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• RAM caching causes severe performance drops

  - by B T

  I have read plenty of threads on memory caching and the standard response of "large cache is good, it shouldn't effect performance", "the kernel knows best". I have recently upgraded from 12.04 to 12.10 and changed from VirtualBox to VMware Workstation and the performance differences are severe (I suspect it is because of the latter). When I am running my virtual machine the system load monitor graph shows less than 50% memory usage generally. System load indicator is showing me that the rest of my RAM is used in the cache all the time. Plain and simple this is the comparison: BEFORE Cache was very sparingly used, pretty much none of my memory usage was the cache Swappiness was 0 (caused my memory to be used first, then swap only if needed) Performance was quite good and logical RAM was used fully first, caching was minimal. I could run enough software to utilize my full 4GB of RAM without any performance degradation whatsoever Swap space was then used as needed which was obviously slower (I am on a HDD) but was still usable when the current program was loaded into memory AFTER Cache is used to fill the full 4GB as soon as my virtual machine is run Swappiness is 0 (same behaviour as before but cache uses full memory straight away) Performance is terrible and unusable while running Ubuntu software Basic things like changing windows takes 2 minutes + Changing screens happens frame by frame over sometimes up to 5 minutes Cannot run an IDE and VM like I could with ease before So basically, any suggestions on how to take my performance back to how it was before while keeping my current setup? My suspicion is VMWare is the problem, but how do I see what is tied to the use of the cache? Surely there is a way to control this behaviour in software as polished as VMware? Thanks EDIT: Could also be important to note that the behaviour differs depending on whether VMware is open or closed. If VMware is open, then the ram will lock at like 50% and 50% cache and go into the complete lock up mentioned above. Contrastingly, if VMware is closed (after being open), then the RAM will continue to rise as it needs / cache will stay as the complete remaining memory and there is no noticeable performance degradation.

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• How to handle media kept on a separate server (PHP)

  - by Sandman

  So, I have three server, and the idea was to keep all media (images, files, movies) on a media server. I never got around to do it but I think I probably should. So these are the three servers: WWW server DB server Media server Visitors obviously connect to the WWW server and currently image resizing and cache:ing is done on the WWW servers as the original files are kept there. So the idea for me is for image functions I have, that does all the image compositioning, resizing and cahceing would just pie the command over to the media server that would return ther path to the finnished file. What I don't know is how to handle functions such as file_exists() and figuring out image dimensions when needed before even any image management comes into play. Do I pipe all these commands to the other server, via HTTP? I was thinking along the ways of doing it this way: function image(##ARGS##){ if ($GLOBALS["media_host"] != "localhost"){ list ($src, $width, height) = file('http://$GLOBALS[media_host]/imgfunc.php?args=##ARGS##'); return "<img src='$src' height and width >"; } .... do other stuff here } Am I approaching this the wrong way? Is there a better way to do this?

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• Google App Engine - Caching generated HTML

  - by Alexander

  I have written a Google App Engine application that programatically generates a bunch of HTML code that is really the same output for each user who logs into my system, and I know that this is going to be in-efficient when the code goes into production. So, I am trying to figure out the best way to cache the generated pages. The most probable option is to generate the pages and write them into the database, and then check the time of the database put operation for a given page against the time that the code was last updated. Then, if the code is newer than the last put to the database (for a particular HTML request), new HTML will be generated and served, and cached to the database. If the code is older than the last put to the database, then I will just get the HTML direct from the database and serve it (therefore avoiding all the CPU wastage of generating the HTML). I am not only looking to minimize load times, but to minimize CPU usage. However, one issue that I am having is that I can't figure out how to programatically check when the version of code uploaded to the app engine was updated. I am open to any suggestions on this approach, or other approaches for caching generated html. Note that while memcache could help in this situation, I believe that it is not the final solution since I really only need to re-generate html when the code is updated (as opposed to every time the memcache expires). Kind Regards, and thank you in advance for any suggestions you may be able to offer. -Alex

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• "Priming" a whole database in MSSQL for first-hit speed

