I am doing a query for all the users on the machine and when it executes it grabs 100% CPU and locks up the system. I have waited up to 5 minutes and nothing happens. In the Task Manager wmiprvse.exe is using all the CPU. When I kill that process everything returns to normal. Here is my code: SelectQuery query = new SelectQuery("Win32_UserAccount", "LocalAccount=1 and Domain='" + GetMachine().DomainName + "'"); using(ManagementObjectSearcher searcher = new ManagementObjectSearcher(query)) { IList<WindowsUser> users = new List<WindowsUser>(); Console.WriteLine("Getting users..."); foreach (ManagementObject envVar in searcher.Get()) { Console.WriteLine("Getting " + envVar["Name"].ToString() + "..."); } } In the console all I see is Getting users... and nothing else. The problem appears to be with searcher.Get(). Does anyone know why this query is taking 100% CPU? Thanks. EDIT: OK I found that it the WMI process is only eating 25% CPU but it doesn't get released if I end the program (the query never finishes). The next time I start an instance the process goes up to 50% CPU, etc, etc until it is at 100%. So my new question is why is the CPU not getting released and how long should a query like this take to complete?

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• Querying Networking Statistics: dlstat(1M)

  - by user12612042

  Oracle Solaris 11 took another big leap forward in networking technologies providing a reliable, secure and scalable infrastructure to meet the growing needs of today's datacenter implementations. Oracle Solaris 11 introduced a new and powerful network stack architecture, also known as Project Crossbow. From Solaris 11 onwards, we introduced a command line tool viz. dlstat(1M) to query network statistics. dlstat (for datalink statistics) is a statistics querying counterpart for dladm(1M) - the datalink administration tool. The tool is very easy to get started. Just type dlstat on a shell prompt on Solaris 11 (or later). For example,: # dlstat LINK IPKTS RBYTES OPKTS OBYTES net0 834.11K 145.91M 575.19K 104.24M net1 7.87K 2.04M 0 0 In this example, the system has two datalinks net0 and net1. The output columns denote input packets/bytes as well as output packets/bytes. The numbers are abbreviated in xxx.xxUnit format. However, one could get the actual counts by simply running dlstat -u R (R for raw): # dlstat -u R LINK IPKTS RBYTES OPKTS OBYTES net0 834271 145931244 575246 104242934 net1 7869 2036958 0 0 In addition, dlstat also supports various subcommands dlstat help The following subcommands are supported: Stats : show-aggr show-ether show-link show-phys show-bridge For more info, run: dlstat help {default|} I will only describe couple of interesting subcommands/options here. For a comprehensive description of all the dlstat subcommands refer dlstat's official manual . For NICs that support multiple rings (e.g. ixgbe), dlstat show-phys -r allows us to query per Rx ring statistics. For example: dlstat show-phys -r net4 LINK TYPE INDEX IPKTS RBYTES net4 rx 0 0 0 net4 rx 1 0 0 net4 rx 2 0 0 net4 rx 3 0 0 net4 rx 4 0 0 net4 rx 5 0 0 net4 rx 6 0 0 net4 rx 7 0 0 In this case, net4 is just a vanity name for an ixgbe datalink. This view is especially useful if one wants to look at the network traffic spread across all the available rings. Furthermore, any of the dlstat commands could be run with -i option to periodically query and display stats. For example, running dlstat show-phys -r net4 -i 5 will emit per Rx ring stats every 5 seconds. This is especially useful while analyzing a live system. Similarly, dlstat show-phys -t could be used to query per Tx ring stats. -r and -t could also be combined as dlstat show-phys -rt to query both Rx as well as Tx stats at the same time. Finally, there is also a quick way to dump ALL the stats. Just run dlstat -A. You probably want to redirect this output to a file because you are going to get a whole load of stats :-).

