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• Changing the indexing on existing table in SQL Server 2000

  - by Raj

  Guys, Here is the scenario: SQL Server 2000 (8.0.2055) Table currently has 478 million rows of data. The Primary Key column is an INT with IDENTITY. There is an Unique Constraint imposed on two other columns with a Non-Clustered Index. This is a vendor application and we are only responsible for maintaining the DB. Now the vendor has recommended doing the following "to improve performance" Drop the PK and Clustered Index Drop the non-clustered index on the two columns with the UNIQUE CONSTRAINT Recreate the PK, with a NON-CLUSTERED index Create a CLUSTERED index on the two columns with the UNIQUE CONSTRAINT I am not convinced that this is the right thing to do. I have a number of concerns. By dropping the PK and indexes, you will be creating a heap with 478 million rows of data. Then creating a CLUSTERED INDEX on two columns would be a really mammoth task. Would creating another table with the same structure and new indexing scheme and then copying the data over, dropping the old table and renaming the new one be a better approach? I am also not sure how the stored procs will react. Will they continue using the cached execution plan, considering that they are not being explicitly recompiled. I am simply not able to understand what kind of "performance improvement" this change will provide. I think that this will actually have the reverse effect. All thoughts welcome. Thanks in advance, Raj

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• Recycle Freed Objects

  - by uray

  suppose I need to allocate and delete object on heap frequently (of arbitrary size), is there any performance benefit if instead of deleting those objects, I will return it back to some "pool" to be reused later? would it give benefit by reduce heap allocation/deallocation?, or it will be slower compared to memory allocator performance, since the "pool" need to manage a dynamic collection of pointers. my use case: suppose I create a queue container based on linked list, and each node of that list are allocated on the heap, so every call to push() and pop() will allocate and deallocate that node: ` template <typename T> struct QueueNode { QueueNode<T>* next; T object; } template <typename T> class Queue { void push(T object) { QueueNode<T>* newNode = QueueNodePool<T>::get(); //get recycled node if(!newNode) { newNode = new QueueNode<T>(object); } // push newNode routine here.. } T pop() { //pop routine here... QueueNodePool<T>::store(unusedNode); //recycle node return unusedNode->object; } } `

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• About redirected stdout in System.Diagnostics.Process

  - by sforester

  I've been recently working on a program that convert flac files to mp3 in C# using flac.exe and lame.exe, here are the code that do the job: ProcessStartInfo piFlac = new ProcessStartInfo( "flac.exe" ); piFlac.CreateNoWindow = true; piFlac.UseShellExecute = false; piFlac.RedirectStandardOutput = true; piFlac.Arguments = string.Format( flacParam, SourceFile ); ProcessStartInfo piLame = new ProcessStartInfo( "lame.exe" ); piLame.CreateNoWindow = true; piLame.UseShellExecute = false; piLame.RedirectStandardInput = true; piLame.RedirectStandardOutput = true; piLame.Arguments = string.Format( lameParam, QualitySetting, ExtractTag( SourceFile ) ); Process flacp = null, lamep = null; byte[] buffer = BufferPool.RequestBuffer(); flacp = Process.Start( piFlac ); lamep = new Process(); lamep.StartInfo = piLame; lamep.OutputDataReceived += new DataReceivedEventHandler( this.ReadStdout ); lamep.Start(); lamep.BeginOutputReadLine(); int count = flacp.StandardOutput.BaseStream.Read( buffer, 0, buffer.Length ); while ( count != 0 ) { lamep.StandardInput.BaseStream.Write( buffer, 0, count ); count = flacp.StandardOutput.BaseStream.Read( buffer, 0, buffer.Length ); } Here I set the command line parameters to tell lame.exe to write its output to stdout, and make use of the Process.OutPutDataRecerved event to gather the output data, which is mostly binary data, but the DataReceivedEventArgs.Data is of type "string" and I have to convert it to byte[] before put it to cache, I think this is ugly and I tried this approach but the result is incorrect. Is there any way that I can read the raw redirected stdout stream, either synchronously or asynchronously, bypassing the OutputDataReceived event? PS: the reason why I don't use lame to write to disk directly is that I'm trying to convert several files in parallel, and direct writing to disk will cause severe fragmentation. Thanks a lot!

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• What's the correct way to do a "catch all" error check on an fstream output operation?

