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• Measuring device drivers CPU/IO utilization caused by my program

  - by Lior Kogan

  Sometimes code can utilize device drivers up to the point where the system is unresponsive. Lately I've optimized a WIN32/VC++ code which made the system almost unresponsive. The CPU usage, however, was very low. The reason was 1000's of creations and destruction of GDI objects (pens, brushes, etc.). Once I refactored the code to create all objects only once - the system became responsive again. This leads me to the question: Is there a way to measure CPU/IO usage of device drivers (GPU/disk/etc) for a given program / function / line of code?

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• Should I commit or rollback a transaction that creates a temp table, reads, then deletes it?

  - by Triynko

  To select information related to a list of hundreds of IDs... rather than make a huge select statement, I create temp table, insert the ids into it, join it with a table to select the rows matching the IDs, then delete the temp table. So this is essentially a read operation, with no permanent changes made to any persistent database tables. I do this in a transaction, to ensure the temp table is deleted when I'm finished. My question is... what happens when I commit such a transaction vs. let it roll it back? Performance-wise... does the DB engine have to do more work to roll back the transaction vs committing it? Is there even a difference since the only modifications are done to a temp table? Related question here, but doesn't answer my specific case involving temp tables: http://stackoverflow.com/questions/309834/should-i-commit-or-rollback-a-read-transaction

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• Data logged to a file; how do I rotate logs and how do I parse the data to not have 'gaps' in the da

  - by phidah

  I've got a web application that, for performance reasons, throws any data sent into a logfile. I've got two concerns with this approach: How do I best rotate logs, in order to not lose data? For each user session multiple requests are logged. Each request has a unique id so there is an easy way for me to tie the requests to the session. The problem is, however, that if I rotate the logs I risk ending up with one request in one log and another request in another log. How do I arrange my parsing in a way that allows me to parse all requests from a given session? I am willing to define a session timelimit, for example that the requests must, at maximum be 30 minutes apart. If I had a hourly log rotation at 00 minutes: What if the user made one request at 13:59 and one at 14:01 - The user would end up having requests in two different logs.

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• Is it really wrong to version documents using CouchDB's default behaviour?

  - by Tomas Sedovic

  This is one of those "I know I shouldn't do this but it's oh so convenient." questions. Sorry about that. I plan to use CouchDB for storing a bunch of documents and keeping their entire revision history. CouchDB does the versioning automatically, but it is strongly discouraged for programmer's use: "You cannot rely on document revisions for any other purpose than concurrency control." From what I've found on the CouchDB wiki, the versions can get deleted either during compaction or during replication. As far as I can tell, Compaction must always be triggered manually and Replication occurs only when there's more than one database server. The question is: if I won't run compaction and will use only single database instance for my documents, can I just use CouchDB's document versioning and expect it to work? What other problems I might run into? E.g. does not running compaction hurt the performance or consume significantly more disk space (than if I did handle the versioning manually)?

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• What is your opinion of the Telerik Extensions for MVC?

  - by Chad

  I've started digging around with using the Telerik Extensions for MVC. They don't integrate seemlessly into my current project, but I could reorganize things to fit it in. But, I'm wondering if it would be worth it in the end. I've been searching for reviews on the extensions, I haven't seen too many. So I'm asking here. On their website they claim: You can achieve unprecedented performance for your web application with the lightweight, semantically rendered Extensions that completely leverage the ASP.NET MVC model of no postbacks, no ViewState, and no page life cycle. So I'm curious, What is your opinion of the Telerik Extensions for MVC?

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• Saving Blob data from SQLite database to a file

  - by Felipe

  Hello, I'm trying to save blob data from a SQLite database (Safari cache: Cache.db) to a file, but for some reason sqlite won't read the whole blob. I eventually would like to do this in ruby, but for now something that works directly in sqlite command prompt is fine. Also, I've read all of the entries that talk about this here on stackoverflow, but most of them only discuss the performance of saving images in blobs and the one entry that does show to save blobs to file is in C# which does not help me. Here is what I've tried: sqlite select * from cfurl_cache_response limit 1; 3501|0|945281827|0|http://www.gospelz.com/components/com_jomcomment/smilies/guest.gif|2010-02-24 16:20:07 sqlite select receiver_data from cfurl_cache_blob_data where entry_ID = 3501; GIF89a( A hexdump of the original (guest.gif) file shows that sqlite stops reading the blob after the first null value: $ hexdump -C guest.gif 00000000 47 49 46 38 39 61 28 00 28 00 f7 00 00 f1 f5 fd |GIF89a(.(.......| sqlite .output test.gif sqlite select receiver_data from cfurl_cache_blob_data where entry_ID = 3501; $ hexdump -C test.gif 00000000 47 49 46 38 39 61 28 0a |GIF89a(.|

