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  • When should we use Views, Temporary Tables and Direct Queries ? What are the Performance issues in a

    - by Shantanu Gupta
    I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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  • C# performance methods of receiving data from a socket?

    - by Daniel
    Lets assume we have a simple internet socket, and its going to send 10 megabytes (because i want to ignore memory issues) of random data through. Is there any performance difference or a best practice method that one should use for receiving data? The final output data should be represented by a byte[]. Yes i know writing an arbitrary amount of data to memory is bad, and if I was downloading a large file i wouldn't be doing it like this. But for argument sake lets ignore that and assume its a smallish amount of data. I also realise that the bottleneck here is probably not the memory management but rather the socket receiving. I just want to know what would be the most efficient method of receiving data. A few dodgy ways can think of is: Have a List and a buffer, after the buffer is full, add it to the list and at the end list.ToArray() to get the byte[] Write the buffer to a memory stream, after its complete construct a byte[] of the stream.Length and read it all into it in order to get the byte[] output. Is there a more efficient/better way of doing this?

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  • What should I use to increase performance. View/Query/Temporary Table

    - by Shantanu Gupta
    I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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  • Does breaking chained Select()s in LINQ to objects hurt performance?

    - by Justin
    Take the following pseudo C# code: using System; using System.Data; using System.Linq; using System.Collections.Generic; public IEnumerable<IDataRecord> GetRecords(string sql) { // DB logic goes here } public IEnumerable<IEmployer> Employers() { string sql = "select EmployerID from employer"; var ids = GetRecords(sql).Select(record => (record["EmployerID"] as int?) ?? 0); return ids.Select(employerID => new Employer(employerID) as IEmployer); } Would it be faster if the two Select() calls were combined? Is there an extra iteration in the code above? Is the following code faster? public IEnumerable<IEmployer> Employers() { string sql = "select EmployerID from employer"; return Query.Records(sql).Select(record => new Employer((record["EmployerID"] as int?) ?? 0) as IEmployer); } I think the first example is more readable if there is no difference in performance.

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  • C++ map performance - Linux (30 sec) vs Windows (30 mins) !!!

    - by sonofdelphi
    I need to process a list of files. The processing action should not be repeated for the same file. The code I am using for this is - using namespace std; vector<File*> gInputFileList; //Can contain duplicates, File has member sFilename map<string, File*> gProcessedFileList; //Using map to avoid linear search costs void processFile(File* pFile) { File* pProcessedFile = gProcessedFileList[pFile->sFilename]; if(pProcessedFile != NULL) return; //Already processed foo(pFile); //foo() is the action to do for each file gProcessedFileList[pFile->sFilename] = pFile; } void main() { size_t n= gInputFileList.size(); //Using array syntax (iterator syntax also gives identical performance) for(size_t i=0; i<n; i++){ processFile(gInputFileList[i]); } } The code works correctly, but... My problem is that when the input size is 1000, it takes 30 minutes - HALF AN HOUR - on Windows/Visual Studio 2008 Express (both Debug and Release builds). For the same input, it takes only 40 seconds to run on Linux/gcc! What could be the problem? The action foo() takes only a very short time to execute, when used separately. Should I be using something like vector::reserve for the map?

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  • How costly performance-wise are these actions in iPhone objective-C?

    - by Alex Gosselin
    This is really a few questions in one, I'm wondering what the performance cost is for these things, as I haven't really been following a best practice of any sort for these. The answers may also be useful to other readers, if somebody knows these. (1) If I need the core data managed object context, is it bad to use #import "myAppDelegate.h" //farther down in the code: NSManagedObjectContext *context = [(myAppDelegate.h*)[[UIApplication sharedApplication] delegate] managedObjectContext]; as opposed to leaving the warning you get if you don't cast the delegate? (2) What is the cheapest way to hard-code a string? I have been using return @"myString"; on occasion in some functions where I need to pass it to a variety of places, is it better to do it this way: static NSString *str = @"myString"; return str; (3) How costly is it to subclass an object i wrote vs. making a new one, in general? (4) When I am using core data and navigating through a hierarchy of some sort, is it necessary to turn things back into faults somehow after I read some info from them? or is this done automatically? Thanks for any help.