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• MAXDOP in SQL Azure

  - by Herve Roggero

  In my search of better understanding the scalability options of SQL Azure I stumbled on an interesting aspect: Query Hints in SQL Azure. More specifically, the MAXDOP hint. A few years ago I did a lot of analysis on this query hint (see article on SQL Server Central:  http://www.sqlservercentral.com/articles/Configuring/managingmaxdegreeofparallelism/1029/).  Here is a quick synopsis of MAXDOP: It is a query hint you use when issuing a SQL statement that provides you control with how many processors SQL Server will use to execute the query. For complex queries with lots of I/O requirements, more CPUs can mean faster parallel searches. However the impact can be drastic on other running threads/processes. If your query takes all available processors at 100% for 5 minutes... guess what... nothing else works. The bottom line is that more is not always better. The use of MAXDOP is more art than science... and a whole lot of testing; it depends on two things: the underlying hardware architecture and the application design. So there isn't a magic number that will work for everyone... except 1... :) Let me explain. The rules of engagements are different. SQL Azure is about sharing. Yep... you are forced to nice with your neighbors.  To achieve this goal SQL Azure sets the MAXDOP to 1 by default, and ignores the use of the MAXDOP hint altogether. That means that all you queries will use one and only one processor.  It really isn't such a bad thing however. Keep in mind that in some of the largest SQL Server implementations MAXDOP is usually also set to 1. It is a well known configuration setting for large scale implementations. The reason is precisely to prevent rogue statements (like a SELECT * FROM HISTORY) from bringing down your systems (like a report that should have been running on a different in the first place) and to avoid the overhead generated by executing too many parallel queries that could cause internal memory management nightmares to the host Operating System. Is summary, forcing the MAXDOP to 1 in SQL Azure makes sense; it ensures that your database will continue to function normally even if one of the other tenants on the same server is running massive queries that would otherwise bring you down. Last but not least, keep in mind as well that when you test your database code for performance on-premise, make sure to set the DOP to 1 on your SQL Server databases to simulate SQL Azure conditions.

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• SPSiteDataQuery Returns Only One List Type At A Time

  - by Brian Jackett

  The SPSiteDataQuery class in SharePoint 2007 is very powerful, but it has a few limitations.  One of these limitations that I ran into this morning (and caused hours of frustration) is that you can only return results from one list type at a time.  For example, if you are trying to query items from an out of the box custom list (list type = 100) and document library (list type = 101) you will only get items from the custom list (SPSiteDataQuery defaults to list type = 100.)  In my situation I was attempting to query multiple lists (created from custom list templates 10001 and 10002) each with their own content types. Solution     Since I am only able to return results from one list type at a time, I was forced to run my query twice with each time setting the ServerTemplate (translates to ListTemplateId if you are defining custom list templates) before executing the query.  Below is a snippet of the code to accomplish this. SPSiteDataQuery spDataQuery = new SPSiteDataQuery(); spDataQuery.Lists = "<Lists ServerTemplate='10001' />"; // ... set rest of properties for spDataQuery   var results = SPContext.Current.Web.GetSiteData(spDataQuery).AsEnumerable();   // only change to SPSiteDataQuery is Lists property for ServerTemplate attribute spDataQuery.Lists = "<Lists ServerTemplate='10002' />";   // re-execute query and concatenate results to existing entity results = results.Concat(SPContext.Current.Web.GetSiteData(spDataQuery).AsEnumerable());   Conclusion     Overall this isn’t an elegant solution, but it’s a workaround for a limitation with the SPSiteDataQuery.  I am now able to return data from multiple lists spread across various list templates.  I’d like to thank those who commented on this MSDN page that finally pointed out the limitation to me.  Also a thanks out to Mark Rackley for “name dropping” me in his latest article (which I humbly insist I don’t belong in such company)  as well as encouraging me to write up a quick post on this issue above despite my busy schedule.  Hopefully this post saves some of you from the frustrations I experienced this morning using the SPSiteDataQuery.  Until next time, Happy SharePoint’ing all.         -Frog Out   Links MSDN Article for SPSiteDataQuery http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spsitedataquery.lists.aspx

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• Entity Framework 4.0: Optimal and horrible SQL

  - by DigiMortal

  Lately I had Entity Framework 4.0 session where I introduced new features of Entity Framework. During session I found out with audience how Entity Framework 4.0 can generate optimized SQL. After session I also showed guys one horrible example about how awful SQL can be generated by Entity Framework. In this posting I will cover both examples. Optimal SQL Before going to code take a look at following model. There is class called Event and I will use this class in my query. Here is the LINQ To Entities query that uses small anonymous type. var query = from e in _context.Events             select new { Id = e.Id, Title = e.Title }; Debug.WriteLine(((ObjectQuery)query).ToTraceString()); Running this code gives us the following SQL. SELECT      [Extent1].[event_id] AS [event_id],      [Extent1].[title] AS [title]  FROM [dbo].[events] AS [Extent1] This is really small – no additional fields in SELECT clause. Nice, isn’t it? Horrible SQL Ayende Rahien blog shows us darker side of Entiry Framework 4.0 queries. You can find comparison betwenn NHibernate, LINQ To SQL and LINQ To Entities from posting What happens behind the scenes: NHibernate, Linq to SQL, Entity Framework scenario analysis. In this posting I will show you the resulting query and let you think how much better it can be done. Well, it is not something we want to see running in our servers. I hope that EF team improves generated SQL to acceptable level before Visual Studio 2010 is released. There is also morale of this example: you should always check out the queries that O/R-mapper generates. Behind the curtains it may silently generate queries that perform badly and in this case you need to optimize you data querying strategy. Conclusion Entity Framework 4.0 is new product with a lot of new features and it is clear that not everything is 100% super in its first release. But it still great step forward and I hope that on 12.04.2010 we have new promising O/R-mapper available to use in our projects. If you want to read more about Entity Framework 4.0 and Visual Studio 2010 then please feel free to follow this link to list of my Visual Studio 2010 and .NET Framework 4.0 postings.