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• Grand Central Strategy for Opening Multiple Files

  - by user276632

  I have a working implementation using Grand Central dispatch queues that (1) opens a file and computes an OpenSSL DSA hash on "queue1", (2) writing out the hash to a new "side car" file for later verification on "queue2". I would like to open multiple files at the same time, but based on some logic that doesn't "choke" the OS by having 100s of files open and exceeding the hard drive's sustainable output. Photo browsing applications such as iPhoto or Aperture seem to open multiple files and display them, so I'm assuming this can be done. I'm assuming the biggest limitation will be disk I/O, as the application can (in theory) read and write multiple files simultaneously. Any suggestions? TIA

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• How to choose the right web application framework?

  - by thenextwebguy

  http://en.wikipedia.org/wiki/Comparison_of_web_application_frameworks Since we are ambitiously aiming to be big, scalability is important, and so are globalization features. Since we are starting out without funding, price/performance and cost of licences/hardware is important. We definitely want to bring AJAX well present in the web interface. But apart from these, there's no further criteria I can come up with. I'm most experienced with C#/ASP.net, PHP and Java, in that order, but don't turn down other languages (Ruby, Python, Scala, etc.). How can we determine from the jungle of frameworks the one that suits best our goal? What other questions should we be asking ourselves? Reference material: articles, book recommendations, websites, etc.?

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• Whats the scope of a c function defined within objective-c class?

  - by roja

  I was reading up about bypassing objective-c's messaging to gain performance (irrelevant to this specific question) when i found an interesting bit of code: #import <Cocoa/Cocoa.h> @interface Fib : NSObject { } - (long long) cFib: (NSUInteger) number; @end @implementation Fib // c implementation of fib long long cFibIMP(NSUInteger number) { return (number < 3) ? 1 : cFib(number - 1) + cFib(number - 2); } // method wrapper for c implementation of fib - (long long) cFib: (NSUInteger) number { return cFibIMP(number); } @end My question is; when using c function, within an objective-c object, what scope is the c function (cFibIMP in this particular case) placed in? Does the objective-c class encapsulate the c function removing change of name-clash or is the c function simply dumped into the global scope of the whole objective-c program?

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• Entity Fremework serialization

  - by Alexandr

  Hello guys! I was confused with my problem. I'm using Entity Framework and want to save entities on hard disk and then to restore them. I have no problem with Serializing/Deserializing but i get an exception "The object cannot be added to the ObjectStateManager because it already has an EntityKey. Use ObjectContext.Attach to attach an object that has an existing key" when i try to add deserialized object to my datacontext. And nothing happens when i just Attach my entity to datacontext How to achieve my goal? Thx in advance! -Alexandr-

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• Writing out BMP files with DataBuffer.TYPE_FLOAT or DataBuffer.TYPE_DOUBLE in java

  - by Basil Dsouza

  Hi Guys, I had a problem working with the image classes in java. I am creating a buffered image with DataBuffer.TYPE_DOUBLE. This all works fine in memory (I think). But the problem starts when I try to write it using ImageIO.write. Initially I was getting no exception at all and instead was only getting an empty output file for my troubles.. After a bit of poking around in the code, i found out that the bmp writer doesnt support writing type_double type of files. From: BMPImageWriterSpi.canEncodeImage: if (dataType < DataBuffer.TYPE_BYTE || dataType > DataBuffer.TYPE_INT) return false; So my question is, does anyone have a way of writing out those kind of images to disk? any documentation or tutorial, or link would be helpful. Thanks, Basil Dsouza

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• C++: set of C-strings

  - by Nicholas

  I want to create one so that I could check whether a certain word is in the set using set::find However, C-strings are pointers, so the set would compare them by the pointer values by default. To function correctly, it would have to dereference them and compare the strings. I could just pass the constructor a pointer to the strcmp() function as a comparator, but this is not exactly how I want it to work. The word I might want to check could be part of a longer string, and I don't want to create a new string due to performance concerns. If there weren't for the set, I would use strncmp(a1, a2, 3) to check the first 3 letters. In fact, 3 is probably the longest it could go, so I'm fine with having the third argument constant. Is there a way to construct a set that would compare its elements by calling strncmp()? Code samples would be greatly appreciated.