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  • Why does the order of the loops affect performance when iterating over a 2D array? [closed]

    - by Mark
    Possible Duplicate: Which of these two for loops is more efficient in terms of time and cache performance Below are two programs that are almost identical except that I switched the i and j variables around. They both run in different amounts of time. Could someone explain why this happens? Version 1 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (i = 0; i < 4000; i++) { for (j = 0; j < 4000; j++) { x[j][i] = i + j; } } } Version 2 #include <stdio.h> #include <stdlib.h> main () { int i,j; static int x[4000][4000]; for (j = 0; j < 4000; j++) { for (i = 0; i < 4000; i++) { x[j][i] = i + j; } } }

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  • ASP.NET Performance tip- Combine multiple script file into one request with script manager

    - by Jalpesh P. Vadgama
    We all need java script for our web application and we storing our JavaScript code in .js files. Now If we have more then .js file then our browser will create a new request for each .js file. Which is a little overhead in terms of performance. If you have very big enterprise application you will have so much over head for this. Asp.net Script Manager provides a feature to combine multiple JavaScript into one request but you must remember that this feature will be available only with .NET Framework 3.5 sp1 or higher versions.  Let’s take a simple example. I am having two javascript files Jscrip1.js and Jscript2.js both are having separate functions. //Jscript1.js function Task1() { alert('task1'); } Here is another one for another file. ////Jscript1.js function Task2() { alert('task2'); } Now I am adding script reference with script manager and using this function in my code like this. <form id="form1" runat="server"> <asp:ScriptManager ID="myScriptManager" runat="server" > <Scripts> <asp:ScriptReference Path="~/JScript1.js" /> <asp:ScriptReference Path="~/JScript2.js" /> </Scripts> </asp:ScriptManager> <script language="javascript" type="text/javascript"> Task1(); Task2(); </script> </form> Now Let’s test in Firefox with Lori plug-in which will show you how many request are made for this. Here is output of that. You can see 5 Requests are there. Now let’s do same thing in with ASP.NET Script Manager combined script feature. Like following <form id="form1" runat="server"> <asp:ScriptManager ID="myScriptManager" runat="server" > <CompositeScript> <Scripts> <asp:ScriptReference Path="~/JScript1.js" /> <asp:ScriptReference Path="~/JScript2.js" /> </Scripts> </CompositeScript> </asp:ScriptManager> <script language="javascript" type="text/javascript"> Task1(); Task2(); </script> </form> Now let’s run it and let’s see how many request are there like following. As you can see now we have only 4 request compare to 5 request earlier. So script manager combined multiple script into one request. So if you have lots of javascript files you can save your loading time with this with combining multiple script files into one request. Hope you liked it. Stay tuned for more!!!.. Happy programming.. Technorati Tags: ASP.NET,ScriptManager,Microsoft Ajax

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  • Any significant performance improvement by using bitwise operators instead of plain int sums in C#?

    - by tunnuz
    Hello, I started working with C# a few weeks ago and I'm now in a situation where I need to build up a "bit set" flag to handle different cases in an algorithm. I have thus two options: enum RelativePositioning { LEFT = 0, RIGHT = 1, BOTTOM = 2, TOP = 3, FRONT = 4, BACK = 5 } pos = ((eye.X < minCorner.X ? 1 : 0) << RelativePositioning.LEFT) + ((eye.X > maxCorner.X ? 1 : 0) << RelativePositioning.RIGHT) + ((eye.Y < minCorner.Y ? 1 : 0) << RelativePositioning.BOTTOM) + ((eye.Y > maxCorner.Y ? 1 : 0) << RelativePositioning.TOP) + ((eye.Z < minCorner.Z ? 1 : 0) << RelativePositioning.FRONT) + ((eye.Z > maxCorner.Z ? 1 : 0) << RelativePositioning.BACK); Or: enum RelativePositioning { LEFT = 1, RIGHT = 2, BOTTOM = 4, TOP = 8, FRONT = 16, BACK = 32 } if (eye.X < minCorner.X) { pos += RelativePositioning.LEFT; } if (eye.X > maxCorner.X) { pos += RelativePositioning.RIGHT; } if (eye.Y < minCorner.Y) { pos += RelativePositioning.BOTTOM; } if (eye.Y > maxCorner.Y) { pos += RelativePositioning.TOP; } if (eye.Z > maxCorner.Z) { pos += RelativePositioning.FRONT; } if (eye.Z < minCorner.Z) { pos += RelativePositioning.BACK; } I could have used something as ((eye.X > maxCorner.X) << 1) but C# does not allow implicit casting from bool to int and the ternary operator was similar enough. My question now is: is there any performance improvement in using the first version over the second? Thank you Tommaso

