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  • Functional programming compared to OOP with classes

    - by luckysmack
    I have been interested in some of the concepts of functional programming lately. I have used OOP for some time now. I can see how I would build a fairly complex app in OOP. Each object would know how to do things that object does. Or anything it's parents class does as well. So I can simply tell Person().speak() to make the person talk. But how do I do similar things in functional programming? I see how functions are first class items. But that function only does one specific thing. Would I simply have a say() method floating around and call it with an equivalent of Person() argument so I know what kind of thing is saying something? So I can see the simple things, just how would I do the comparable of OOP and objects in functional programming, so I can modularize and organize my code base? For reference, my primary experience with OOP is Python, PHP, and some C#. The languages that I am looking at that have functional features are Scala and Haskell. Though I am leaning towards Scala. Basic Example (Python): Animal(object): def say(self, what): print(what) Dog(Animal): def say(self, what): super().say('dog barks: {0}'.format(what)) Cat(Animal): def say(self, what): super().say('cat meows: {0}'.format(what)) dog = Dog() cat = Cat() dog.say('ruff') cat.say('purr')

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  • Strengthening code with possibly useless exception handling

    - by rdurand
    Is it a good practice to implement useless exception handling, just in case another part of the code is not coded correctly? Basic example A simple one, so I don't loose everybody :). Let's say I'm writing an app that will display a person's information (name, address, etc.), the data being extracted from a database. Let's say I'm the one coding the UI part, and someone else is writing the DB query code. Now imagine that the specifications of your app say that if the person's information is incomplete (let's say, the name is missing in the database), the person coding the query should handle this by returning "NA" for the missing field. What if the query is poorly coded and doesn't handle this case? What if the guy who wrote the query handles you an incomplete result, and when you try to display the informations, everything crashes, because your code isn't prepared to display empty stuff? This example is very basic. I believe most of you will say "it's not your problem, you're not responsible for this crash". But, it's still your part of the code which is crashing. Another example Let's say now I'm the one writing the query. The specifications don't say the same as above, but that the guy writing the "insert" query should make sure all the fields are complete when adding a person to the database to avoid inserting incomplete information. Should I protect my "select" query to make sure I give the UI guy complete informations? The questions What if the specifications don't explicitly say "this guy is the one in charge of handling this situation"? What if a third person implements another query (similar to the first one, but on another DB) and uses your UI code to display it, but doesn't handle this case in his code? Should I do what's necessary to prevent a possible crash, even if I'm not the one supposed to handle the bad case? I'm not looking for an answer like "(s)he's the one responsible for the crash", as I'm not solving a conflict here, I'd like to know, should I protect my code against situations it's not my responsibility to handle? Here, a simple "if empty do something" would suffice. In general, this question tackles redundant exception handling. I'm asking it because when I work alone on a project, I may code 2-3 times a similar exception handling in successive functions, "just in case" I did something wrong and let a bad case come through.

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  • HTTP status 405 - HTTP method POST is not supported by this URL