  - by David Spillett

  For a particular apps I have a set of queries that I run each time the database has been restarted for any reason (server reboot usually). These "prime" SQL Server's page cache with the common core working set of the data so that the app is not unusually slow the first time a user logs in afterwards. One instance of the app is running on an over-specced arrangement where the SQL box has more RAM than the size of the database (4Gb in the machine, the DB is under 1.5Gb currently and unlikely to grow too much relative to that in the near future). Is there a neat/easy way of telling SQL Server to go away and load everything into RAM? It could be done the hard way by having a script scan sysobjects & sysindexes and running SELECT * FROM <table> WITH(INDEX(<index_name>)) ORDER BY <index_fields> for every key and index found, which should cause every used page to be read at least once and so be in RAM, but is there a cleaner or more efficient way? All planned instances where the database server is stopped are out-of-normal-working-hours (all the users are at most one timezone away and unlike me none of them work at silly hours) so such a process (until complete) slowing down users more than the working set not being primed at all would is not an issue.

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• bin-deploying DLLs banned in leiu of GAC on shared IIS 6 servers

  - by craigmoliver

  I need to solicit feedback about a recent security policy change at an organization I work with. They have recently banned the bin-deployment of DLLs to shared IIS 6 application servers. These servers host many isolated web application pools. The new rules require all DLLs to be installed in GAC. The is a problem for me because I bin-deploy several dlls including the ASP.NET MVC Framework, HTML Agility Pack, ELMAH, and my own shared class libraries. I do this because: Eliminates web application server dependencies to the Global Assembly Cache. Allows me (the developer) to have control of what goes on inside my application. Enables the application to deployed as a "package". Removes application deployment burden from the server administrators. Now, here are my questions. From a security perspective what are the advantages to using the GAC vs. bin-deployment? Is it possible to host multiple versions of the same DLL in the GAC? Has anyone run into similar restrictions?

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• Why does my javascript file sometimes compressed while sometimes not?(IIS Gzip problem)

  - by Kevin Yang

  i enable gzip for javascript file in my iis settings, here 's the corresponding config section. <httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files"> <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" staticCompressionLevel="10" dynamicCompressionLevel="8" /> <dynamicTypes> <add mimeType="text/*" enabled="true" /> <add mimeType="message/*" enabled="true" /> <add mimeType="application/soap+msbin1" enabled="true" /> <add mimeType="*/*" enabled="false" /> </dynamicTypes> <staticTypes> <add mimeType="text/*" enabled="true" /> <add mimeType="message/*" enabled="true" /> <add mimeType="application/javascript" enabled="true" /> <add mimeType="application/x-javascript" enabled="true" /> <add mimeType="*/*" enabled="false" /> </staticTypes> </httpCompression> currently, when i download my js file, it seems that sometimes server return the gzip one, and sometimes not. i dont know why, and how to debug that. If a file is already gzipped, it should be cached in local disk, and next time someone visit that file again, iis kernel should return the cache gzip file directly without compressing it again. Is that right?

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• HTML5 Local Storage of audio element source - is it possible?

  - by andrewdotcom

  Hi stackoverflow experts I've been experimenting with the audio and local storage features of html5 of late and have run into something that has me stumped. I'd like to be able to cache or store the source of the audio element locally to enable speedier and offline playback. The problem is I can't see how this is possible with the current implementation. I have tried the following using webkit: Creating a manifest file to set up local caching but the audio file appears not to be a cacheable item maybe due to the way it is stream or something I have also attempted to use javascript to put an audio object into local storage but the size of the mp3 makes this impossible due to memory issues (i think). I have tried to use the data uri and base64 to use the html as a audio transport that can be cached but again the filesize makes this prohibitive. Also the audio element does not seem to like this in webkit (works fine in mozilla) I have tried several methods of putting the data into the local database store. Again suffering the same issues as the other cases. I'd love to hear any other ideas anyone may have as to how I could achieve my goal of offline playback using caching/local storage in webkit.

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• Elegent methods for caching search results from RESTful service?