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  • Derby vs PostgreSql Performance Comparison

    - by Austin
    We are doing research right now on whether to switch our postgresql db to an embedded Derby db. Both would be using glassfish 3 for our data layer. Anybody have any opinions or knowledge that could help us decide? Thanks! edit: we are writing some performance tests ourselves right now. Looking for answers more based on experience / first hand knowledge

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  • Performance comparison of Dictionaries

    - by Hun1Ahpu
    I'm interested in performance values (big-O analysis) of Lookup and Insert operation for .Net Dictionaries: HashTable, SortedList, StringDictionary, ListDictionary, HybridDictionary, NameValueCollection Link to a web page with the answer works for me too.

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  • Bash or Zsh - which one and why?

    - by Andrew
    So, the question pretty much says it all. I'm on Snow Leopard, and I do a lot of web development, particularly in Rails 3 which makes heavy use of the console. I've seen some notable bloggers etc. mention Zsh as their preference over Bash, but I don't know what difference it would make. Could anyone give me a good comparison of what difference there is and what might make one prefer one option or the other? Thanks!

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  • Comparison of algorithmic approaches to the N queens problem

    - by iceman
    I wanted to evaluate performance comparisons for various approaches to solving the N queens problem. Mainly AI metaheuristics based algorithms like simulated annealing, tabu search and genetic algorithm etc compared to exact methods(like backtracking). Is there any code available for study? A lot of real-world optimization problems like it consider cooperative schemes between exact methods and metaheuristics.

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  • Scalability comparison between different DBMSs

    - by Björn Lindfors
    By what factor does the performance (read queries/sec) increase when a machine is added to a cluster of machines running either: a Bigtable-like database MySQL? Google's research paper on Bigtable suggests that "near-linear" scaling is achieved can be achieved with Bigtable. This page here featuring MySQL's marketing jargon suggests that MySQL is capable of scaling linearly. Where is the truth?

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  • EF4 Import/Lookup thousands of records - my performance stinks!

    - by Dennis Ward
    I'm trying to setup something for a movie store website (using ASP.NET, EF4, SQL Server 2008), and in my scenario, I want to allow a "Member" store to import their catalog of movies stored in a text file containing ActorName, MovieTitle, and CatalogNumber as follows: Actor, Movie, CatalogNumber John Wayne, True Grit, 4577-12 (repeated for each record) This data will be used to lookup an actor and movie, and create a "MemberMovie" record, and my import speed is terrible if I import more than 100 or so records using these tables: Actor Table: Fields = {ID, Name, etc.} Movie Table: Fields = {ID, Title, ActorID, etc.} MemberMovie Table: Fields = {ID, CatalogNumber, MovieID, etc.} My methodology to import data into the MemberMovie table from a text file is as follows (after the file has been uploaded successfully): Create a context. For each line in the file, lookup the artist in the Actor table. For each Movie in the Artist table, lookup the matching title. If a matching Movie is found, add a new MemberMovie record to the context and call ctx.SaveChanges(). The performance of my implementation is terrible. My expectation is that this can be done with thousands of records in a few seconds (after the file has been uploaded), and I've got something that times out the browser. My question is this: What is the best approach for performing bulk lookups/inserts like this? Should I call SaveChanges only once rather than for each newly created MemberMovie? Would it be better to implement this using something like a stored procedure? A snippet of my loop is roughly this (edited for brevity): while ((fline = file.ReadLine()) != null) { string [] token = fline.Split(separator); string Actor = token[0]; string Movie = token[1]; string CatNumber = token[2]; Actor found_actor = ctx.Actors.Where(a => a.Name.Equals(actor)).FirstOrDefault(); if (found_actor == null) continue; Movie found_movie = found_actor.Movies.Where( s => s.Title.Equals(title, StringComparison.CurrentCultureIgnoreCase)).FirstOrDefault(); if (found_movie == null) continue; ctx.MemberMovies.AddObject(new MemberMovie() { MemberProfileID = profile_id, CatalogNumber = CatNumber, Movie = found_movie }); try { ctx.SaveChanges(); } catch { } } Any help is appreciated! Thanks, Dennis