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• How to think in data stores instead of databases?

  - by Jim

  As an example, Google App Engine uses data stores, not a database, to store data. Does anybody have any tips for using data stores instead of databases? It seems I've trained my mind to think 100% in object relationships that map directly to table structures, and now it's hard to see anything differently. I can understand some of the benefits of data stores (e.g. performance and the ability to distribute data), but some good database functionality is sacrificed (e.g. joins). Does anybody who has worked with data stores like BigTable have any good advice to working with them?

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• java looping - declaration of a Class outside / inside the loop

  - by lisak

  when looping, for instance: for ( int j = 0; j < 1000; j++) {}; and I need to instantiate 1000 objects, how does it differ when I declare the object inside the loop from declaring it outside the loop ?? for ( int j = 0; j < 1000; j++) {Object obj; obj =} vs Object obj; for ( int j = 0; j < 1000; j++) {obj =} It's obvious that the object is accessible either only from the loop scope or from the scope that is surrounding it. But I don't understand the performance question, garbage collection etc. What is the best practice ? Thank you

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• render HTML (convert to bitmap)

  - by MK

  Can somebody recommend the best (and preferably portable) way to render HTML documents onto a bitmap? As far as I understand my main 2 options are WebKit and Gecko, but I wasn't able to find a good starting point on how to do it. When I last tried doing this 5 years ago, I ended up using Gecko to send the document to a printer, which is not really what I need. I need rendering to a in-memory bitmap. To clarify: server side, no Java, no .NET, batch processing, performance, not interactive, no Javascript.

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• Machine learning in OCaml or Haskell?

  - by griffin

  I'm hoping to use either Haskell or OCaml on a new project because R is too slow. I need to be able to use support vectory machines, ideally separating out each execution to run in parallel. I want to use a functional language and I have the feeling that these two are the best so far as performance and elegance are concerned (I like Clojure, but it wasn't as fast in a short test). I am leaning towards OCaml because there appears to be more support for integration with other languages so it could be a better fit in the long run (e.g. OCaml-R). Does anyone know of a good tutorial for this kind of analysis, or a code example, in either Haskell or OCaml?

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• Jquery selectors by CSS class in IE is really slow--workarounds?

  - by Sam Lee

  I have a web app where I have several elements with class="classA". I want to select and apply a function to all of them. I am doing the obvious thing, which is $(".classA").each(function () { ... }). This works just fine in Chrome/Safari/Firefox but is really slow in IE. It turns out IE has serious performance issues when selecting things by CSS class in jQuery. I was wondering if anyone has suggestions on good ways to deal with this. I can't use ID selectors because there can be multiple DOM elements I want to select.

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• Java 1.5.0_16 corrupted colours when saving jpg image

  - by Coder

  Hi, i have a loaded image from disk (stored as a BufferedImage), which i display correctly on a JPanel but when i try to re-save this image using the command below, the image is saved in a reddish hue. ImageIO.write(image, "jpg", fileName); Note! image is a BufferedImage and fileName is a File object pointing to the filename that will be saved which end in ".jpg". I have read that there were problems with ImageIO methods in earlier JDKs but i'm not on one of those versions as far as i could find. What i am looking for is a way to fix this issue without updating the JDK, however having said that i would still like to know in what JDK this issue was fixed in (if it indeed is still a bug with the JDK i'm using). Thanks.

