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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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• 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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• 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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• 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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• 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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• problem with dmg file

  - by madalina

  Hello, I have created a dmg file named try.dmg which contains an executable application myapplication.app together with a compiled library mylibrary.lib; I used Disk Utility in order to create the try.dmg file. I mounted the try.dmg file on my computer and I opened the application myapplication.app with no problems. Still, I tried to do the same thing on another Macintosh, with the same operating system Mac OS X, but I got some problems: I mounted the try.dmg file and then when I tried to open the application myapplication.app I got an error message, that the application has quit unexpectedly. Can someone explain me what is it happening? How come this try.dmg file can be mounted and the application can be opened with no problems on my computer with Mac OS X, but on another computer with Mac OS X, after I mount the try.dmg file I get errors when I try opening the application? Thank you very much for your help. Best wishes, Madalina

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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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• Is writing to a socket an arbitrary limitation of the sendfile() syscall?

  - by Sufian

  Prelude sendfile() is an extremely useful syscall for two reasons: First, it's less code than a read()/write() (or recv()/send() if you prefer that jive) loop. Second, it's faster (less syscalls, implementation may copy between devices without buffer, etc...) than the aforementioned methods. Less code. More efficient. Awesome. In UNIX, everything is (mostly) a file. This is the ugly territory from the collision of platonic theory and real-world practice. I understand that sockets are fundamentally different than files residing on some device. I haven't dug through the sources of Linux/*BSD/Darwin/whatever OS implements sendfile() to know why this specific syscall is restricted to writing to sockets (specifically, streaming sockets). I just want to know... Question What is limiting sendfile() from allowing the destination file descriptor to be something besides a socket (like a disk file, or a pipe)?

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• Recreation of MySQL DB using "mysql mydb < mydb.sql" is really slow when the table has tens of milli

  - by Jian Lin

  It seems that a MySQL database that has a table with tens of millions of records will get a big INSERT INTO statement when the following mysqldump some_db > some_db.sql is done to back up the database. (is it 1 insert statement that handles all the records?) So when reconstructing the DB using mysql some_db < some_db.sql then the CPU is hardly busy (about 1.8% usage by the mysql process... I don't see a mysqld either?) and also the hard disk doesn't seem to be too busy... Last time, the whole restore process took 5 hours. Is there a way to make it faster? Such as, when doing mysqldump, can it break the INSERT statement into shorter ones, so that the mysql doesn't need to parse the line so hard when restoring the DB?

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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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• 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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• How to return an image in an HTTP response with CherryPy

  - by colinmarc

  I have code which generates a Cairo ImageSurface, and I expose it like so: def preview(...): surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height) ... cherrypy.response.headers['Content-Type'] = "image/png" return surface.get_data() preview.exposed = True This doesn't work (browsers report that the image has errors). I've tested that surface.write_to_png('test.png') works, but I'm not sure what to dump the data into to return it. I'm guessing some file-like object? According to the pycairo documentation, get_data() returns a buffer. I've also now tried: tempf = os.tmpfile() surface.write_to_png(tempf) return tempf Also, is it better to create and hold this image in memory (like I'm trying to do) or write it to disk as a temp file and serve it from there? I only need the image once, then it can be discarded.

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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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• 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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• How to Serialize Binary Tree

  - by Veljko Skarich

  I went to an interview today where I was asked to serialize a binary tree. I implemented an array-based approach where the children of node i (numbering in level-order traversal) were at the 2*i index for the left child and 2*i + 1 for the right child. The interviewer seemed more or less pleased, but I'm wondering what serialize means exactly? Does it specifically pertain to flattening the tree for writing to disk, or would serializing a tree also include just turning the tree into a linked list, say. Also, how would we go about flattening the tree into a (doubly) linked list, and then reconstructing it? Can you recreate the exact structure of the tree from the linked list? Thank you/

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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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• 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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• 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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• 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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• 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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• [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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• Optimising local image loading/rendering on iPhone

  - by Tricky

  Hi, I'm looking to create an interface where the user can navigate through large volumes of images. Each image has a thumbnail of 128x128 that I wish to display and will be kind of similar to coverflow in operation. I have this all working in principle but am becoming stuck when navigating through content at speed. The interface begins to stutter and becoming jerky. I believe this is primarily because of disk i/o and the cost of rendering each image. Is there anyway this can be handed over to a seperate thread simply? Defaulting to a greyed out thumbnail until the image has loaded? How have Apple managed to achieve this in coverflow? Many thanks,

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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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