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  • How to compare mp3, flac audio data in a file, ignoring header data (ID3 tag) etc.?

    - by Rob
    I've backed up some audio files up in 2 places and added ID3 tags into one backup but not the other, since time has passed my own memory has faded on whether the backups are actually the same, but now one has ID3 data and the other doesn't, basic binary compare will fail and inspection will be cumbersome. Is there a tool to compare just the audio data (not the header, ID3) in mp3s, flac files, and other files using header data such as ID3. started a thread on beyond compare here: http://www.scootersoftware.com/vbulletin/showthread.php?t=7413 would consider other comparison software that does this task

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  • turn off disable the performance cache

    - by jessie
    OK I run a streaming website and my CMS is giving me an error when uploading videos "Failed To Find Flength File" ok so I did some research. The answer I got from the coder was below. I did do all that, but the only thing I could not do is turn off what he refers to as performance cache, talked about in the last sentence... I am on a Cent OS Assuming the script is set up properly, you are probably dealing with some kind of write-caching. Some servers perform write-caching which prevents writing out the flength file or the entire CGITemp file during the upload. The flength file or the CGITemp file do not actually hit the disk until the upload is complete, making it worthless for reporting on progress during the upload. This may be fixed using a .htaccess file assuming your host supports them. Here is a link to an excellent tutorial on using .htaccess files. I strongly recommend giving it a quick read before attempting to install your own .htaccess file. 1. A mod_security module for Apache. To fix it just create a file called .htaccess (that's a period followed by "htaccess") and put the following lines in that file. Upload the file into the directory where the Uber-Uploader CGI ".pl" scripts resides, or in some directory above it (like your server's DOCUMENT_ROOT, i.e. the top-level of your webspace). htaccess files must be uploaded as ASCII mode, not BINARY. You may need to CHMOD the htaccess file to 644 or (RW-R--R--). # Turn off mod_security filtering. SecFilterEngine Off # The below probably isn't needed, # but better safe than sorry. SecFilterScanPOST Off If the above method does not work, try putting the following lines into the file SetEnvIfNoCase Content-Type \ "^multipart/form-data;" "MODSEC_NOPOSTBUFFERING=Do not buffer file uploads" mod_gzip_on No 2. "Performance Cache" enabled on OS X SERVER. If you're running OS X Server and the progress bar isn't working, it could be because of "performance caching." Apparently if ANY of your hosted sites are using performance caching, then by default, all sites (domains) will attempt to. The fix then is to disable the performance cache on all hosted sites.

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  • compare windows server for patch/update/hotfix installs

    - by user12002221
    Are there any tools that can be used to connect to windows 2008 servers, and get a comparison of the installed patches/updates on the servers, showing what is installed on one and not on the other? This is to help isolate an issue we are seeing on a specific windows server, in a load balanced setup. There is a certain performance/locking issue, which is mitigated whenever one of the servers is disabled. Please share, if you have any suggestions. Thanks in advance!

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  • why my test performance class gives me inconsistent results even after proper warm-up?

