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• Why would you want a case sensitive database?

  - by Khorkrak

  What are some reasons for choosing a case sensitive collation over a case insensitive one? I can see perhaps a modest performance gain for the DB engine in doing string comparisons. Is that it? If your data is set to all lower or uppercase then case sensitive could be reasonable but it's a disaster if you store mixed case data and then try to query it. You have then apply a lower() function on the column so that it'll match the corresponding lower case string literal. This prevents index usage in every dbms. So wondering why anyone would use such an option.

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• New to AVL tree implementation.

  - by nn

  I am writing a sliding window compression algorithm (LZ77) that searches for phrases in a "moving" dictionary. So far I have written a BST where each node is stored in an array and it's index in the array is also the value of the starting position in the window itself. I am now looking at transforming the BST to an AVL tree. I am a little confused at the sample implementations I have seen. Some only appear to store the balance factors whereas others store the height of each tree. Are there any performance advantage/disadvantages of storing the height and/or balance factor for each node? Apologies if this is a very simple question, but I'm still not visualizing how I want to restructure my BST to implement height balancing. Thanks.

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• Using one sqlconnection/sqlcommand through 2 DB-bound methods

  - by dotnetdev

  I have a class with a method which gets data from a database through a SELECT stored proc. This method uses a SqlDbReader by returning ExecuteReader() on a SqlCommand. The connection and everything is made in this method, with fields (such as connection string) set as class level fields. I now need to populate an array based on the results of this query (so the columns of each row will go into the array with its own index). However, this query will not select all of the data from one table which is involved. I can write the queries to get what I need, but how can I use one connection throughout the class? If I instantiate the connection object and call Open() in the constructor, I get an exception @ runtime. I'm hoping for something like this: // At class level: sqlconn.Open(); // sqlcommand set up Method() { // Fire stored proc // Insert results in a collection } Method2() { // Pass same collection in (use same one), // Add new row columns into same collection } How can I do this with strict performance in mind? Thanks

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• How to improve INSERT INTO ... SELECT locking behavior

  - by Artem

  In our production database, we ran the following pseudo-code SQL batch query running every hour: INSERT INTO TemporaryTable (SELECT FROM HighlyContentiousTableInInnoDb WHERE allKindsOfComplexConditions are true) Now this query itself does not need to be fast, but I noticed it was locking up HighlyContentiousTableInInnoDb, even though it was just reading from it. Which was making some other very simple queries take ~25 seconds (that's how long that other query takes). Then I discovered that InnoDB tables in such a case are actually locked by a SELECT! http://www.mysqlperformanceblog.com/2006/07/12/insert-into-select-performance-with-innodb-tables/ But I don't really like the solution in the article of selecting into an OUTFILE, it seems like a hack (temporary files on filesystem seem sucky). Any other ideas? Is there a way to make a full copy of an InnoDB table without locking it in this way during the copy. Then I could just copy the HighlyContentiousTable to another table and do the query there.

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• writing a fast parser in python

  - by panzi

  I've written a hands-on recursive pure python parser for a some file format (ARFF) we use in one lecture. Now running my exercise submission is awfully slow. Turns out by far the most time is spent in my parser. It's consuming a lot of CPU time, the HD is not the bottleneck. I wonder what performant ways are there to write a parser in python? I'd rather not rewrite it in C. I tried to use jython, but that decreased performance a lot! The files I parse are partially huge ( 150 MB) with very long lines. My current parser only needs a look-ahead of one character. I'd post the source here but I don't know if that's such a good idea. After all the submission deadline has not jet ended. But then, the focus in this exercise is not the parser. You can choose whatever language you want to use and there already is a parser for Java.

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• WCF - Network Cost

  - by Mubashar Ahmad

  Dear Devs I have a wcf service deployed on IIS with basicHttpBinding and aspNetCompatibilityEnabled=true I have a test client as well which invokes multiple service functions simultaneously. To check the performance of service call on client and server I calculated the Avg time it takes to complete a service request on client(in proxy code) and on server as well. after a test of 8 hrs (server and client were on the same machine) i came to know that average response time on client is around 34ms where as the Avg execution time on server is around 3ms so the difference is 31ms. I would like to know why every call is taking 31ms is it justified? and how can i reduce this?

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• Validation Rules in Webtesting using VS2010

  - by Lexipain

  I'm creating a simple webtest (Recorded Web performance test) that makes sure that a correct error message is displayed if i try to login with a username that does not exist. However, there are two types of error messages that handle incorrect login info. One is for all the usernames that do not exist and therefore are not allowed, and the other is for usernames that start with the letter 'Q' (which is not allowed for a few reasons). Now what i want to do is use the 'Find Text' validation rule and the test should pass if ONE of the 'Find Text' parameters is found, and in that case i want the second 'Find Text' rule to be ignored so it doesn't fail the test. In other words the test should always pass if one of the 'Find Test' rules is found. How can i achieve that? Is there some if,else statement that i can use for this?

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• Should I use `!IsGood` or `IsGood == false`?