  - by Truncheon

  What's the correct way to check for a general error when sending data to an fstream? UPDATE: My main concern regards some things I've been hearing about a delay between output and any data being physically written to the hard disk. My assumption was that the command "save_file_obj << save_str" would only send data to some kind of buffer and that the following check "if (save_file_obj.bad())" would not be any use in determining if there was an OS or hardware problem. I just wanted to know what was the definitive "catch all" way to send a string to a file and check to make certain that it was written to the disk, before carrying out any following actions such as closing the program. I have the following code... int Saver::output() { save_file_handle.open(file_name.c_str()); if (save_file_handle.is_open()) { save_file_handle << save_str.c_str(); if (save_file_handle.bad()) { x_message("Error - failed to save file"); return 0; } save_file_handle.close(); if (save_file_handle.bad()) { x_message("Error - failed to save file"); return 0; } return 1; } else { x_message("Error - couldn't open save file"); return 0; } }

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• ajax html vs xml/json responses - perfomance or other reasons

  - by pedalpete

  I've got a fairly ajax heavy site and some 3k html formatted pages are inserted into the DOM from ajax requests. What I have been doing is taking the html responses and just inserting the whole thing using jQuery. My other option is to output in xml (or possibly json) and then parse the document and insert it into the page. I've noticed it seems that most larger site do things the json/xml way. Google Mail returns xml rather than formatted html. Is this due to performance? or is there another reason to use xml/json vs just retrieving html? From a javascript standpoint, it would seem injecting direct html is simplest. In jQuery I just do this jQuery.ajax({ type: "POST", url: "getpage.php", data: requestData, success: function(response){ jQuery('div#putItHear').html(response); } with an xml/json response I would have to do jQuery.ajax({ type: "POST", url: "getpage.php", data: requestData, success: function(xml){ $("message",xml).each(function(id) { message = $("message",xml).get(id); $("#messagewindow").prepend(""+$("author",message).text()+ ": "+$("text",message).text()+ ""); }); } }); clearly not as efficient from a code standpoint, and I can't expect that it is better browser performance, so why do things the second way?

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• Assemble an image browser side with JavaScript or Flash?

  - by Kris Walker

  Would it be possible to assemble an image on the browser by 'concatenating' other downloaded images together? The use case is this. The page will display 36 different tiles (small images). The user should be able to arrange those tiles into a 6 x 6 grid and save the resulting grid to disk as an image. The best solution would be to do it all in the browser without Flash. The next best solution would be to allow the user to create the grid in the browser with simple JavaScript drag and drop functionality and then send the coordinates to the server for image processing. The last solution would be to do it all in the browser with Flash. Is it even possible for Flash to create an image and then allow the user to save it from the browser? I am familiar with the Pixastic JavaScript library ( http://www.pixastic.com/ ), but it relies on getting image data to and from a canvas element which is not very well supported. What if I send the tile images to the browser as base64 encoded strings? Could I use JavaScript to create the 6 x 6 grid image? And if so, is there some way of allowing the user to get it onto disk without relying on the canvas element?

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• Which are the RDBMS that minimize the server roundtrips? Which RDBMS are better (in this area) than

  - by user193655

  When the latency is high ("when pinging the server takes time") the server roundtrips make the difference. Now I don't want to focus on the roundtrips created in programming, but the roundtrips that occur "under the hood" in the DB engine, so the roundtrips that are 100% dependant on how the RDBMS is written itself. I have been told that FireBird has more roundtrips than MySQL. But this is the only information I know. I am currently supporting MS SQL but I'd like to change RDBMS (because I use Express Editions and in my scenario they are quite limiting from the performance point of view), so to make a wise choice I would like to include also this point into "my RDBMS comparison feature matrix" to understand which is the best RDBMS to choose as an alternative to MS SQL. So the bold sentence above would make me prefer MySQL to Firebird (for the roundtrips concept, not in general), but can anyone add informations? And MS SQL where is it located? Is someone able to "rank" the roundtrip performance of the main RDBMS, or at least: MS SQL, MySql, Postegresql, Firebird (I am not interested in Oracle since it is not free, and if I have to change I would change to a free RDBMS). Anyway MySql (as mentioned several times on stackoverflow) has a not clear future and a not 100% free license. So my final choice will probably dall on PostgreSQL or Firebird. Additional info: somehow you can answer my question by making a simple list like: MSSQL:3; MySQL:1; Firebird:2; Postgresql:2 (where 1 is good, 2 average, 3 bad). Of course if you can post some links where the roundtrips per RDBMSs are compared it would be great