    - by Wont Say
    I am getting this "HTTP method POST is not supported by this URL" error when I run my project. The funny thing is, it was running perfectly fine two days ago. After I made a few changes to my code but then restored my original code and its giving me this error. Could you please help me? Here is my index.html: <form method="post" action="login.do"> <div> <table> <tr><td>Username: </td><td><input type="text" name="e_name"/> </td> </tr> <tr><td> Password: </td><td><input type="password" name="e_pass"/> </td> </tr> <tr><td></td><td><input type="submit" name ="e_submit" value="Submit"/> Here is my Login servlet: public class Login extends HttpServlet { /** * Processes requests for both HTTP * <code>GET</code> and * <code>POST</code> methods. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, SQLException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { /* * TODO output your page here. You may use following sample code. */ int status; String submit = request.getParameter("e_submit"); String submit2 = request.getParameter("a_submit"); out.println("Here1"); String e_name = request.getParameter("e_name"); String e_password = request.getParameter("e_pass"); String a_name = request.getParameter("a_name"); String a_password = request.getParameter("a_pass"); out.println(e_name+e_password+a_name+a_password); Author author = new Author(a_name,a_password); Editor editor = new Editor(e_name,e_password); // If it is an AUTHOR login: if(submit==null){ status = author.login(author); out.println("Author Login"); //Incorrect login details if(status==0) { out.println("Incorrect"); RequestDispatcher view = request.getRequestDispatcher("index_F.html"); view.forward(request, response); } //Correct login details --- AUTHOR else { out.println("Correct login details"); HttpSession session = request.getSession(); session.setAttribute(a_name, "a_name"); RequestDispatcher view = request.getRequestDispatcher("index_S.jsp"); view.forward(request, response); } } //If it is an EDITOR login else if (submit2==null){ status = editor.login(editor); //Incorrect login details if(status==0) { RequestDispatcher view = request.getRequestDispatcher("index_F.html"); view.forward(request, response); } //Correct login details --- EDITOR else { out.println("correct"); HttpSession session = request.getSession(); session.setAttribute(e_name, "e_name"); session.setAttribute(e_password, "e_pass"); RequestDispatcher view = request.getRequestDispatcher("index_S_1.html"); view.forward(request, response); } } out.println("</body>"); out.println("</html>"); } finally { out.close(); } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doGet(req, resp); }} And my web.xml looks like this: <?xml version="1.0" encoding="UTF-8"?> <servlet> <servlet-name>action</servlet-name> <servlet-class>org.apache.struts.action.ActionServlet</servlet-class> <init-param> <param-name>config</param-name> <param-value>/WEB-INF/struts-config.xml</param-value> </init-param> <init-param> <param-name>debug</param-name> <param-value>2</param-value> </init-param> <init-param> <param-name>detail</param-name> <param-value>2</param-value> </init-param> <load-on-startup>2</load-on-startup> </servlet> <servlet> <servlet-name>Login</servlet-name> <servlet-class>controller.Login</servlet-class> </servlet> <servlet-mapping> <servlet-name>action</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>Login</servlet-name> <url-pattern>/login.do</url-pattern> </servlet-mapping> <session-config> <session-timeout> 30 </session-timeout> </session-config> <welcome-file-list> <welcome-file>index.html</welcome-file> </welcome-file-list> I use Glassfish v3 server - let me know anything else you need to know

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  • Lucene: Fastest way to return the document occurance of a phrase?

    - by dont say the kid's name
    Hi Guys, I am trying to use Lucene (actually PyLucene!) to find out how many documents contain my exact phrase. My code currently looks like this... but it runs rather slow. Does anyone know a faster way to return document counts? phraseList = ["some phrase 1", "some phrase 2"] #etc, a list of phrases... countsearcher = IndexSearcher(SimpleFSDirectory(File(STORE_DIR)), True) analyzer = StandardAnalyzer(Version.LUCENE_CURRENT) for phrase in phraseList: query = QueryParser(Version.LUCENE_CURRENT, "contents", analyzer).parse("\"" + phrase + "\"") scoreDocs = countsearcher.search(query, 200).scoreDocs print "count is: " + str(len(scoreDocs))

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  • Delegates: A Practical Understanding

    - by samerpaul
    It's been a while since I have written on this blog, and I'm planning on reviving it this summer, since I have more time to do so again.I've also recently started working on the iPhone platform, so I haven't been as busy in .NET as before.In either case, today's blog post applies to both C# and Objective-C, because it's more about a practical understanding of delegates than it is about code. When I was learning coding, I felt like delegates was one of the hardest things to conceptually understand, and a lot of books don't really do a good job (in my opinion) of explaining it. So here's my stab at it.A Real Life Example of DelegatesLet's say there are three of you. You, your friend, and your brother. You're each in a different room in your house so you can't hear each other, even if you shout. 1)You are playing a computer game2) Friend is building a puzzle3) Brother is nappingNow, you three are going to stay in your room but you want to be informed if anything interesting is happening to the one of you. Let's say you (playing the computer game) want to know when your brother wakes up.You could keep walking to the room, checking to see if he's napping, and then walking back to your room. But that would waste a lot of time / resources, and what if you miss when he's awake before he goes back to sleep? That would be bad.Instead, you hand him a 2-way radio that works between your room and his room. And you inform him that when he wakes up, he should press a button on the radio and say "I'm awake". You are going to be listening to that radio, waiting for him to say he's awake. This, in essence, is how a delegate works.You're creating an "object" (the radio) that allows you to listen in on an event you specify. You don't want him to send any other messages to you right now, except when he wakes up. And you want to know immediately when he does, so you can go over to his room and say hi. (the methods that are called when a delegate event fires). You're also currently specifying that only you are listening on his radio.Let's say you want your friend to come into the room at the same time as you, and do something else entirely, like fluff your brother's pillow. You will then give him an identical radio, that also hooks into your brother's radio, and inform him to wait and listen for the "i'm awake" signal.Then, when your brother wakes up, he says "I'm awake!" and both you and your friend walk into the room. You say hi, and your friend fluffs the pillow, then you both exit.Later, if you decide you don't care to say hi anymore, you turn off your radio. Now, you have no idea when your brother is awake or not, because you aren't listening anymore.So again, you are each classes in this example, and each of you have your own methods. You're playing a computer game (PlayComputerGame()), your friend is building a puzzle (BuildPuzzle()) and your brother is napping (Napping()). You create a delegate (ImAwake) that you set your brother to do, when he wakes up. You listen in on that delegate (giving yourself a radio and turning it on), and when you receive the message, you fire a new method called SayHi()). Your friend is also wired up to the same delegate (using an identical radio) and fires the method FluffPillow().Hopefully this makes sense, and helps shed some light on how delegates operate. Let me know! Feel free to drop me a line at Twitter (preferred method of contact) here: samerabousalbi