  - by Paul

  I have a RESTful web service which I access from the browser using JavaScript. As an example, say that this web service returns a list of all the Message resources assigned to me when I send a GET request to /messages/me. For performance reasons, I'd like to cache this response so that I don't have to re-fetch it every time I visit my Manage Messages web page. The cached response would expire after 5 minutes. If a Message resource is created "behind my back", say by the system admin, it's possible that I won't know about it for up to 5 minutes, until the cached search response expires and is re-fetched. This is acceptable, because it creates no confusion for me. However if I create a new Message resource which I know should be part of the search response, it becomes confusing when it doesn't appear on my Manage Messages page immediately. In general, when I knowingly create/delete/update a resource that invalidates a cached search response, I need that cached response to be expired/flushed immediately. The core problem which I can't figure out: I see no simple way of connecting the task of creating/deleting/updating a resource with the task of expiring the appropriate cached responses. In this example it seems simple, I could manually expire the cached search response whenever I create/delete/update a(ny) Message resource. But in a more complex system, keeping track of which search responses to expire under what circumstances will get clumsy quickly. If someone could suggest a simple solution or some clarifying thoughts, I'd appreciate it.

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• How to tell the Browser the character encoding of a HTML website regardless of Server Content.-Type Headers?

  - by hakre

  I have a HTML page that correctly (the encoding of the physical on disk matches it) announces it's Content-Type: <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content= "text/html; charset=utf-8"> <title> ... Opening the file from disk in browser (Google Chrome, Firefox) works fine. Requesting it via HTTP, the webserver sends a different Content-Type header: $ curl -I http:/example.com/file.html HTTP/1.1 200 OK Date: Fri, 19 Oct 2012 10:57:13 GMT ... Content-Type: text/html; charset=ISO-8859-1 (see last line). The browser then uses ISO-8859-1 to display which is an unwanted result. Is there a common way to override the server headers send to the browser from within the HTML document?

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• How to install Chrome browser properly via command line?

  - by Bad Learner

  Setting up and managing an Ubuntu server all by myself, in coming months, is a part of my current plans. Hence, I am planning a swtich from Windows to Linux - - Ubuntu. I now need to get some grip on the command line, since I am all used to Windows' GUI. Anyway... the most obvious start is installing apps on my computer, and I thought I should learn to do it via CLI. And this is what I did: $ apt-cache search chrome browser the results showed that the proper term is "chrome-browser," so... $ sudo apt-get install chrome-browser And then "Y" for the Y/n question. But the installation threw errors. (I do not have my PC at hand, so can't mention what error exactly.) Does someone see anything wrong with the commands I issued? I am probably missing some command(s) in between, I think.

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• Are there any concerns with using a static read-only unit of work so that it behaves like a cache?

  - by Rowan Freeman

  Related question: How do I cache data that rarely changes? I'm making an ASP.NET MVC4 application. On every request the security details about the user will need to be checked with the area/controller/action that they are accessing to see if they are allowed to view it. The security information is stored in the database. For example: User Permission UserPermission Action ActionPermission A "Permission" is a token that is applied to an MVC action to indicate that the token is required in order to access the action. Once a user is given the permission (via the UserPermission table) then they have the token and can therefore access the action. I've been looking in to how to cache this data (since it rarely changes) so that I'm only querying in-memory data and not hitting a database (which is a considerable performance hit at the moment). I've tried storing things in lists, using a caching provider but I either run in to problems or performance doesn't improve. One problem that I constantly run in to is that I'm using lazy loading and dynamic proxies with EntityFramework. This means that even if I ToList() everything and store them somewhere static, the relationships are never populated. For example, User.Permissions is an ICollection but it's always null. I don't want to Include() everything because I'm trying to keep things simple and generic (and easy to modify). One thing I know is that an EntityFramework DbContext is a unit of work that acts with 1st-level caching. That is, for the duration of the unit of work, everything that is accessed is cached in memory. I want to create a read-only DbContext that will exist indefinitely and will only be used to read about permission data. Upon testing this it worked perfectly; my page load times went from 200ms+ to 20ms. I can easily force the data to refresh at certain intervals or simply leave it to refresh when the application pool is recycled. Basically it will behave like a cache. Note that the rest of the application will interact with other contexts that exist per request as normal. Is there any disadvantage to this approach? Could I be doing something different?

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• What causes a JRE 6 JVM code cache leak?

  - by Arturo Knight

  Since switching to JRE 6, my server's code cache usage (non-heap) keeps growing indefinitely. My application creates a lot of classes at runtime, BUT these classes are successfully unloaded during the GC process. I can see these classes getting unloaded in the gc logs and also the permGen usage stays constant. I specifically make sure in my code that these classes are orphaned once I am finished with them and so they correctly get garbage collected from permGen. The code cache however keeps growing. I only became aware of the code cache after switching to JRE 6. So I guess my questions are: Does GC include the code cache? What could cause a code cache memory leak, specifically. Is there a bug in JDK 6 in this area?