  - by chills42

  I keep seeing code that does checks like this if (IsGood == false) { DoSomething(); } or this if (IsGood == true) { DoSomething(); } I hate this syntax, and always use the following syntax. if (IsGood) { DoSomething(); } or if (!IsGood) { DoSomething(); } Is there any reason to use '== true' or '== false'? Is it a readability thing? Do people just not understand Boolean variables? Also, is there any performance difference between the two?

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• Multiple Socket Connections

  - by BSchlinker

  I need to write a server which accepts connections from multiple client machines, maintains track of connected clients and sends individual clients data as necessary. Sometimes, all clients may be contacted at once with the same message, other times, it may be one individual client or a group of clients. Since I need confirmation that the clients received the information and don't want to build an ACK structure for a UDP connection, I decided to use a TCP streaming method. However, I've been struggling to understand how to maintain multiple connections and keep them idle. I seem to have three options. Use a fork for each incoming connection to create a separate child process, use pthread_create to create an entire new thread for each process, or use select() to wait on all open socket IDs for a connection. Recommendations as to how to attack this? I've begun working with pthreads but since performance will likely not be an issue, multicore processing is not necessary and perhaps there is a simpler way.

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• Optimizing for speed - 4 dimensional array lookup in C

  - by Tiago

  I have a fitness function that is scoring the values on an int array based on data that lies on a 4D array. The profiler says this function is using 80% of CPU time (it needs to be called several million times). I can't seem to optimize it further (if it's even possible). Here is the function: unsigned int lookup_array[26][26][26][26]; /* lookup_array is a global variable */ unsigned int get_i_score(unsigned int *input) { register unsigned int i, score = 0; for(i = len - 3; i--; ) score += lookup_array[input[i]][input[i + 1]][input[i + 2]][input[i + 3]]; return(score) } I've tried to flatten the array to a single dimension but there was no improvement in performance. This is running on an IA32 CPU. Any CPU specific optimizations are also helpful. Thanks

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• How to achieve a palette effect on iPhone using OpenGL

  - by Joe

  I'm porting a 2d retro game to iPhone that has the following properties: targets OpenGL ES 1.1 entire screen is filled with tiles (textured triangle strip tile textured using a single 256x256 RGBA texture image the texture is passed to OpenGL once at the start of the game only 4 displayed colours are used one of the displayed colours is black The original game flashed the screen when time starts to run out by toggling the black pixels to white using an indexed palette. What is the best (i.e. most efficient) way to achieve this in OpenGL ES 1.1? My thoughts so far: Generate an alternative texture with white instead of black pixels, and pass to OpenGL when the screen is flashing Render a white poly underneath the background and render the texture with alpha on to display it Try and render a poly on top with some blending that achieves the effect (not sure this is possible) I'm fairly new to OpenGL so I'm not sure what the performance drawbacks of each of these are, or if there's a better way of doing this.

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• Tomcat - virtualhosting - name / ip / port - based

  - by lisak

  Hey, what are the usage scenarios for these kinds of virtual hosting ? Name Based - typical tomcat virtual hosting, one HOME instance with many contexts, each as an individual host IP based / port based - multiple instances of tomcat ( how is it with performance and memory consuption?) running on IP aliases (virtual IPs) for one network adapter, usually behind http apache server that can run name based virtual hostings. Otherwise I can't figure out how would I forward requests in iptables/firewall based on IP address, which is just one. How is IP based virtual hosting done as to Tomcat and multiple instances ? I'd like to hear some usage scenarios from your experience. How are you running your applications. Cause there are applications having it's own modified classloader and they are developed in a way to run alone withing a tomcat instance. Then there are trivial applications which can run within one instance without problems. Many thanks

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• PHP Initialising strings as boolean first

  - by Anriëtte Myburgh

  I'm in the habit of initialising variables in PHP to false and then applying whatever (string, boolean, float) value to it later. Which would you reckon is better? $name = false; if (condition == true) { $name = $something_else; } if ($name) { …do something… } vs. $name =''; if (condition == true) { $name = $something_else; } if (!empty($name)) { …do something… } Which would you reckon can possibly give better performance? Which method would you use?

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• ASP.NET Download All Files as Zip

  - by Ronnie Overby

  I have a folder on my web server that has hundreds of mp3 files in it. I would like to provide the option for a user to download a zipped archive of every mp3 in the directory from a web page. I want to compress the files programmatically only when needed. Because the zip file will be quite large, I am thinking that I will need to send the zip file to the response stream as it is being zipped, for performance reasons. Is this possible? How can I do it?

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• Choosing between ExtJS and YUI based of application parameters.