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• [jscript] Good (better) substition for setInterval or setTimeout

  - by riffnl

  I've got a masterpage with some nice UI (jQuery) features. One of these options is interefering with my embedded YouTube (or other alike-) objects. On each, in this case, setInterval event the embedded video stops displaying new frames (for like a second). More detail: I've got a "polaroid" gallery (in the header) with only 5 100x100 images in it (test: preloading has no effect on performance) and my gallery will show or hide them (fade-in / fade-out) after a period of time. (test: non-animated display:hide or display:block has no effect on performance). After some testing and I've come to the conclusion that it isn't the "animated" showing or hiding of the pictures, but it's the interval itself (- since altering to display:hide or block had the same result). Perhaps it is my "gallery" "function" on itself ... function poladroid() { if (!galleryHasFocus) { if (galleryMax >= 0) { galleryCurrent++; if (galleryCurrent > galleryMax) { galleryCurrent = 0; showPictures = !showPictures; } if (showPictures) { $('#pic-' + galleryCurrent.toString()).show("slow"); } else { $('#pic-' + galleryCurrent.toString()).hide("slow"); } } } if (!intervalSet) { window.setInterval("poladroid()", 3000); intervalSet = true; } } It's not like my function is doing really awkward stuff is it? So, I was thinking I needed a more "loose" interval function.. but is there an option for it?

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• Problems with Json Serialize Dictionary<Enum, Int32>

  - by dbemerlin

  Hi, whenever i try to serialize the dictionary i get the exception: System.ArgumentException: Type 'System.Collections.Generic.Dictionary`2[[Foo.DictionarySerializationTest+TestEnum, Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' is not supported for serialization/deserialization of a dictionary, keys must be strings or object My Testcase is: public class DictionarySerializationTest { private enum TestEnum { A, B, C } public void SerializationTest() { Dictionary<TestEnum, Int32> data = new Dictionary<TestEnum, Int32>(); data.Add(TestEnum.A, 1); data.Add(TestEnum.B, 2); data.Add(TestEnum.C, 3); JavaScriptSerializer serializer = new JavaScriptSerializer(); String result = serializer.Serialize(data); // Throws } public void SerializationStringTest() { Dictionary<String, Int32> data = new Dictionary<String, Int32>(); data.Add(TestEnum.A.ToString(), 1); data.Add(TestEnum.B.ToString(), 2); data.Add(TestEnum.C.ToString(), 3); JavaScriptSerializer serializer = new JavaScriptSerializer(); String result = serializer.Serialize(data); // Succeeds } } Of course i could use .ToString() whenever i enter something into the Dictionary but since it's used quite often in performance relevant methods i would prefer using the enum. My only solution is using .ToString() and converting before entering the performance critical regions but that is clumsy and i would have to change my code structure just to be able to serialize the data. Does anyone have an idea how i could serialize the dictionary as <Enum, Int32>? I use the System.Web.Script.Serialization.JavaScriptSerializer for serialization.

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• Good web hosting for ASP.NET MVC 1.0 app

  - by magellings

  I'm looking for hosting for an ASP.NET MVC 1.0 app. I've narrowed down with research to either asphostportal, asphostcentral, godaddy, or 1&1. I've ruled out crystaltech and softsyshosting due to price with better plans. Will be running a small e-commerce site written with ASP.NET MVC 1.0 and want to be sure it will work, as well as looking for cheapest price with best value in regards to disk space/bandwidth. And bandwidth is basically how much data can be sent from your site per month right? Any opinions appreciated as I'm finding this tough to narrow down. I know you can bin deploy MVC but heard full trust mode is required as well as some routing rules in IIS. 1&1 says they can't enable full trust. This is what I was looking at: name data(disk space/bandwidth) price MVCenabled crystal tech 500MB/50GB 7.95 + 7.95 setup 2000MB/200GB 16.95 softsyshosting 500MB/5GB 3.50 + 12/year domain 1000MB/10GB 5.84 3000MB/30GB 13.33 asphostportal 5GB/50GB 5.75 + 8.99/year yes 10GB/100GB 10.25 asphostcentral 2GB/15GB 4.99 yes 3GB/30GB 7.99/month domain free 5GB/40GB 11.99 godaddy 10GB/300GB 10.69 + 4.74/month 150GB/1500GB 6.99/month 1&1 10GB/unlimited 3.99 + free domain 150GB/unlimited 6.99 1&1 seems to be best value if MVC app will work. I'm a bit confused on bandwidth being unlimited. May seem like a good thing, but what if one website on the server is a resource hog because of this?