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• JQuery Ajax Load Mobile Browser Back Functionality

  - by Brad

  Currently working on a mobile site using the .load() technique: $.ajaxSetup ({cache: false}); contentLoad(); function contentLoad() { $('a.inline').click(function(){ var toLoad = $(this).attr('href')+' #content'; $('#loading').show(); $('#content').load(toLoad,'',showNewContent) function showNewContent() { $('#loading').hide(); $('#content').show(); contentLoad(); } return false; }); } How would I be able to integrate back and forward button functionality into mobile browsers? Hope this is possible. Thanks in advance.

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• How can one cache bust files referenced in a LESS file when using Symfony2, Twig, and Assetic?

  - by user3719083

  I have a web site built on Symfony2 which uses twig templates, LESS, and assetic. In order to cache bust assets, I'm simply using this in my config.yml: framework: templating: engines: ['twig'] assets_version: 'asset-version-here' And then I use the asset() function to load the asset and the cache busting is handled for me. However, the concern I have is when I load my LESS (css) file, there are references to other files, and I would like to know how these files can be cache busted as well. Example: .someSelector { background:url('../images/filename.png'); } How can I make sure that the referenced file, filename.png is cache busted upon deployment? The asset files referenced in Twig using asset() are cache busted automatically upon deployment (I use a deployment script hook that updates the assets_version in the framework's config), but those referenced in a stylesheet are not. How can I do this?

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• PDF coming as text on browser

  - by spt3210

  I am trying to display a PDF from database (byte[]) to user. I am using code below to render PDF. It is giving me PDF as binary text as shown below. Instead of open in PDF application it is rendering PDF as text. Response.Buffer = true; Response.Charset = ""; Response.Cache.SetCacheability(HttpCacheability.NoCache); //Response.AddHeader("Content-Length", fileToDownload.Length.ToString()); //Response.AddHeader("Content-Disposition", "inline; name=RemoteUserGuide.pdf"); Response.AppendHeader("content-length", fileToDownload.Length.ToString()); Response.ContentType = "application/pdf"; Response.BinaryWrite(fileToDownload); Response.Flush(); ////Response.Close(); Response.End(); Any Ideas?

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• Is a PHP-only "cache engine" ever worth it?

  - by adsads

  I wrote a rather small skeleton for my web apps and thought that I would also add a small cache for it. It is rather simple: If the current page exists as a file in the cache and the file isn't too old, read it out and exit instead of rebuilding the page If the current page isn't cached/outdated recalc the page and save it However, the bad thing about it is: My performance tests with a page that receives 40 relatively long posts via a MySQL query said that with using the cache, it took even longer to handle a single request (1000 tests each) How can that happen? Should I just remove the complete raw-PHP cache and relieve on the availability of some PHP cache like memcached or so?

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• How can I remove a browser's cache server-side, using ASP.NET?

  - by Noman

  How can I remove a browser's cache server-side, using ASP.NET (C#)? A coupon shows by itself (I believe it comes from cache as I did also browse for other apparel sites). It breaks my JavaScript as well as my server-side code, as I am using an UpdatePanel for Ajax, and it duplicates the UpdatePanel's ID. I have renamed the UpdatePanel's ID, but it makes no difference. It generates "Invalid view State" exception. The coupon name is "FastSave" What I have tried: Response.Cache.SetExpires(DateTime.UtcNow.AddMinutes(-1)); Response.Cache.SetCacheability(HttpCacheability.NoCache); Response.Cache.SetNoStore();

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• Is it possible to disable user sessions for guest in Joomla 1.5