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• EJB Named Criteria - Apply bind variable in Backingbean

  - by Deepak Siddappa

  EJB Named criteria are predefined and reusable where-clause definitions that are dynamically applied to a ViewObject query. Here we often use to filter the ViewObject SQL statement query based on Where Clause conditions.Take a scenario where we need to filter the SQL statements query based on Where Clause conditions, instead of playing with SQL statements use the EJB Named Criteria which is supported by default in ADF and set the Bind Variable parameter at run time.You can download the sample workspace from here [Runs with Oracle JDeveloper 11.1.2.0.0 (11g R2) + HR Schema] Implementation StepsCreate Java EE Web Application with entity based on Employees table, then create a session bean and data control for the session bean.Open the DataControls.dcx file and create sparse xml for as shown below. In sparse xml navigate to Named criteria tab -> Bind Variable section, create binding variable deptId. Now create a named criteria and map the query attributes to the bind variable. In the ViewController create index.jspx page, from data control palette drop employeesFindAll->Named Criteria->EmployeesCriteria->Table as ADF Read-Only Filtered Table and create the backingBean as "IndexBean".Open the index.jspx page and remove the "filterModel" binding from the table, add <af:inputText />, command button and bind them to backingBean. For command button create the actionListener as "applyEmpCriteria" and add below code to the file. public void applyEmpCriteria(ActionEvent actionEvent) { DCIteratorBinding dc = (DCIteratorBinding)evaluteEL("#{bindings.employeesFindAllIterator}"); ViewObject vo = dc.getViewObject(); vo.applyViewCriteria(vo.getViewCriteriaManager().getViewCriteria("EmployeesCriteria")); vo.ensureVariableManager().setVariableValue("deptId", this.getDeptId().getValue()); vo.executeQuery(); } /** * Programmtic evaluation of EL * * @param el EL to evalaute * @return Result of the evalutaion */ public Object evaluteEL(String el) { FacesContext fctx = FacesContext.getCurrentInstance(); ELContext elContext = fctx.getELContext(); Application app = fctx.getApplication(); ExpressionFactory expFactory = app.getExpressionFactory(); ValueExpression valExp = expFactory.createValueExpression(elContext, el, Object.class); return valExp.getValue(elContext); } Run the index.jspx page, enter departmentId value as 90 and click in ApplyEmpCriteria button. Now the bind variable for the Named criteria will be applied at runtime in the backing bean and it will re-execute ViewObject query to filter based on where clause condition.

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• Design pattern to handle queries using multiple models

  - by coderkane

  I am presented with a dilemma while trying to re-designing the class structure for my PHP/MySQL application to make it more elegant and conform it to the SOLID principle. The problem goes like this: Let as assume, there is an abstract class called person which has certain properties to define a generic person, such as name, age, date of birth etc. There are two classes, student, and teacher, that implements this abstract class. They add their own unique properties to it. I have designed all the three classes to include all the operational logic (details of which are not relevant in context of the question). Now, I need to create views/reports/data grids which contain details from multiple classes, for example, say, a list of all students doing projects in Chemistry mentored by a teacher whose name is the parameter to the query. This is just one example of a view, there are many different views in the application, which uses data from 3-4 tables, and each of them have multiple input parameters to generate them. Considering this particular example, I have written the relevant query using JOIN and the results are as expected and proper, now here is the dilemma: Keeping in mind the single responsibility principle, where should I keep this query? It does not belong to either Student class, or Teacher class or any other classes currently present. a) Should I create a new class, say dataView class, and design it as a MVC pattern and keep the query there? What about the other views? how do they fit in this architecture? b) Should I not keep the query in code at all, and make it DB View ? c) Am I completely wrong in the approach? If so what is the right approach? My considerations are as follows: a) should be easy to add new views later on if requirement comes, without having to copy-paste-modify code b) would like to make it as loosely coupled as possible so that if minor db structure changes happen, it does not break I did google searches on report design and OOP report generators, but all the result seem to focus on the visual design of the report rather than fetching the data. I have already taken care of the visual aspect of the report using MVC with html templates. I am sure this is a very fundamental problem with known solution, but I am somehow not able to find it (maybe searching with wrong keyword). Edit1: Modified the title to make it more relevant Edit2: The accepted answer got me thinking in the right direction and identify my design flaws, which eventually led me to find this question and the solution in Stack Overflow which gave me the detailed answer to clear the confusion.