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• Python, Ruby, and C#: Use cases?

  - by thaorius

  Hi everyone. For as long as I can remember, I've always had a "favorite" language, which I use for most projects, until, for some particular reason, there is no way/point on using it for project XYZ. At that point, I find myself rusty (and sometimes outdated) on other languages+libraries+toolchains. So I decided, I would just use some languages/libs/tools for some things, and some for other, effectively keeping them fresh (there would obviously be exceptions, I'm not looking for an arbitrary rule set, but some guidelines). I wanted an opinion on what would be your standard use cases (new projects) for Python, Ruby, and C# (Mono). At the moment, I have time like this:Languages: C#: Mid-Large Sized Projects (mainly server-side daemons) High Performance (I hardly ever need C's performance, but Python just doesn't cut it) Relatively Low Footprint (vs the JVM, for example) Ruby: Web Applications Python: General Use Scripts (automation, system config, etc) Small-Mid Sized Projects Prototyping Web Applications About Ruby, I have no idea what to use it for that I can't use Python for (specially considering Python is more easily found installed by default). And I like both languages (though I'm really new to Ruby), which makes things even worse. As for C#, I have not used a Windows powered computer in a few years, I don't make things for Windows computers, and I don't mind waiting for Mono to implement some new features. That being said, I haven't found many people on the internet using it for server-sided *nix programming (not web related). I would appreciate some insight on this too. Thanks for your time.

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• What happens when value types are created?

  - by Bob

  I'm developing a game using XNA and C# and was attempting to avoid calling new struct() type code each frame as I thought it would freak the GC out. "But wait," I said to myself, "struct is a value type. The GC shouldn't get called then, right?" Well, that's why I'm asking here. I only have a very vague idea of what happens to value types. If I create a new struct within a function call, is the struct being created on the stack? Will it simply get pushed and popped and performance not take a hit? Further, would there be some memory limit or performance implications if, say, I need to create many instances in a single call? Take, for instance, this code: spriteBatch.Draw(tex, new Rectangle(x, y, width, height), Color.White); Rectangle in this case is a struct. What happens when that new Rectangle is created? What are the implications of having to repeat that line many times (say, thousands of times)? Is this Rectangle created, a copy sent to the Draw method, and then discarded (meaning no memory getting eaten up the more Draw is called in that manner in the same function)? P.S. I know this may be pre-mature optimization, but I'm mostly curious and wish to have a better understanding of what is happening.

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• Some optimization about the code (computing ranks of a vector)?

  - by user1748356

  The following code is a function (performance-critical) to compute tied ranks of a vector: mergeSort(x,inds,ci); //a sort function to sort vector x of length ci, also returns keys (inds) of x. int tj=0; double xi=x[0]; for (int j = 1; j < ci; ++j) { if (x[j] > xi) { double rankvalue = 0.5 * (j - 1 + tj); for (int k = tj; k < j; ++k) { ranks[inds[k]]=rankvalue; }; tj = j; xi = x[j]; }; }; double rankvalue = 0.5 * (ci - 1 + tj); for (int k = tj; k < ci; ++k) { ranks[inds[k]]=rankvalue; }; The problem is, the supposed performance bottleneck mergeSort(), which is O(NlogN) is several times faster than the other part of codes (which is O(N)), which suggests there is room for huge improvment with the other part of the codes, any advices?

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• Agile language for 2d game prototypes?

  - by instanceofTom

  Occasionally ( read: when my fiancé allows ) I like to prototype different game or game-like ideas I have. Usually I use Java or C# (not xna yet) because they are the languages I have the most practice with. However I would like to learn something more suited to agile development; a language in which it would be easier to knock out quick prototypes. At my job I have recently been working with looser (weak/dynamically typed) languages, specifically python and groovy, and I think something similar would fit what I am looking for. So, my question is: What languages (and framework/engine) would be good for rapidly developing prototypes of 2d game concepts? A few notes: I don't need blazing fast bitcrunching performance. In this case I would strongly prefer ease of development over performance. I'd like to use a language with a healthy community, which to me means a fair amount of maintained 3rd party, libraries. I'd like the language to be cross-platform friendly, I work on a variety of different operating systems and would like something that is portable with minimum effort. I can't imagine myself using a language with out decent options for debugging and editor syntax highlighting support. Note: If you are aware of a Java or C# library/framework that you think streamlines producing game prototypes I open to learning something new for those languages too