  - by WebolizeR

  Hi; Is it possible to disable session handling in Joomla 1.5 for guests. I donot use user system in the frontend, i assumed that it's not needed to run queries like below: Site will use APC or Memcache as caching system under heavy load, so it's important for me tHanks for your comments # DELETE FROM jos_session WHERE ( time < '1274709357' ) # SELECT * FROM jos_session WHERE session_id = '70c247cde8dcc4dad1ce111991772475' # UPDATE jos_session SET time='1274710257',userid='0',usertype='',username='',gid='0',guest='1',client_id='0',data='__default|a:8:{s:15:\"session.counter\";i:5;s:19:\"session.timer.start\";i:1274709740;s:18:\"session.timer.last\";i:1274709749;s:17:\"session.timer.now\";i:1274709754;s:22:\"session.client.browser\";s:88:\"Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3\";s:8:\"registry\";O:9:\"JRegistry\":3:{s:17:\"_defaultNameSpace\";s:7:\"session\";s:9:\"_registry\";a:1:{s:7:\"session\";a:1:{s:4:\"data\";O:8:\"stdClass\":0:{}}}s:7:\"_errors\";a:0:{}}s:4:\"user\";O:5:\"JUser\":19:{s:2:\"id\";i:0;s:4:\"name\";N;s:8:\"username\";N;s:5:\"email\";N;s:8:\"password\";N;s:14:\"password_clear\";s:0:\"\";s:8:\"usertype\";N;s:5:\"block\";N;s:9:\"sendEmail\";i:0;s:3:\"gid\";i:0;s:12:\"registerDate\";N;s:13:\"lastvisitDate\";N;s:10:\"activation\";N;s:6:\"params\";N;s:3:\"aid\";i:0;s:5:\"guest\";i:1;s:7:\"_params\";O:10:\"JParameter\":7:{s:4:\"_raw\";s:0:\"\";s:4:\"_xml\";N;s:9:\"_elements\";a:0:{}s:12:\"_elementPath\";a:1:{i:0;s:74:\"C:\xampp\htdocs\sites\iv.mynet.com\libraries\joomla\html\parameter\element\";}s:17:\"_defaultNameSpace\";s:8:\"_default\";s:9:\"_registry\";a:1:{s:8:\"_default\";a:1:{s:4:\"data\";O:8:\"stdClass\":0:{}}}s:7:\"_errors\";a:0:{}}s:9:\"_errorMsg\";N;s:7:\"_errors\";a:0:{}}s:13:\"session.token\";s:32:\"a2b19c7baf223ad5fd2d5503e18ed323\";}' WHERE session_id='70c247cde8dcc4dad1ce111991772475'

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• Is MySQL caching occurring, how to fix it?

  - by rlb.usa

  I think that MySQL or ASP.NET is caching my queries. I edited my MySQL sproc to remove some parameters but it keeps saying that those parameters are missing. Here is what happens: ASP.NET app calls a MySQL stored procedure. Everything works perfect. I delete some parameters from the sproc and ASP.NET parameter list accordingly. All parameters exactly match in case and order from the new ASP.NET and MySQL sproc code Upon execution, it fails, saying : System.ArgumentException: Parameter 'deleted_parameter_foo_bar' not found in the collection. at MySql.Data.MySqlClient.MySqlParameterCollection ... I delete the sproc from the database, restart my browser, and reexecute the ASP.NET page. It says the same error, that the parameter is missing - but the sproc itself doesn't exist anymore. ( I know 100% that I am editing/deleting from the right database. ) How do I fix this or make it work again; I want it to use my new sproc instead of the old one ? _o

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• Count number of queries executed by NHibernate in a unit test

  - by Bittercoder

  In some unit/integration tests of the code we wish to check that correct usage of the second level cache is being employed by our code. Based on the code presented by Ayende here: http://ayende.com/Blog/archive/2006/09/07/MeasuringNHibernatesQueriesPerPage.aspx I wrote a simple class for doing just that: public class QueryCounter : IDisposable { CountToContextItemsAppender _appender; public int QueryCount { get { return _appender.Count; } } public void Dispose() { var logger = (Logger) LogManager.GetLogger("NHibernate.SQL").Logger; logger.RemoveAppender(_appender); } public static QueryCounter Start() { var logger = (Logger) LogManager.GetLogger("NHibernate.SQL").Logger; lock (logger) { foreach (IAppender existingAppender in logger.Appenders) { if (existingAppender is CountToContextItemsAppender) { var countAppender = (CountToContextItemsAppender) existingAppender; countAppender.Reset(); return new QueryCounter {_appender = (CountToContextItemsAppender) existingAppender}; } } var newAppender = new CountToContextItemsAppender(); logger.AddAppender(newAppender); logger.Level = Level.Debug; logger.Additivity = false; return new QueryCounter {_appender = newAppender}; } } public class CountToContextItemsAppender : IAppender { int _count; public int Count { get { return _count; } } public void Close() { } public void DoAppend(LoggingEvent loggingEvent) { if (string.Empty.Equals(loggingEvent.MessageObject)) return; _count++; } public string Name { get; set; } public void Reset() { _count = 0; } } } With intended usage: using (var counter = QueryCounter.Start()) { // ... do something Assert.Equal(1, counter.QueryCount); // check the query count matches our expectations } But it always returns 0 for Query count. No sql statements are being logged. However if I make use of Nhibernate Profiler and invoke this in my test case: NHibernateProfiler.Intialize() Where NHProf uses a similar approach to capture logging output from NHibernate for analysis via log4net etc. then my QueryCounter starts working. It looks like I'm missing something in my code to get log4net configured correctly for logging nhibernate sql ... does anyone have any pointers on what else I need to do to get sql logging output from Nhibernate?