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  • Someone is using the struct name as a variable name too. What does the code really say? (c++)

    - by EvilTeach
    This morning we found an old chunk of code that was causing a library call to crash. struct fred { int a; int b; int c; }; fred fred[MAX_SIZE+1]; memset( fred, 0, sizeof(fred) * MAX_SIZE+1 ); It appears that the sizeof(fred) may have been the full array size, rather than the structure size, as it was overwriting a great deal of memory. The fact that it compiled without warning on several different systems seemed odd. Is there a correct semantic for this case where the type and variable name are colliding? or is this some sort of undefined behavior? or just a defect? I haven't been been clever enough to find anything on Google or our language help. Thanks Evil

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  • IO::Pipe - close(<handle>) does not set $?

    - by danboo
    My understanding is that closing the handle for an IO::Pipe object should be done with the method ($fh->close) and not the built-in (close($fh)). The other day I goofed and used the built-in out of habit on a IO::Pipe object that was opened to a command that I expected to fail. I was surprised when $? was zero, and my error checking wasn't triggered. I realized my mistake. If I use the built-in, IO:Pipe can't perform the waitpid() and can't set $?. But what I was surprised by was that perl seemed to still close the pipe without setting $? via the core. I worked up a little test script to show what I mean: use 5.012; use warnings; use IO::Pipe; say 'init pipes:'; pipes(); my $fh = IO::Pipe->reader(q(false)); say 'post open pipes:'; pipes(); say 'return: ' . $fh->close; #say 'return: ' . close($fh); say 'status: ' . $?; say q(); say 'post close pipes:'; pipes(); sub pipes { for my $fd ( glob("/proc/self/fd/*") ) { say readlink($fd) if -p $fd; } say q(); } When using the method it shows the pipe being gone after the close and $? is set as I expected: init pipes: post open pipes: pipe:[992006] return: 1 status: 256 post close pipes: And, when using the built-in it also appears to close the pipe, but does not set $?: init pipes: post open pipes: pipe:[952618] return: 1 status: 0 post close pipes: It seems odd to me that the built-in results in the pipe closure, but doesn't set $?. Can anyone help explain the discrepancy? Thanks!

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  • Screen (command-line program) bug?