  - by Kabeer

  Hello. I need help in taking call to choose between Ext JS and YUI libraries. Here are the key factors I have derived from my application requirements & development process: Complex, windows forms like controls Widgets, Layouts, Utilities Inter widget communication Easy to extend Easy to learn Intuitive & concise coding Strong exception handling Active support / community To update with upcoming technologies (HTML5, etc.) Skins & Themes to be easy to change Skins & Themes to support variety (a text box for different context to appear differently) Support & Utilities for standard protocols (XmlHttp, JSON) Good performance (responsive) Cost is not crucial, but I don't mind saving :)

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• Concatenation Operator - PHP

  - by Chaitanya

  This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: a. by not using the concatenation operator, does it effect the performance? b. If it doesn't why at all have the concatenation operator. c. Why have 2 modes of implementation when one does the work?

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• Python: split a list based on a condition?

  - by Parand

  What's the best way, both aesthetically and from a performance perspective, to split a list of items into multiple lists based on a conditional? The equivalent of: good = [x for x in mylist if x in goodvals] bad = [x for x in mylist if x not in goodvals] is there a more elegant way to do this? Update: here's the actual use case, to better explain what I'm trying to do: # files looks like: [ ('file1.jpg', 33L, '.jpg'), ('file2.avi', 999L, '.avi'), ... ] IMAGE_TYPES = ('.jpg','.jpeg','.gif','.bmp','.png') images = [f for f in files if f[2].lower() in IMAGE_TYPES] anims = [f for f in files if f[2].lower() not in IMAGE_TYPES]

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• Very long strings as primary keys in a database for caching

  - by Bill Zimmerman

  Hi, I am working on a web app that allows users to create dynamic PDF files based on what they enter into a form (it is not very structured data). The idea is that User 1 enters several words (arbitrary # of words, practically capped of course), for example: A B C D E There is no such string in the database, so I was thinking: Store this string as a primary key in a MySQL database (it could be maybe around 50-100k of text, but usually probably less than 200 words) Generate the PDF file, and create a link to it in the database When the next user requests A B C D E, then I can just serve the file instead of recreating it each time. (simple cache) The PDF is cpu intensive to generate, so I am trying to cache as much as I can... My questions are: Does anyone have any alternative ideas to my approach What will the database performance be like? Is there a better way to design the schema than using the input string as the primary key?

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• Building a case for solr

  - by Midhat

  Our product consists of multiple applications, All using Lucene. 2 of the applications I am involved with have Lucene indexes of about 3 GB and 12GB. Another team is building an application, for which they estimate the LUCENE INDEX size to be close to 1 Terabyte. New documents are added to the indexes every 15 days approx. We do not have any apparent performance issues with the current applications. So my question is SHould we be using Solr now? When should one stop using Lucene and graduate to Solr? Any disadvantages/problems for using Solr? The client applications are made in ASP.Net, but I assume they will be able to use a solr server using solrnet

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• Using Windows media foundation

  - by Martin Beckett

  Ok so my new gig is high performance video (think Google streetview but movies) - the hard work is all embedded capture and image processing but: I was looking at the new MS video offerings to display content = Windows Media Foundation. Is anyone actually using this ? There are no books on the topic. The only documentation is a developer team blog with a single entry 9 months old. I thought we had got past having to learn an MS api by spying on the com control messages! Is it just another wrapper around the same old activeX control?

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• [java] Efficiency of while(true) ServerSocket Listen

  - by Submerged

  I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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• how does NTFS actually work with B-tree ?

  - by bakra

  To improve performance, NTFS directories use a special data management structure called a B-tree. "B-tree" concept here refers to a "tree of storage units" that hold the contents of an individual directory. What I don't understand is where on the disk is this tree stored? Its surely not created every-time we reboot...that would take lots of time. and since its a tree(dynamic Data structure) unlike arrays it will grow. so space needs to be allocated every-time it grows. so how is this "dynamic meta-data" stored ?

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• Profiling statements inside a User-Defined Function

  - by Craig Walker

  I'm trying to use SQL Server Profiler (2005) to track down some application performance problems. One of the calls being made is to a table-valued user-defined function. This function wraps a select that joins several tables together. In SQL Server Profiler, the call to the UDF is logged. However, the select that underlies the UDF isn't being logged at all. Because of this, I'm not getting useful data on which tables & indexes are being hit. I'd like to feed this info into the Database Tuning Advisor for some indexing advice. Is there any way (short of unwrapping the queries themselves) to log the tables called by UDFs in Profiler?

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• Precompile Lambda Expression Tree conversions as constants?

  - by Nathan

  It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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• Best way to handle SQL Server fulltext index updates

  - by tlianza

  Hi all, I have a fulltext index which doesn't need to be immediately up-to-date, I'd like to spare myself the I/O (when I do bulk updates, I see a ton of I/O related to the index) and do the index updates during low usage times (nightly, perhaps even weekly). It seems there are two ways to go about this: Turn off change tracking (SET CHANGE_TRACKING OFF) and add a timestamp field to the indexed table, so that you can run alter fulltext index on <table> start INCREMENTAL population, or Enable change tracking, but set it to MANUAL, so that you can run alter fulltext index on <table> start UPDATE population when you need it updated. Is there a preferred method? I couldn't tell from this overview if there was a performance benefit one way or the other. Tom

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