    - by colinfang
    i made a class which helps me measure time for any methods in Ticks. Basically, it runs testing method 100x, and force GC, then it records time taken for another 100x method runs. x64 release ctrl+f5 VS2012/VS2010 the results are following: 2,914 2,909 2,913 2,909 2,908 2,907 2,909 2,998 2,976 2,855 2,446 2,415 2,435 2,401 2,402 2,402 2,399 2,401 2,401 2,400 2,399 2,400 2,404 2,402 2,401 2,399 2,400 2,402 2,404 2,403 2,401 2,403 2,401 2,400 2,399 2,414 2,405 2,401 2,407 2,399 2,401 2,402 2,401 2,404 2,401 2,404 2,405 2,368 1,577 1,579 1,626 1,578 1,576 1,578 1,577 1,577 1,576 1,578 1,576 1,578 1,577 1,578 1,576 1,578 1,577 1,579 1,585 1,576 1,579 1,577 1,579 1,578 1,579 1,577 1,578 1,577 1,578 1,576 1,578 1,577 1,578 1,599 1,579 1,578 1,582 1,576 1,578 1,576 1,579 1,577 1,578 1,577 1,591 1,577 1,578 1,578 1,576 1,578 1,576 1,578 As you can see there are 3 phases, first is ~2,900, second is ~2,400, then ~1,550 What might be the reason to cause it? the test performance class code follows: public static void RunTests(Func<long> myTest) { const int numTrials = 100; Stopwatch sw = new Stopwatch(); double[] sample = new double[numTrials]; Console.WriteLine("Checksum is {0:N0}", myTest()); sw.Start(); myTest(); sw.Stop(); Console.WriteLine("Estimated time per test is {0:N0} ticks\n", sw.ElapsedTicks); for (int i = 0; i < numTrials; i++) { myTest(); } GC.Collect(); string testName = myTest.Method.Name; Console.WriteLine("----> Starting benchmark {0}\n", myTest.Method.Name); for (int i = 0; i < numTrials; i++) { sw.Restart(); myTest(); sw.Stop(); sample[i] = sw.ElapsedTicks; } double testResult = DataSetAnalysis.Report(sample); for (int j = 0; j < numTrials; j = j + 5) Console.WriteLine("{0,8:N0} {1,8:N0} {2,8:N0} {3,8:N0} {4,8:N0}", sample[j], sample[j + 1], sample[j + 2], sample[j + 3], sample[j + 4]); Console.WriteLine("\n----> End of benchmark"); }

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  • Web Site Performance and Assembly Versioning – Part 2 Versioning Combined Files Using Subversion

    - by capgpilk
    Ok so it took a while to post this second part. Many apologies, we had a big roll out of a new platform at work and many things had to get sidelined. So this is the second part in a short series of website performance and using versioning to help improve it. Minification and Concatination of JavaScript and CSS Files Versioning Combined Files Using Subversion – this post Versioning Combined Files Using Mercurial – published shortly In the previous post we used AjaxMin to shrink js and css files then concatenated them into one file each which had the file name of site-script.combined.min.js and site-style.combined.min.css. These file names are fine, but you can configure IIS 7 to cache these static files and so lower the amount of data transferred between server and client. This is done by editing the response headers in IIS. 1. In IIS7 Manager, choose the directory where these files are located and select HTTP Response Headers. 2. Check the Expire Web Content and set a time period well into the future. 3. When refreshing the web page, the server will respond with HTTP 304 forcing the browser to retrieve the file from its cache. 4. As can be seen in FireBug, the Cache-Control header has a max age of 31536000 seconds which equates to 365 days.   The server will always send this HTTP 304 message unless the file changes forcing it to send new content. To help force this we can change the file name based on the latest build using the SVN revision number in the filename. So we have lowered data transfer on content that hasn’t changed, but forced it to be sent when you have made a change to the css or js files. Now to get the SVN revision number in to the file name. 1. Import the MSBuildCommunityTasks targets which can be dowloaded from here. 1: <Import Project="$(MSBuildExtensionsPath) 2: \MSBuildCommunityTasks 3: \MSBuild.Community.Tasks.Targets" /> 2. Edit the BeforeBuild target to call out to svn and get the latest revision 1: <SvnVersion LocalPath="$(MSBuildProjectDirectory)" 2: ToolPath="$(ProgramFiles)\VisualSVN Server\bin"> 3: <Output TaskParameter="Revision" PropertyName="Revision" /> 4: </SvnVersion> 3. Set it to update the project AssemblyInfo.cs file for the svn revision. 1: <FileUpdate Files="Properties\AssemblyInfo.cs" 2: Regex="(\d+)\.(\d+)\.(\d+)\.(\d+)" 3: ReplacementText="$1.$2.$3.$(Revision)" /> 4. Now edit the AfterBuild target to get the full dll version. You could combine these two steps and just get the version from svn, I am working on one project that updates the AssemblyInfo file and another project that allows manual editing of the file, but needs that version within the file name; so I just combined the two for this post. 1: <MSBuild.ExtensionPack.Framework.Assembly 2: TaskAction="GetInfo" 3: NetAssembly="$(OutputPath)\mydll.dll"> 4: <Output TaskParameter="OutputItems" ItemName="Info" /> 5: </MSBuild.ExtensionPack.Framework.Assembly> 6: <Message Text="Version: %(Info.AssemblyVersion)" 7: Importance="High" /> 5. Use this Info.AssemblyVersion to write out the combined css and js files as described in the last post. 1: <WriteLinestoFile File="Scripts\site-%(Info.AssemblyVersion).combined.min.js" 2: Lines="@(JSLinesSite)" Overwrite="true" />   In the next post I will cover doing the same, but for a Mercurial repository.

