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• Behaviors in Blend 4 (Silverlight TV #30)

  Thanks to all of you, last week we flew past 1,000,000 views of Silverlight TV! Were not stopping here, we have a ton in store for the second half of the year. But first, a quick thank you to all of you for tuning in and for all of our great guests who have brought their A-game to the show and helped make Silverlight TV the * most popular Silverlight show on the internet ;-) * disclaimer: I have totally not researched that ;-) Now back to this weeks episode which Adam looks very excited about!...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Qt vs WPF/.NET

  - by aaronc

  My company is trying to make the decision between using Qt/C++ for our GUI framework or migrating to .NET and using WPF. We have up to this point been using MFC. It seems that .NET/WPF is technically the most advanced and feature-rich platform. I do, however, have several concerns. These include: Platform support Framework longevity (i.e. future-proofing) Performance and overhead For this application we are willing to sacrifice support for Windows 2000, Macs, and Linux. But, the issue is more related to Microsoft's commitment to the framework and their extant platforms. It seems like Microsoft has a bad habit of coming up with something new, hyping it for a few years, and then relegating it to the waste-bin essentially abandoning the developers who chose it. First it was MFC and VB6, then Windows Forms, and now there's WPF. Also with .NET, versions of Windows were progressively nicked off the support list. Looks like WPF could be here to stay for a while, but since its not open source its really in Microsoft's hands. I'm also concerned about the overhead and performance of WPF since some of our applications involve processing large amounts of information and doing real-time data capture. Qt seems like a really good option, but it doesn't have all the features of WPF/.NET couldn't use languages like C#. Basically, what does the community think about Microsoft's commitment to WPF compared with previous frameworks? Are the performance considerations significant enough to avoid using it for a realtime app? And, how significant are the benefits of WPF/.NET in terms of productivity and features compared to Qt?

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• WPF - LayoutUpdated event firing repeatedly

  - by Drew Noakes

  I've been adding a bit of animation to my WPF application. Thanks to Dan Crevier's unique solution to animating the children of a panel combined with the awesome WPF Penner animations it turned out to be fairly straightforward to make one of my controls look great and have its children move about with some nice animation. Unfortunately this all comes with a performance overhead. I'm happy to have the performance hit when items are added/removed or the control is resized, but it seems that this perf hit occurs consistently throughout the application's lifetime, even when items are completely static. The PanelLayoutAnimator class uses an attached property to hook the UIElement.LayoutUpdated.aspx) event. When this event fires, render transforms are animated to cause the children to glide to their new positions. Unfortunately it seems that the LayoutUpdated event fires every second or so, even when nothing is happening in the application (at least I don't think my code's doing anything -- the app doesn't have focus and the mouse is steady.) As the reason for the event is not immediately apparent to the event handler, all children of the control have to be reevaluated. This event is being called about once a second when idle. The frequency increases when actually using the app. So my question is, how can I improve the performance here? Any answer that assists would be appreciated, but I'm currently stuck on these sub-questions: What causes the LayoutUpdated event to fire so frequently? Is this supposed to happen, and if not, how can I find out why it's firing and curtail it? Is there a more convenient way within the handler to know whether something has happened that might have moved children? If so, I could bail out early and avoid the overhead of looping each child. For now I will work around this issue by disabling animation when there are more than N children in the panel.

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• Is parsing JSON faster than parsing XML

  - by geme_hendrix

  I'm creating a sophisticated JavaScript library for working with my company's server side framework. The server side framework encodes its data to a simple XML format. There's no fancy namespacing or anything like that. Ideally I'd like to parse all of the data in the browser as JSON. However, if I do this I need to rewrite some of the server side code to also spit out JSON. This is a pain because we have public APIs that I can't easily change. What I'm really concerned about here is performance in the browser of parsing JSON versus XML. Is there really a big difference to be concerned about? Or should I exclusively go for JSON? Does anyone have any experience or benchmarks in the performance difference between the two? I realize that most modern web developers would probably opt for JSON and I can see why. However, I really am just interested in performance. If there's a proven massive difference then I'm prepared to spend the extra effort in generating JSON server side for the client.

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• What does SQL Server's BACKUPIO wait type mean?