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• Subversion for version control

  - by Gabriel Parenza

  Hi, I am working on an application whose primary purpose would be to provide source control management. My idea is to use to SVNKit for file check-out and check-in. However, while working with SVNKit, I realised it does not have the speed I was looking for. For instance, whenever developers create a ChangeRequest, which can encompass change in 3-40 files, I have to create a directory structure distributed across 32 folders. Doing so takes around 50 seconds, Another instance is that after creating change request developers can add files to the request. Copying even a single file from Trunk to branch takes around 6-7 secs. My question is has anyone had experience like this and what did you do to improve the performance? Moreover, is my approach correct? NOTE: I am using "http" protocol and can't use "svn" protocol.

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• spl_object_hash for PHP < 5.2 (unique ID for object instances)

  - by Rowan

  I'm trying to get unique IDs for object instances in PHP 5+. The function, spl_object_hash() is available from PHP 5.2 but I'm wondering if there's a workaround for older versions. There are a couple of functions in the comments on php.net but they're not working for me. The first (simplified): function spl_object_hash($object){ if (is_object($object)){ return md5((string)$object); } return null; } does not work with native objects (such as DOMDocument), and the second: function spl_object_hash($object){ if (is_object($object)){ ob_start(); var_dump($object); $dump = ob_get_contents(); ob_end_clean(); if (preg_match('/^object\(([a-z0-9_]+)\)\#(\d)+/i', $dump, $match)) { return md5($match[1] . $match[2]); } } return null; } looks like it could be a major performance buster! Does anybody have anything up their sleeve?

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• Using * in SELECT Query

  - by libregeek

  I am currently porting an application written in MySQL3 and PHP4 to MySQL5 and PHP5. On analysis I found several SQL queries which uses "select * from tablename" even if only one column(field) is processed in PHP. The table has almost 60 columns and it has a primary key. In most cases, the only column used is id which is the primary key. Will there be any performance boost if I use queries in which the column names are explicitly mentioned instead of * ? (In this application there is only one method which we need all the columns and all other methods return only a subset of the columns)

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• MySqlDataAdapter or MySqlDataReader for bulk transfer?

  - by Jeff Meatball Yang

  I'm using the MySql connector for .NET to copy data from MySql servers to SQL Server 2008. Has anyone experienced better performance using one of the following, versus the other? DataAdapter and calling Fill to a DataTable in chunks of 500 DataReader.Read to a DataTable in a loop of 500 I am then using SqlBulkCopy to load the 500 DataTable rows, then continue looping until the MySql record set is completely transferred. I am primarily concerned with using a reasonable amount of memory and completing in a short amount of time. Any help would be appreciated!

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• Colouring JTree's TreeNodes

  - by Amadan

  I have a JTree which I give objects that implement the TreeNode interface, and a custom TreeModel to display them (not using DefaultMutableTreeNode). I would like to change the text colour of some nodes. I can't find anything in the docs, except javax.swing.tree.DefaultTreeCellRenderer.setTextNonSelectionColor(Color newColor), but it will change everything indiscriminately, and I only need it for some nodes (specifically, broken links, i.e. nodes whose corresponding files can't be found on the disk, should be greyed out, the rest should be default). Can it be done, and how?

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• Partition of tables in MySQL

  - by Joel

  Hello, I have read that in a case where a table has many columns, but most of the time only one of them is used (say a title column in a forum post), a way to increase performance would be a partition to two tables, where one will contain only the title and the other one will contain the other columns (such as the forum post body). However, in case I use select ForumTitle from Forum; won't that be good enough to prevent the load of all columns (such as the forum post's body) to the memory, and eliminate the need of partition? Thanks, Joel

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• Choosing a plotting library for web/browser application

  - by Goro

  Hello, I am looking for a plotting/graphing library (mostly to do line plots) for my application. I have been looking at JavaScript APIs (like Google's) but I found them to be slowing down things at client side (I am plotting a quite large number of points). I also found that with client-side libraries, the performance was quite varied depending on the user's computer. With moving to a server-side library I would cut down on this variance, and would have more control over data flow (my data is in a MySQL database). I have then looked at some PHP-based plotting libraries, but a lot of them seem to be "forgotten" (no new version for years). I have been eying pChart, but it has not had an update in almost two years. First, what would you recommend: server-side or client-side approach? Second, what library would you recommend. Paid libraries are definitely an option, as I don't mind paying for quality software that would cut down on my development time. Thanks,

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