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  • quick look at: dm_db_index_physical_stats

    - by fatherjack
    A quick look at the key data from this dmv that can help a DBA keep databases performing well and systems online as the users need them. When the dynamic management views relating to index statistics became available in SQL Server 2005 there was much hype about how they can help a DBA keep their servers running in better health than ever before. This particular view gives an insight into the physical health of the indexes present in a database. Whether they are use or unused, complete or missing some columns is irrelevant, this is simply the physical stats of all indexes; disabled indexes are ignored however. In it’s simplest form this dmv can be executed as:   The results from executing this contain a record for every index in every database but some of the columns will be NULL. The first parameter is there so that you can specify which database you want to gather index details on, rather than scan every database. Simply specifying DB_ID() in place of the first NULL achieves this. In order to avoid the NULLS, or more accurately, in order to choose when to have the NULLS you need to specify a value for the last parameter. It takes one of 4 values – DEFAULT, ‘SAMPLED’, ‘LIMITED’ or ‘DETAILED’. If you execute the dmv with each of these values you can see some interesting details in the times taken to complete each step. DECLARE @Start DATETIME DECLARE @First DATETIME DECLARE @Second DATETIME DECLARE @Third DATETIME DECLARE @Finish DATETIME SET @Start = GETDATE() SELECT * FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, DEFAULT) AS ddips SET @First = GETDATE() SELECT * FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, 'SAMPLED') AS ddips SET @Second = GETDATE() SELECT * FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, 'LIMITED') AS ddips SET @Third = GETDATE() SELECT * FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, 'DETAILED') AS ddips SET @Finish = GETDATE() SELECT DATEDIFF(ms, @Start, @First) AS [DEFAULT] , DATEDIFF(ms, @First, @Second) AS [SAMPLED] , DATEDIFF(ms, @Second, @Third) AS [LIMITED] , DATEDIFF(ms, @Third, @Finish) AS [DETAILED] Running this code will give you 4 result sets; DEFAULT will have 12 columns full of data and then NULLS in the remainder. SAMPLED will have 21 columns full of data. LIMITED will have 12 columns of data and the NULLS in the remainder. DETAILED will have 21 columns full of data. So, from this we can deduce that the DEFAULT value (the same one that is also applied when you query the view using a NULL parameter) is the same as using LIMITED. Viewing the final result set has some details that are worth noting: Running queries against this view takes significantly longer when using the SAMPLED and DETAILED values in the last parameter. The duration of the query is directly related to the size of the database you are working in so be careful running this on big databases unless you have tried it on a test server first. Let’s look at the data we get back with the DEFAULT value first of all and then progress to the extra information later. We know that the first parameter that we supply has to be a database id and for the purposes of this blog we will be providing that value with the DB_ID function. We could just as easily put a fixed value in there or a function such as DB_ID (‘AnyDatabaseName’). The first columns we get back are database_id and object_id. These are pretty explanatory and we can wrap those in some code to make things a little easier to read: SELECT DB_NAME([ddips].[database_id]) AS [DatabaseName] , OBJECT_NAME([ddips].[object_id]) AS [TableName] … FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, NULL) AS ddips  gives us   SELECT DB_NAME([ddips].[database_id]) AS [DatabaseName] , OBJECT_NAME([ddips].[object_id]) AS [TableName], [i].[name] AS [IndexName] , ….. FROM [sys].[dm_db_index_physical_stats](DB_ID(), NULL, NULL, NULL, NULL) AS ddips INNER JOIN [sys].[indexes] AS i ON [ddips].[index_id] = [i].[index_id] AND [ddips].[object_id] = [i].[object_id]     These handily tie in with the next parameters in the query on the dmv. If you specify an object_id and an index_id in these then you get results limited to either the table or the specific index. Once again we can place a  function in here to make it easier to work with a specific table. eg. SELECT * FROM [sys].