    - by VioletCrime
    fired up my Minecraft server again after about a year off. My server used to run 11.04, which has since been upgraded to 12.04; I lost my management scripts in the upgrade (thought I'd backed up the user's home directory), but whatever, I enjoy developing stuff like that anyways. However, this time around, I'm running into issues. I start the Minecraft server using a detached screen, however the script is unable to 'stuff' commands into the screen instance until I attach to the screen then detach again? Once I do that, I can stuff anything I want into the server's terminal using the -X option, until I stop/start the server again, then I have to reattach and detach in order to restore functionality? Here's the manager script: #!/bin/bash #Name of the screen housing the server (set with the -S flag at startup) SCREENNAME=minecraft1 #Name of the folder housing the Minecraft world FOLDERNAME=world1 startServer (){ if screen -list | grep "$SCREENNAME" > /dev/null then echo "Cannot start Minecraft server; it is already running!" else screen -dmS $SCREENNAME java -Xmx1024M -Xms1024M -jar minecraft_server.jar sleep 2 if screen -list | grep "$SCREENNAME" > /dev/null then echo "Minecraft server started; happy mining!" else echo "ERROR: Minecraft server failed to start!" fi fi; } stopServer (){ if screen -list | grep "$SCREENNAME" > /dev/null then echo "Server is running. Giving a 1-minute warning." screen -S $SCREENNAME -X stuff "/say Shutting down (halt) in one minute." screen -S $SCREENNAME -X stuff $'\015' sleep 45 screen -S $SCREENNAME -X stuff "/say Shutting down (halt) in 15 seconds." screen -S $SCREENNAME -X stuff $'\015' sleep 15 screen -S $SCREENNAME -X stuff "/stop" screen -S $SCREENNAME -X stuff $'\015' else echo "Server is not running; nothing to stop." fi; } stopServerNow (){ if screen -list | grep "$SCREENNAME" > /dev/null then echo "Server is running. Giving a 5-second warning." screen -S $SCREENNAME -X stuff "/say EMERGENCY SHUTDOWN! 5 seconds to halt." screen -S $SCREENNAME -X stuff $'\015' sleep 5 screen -S $SCREENNAME -X stuff "/stop" screen -S $SCREENNAME -X stuff $'\015' else echo "Server is not running; nothing to stop." fi; } restartServer (){ if screen -list | grep "$SCREENNAME" > /dev/null then echo "Server is running. Giving a 1-minute warning." screen -S $SCREENNAME -X stuff "/say Shutting down (restart) in one minute." screen -S $SCREENNAME -X stuff $'\015' sleep 45 screen -S $SCREENNAME -X stuff "/say Shutting down (restart) in 15 seconds." screen -S $SCREENNAME -X stuff $'\015' sleep 15 screen -S $SCREENNAME -X stuff "/stop" screen -S $SCREENNAME -X stuff $'\015' sleep 2 startServer else echo "Cannot restart server: it isn't running." fi; } #In order for this function to work, a directory 'backup/$FOLDERNAME' must exist in the same #directory that '$FOLDERNAME' resides backupWorld (){ if screen -list | grep "$SCREENNAME" > /dev/null then echo "Server is running. Giving a 1-minute warning." screen -S $SCREENNAME -X stuff "/say Shutting down (backup) in one minute." screen -S $SCREENNAME -X stuff $'\015' screen -S $SCREENNAME -X stuff "/say Server should be down for no more than a few seconds." screen -S $SCREENNAME -X stuff $'\015' sleep 45 screen -S $SCREENNAME -X stuff "/say Shutting down for backup in 15 seconds." screen -S $SCREENNAME -X stuff $'\015' sleep 15 screen -S $SCREENNAME -X stuff "/stop" screen -S $SCREENNAME -X stuff $'\015' fi sleep 2 if screen -list | grep $SCREENNAME > /dev/null then echo "Server is still running? Error." else cd .. tar -czvf backup0.tar.gz $FOLDERNAME mv backup0.tar.gz backup/$FOLDERNAME cd backup/$FOLDERNAME rm backup10.tar.gz mv backup9.tar.gz backup10.tar.gz mv backup8.tar.gz backup9.tar.gz mv backup7.tar.gz backup8.tar.gz mv backup6.tar.gz backup7.tar.gz mv backup5.tar.gz backup6.tar.gz mv backup4.tar.gz backup5.tar.gz mv backup3.tar.gz backup4.tar.gz mv backup2.tar.gz backup3.tar.gz mv backup1.tar.gz backup2.tar.gz mv backup0.tar.gz backup1.tar.gz cd ../../$FOLDERNAME screen -dmS $SCREENNAME java -Xmx1024M -Xms1024M -jar minecraft_server.jar; sleep 2 if screen -list | grep "$SCREENNAME" > /dev/null then echo "Minecraft server restarted; happy mining!" else echo "ERROR: Minecraft server failed to start!" fi fi; } printCommands (){ echo echo "$0 usage:" echo echo "Start : Starts the server on a detached screen." echo "Stop : Stop the server; includes a 1-minute warning." echo "StopNOW : Stops the server with only a 5-second warning." echo "Restart : Stops the server and starts the server again." echo "Backup : Stops the server (1 min), backs up the world, and restarts." echo "Help : Display this message." } #Forces case-insensitive string comparisons shopt -s nocasematch #Primary 'Switch' if [[ $1 = "start" ]] then startServer elif [[ $1 = "stop" ]] then stopServer elif [[ $1 = "stopnow" ]] then stopServerNow elif [[ $1 = "backup" ]] then backupWorld elif [[ $1 = "restart" ]] then restartServer else printCommands fi

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  • Office 2010 Trust Center settings: How to enable data connections in the "old" way?