  - by solublefish

  I'm using Sql Server 2008 ("R1"), with some maintenance plans that back up my databases to a network share. Some of my backup jobs show long waits of type "BACKUPIO". Of course it seems like this is an I/O subsystem limitation, but I'm skeptical. Perfmon stats for I/O on the production (source) server are well within normal trends for that server. The destination server shows a sustained 7MB/s write rate, which seems incredibly low, even for a slow disk. The network link is gigabit ethernet and nowhere near saturated. The few docs I've turned up about BACKUPIO indicate that it's not specifically a wait on I/O, surprisingly enough. This MSFT doc says it's abnormal unless you're using a tape drive, which I'm not. But it doesn't say (or I don't understand) exactly what resource is missing. http://www.docstoc.com/docs/24580659/Performance-Tuning-in-SQL-Server-2005 And this piece says it's not related to I/O performance at all. http://www.informit.com/articles/article.aspx?p=686168&seqNum=5 "Note that BACKUPIO and IO_AUDIT_MUTEX are not related to IO performance." Anyway, does anyone know what BACKUPIO actually means and/or what I can do to diagnose or eliminate it?

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• Forcing CLLocationManager updates - does it help or hurt?

  - by Steve N

  I've been trying to find any way to optimize the performance of my location-based iPhone application and have seen some people mention that you can force location updates by starting and stopping your CLLocationManager. I need the best accuracy I can get, and the user in my case would probably like to see updates every few seconds (say, 10 seconds) as they walk around. I've set the filters accordingly, but I notice that sometimes I don't get any updates on the device for quite some time. I'm testing the following approach, which forces an update when a fixed time interval passes (I'm using 20 seconds). My gut tells me this really won't help me provide more accurate updates to the user, and that just leaving CLLocationManager running all the time is probably the best approach. - (void)forceLocationUpdate { [[LocationManager locationManager] stopUpdates]; [[LocationManager locationManager] startUpdates]; [self performSelector:@selector(forceLocationUpdate) withObject:nil afterDelay:20.0]; } My question is- does forcing updates from CLLocationManager actually improve core location performance? Does it hurt performance? If I'm outside in an open field with good GPS reception, will this help then? Does anyone have experience trying this? Thanks in advance, Steve

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• ASP.NET Applications Requests/Sec suddenly jumps to a value of about 70 million/sec. on 8 core web

  - by Subhrajit Roy

  We are doing performance testing of an ASP.NET web application with VSTS 2008. We start with 2000 users and slowly ramp up to 5000 users (reaches this user load at around 2.5 hours after the tests start, after this we stay at this user load). The total test duration is of about 6 hours During these runs we have found that the counter Requests/Sec (under category ASP.NET applications) suddenly spikes to a values of 36-72 millions !!!. This keeps on happening intermittently i.e we see this issue once in every 3 performance runs that we give on the same application. In our testing environment we have 4 web servers and interestingly enough we have found that this issue occurs only in the 8 core web servers. Summarizing ... Issue : The counter Requests/Sec (under category ASP.NET Applications) suddenly jumps to a value of about 70 million/sec. on 8 core web servers. This results in an increase in SQL server connections opened by the application. Response time goes for a toss. Error rates also show similar behaviour. However the counter ISAPI Extention Requests/sec does not show any abnormal increase. The graph of this counter almost overlaps with that of counter Requests/Sec till the time of the appearance of the spike.When the spike appears , this counter (ISAPI Extention Requests/sec) actually shows a drop. Test Settings : Performance test run with Visual Studio Team System 2008. Soak test run for 6 hours. Maximum user load 5000 users. This is load is attained at about 2.5 hours into the run and mainted for remaining duration.(i.e for around 3.5 more hrs) This issue is reproducible though happens intermittently. (i.e occurs one in three or four runs) Test Environment : Web site deployed on 4 Web Servers (Windows Server 2003). Of these 2 are 4 core machines and the remaining 2 are 8 core ones. .NET Framework 3.5 SP1 installed on all 4 web servers. Application hosted on IIS 6.0 run in Worker process isolation mode.

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• Where are tables in Mnesia located?