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• Programmatically downloaded file is larger than it should be

  - by Dan Revell

  I'm trying to download a file from SharePoint. The file itself is an InfoPath template although this is probably inconsequential. If I put the url into internet explorer and save the file to disk, it comes in at 4.47KB and works correctly. If I try to download from the same Url in code the it comes back as 21.9KB and is corrupt. Why it's coming down as corrupt I'm trying to work out. The following are two ways of downloading the file that both produce the corrupt file at 21.9KB: /// web client { WebClient wc = new WebClient(); wc.Credentials = CredentialCache.DefaultCredentials; wc.DownloadFile(templateUri, file); byte[] bytes = wc.DownloadData(templateUri); } /// web request { WebRequest request = WebRequest.Create(templateUri); request.Credentials = CredentialCache.DefaultCredentials; WebResponse responce = request.GetResponse(); StreamReader sr = new StreamReader(responce.GetResponseStream()); byte[] bytes = System.Text.Encoding.UTF8.GetBytes(sr.ReadToEnd()); } And this is how I write the data to disk using (FileStream fs = new FileStream(file, FileMode.Create, FileAccess.Write)) { fs.Write(bytes, 0, bytes.Length); }

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• Creating a tar file with checksums included

  - by wazoox

  Here's my problem : I need to archive to tar files a lot ( up to 60 TB) of big files (usually 30 to 40 GB each). I would like to make checksums ( md5, sha1, whatever) of these files before archiving; however not reading every file twice (once for checksumming, twice for tar'ing) is more or less a necessity to achieve a very high archiving performance (LTO-4 wants 120 MB/s sustained, and the backup window is limited). So I'd need some way to read a file, feeding a checksumming tool on one side, and building a tar to tape on the other side, something along : tar cf - files | tee tarfile.tar | md5sum - Except that I don't want the checksum of the whole archive (this sample shell code does just this) but a checksum for each individual file in the archive. I've studied GNU tar, Pax, Star options. I've looked at the source from Archive::Tar. I see no obvious way to achieve this. It looks like I'll have to hand-build something in C or similar to achieve what I need. Perl/Python/etc simply won't cut it performance-wise, and the various tar programs miss the necessary "plugin architecture". Does anyone know of any existing solution to this before I start code-churning ?

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• How does C#'s DateTime.Now affect query plan caching in SQL Server?

  - by Bill Paetzke

  Given: Let's say we have a stored procedure. It reports data back to a user on a webpage. The user can set a date range. If the user sets today's date as the "end date," which includes today's data, the web app passes DateTime.Now to the sql proc. Let's say that one user runs a report--5/1/2010 to now--over and over several times. On the webpage, the user sees "5/1/2010" to "5/4/2010." But the web app passes DateTime.Now to the sql proc as the end date. So, the end date in the proc will always be different, although the user is querying a similar date range. Assume the number of records in the table and number of users are large. So any performance gains matter. Hence the importance of the question. Question: Does passing DateTime.Now as a parameter to a proc prevent SQL Server from caching the query plan? If so, then is the web app missing out on huge performance gains? Possible Solution: I thought DateTime.Today.AddDays(1) would be a possible solution. It would allow the user to get the latest data and always pass the same end date to the sql proc--"5/5/2010" in this case. Please speak to this as well. Sample proc and execution (if that helps to understand): CREATE PROCEDURE GetFooData @StartDate datetime @EndDate datetime AS SELECT * FROM Foo WHERE LogDate >= @StartDate AND LogDate < @EndDate Here's a sample execution using DateTime.Now: EXEC GetFooData '2010-05-01', '2010-05-04 15:41:27' -- passed in DateTime.Now Here's a sample execution using DateTime.Today.AddDays(1) EXEC GetFooData '2010-05-01', '2010-05-05' -- passed in DateTime.Today.AddDays(1) The same data is returned for both procs, since the current time is: 2010-05-04 15:41:27.