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• Recommended textbook for machine-level programming?

  - by Norman Ramsey

  I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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• Send multidimensional array to php with jQuery

  - by robertdd

  hy, i have a little, big problem here :) after i upload some images i get a list with all the images. I have some jQuery function for rotate, duplicate, delete, shuffle images! when i select a image and hit delete i send a post to php with the alt="" value of the image,i identify the picture and edit. I want to make a save button, Instead of sending a post every time i rotate a image, better send a post after editing the list of images with an array that contains all data? my php array after upload looks like this: [files] => Array ( [lcxkijgr] => lcxkijgr.jpg [xcewxpfv] => xcewxpfv.jpg [rtiurwxf] => rtiurwxf.jpg [gsbxdsdc] => gsbxdsdc.jpg ) say that I uploaded 4 pictures, firs picture i rotate 90 degrees second i want to duplicate third i rotate 270 degrees and the fourth image i delete i can do all this only with jQuery, but on the server the images are the same, after a refresh the images are the same this is the list with the images: <div class="upimage"> <ul id="upimagesQueue"> <li id="upimagesHPVEJM"> <a href="javascript:jQuery('#upimagesHPVEJM').showlargeimage('HPVEJM')"> <img alt="lcxkijgr" src="uploads/s6id9r9icnp8q9102h8md9kfd7/lcxkijgr.jpg?1272087830477" id="HPVEJM" style="display: block;" > </a> </li> <li id="upimagesSTCSAV"> <a href="javascript:jQuery('#upimagesSTCSAV').showlargeimage('STCSAV')"> <img alt="xcewxpfv" src="uploads/s6id9r9icnp8q9102h8md9kfd7/xcewxpfv.jpg?1272087831360" id="STCSAV" style="display: block;" > </a> </li> <li id="upimagesBFPUEQ"> <a href="javascript:jQuery('#upimagesBFPUEQ').showlargeimage('BFPUEQ')"> <img alt="rtiurwxf" src="uploads/s6id9r9icnp8q9102h8md9kfd7/rtiurwxf.jpg?1272087832162" id="BFPUEQ" style="display: block;" > </a> </li> <li id="upimagesRKXNSV"> <a href="javascript:jQuery('#upimagesRKXNSV').showlargeimage('RKXNSV')"> <img alt="gsbxdsdc" src="uploads/s6id9r9icnp8q9102h8md9kfd7/gsbxdsdc.jpg?1272087832957" id="RKXNSV" style="display: block;"> </a> </li> <ul> </div> is ok if i make one array like this: array{ imgFromLi = array(img1,img2,img3,img4,img5,img6) rotate = array{img1=90, img2=270, img3=90} delete = array{img4,img5,img6} duplicate = array{img2, img3} } how i can make/send/cache this array?? sorry for my very bad english

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• No more memory available in Mathematica, Fit the parameters of system of differential equation