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• how to use SQL wildcard % with Queryset extra>select?

  - by tylias

  I'm trying to add weights to search terms I'm using to filter a queryset. Using the '%' wildcard is causing me some problems. I'm using the extra() modifier to add a weight parameter to the queryset, which I will be using to inform a sort ordering. (See http://docs.djangoproject.com/en/1.1/ref/models/querysets/#extra-select-none-where-none-params-none-tables-none-order-by-none-select-params-none ) Here's the gist of the code: def viewname(request) ... exact_matchstrings="" exact_matchstrings.append("(accountprofile.first_name LIKE '" + term + "')") exact_matchstrings.append("(accountprofile.first_name LIKE '" + term + '\%' + "')") extraquerystring = " + ".join(exact_matchstrings) return_queryset = return_queryset.extra( select = { 'match_weight': extraquerystring }, ) The effect I'm going for is that if the search term matches exactly, the weight associated with the record is 2, but if the term merely starts with the search term and isn't an exact match, the weight is 1. (for example, if 'term' = 'Jon', an entry with first_name='Jon' gets a weight of 2 but an entry with an entry with first_name = 'Jonathan' gets a weight of 1.) I can test the statement in SQL and it seems to work well enough. If I make this SQL query from the mysql shell, no problem: select (first_name like "Carl") + (first_name like "Car%") from accountprofile; But trying to run it via the extra() modifier in my view code and evaluating the resulting queryset gives me the following error: Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 68, in __repr__ data = list(self[:REPR_OUTPUT_SIZE + 1]) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 83, in __len__ self._result_cache.extend(list(self._iter)) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 238, in iterator for row in self.query.results_iter(): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 287, in results_iter for rows in self.execute_sql(MULTI): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 2369, in execute_sql cursor.execute(sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/util.py", line 22, in execute sql = self.db.ops.last_executed_query(self.cursor, sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 217, in last_executed_query return smart_unicode(sql) % u_params ValueError: unsupported format character ''' (0x27) at index 309 I've tried it escaping and not escaping % wildcard but that doesn't solve the problem. Doesn't seem to affect it at all, really. Any ideas?

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• Django + FastCGI - randomly raising OperationalError

  - by ibz

  I'm running a Django application. Had it under Apache + mod_python before, and it was all OK. Switched to Lighttpd + FastCGI. Now I randomly get the following exception (neither the place nor the time where it appears seem to be predictable). Since it's random, and it appears only after switching to FastCGI, I assume it has something to do with some settings. Found a few results when googleing, but they seem to be related to setting maxrequests=1. However, I use the default, which is 0. Any ideas where to look for? PS. I'm using PostgreSQL. Might be related to that as well, since the exception appears when making a database query. Thanks. File "/usr/lib/python2.6/site-packages/django/core/handlers/base.py", line 86, in get_response response = callback(request, *callback_args, **callback_kwargs) File "/usr/lib/python2.6/site-packages/django/contrib/admin/sites.py", line 140, in root if not self.has_permission(request): File "/usr/lib/python2.6/site-packages/django/contrib/admin/sites.py", line 99, in has_permission return request.user.is_authenticated() and request.user.is_staff File "/usr/lib/python2.6/site-packages/django/contrib/auth/middleware.py", line 5, in __get__ request._cached_user = get_user(request) File "/usr/lib/python2.6/site-packages/django/contrib/auth/__init__.py", line 83, in get_user user_id = request.session[SESSION_KEY] File "/usr/lib/python2.6/site-packages/django/contrib/sessions/backends/base.py", line 46, in __getitem__ return self._session[key] File "/usr/lib/python2.6/site-packages/django/contrib/sessions/backends/base.py", line 172, in _get_session self._session_cache = self.load() File "/usr/lib/python2.6/site-packages/django/contrib/sessions/backends/db.py", line 16, in load expire_date__gt=datetime.datetime.now() File "/usr/lib/python2.6/site-packages/django/db/models/manager.py", line 93, in get return self.get_query_set().get(*args, **kwargs) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 304, in get num = len(clone) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 160, in __len__ self._result_cache = list(self.iterator()) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 275, in iterator for row in self.query.results_iter(): File "/usr/lib/python2.6/site-packages/django/db/models/sql/query.py", line 206, in results_iter for rows in self.execute_sql(MULTI): File "/usr/lib/python2.6/site-packages/django/db/models/sql/query.py", line 1734, in execute_sql cursor.execute(sql, params) OperationalError: server closed the connection unexpectedly This probably means the server terminated abnormally before or while processing the request.

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