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• How to scale a PHP application (servers, mysql, memcache)

  - by Stéphane Goetz

  Hi, I'm currently creating a website for a social project in switzerland. And before there is an overflow of user, I want to prepare the application to scale. I answered by myself many questions but some are left. I explain what I want to do. First at the beginnning, the Application will have only one server (short time) with DNS, PHP, Mysql, Data, and memcache. Second Then I will split them in two DNS, Mysql, memcache Data, PHP Third Here is the problem, I don't know how to do it exactly here to keep the application running well. I could do : Front : Load Balancer, memcache, DNS Web 1 : PHP, DATA Web 2 : PHP, DATA Mysql This would be the scheme, all PHP sessions are kept in the DB. BUT, how do I sync the data? do I run a Rsync to keep them up to date. do I put them on a separate disk (network disk) to be sure ? but in this case, how can I do in case of user uploads ? and if the website gets more success and we have to go on greater structures, would'nt it create some latency on updates ? or would it be a good thing to go directly to amazon's web services ? some infos I use codeigniter as Framework. I use linux as webserver (distribution not chosen now, but should be Debian) Thanks in advance for your answers.

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• How to read time from recorded surveillance camera video?

  - by stressed_geek

  I have a problem where I have to read the time of recording from the video recorded by a surveillance camera. The time shows up on the top-left area of the video. Below is a link to screen grab of the area which shows the time. Also, the digit color(white/black) keeps changing during the duration of the video. http://i55.tinypic.com/2j5gca8.png Please guide me in the direction to approach this problem. I am a Java programmer so would prefer an approach through Java. EDIT: Thanks unhillbilly for the comment. I had looked at the Ron Cemer OCR library and its performance is much below our requirement. Since the ocr performance is less than desired, I was planning to build a character set using the screen grabs for all the digits, and using some image/pixel comparison library to compare the frame time with the character-set which will show a probabilistic result after comparison. So I was looking for a good image comparison library(I would be OK with a non-java library which I can run using the command-line). Also any advice on the above approach would be really helpful.

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• NASM - Load code from USB Drive

  - by new123456

  Hola, Would any assembly gurus know the argument (register dl) that signifies the first USB drive? I'm working through a couple of NASM tutorials, and would like to get a physical boot (I can get a clean one with qemu). This is the section of code that loads the "kernel" data from disk: loadkernel: mov si, LMSG ;; 'Loading kernel',13,10,0 call prints ;; ex puts() mov dl, 0x00 ;; The disk to load from mov ah, 0x02 ;; Read operation mov al, 0x01 ;; Sectors to read mov ch, 0x00 ;; Track mov cl, 0x02 ;; Sector mov dh, 0x00 ;; Head mov bx, 0x2000 ;; Buffer end mov es, bx mov bx, 0x0000 ;; Buffer start int 0x13 jc loadkernel mov ax, 0x2000 mov ds, ax jmp 0x2000:0x00 If it makes any difference, I'm running a stock Dell Inspiron 15 BIOS. Apparently, the correct value for me is 0x80. The BIOS loads the hard drives and labels them starting at 0x80 according to this answer. My particular BIOS decides to load the USB drive up as the first, for some reason, so I can boot from there.

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• Any merit to a lazy-ish juxt function?

  - by NielsK

  In answering a question about a function that maps over multiple functions with the same arguments (A: juxt), I came up with a function that basically took the same form as juxt, but used map: (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply %1 %2) funs (repeat args)))) => ((juxt inc dec str) 1) [2 0 "1"] => ((could-be-lazy-juxt inc dec str) 1) (2 0 "1") => ((juxt * / -) 6 2) [12 3 4] => ((could-be-lazy-juxt * / -) 6 2) (12 3 4) As posted in the original question, I have little clue about the laziness or performance of it, but timing in the REPL does suggest something lazy-ish is going on. => (time (apply (juxt + -) (range 1 100))) "Elapsed time: 0.097198 msecs" [4950 -4948] => (time (apply (could-be-lazy-juxt + -) (range 1 100))) "Elapsed time: 0.074558 msecs" (4950 -4948) => (time (apply (juxt + -) (range 10000000))) "Elapsed time: 1019.317913 msecs" [49999995000000 -49999995000000] => (time (apply (could-be-lazy-juxt + -) (range 10000000))) "Elapsed time: 0.070332 msecs" (49999995000000 -49999995000000) I'm sure this function is not really that quick (the print of the outcome 'feels' about as long in both). Doing a 'take x' on the function only limits the amount of functions evaluated, which probably is limited in it's applicability, and limiting the other parameters by 'take' should be just as lazy in normal juxt. Is this juxt really lazy ? Would a lazy juxt bring anything useful to the table, for instance as a compositing step between other lazy functions ? What are the performance (mem / cpu / object count / compilation) implications ? Is that why the Clojure juxt implementation is done with a reduce and returns a vector ? Edit: Somehow things can always be done simpler in Clojure. (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply % args) funs)))

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• Where to store site settings: DB? XML? CONFIG? CLASS FILES?