  - by user1058051

  I encountered a memory problem in Mathematica, when I tried to process my experimental data. It's a system of two differential equations and I need to find most suitable parameters. Unfortunately I am not a Pro in Mathematica, so the program used a lot of memory, when the parameter epsilon is more than 0.4. When it less than 0.4, the program work properly. The command 'historylength = 0' and attempts to reduce the Accuracy Goal and WorkingPrecision didn`t help. I can't use ' clear Cache ', because there isnt a circle. I'm trying to understand what mistakes I made, and how I may limit the memory usage. I have already bought extra-RAM, now its 4GB, and now I haven't free memory-slots in motherboard Remove["Global`*"]; T=13200; L = 0.085; e = 0.41; v = 0.000557197; q = 0.1618; C0 = 0.0256; R = 0.00075; data = {{L,600,0.141124587},{L,1200,0.254134509},{L,1800,0.342888644}, {L,2400,0.424476295},{L,3600,0.562844542},{L,4800,0.657111356}, {L,6000,0.75137817},{L,7200,0.815876516},{L,8430,0.879823594}, {L,9000,0.900771775},{L,13200,1}}; model[(De_)?NumberQ, (Kf_)?NumberQ, (Y_)?NumberQ] := model[De, Kf, Y] = yeld /.Last[Last[ NDSolve[{ v (Ci^(1,0))[z,t]+(Ci^(0,1))[z,t]== -((3 (1-e) Kf (Ci[z,t]-C0))/ (R e (1-(R Kf (1-R/r[z,t]))/De))), (r^(0,1))[z,t]== (R^2 Kf (Ci[z,t]-C0))/ (q r[z,t]^2 (1-(R Kf (1-R/r[z,t]))/De)), (yeld^(0,1))[z,t]== Y*(v e Ci[z,t])/(L q (1-e)), r[z,0]==R, Ci[z,0]==0, Ci[0,t]==0, yeld[z,0]==0}, {r[z,t],Ci[z,t],yeld},{z,0,L},{t,0,T}]]] fit = FindFit[data, {model[De, Kf, Y][z, t], {Y > 0.97, Y < 1.03, Kf > 10^-6, Kf < 10^-4, De > 10^-13, De < 10^-9}}, {{De,7*10^-13}, {Kf, 10^-5}, {Y, 1}}, {z, t}, Method -> NMinimize] data = {{600,0.141124587},{1200,0.254134509},{1800,0.342888644}, {2400,0.424476295},{3600,0.562844542},{4800,0.657111356}, {6000,0.75137817},{7200,0.815876516},{8430,0.879823594}, {9000,0.900771775},{13200,1}}; YYY = model[ De /. fit[[1]], Kf /. fit[[2]], Y /. fit[[3]]]; Show[Plot[Evaluate[YYY[L,t]],{t,0,T},PlotRange->All], ListPlot[data,PlotStyle->Directive[PointSize[Medium],Red]]] the link on the .nb file http://www.4shared.com/folder/249TSjlz/_online.html

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• Is my dns server being attacked? And what should I do about it?

  - by Mnebuerquo

  I've been having some intermittent dns problems with a web server, where certain isp's dns servers don't have my hostnames in cache and fail to look them up. At the same time, queries to opendns for those hostnames resolve correctly. It's intermittent, and it always works fine for me, so it's hard to identify the problem when someone reports connectivity problems to my site. In trying to figure this out, I've been looking at my logs to see if there are any errors I should know about. I found thousands of the following messages in my logs, from different ip's, but all requesting similar dns records: May 12 11:42:13 localhost named[26399]: client 94.76.107.2#36141: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:42:13 localhost named[26399]: client 94.76.107.2#29075: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:42:13 localhost named[26399]: client 94.76.107.2#47924: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:42:13 localhost named[26399]: client 94.76.107.2#4727: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:42:14 localhost named[26399]: client 94.76.107.2#16153: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:42:14 localhost named[26399]: client 94.76.107.2#40267: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:43:35 localhost named[26399]: client 82.209.240.241#63507: query (cache) 'burningpianos.com/MX/IN' denied May 12 11:43:35 localhost named[26399]: client 82.209.240.241#63721: query (cache) 'burningpianos.org/MX/IN' denied May 12 11:43:36 localhost named[26399]: client 82.209.240.241#3537: query (cache) 'burningpianos.com/MX/IN' denied I've read of Dan Kaminski's dns cache poisoning vulnerability, and I'm wondering if these log records are an attempt by some evildoer to attack my dns server. There are thousands of records in my logs, all requesting "burningpianos", some for com and some for org, most looking for an mx record. There are requests from multiple ip's, but each ip will request hundreds of times per day. So this smells to me like an attack. What is the defense against this?

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