    - by GSerg
    We're planning an upgrade Office 2003 - 2010 and have identified a big problem. In Office 2003, if the workbook you're opening contains a query table that fetches data from a data source automatically (upon file open or in certain intervals), then a security dialog pops up - whether you want to allow that. If you say Yes, the queries will refresh automatically when they need to. If you say No, the queries will not refresh automatically, neither on file open nor on time intervals, but you will be able to refresh any of them manually at any time by right-clicking and selecting Refresh. There is also a registry parameter to say, Don't display that dialog, just allow the queries. This is exactly what we want. On users' computers we have the registry parameter applied, so the users never see any dialogs. On developers' computers the parameter is not applied, so every time a file is opened the developer decides whether to allow the auto-refreshing for the current session. Usually the answer is No, because for developing, it is essential to not have quieres refresh when they want to, but instead, refresh them when the developer wants. The problem is that in Office 2010 which we are testing we can't find a way to achieve this functionality: The allow/disallow messages are now grouped into one yellow button, that either allows everything or disallows everything (including, say, macros, if macro security is set to "Disable, but ask"). If you don't click the yellow Allow button, the queries are disabled completely, not just for automatic execution. You cannot right-click and refresh a particular query -- doing that would summon a security dialog prompting for enabling queries, and if you say Yes, all queries in the document will be enabled for auto-execution and will start executing immediately. This sort of ruins our development environment. Is there a way to get the trust thingies in Office 2010 to work in the same way as before? Is there a yet another registry parameter to say, Prompt for auto-refresh, but allow manual refresh even when auto-refresh is disabled?

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  • T-SQL Script to Delete All The Relationships Between A Bunch Of Tables in a Schema and Other Bunch i

    - by Galilyou
    Guys, I have a set of tables (say Account, Customer) in a schema (say dbo) and I have some other tables (say Order, OrderItem) in another schema (say inventory). There's a relationship between the Order table and the Customer table. I want to delete all the relationships between the tables in the first schema (dbo) and the tables in the second schema (inventory), without deleting the relationships between tables inside the same schema. Is that possible? Any help appreciated.

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  • Swift : missing argument label 'xxx' in call

    - by henry4343
    func say(name:String, msg:String) { println("\(name) say \(msg)") } say("Henry","Hi,Swift") <---- error because missing argument label 'msg' in call I need to use say("Henry",msg:"Hi,Swift") Why ? If I put more than two var in func so that I need to write var name instead of first var when I call this func It's really trouble, and I don't see any explain in iBook Swift tutorial. Can someone give me a help ... Thanks

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  • why am i getting StackOverflowError?

    - by IttayD
    In groovyConsole I have this: import groovy.util.* import org.codehaus.groovy.runtime.* def gse = new GroovyScriptEngine("c:\\temp") def script = gse.loadScriptByName("say.groovy") this.metaClass.mixin script say("bye") say.groovy contains def say(String msg) { println(msg) }

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  • How can I handle arbitrary text as "nouns" in Inform 7?

    - by Beska
    In Inform, I'd like to be able to create a new action, and have it be able to work on aribitrary text. I can easily create a new action that will work on existing things. Finding is an action with past participle found, applying to one thing. Understand "Find [something]" as finding. Carry out finding: say "You find [the noun]." But this only works on items that exist within the game world. If I try to "find fdsljk", for instance, it will fail because I haven't created a "fdsljk". I'd like to be able to "find fdsljk" and then be able to grab that extra text and respond with it...something like "You find the fdsljk." I was thinking that something like A foo is a kind of value. Finding is an action with past participle found, applying to one foo. Understand "Find [something]" as finding. Carry out finding: say "You find [the foo]." might be close...but it doesn't work. I get an error that reads: You wrote 'say "You find [the foo]."' , and in particular 'the foo': but this asked to say something of a kind which can't be said, or rather, printed. Although this problem can arise when you use complicated text substitutions which come in variant forms depending on the kinds of value used, far more often what this means is just that you tried to use a substituted value (e.g., in 'say "The dial reads [V]."') of a kind which could not be printed out. For instance, if V is a number or a piece of text, there is no problem: but if V is a parsing topic, say an entry in a 'topic' column of a table, then this problem will arise. The italics are mine, and highlight the key...I think this should be doable, but I'm taking the wrong path. Clues?