[dm_db_index_physical_stats] (DB_ID(), OBJECT_ID(‘AdventureWorks2008.Person.Address’) , 1, NULL, NULL) AS ddips   Note: Despite me showing that functions can be placed directly in the parameters for this dmv, best practice recommends that functions are not used directly in the function as it is possible that they will fail to return a valid object ID. To be certain of not passing invalid values to this function, and therefore setting an automated process off on the wrong path, declare variables for the OBJECT_IDs and once they have been validated, use them in the function: DECLARE @db_id SMALLINT; DECLARE @object_id INT; SET @db_id = DB_ID(N’AdventureWorks_2008′); SET @object_id = OBJECT_ID(N’AdventureWorks_2008.Person.Address’); IF @db_id IS NULL BEGINPRINT N’Invalid database’; ENDELSE IF @object_id IS NULL BEGINPRINT N’Invalid object’; ENDELSE BEGINSELECT * FROM sys.dm_db_index_physical_stats (@db_id, @object_id, NULL, NULL , ‘LIMITED’); END; GO In cases where the results of querying this dmv don’t have any effect on other processes (i.e. simply viewing the results in the SSMS results area)  then it will be noticed when the results are not consistent with the expected results and in the case of this blog this is the method I have used. So, now we can relate the values in these columns to something that we recognise in the database lets see what those other values in the dmv are all about. The next columns are: We’ll skip partition_number, index_type_desc, alloc_unit_type_desc, index_depth and index_level  as this is a quick look at the dmv and they are pretty self explanatory. The final columns revealed by querying this view in the DEFAULT mode are avg_fragmentation_in_percent. This is the amount that the index is logically fragmented. It will show NULL when the dmv is queried in SAMPLED mode. fragment_count. The number of pieces that the index is broken into. It will show NULL when the dmv is queried in SAMPLED mode. avg_fragment_size_in_pages. The average size, in pages, of a single fragment in the leaf level of the IN_ROW_DATA allocation unit. It will show NULL when the dmv is queried in SAMPLED mode. page_count. Total number of index or data pages in use. OK, so what does this give us? Well, there is an obvious correlation between fragment_count, page_count and avg_fragment_size-in_pages. We see that an index that takes up 27 pages and is in 3 fragments has an average fragment size of 9 pages (27/3=9). This means that for this index there are 3 separate places on the hard disk that SQL Server needs to locate and access to gather the data when it is requested by a DML query. If this index was bigger than 72KB then having it’s data in 3 pieces might not be too big an issue as each piece would have a significant piece of data to read and the speed of access would not be too poor. If the number of fragments increases then obviously the amount of data in each piece decreases and that means the amount of work for the disks to do in order to retrieve the data to satisfy the query increases and this would start to decrease performance. This information can be useful to keep in mind when considering the value in the avg_fragmentation_in_percent column. This is arrived at by an internal algorithm that gives a value to the logical fragmentation of the index taking into account the multiple files, type of allocation unit and the previously mentioned characteristics if index size (page_count) and fragment_count. Seeing an index with a high avg_fragmentation_in_percent value will be a call to action for a DBA that is investigating performance issues. It is possible that tables will have indexes that suffer from rapid increases in fragmentation as part of normal daily business and that regular defragmentation work will be needed to keep it in good order. In other cases indexes will rarely become fragmented and therefore not need rebuilding from one end of the year to another. Keeping this in mind DBAs need to use an ‘intelligent’ process that assesses key characteristics of an index and decides on the best, if any, defragmentation method to apply should be used. There is a simple example of this in the sample code found in the Books OnLine content for this dmv, in example D. There are also a couple of very popular solutions created by SQL Server MVPs Michelle Ufford and Ola Hallengren which I would wholly recommend that you review for much further detail on how to