  - by Emin

  I am re-building a news portal of which already have a large number of visits every day. One of the major concerns when re-building this site was to maximize performance and speed. Having said this, we have done many things from caching, to all sort of other measures to ensure speed. Now towards the end of the project, I am having a dilemma of where to store my site settings that would least affect performance. The site settings will include things such as: Domain, DefaultImgPath, Google Analytics code, default emails of editors as well as more dynamic design/display feature settings such as the background color of specific DIVs and default color for links etc.. As far as I know, I have 4 choices in storing all these info. Database: Storing general settings in the DB and caching them may be a solution however, I want to limit the access to the database for only necessary and essential functions of the project which generally are insert/update/delete news items, author articles etc.. XML: I can store these settings in an XML file but I have not done this sort of thing before so I don't know what kind of problems -if any- I might face in the future. CONFIG: I can also store these settings in web.config CLASS FILE: I can hard code all these settings in a SiteSettings class, but since the site admin himself will be able to edit these settings, It may not be the best solution. Currently, I am more close to choosing web.config but letting people fiddle with it too often is something I do not want. E.g. if somehow, I miss out a validation for something and it breaks the web.config, the whole site will go down. My concern basically is that, I cannot forsee any possible consequences of using any of the methods above (or is there any other?), I was hoping to get this question over to more experienced people out here who hopefully help make my decision.

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• How does DateTime.Now affect query plan caching in SQL Server?

  - by Bill Paetzke

  Question: Does passing DateTime.Now as a parameter to a proc prevent SQL Server from caching the query plan? If so, then is the web app missing out on huge performance gains? Possible Solution: I thought DateTime.Today.AddDays(1) would be a possible solution. It would pass the same end-date to the sql proc (per day). And the user would still get the latest data. Please speak to this as well. Given Example: Let's say we have a stored procedure. It reports data back to a user on a webpage. The user can set a date range. If the user sets today's date as the "end date," which includes today's data, the web app passes DateTime.Now to the sql proc. Let's say that one user runs a report--5/1/2010 to now--over and over several times. On the webpage, the user sees 5/1/2010 to 5/4/2010. But the web app passes DateTime.Now to the sql proc as the end date. So, the end date in the proc will always be different, although the user is querying a similar date range. Assume the number of records in the table and number of users are large. So any performance gains matter. Hence the importance of the question. Example proc and execution (if that helps to understand): CREATE PROCEDURE GetFooData @StartDate datetime @EndDate datetime AS SELECT * FROM Foo WHERE LogDate >= @StartDate AND LogDate < @EndDate Here's a sample execution using DateTime.Now: EXEC GetFooData '2010-05-01', '2010-05-04 15:41:27' -- passed in DateTime.Now Here's a sample execution using DateTime.Today.AddDays(1) EXEC GetFooData '2010-05-01', '2010-05-05' -- passed in DateTime.Today.AddDays(1) The same data is returned for both procs, since the current time is: 2010-05-04 15:41:27.

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• Wrapping unmanaged C++ with C++/CLI - a proper approach.

  - by Jamie

  Hi there, as stated in the title, I want to have my old C++ library working in managed .NET. I think of two possibilities: 1) I might try to compile the library with /clr and try "It Just Works" approach. 2) I might write a managed wrapper to the unmanaged library. First of all, I want to have my library working FAST, as it was in unmanaged environment. Thus, I am not sure if the first approach will not cause a large decrease in performance. However, it seems to be faster to implement (not a right word :-)) (assuming it will work for me). On the other hand, I think of some problems that might appear while writing a wrapper (e.g. how to wrap some STL collection (vector for instance)?) I think of writing a wrapper residing in the same project as the unmanaged C++ resides - is that a reasonable approach (e.g. MyUnmanagedClass and MyManagedClass in the same project, the second wrapping the other)? What would you suggest in that problem? Which solution is going to give me better performance of the resulting code? Thank you in advance for any suggestions and clues! Cheers

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