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  • Question about DBD::CSB Statement-Functions

    - by sid_com
    From the SQL::Statement::Functions documentation: Function syntax When using SQL::Statement/SQL::Parser directly to parse SQL, functions (either built-in or user-defined) may occur anywhere in a SQL statement that values, column names, table names, or predicates may occur. When using the modules through a DBD or in any other context in which the SQL is both parsed and executed, functions can occur in the same places except that they can not occur in the column selection clause of a SELECT statement that contains a FROM clause. # valid for both parsing and executing SELECT MyFunc(args); SELECT * FROM MyFunc(args); SELECT * FROM x WHERE MyFuncs(args); SELECT * FROM x WHERE y < MyFuncs(args); # valid only for parsing (won't work from a DBD) SELECT MyFunc(args) FROM x WHERE y; Reading this I would expect that the first SELECT-statement of my example shouldn't work and the second should but it is quite the contrary. #!/usr/bin/env perl use warnings; use strict; use 5.010; use DBI; open my $fh, '>', 'test.csv' or die $!; say $fh "id,name"; say $fh "1,Brown"; say $fh "2,Smith"; say $fh "7,Smith"; say $fh "8,Green"; close $fh; my $dbh = DBI->connect ( 'dbi:CSV:', undef, undef, { RaiseError => 1, f_ext => '.csv', }); my $table = 'test'; say "\nSELECT 1"; my $sth = $dbh->prepare ( "SELECT MAX( id ) FROM $table WHERE name LIKE 'Smith'" ); $sth->execute (); $sth->dump_results(); say "\nSELECT 2"; $sth = $dbh->prepare ( "SELECT * FROM $table WHERE id = MAX( id )" ); $sth->execute (); $sth->dump_results(); outputs: SELECT 1 '7' 1 rows SELECT 2 Unknown function 'MAX' at /usr/lib/perl5/site_perl/5.10.0/SQL/Parser.pm line 2893. DBD::CSV::db prepare failed: Unknown function 'MAX' at /usr/lib/perl5/site_perl/5.10.0/SQL/Parser.pm line 2894. [for Statement "SELECT * FROM test WHERE id = MAX( id )"] at ./so_3.pl line 30. DBD::CSV::db prepare failed: Unknown function 'MAX' at /usr/lib/perl5/site_perl/5.10.0/SQL/Parser.pm line 2894. [for Statement "SELECT * FROM test WHERE id = MAX( id )"] at ./so_3.pl line 30. Could someone explaine me this behavior?

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  • SQL SERVER – Guest Posts – Feodor Georgiev – The Context of Our Database Environment – Going Beyond the Internal SQL Server Waits – Wait Type – Day 21 of 28