care for your SQL Server indexes. Right, let’s get back on track then. Querying the dmv with the fifth parameter value as ‘DETAILED’ takes longer because it goes through the index and refreshes all data from every level of the index. As this blog is only a quick look a we are going to skate right past ghost_record_count and version_ghost_record_count and discuss avg_page_space_used_in_percent, record_count, min_record_size_in_bytes, max_record_size_in_bytes and avg_record_size_in_bytes. We can see from the details below that there is a correlation between the columns marked. Column 1 (Page_Count) is the number of 8KB pages used by the index, column 2 is how full each page is (how much of the 8KB has actual data written on it), column 3 is how many records are recorded in the index and column 4 is the average size of each record. This approximates to: ((Col1*8) * 1024*(Col2/100))/Col3 = Col4*. avg_page_space_used_in_percent is an important column to review as this indicates how much of the disk that has been given over to the storage of the index actually has data on it. This value is affected by the value given for the FILL_FACTOR parameter when creating an index. avg_record_size_in_bytes is important as you can use it to get an idea of how many records are in each page and therefore in each fragment, thus reinforcing how important it is to keep fragmentation under control. min_record_size_in_bytes and max_record_size_in_bytes are exactly as their names set them out to be. A detail of the smallest and largest records in the index. Purely offered as a guide to the DBA to better understand the storage practices taking place. So, keeping an eye on avg_fragmentation_in_percent will ensure that your indexes are helping data access processes take place as efficiently as possible. Where fragmentation recurs frequently then potentially the DBA should consider; the fill_factor of the index in order to leave space at the leaf level so that new records can be inserted without causing fragmentation so rapidly. the columns used in the index should be analysed to avoid new records needing to be inserted in the middle of the index but rather always be added to the end. * – it’s approximate as there are many factors associated with things like the type of data and other database settings that affect this slightly.  Another great resource for working with SQL Server DMVs is Performance Tuning with SQL Server Dynamic Management Views by Louis Davidson and Tim Ford – a free ebook or paperback from Simple Talk. Disclaimer – Jonathan is a Friend of Red Gate and as such, whenever they are discussed, will have a generally positive disposition towards Red Gate tools. Other tools are often available and you should always try others before you come back and buy the Red Gate ones. All code in this blog is provided “as is” and no guarantee, warranty or accuracy is applicable or inferred, run the code on a test server and be sure to understand it before you run it on a server that means a lot to you or your manager.

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  • Shared to Dedicated or Amazon CloudFront to improve performances and keep secured?

    - by user978548
    I have a Wordpress which currently takes about 1.8s to 2.5s for the home page to completely load in my country. The page weight is about 700Ko (static content included). In order to increase performances, I'm considering two solutions: Switching to a dedicated host. Using amazon s3 cloudfront to serve static contents. My current shared hosting have servers in a neighboring country but not exactly in mine, and both amazon and the dedicated hosting have some, so that's already an advantage. So considering all that, I still have three questions remaining: Currently having a low traffic (100 unique visitors/days, but growing) will it make a huge difference between my shared hosting and a dedicated server ? Knowing that I already use a cookie-less domain to deliver static contents (but using a redirection to the same server), would using amazon s3 make a real difference ? Talking about the cons of dedicated vs amazon s3, if I choose for the dedicated server something like Ubuntu server and do daily package updates and have only port 80 open, would it be sufficient in terms of security (in comparison with my current shared hosting which manage everything for me) ?

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