    - by pinaldave
    This guest post is submitted by Feodor. Feodor Georgiev is a SQL Server database specialist with extensive experience of thinking both within and outside the box. He has wide experience of different systems and solutions in the fields of architecture, scalability, performance, etc. Feodor has experience with SQL Server 2000 and later versions, and is certified in SQL Server 2008. In this article Feodor explains the server-client-server process, and concentrated on the mutual waits between client and SQL Server. This is essential in grasping the concept of waits in a ‘global’ application plan. Recently I was asked to write a blog post about the wait statistics in SQL Server and since I had been thinking about writing it for quite some time now, here it is. It is a wide-spread idea that the wait statistics in SQL Server will tell you everything about your performance. Well, almost. Or should I say – barely. The reason for this is that SQL Server is always a part of a bigger system – there are always other players in the game: whether it is a client application, web service, any other kind of data import/export process and so on. In short, the SQL Server surroundings look like this: This means that SQL Server, aside from its internal waits, also depends on external waits and settings. As we can see in the picture above, SQL Server needs to have an interface in order to communicate with the surrounding clients over the network. For this communication, SQL Server uses protocol interfaces. I will not go into detail about which protocols are best, but you can read this article. Also, review the information about the TDS (Tabular data stream). As we all know, our system is only as fast as its slowest component. This means that when we look at our environment as a whole, the SQL Server might be a victim of external pressure, no matter how well we have tuned our database server performance. Let’s dive into an example: let’s say that we have a web server, hosting a web application which is using data from our SQL Server, hosted on another server. The network card of the web server for some reason is malfunctioning (think of a hardware failure, driver failure, or just improper setup) and does not send/receive data faster than 10Mbs. On the other end, our SQL Server will not be able to send/receive data at a faster rate either. This means that the application users will notify the support team and will say: “My data is coming very slow.” Now, let’s move on to a bit more exciting example: imagine that there is a similar setup as the example above – one web server and one database server, and the application is not using any stored procedure calls, but instead for every user request the application is sending 80kb query over the network to the SQL Server. (I really thought this does not happen in real life until I saw it one day.) So, what happens in this case? To make things worse, let’s say that the 80kb query text is submitted from the application to the SQL Server at least 100 times per minute, and as often as 300 times per minute in peak times. Here is what happens: in order for this query to reach the SQL Server, it will have to be broken into a of number network packets (according to the packet size settings) – and will travel over the network. On the other side, our SQL Server network card will receive the packets, will pass them to our network layer, the packets will get assembled, and eventually SQL Server will start processing the query – parsing, allegorizing, generating the query execution plan and so on. So far, we have already had a serious network overhead by waiting for the packets to reach our Database Engine. There will certainly be some processing overhead – until the database engine deals with the 80kb query and its 20 subqueries. The waits you see in the DMVs are actually collected from the point the query reaches the SQL Server and the packets are assembled. Let’s say that our query is processed and it finally returns 15000 rows. These rows have a certain size as well, depending on the data types returned. This means that the data will have converted to packages (depending on the network size package settings) and will have to reach the application server. There will also be waits, however, this time you will be able to see a wait type in the DMVs called ASYNC_NETWORK_IO. What this wait type indicates is that the client is not consuming the data fast enough and the network buffers are filling up. Recently Pinal Dave posted a blog on Client Statistics. What Client Statistics does is captures the physical flow characteristics of the query between the client(Management Studio, in this case) and the server and back to the client. As you see in the image, there are three categories: Query Profile Statistics, Network Statistics and Time Statistics. Number of server roundtrips–a roundtrip consists of a request sent to the server and a reply from the server to the client. For example, if your query has three select statements, and they are separated by ‘GO’ command, then there will be three different roundtrips. TDS Packets sent from the client – TDS (tabular data stream) is the language which SQL Server speaks, and in order for applications to communicate with SQL Server, they need to pack the requests in TDS packets. TDS Packets sent from the client is the number of packets sent from the client; in case the request is large, then it may need more buffers, and eventually might even need more server roundtrips. TDS packets received from server –is the TDS packets sent by the server to the client during the query execution. Bytes sent from client – is the volume of the data set to our SQL Server, measured in bytes; i.e. how big of a query we have sent to the SQL Server. This is why it is best to use stored procedures, since the reusable code (which already exists as an object in the SQL Server) will only be called as a name of procedure + parameters, and this will minimize the network pressure. Bytes received from server – is the amount of data the SQL Server has sent to the client, measured in bytes. Depending on the number of rows and the datatypes involved, this number will vary. But still, think about the network load when you request data from SQL Server. Client processing time – is the amount of time spent in milliseconds between the first received response packet and the last received response packet by the client. Wait time on server replies – is the time in milliseconds between the last request packet which left the client and the first response packet which came back from the server to the client. Total execution time – is the sum of client processing time and wait time on server replies (the SQL Server internal processing time) Here is an illustration of the Client-server communication model which should help you understand the mutual waits in a client-server environment. Keep in mind that a query with a large ‘wait time on server replies’ means the server took a long time to produce the very first row. This is usual on queries that have operators that need the entire sub-query to evaluate before they proceed (for example, sort and top operators). However, a query with a very short ‘wait time on server replies’ means that the query was able to return the first row fast. However a long ‘client processing time’ does not necessarily imply the client spent a lot of time processing and the server was blocked waiting on the client. It can simply mean that the server continued to return rows from the result and this is how long it took until the very last row was returned. The bottom line is that developers and DBAs should work together and think carefully of the resource utilization in the client-server environment. From experience I can say that so far I have seen only cases when the application developers and the Database developers are on their own and do not ask questions about the other party’s world. I would recommend using the Client Statistics tool during new development to track the performance of the queries, and also to find a synchronous way of utilizing resources between the client – server – client. Here is another example: think about similar setup as above, but add another server to the game. Let’s say that we keep our media on a separate server, and together with the data from our SQL Server we need to display some images on the webpage requested by our user. No matter how simple or complicated the logic to get the images is, if the images are 500kb each our users will get the page slowly and they will still think that there is something wrong with our data. Anyway, I don’t mean to get carried away too far from SQL Server. Instead, what I would like to say is that DBAs should also be aware of ‘the big picture’. I wrote a blog post a while back on this topic, and if you are interested, you can read it here about the big picture. And finally, here are some guidelines for monitoring the network performance and improving it: Run a trace and outline all queries that return more than 1000 rows (in Profiler you can actually filter and sort the captured trace by number of returned rows). This is not a set number; it is more of a guideline. The general thought is that no application user can consume that many rows at once. Ask yourself and your fellow-developers: ‘why?’. Monitor your network counters in Perfmon: Network Interface:Output queue length, Redirector:Network errors/sec, TCPv4: Segments retransmitted/sec and so on. Make sure to establish a good friendship with your network administrator (buy them coffee, for example J ) and get into a conversation about the network settings. Have them explain to you how the network cards are setup – are they standalone, are they ‘teamed’, what are the settings – full duplex and so on. Find some time to read a bit about networking. In this short blog post I hope I have turned your attention to ‘the big picture’ and the fact that there are other factors affecting our SQL Server, aside from its internal workings. As a further reading I would still highly recommend the Wait Stats series on this blog, also I would recommend you have the coffee break conversation with your network admin as soon as possible. This guest post is written by Feodor Georgiev. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL

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  • How can I learn to effectively write Pythonic code?

    - by Matt Fenwick
    I'm tired of getting downvoted and/or semi-rude comments on my Python answers, saying things like "this isn't Pythonic" or "that's not the Python way of doing things". To clarify, I'm not tired of getting corrected and downvoted, and I'm not tired of being wrong: I'm tired of feeling like there's a whole field of Python that I know nothing about, and seems to be implicit knowledge of experienced Python programmers. Doing a google search for "Pythonic" reveals a wide range of interpretations. The wikipedia page says: A common neologism in the Python community is pythonic, which can have a wide range of meanings related to program style. To say that code is pythonic is to say that it uses Python idioms well, that it is natural or shows fluency in the language. Likewise, to say of an interface or language feature that it is pythonic is to say that it works well with Python idioms, that its use meshes well with the rest of the language. It also discusses the term "unpythonic": In contrast, a mark of unpythonic code is that it attempts to write C++ (or Lisp, Perl, or Java) code in Python—that is, provides a rough transcription rather than an idiomatic translation of forms from another language. The concept of pythonicity is tightly bound to Python's minimalist philosophy of readability and avoiding the "there's more than one way to do it" approach. Unreadable code or incomprehensible idioms are unpythonic. I suspect one way to learn the Pythonic way is just to program in Python a whole bunch. But I bet I could write a bunch of crap and not improve that much without some guidance, whereas a good resource might speed up the learning process significantly. PEP 8 might be exactly what I'm looking for, or maybe not. I'm not sure; on the one hand it covers a lot of ground, but on the other hand, I feel like it's more suited as a reference for knowledgeable programmers than a tutorial for fresh 'uns. How do I get my foot in the Pythonic/Python way of doing things door?

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  • Does SQL Server Maintainance Cleanup consider exact times when deleting old backups?

    - by Heinzi
    Let's say I have a daily maintainance task that: Backups all databases and then removes backups that are older than 3 days. Now let's say the first backup at day 1, starting at 10:00, results in the following files db1.bak 2012-01-01 10:04 db2.bak 2012-01-01 10:06 Now let's say at day 4 the first step of the maintainance task (backup the DBs) happens to finish at 10:05. Will SQL Server delete db1.bak and keep db2.bak (would be logical, but might be surprising for the user) or keep both or remove both?

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