  - by Sanoj

  I try to compare Mnesia with more traditional databases. As I understand it tables in Mnesia can be located to: ram_copies - tables are stored in RAM only, so no durability as in ACID. disc_copies - tables are located on disc and a copy is located in RAM, so the table can not be bigger than the available memory? disc_only_copies - tables are located to disc only, so no caching in memory and worse performance? And the size of the table are limited to the size of dets or the table has to be fragmented. So if I want the performance of doing reads from RAM and the durability of writes to disc, then the size of the tables are very limited compared to a traditional RDBMS like MySQL or PostgreSQL. I know that Mnesia aren't meant to replace traditional RDBMS:s, but can it be used as a big RDBMS or do I have to look for another database? The server I will use is a VPS with limited amount of memory, around 512MB, but I want good database performance. Are disc_copies and the other types of tables in Mnesia so limited as I have understood?

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• structured vs. unstructured data in db

  - by Igor

  the question is one of design. i'm gathering a big chunk of performance data with lots of key-value pairs. pretty much everything in /proc/cpuinfo, /proc/meminfo/, /proc/loadavg, plus a bunch of other stuff, from several hundred hosts. right now, i just need to display the latest chunk of data in my UI. i will probably end up doing some analysis of the data gathered to figure out performance problems down the road, but this is a new application so i'm not sure what exactly i'm looking for performance-wise just yet. i could structure the data in the db -- have a column for each key i'm gathering. the table would end up being O(100) columns wide, it would be a pain to put into the db, i would have to add new columns if i start gathering a new stat. but it would be easy to sort/analyze the data just using SQL. or i could just dump my unstructured data blob into the table. maybe three columns -- host id, timestamp, and a serialized version of my array, probably using JSON in a TEXT field. which should I do? am i going to be sorry if i go with the unstructured approach? when doing analysis, should i just convert the fields i'm interested in and create a new, more structured table? what are the trade-offs i'm missing here?

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• Splitting MS Access Database - Front End Part Location

  - by kristof

  One of the best practices as specified by Microsoft for Access Development is splitting Access application into 2 parts; Front End that hold all the object except tables and the Back End that holds the tables. The msdn page links there to the article Splitting Microsoft Access Databases to Improve Performance and Simplify Maintainability that describes the process in details. It is recommended that in multi user environment the Back End is stored on the server/shared folder while the Front End is distributed to each user. That implies that each time there are any changes made to the front end they need to be deployed to every user machine. My question is: Assuming that the users themselves do not have rights to modify the Front End part of the application what would be the drawbacks/dangers of leaving this on the server as well next to the Back End copy? I can see the performance issues here, but are there any dangers here like possible corruptions etc? Thank you EDIT Just to clarify, the scenario specified in question assumes one Front End stored on the server and shared by users. I understand that the recommendation is to have FE deployed to each user machine, but my question is more about what are the dangers if that is not done. E.g. when you are given an existing solution that uses the approach of both FE and BE on the server. Assuming the the performance is acceptable and the customer is reluctant to change the approach would you still push the change? And why exactly? For example the danger of possible data corruption would definitely be the strong enough argument, but is that the case? It is a part of follow up of my previous question From SQL Server to MS Access 2007

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• SQL Server 2008: CASE vs IF-ELSE-IF vs GOTO

  - by Saharsh Shah

  I have some rules in my application and I have written the business logic of that rules in my procedure. At the time of creation of procedure I came to know that CASE statement won't work in my scenario. So I have tried two ways to perform same operations (using IF-ELSE-IF or GOTO) shown as below. Method 1 Using IF-ELSE-IF conditions: DECLARE @V_RuleId SMALLINT; IF (@V_RuleId = 1) BEGIN /*My business logic*/ END ELSE IF (@V_RuleId = 2) BEGIN /*My business logic*/ END ELSE IF (@V_RuleId = 3) BEGIN /*My business logic*/ END /* ... ... ... ...*/ ELSE IF (@V_RuleId = 19) BEGIN /*My business logic*/ END ELSE IF (@V_RuleId = 20) BEGIN /*My business logic*/ END Method 2 Using GOTO statement: DECLARE @V_RuleId SMALLINT, @V_Temp VARCHAR(100); SET @V_Temp = 'GOTO RULE' + CONVERT(VARCHAR, @V_RuleId); EXECUTE sp_executesql @V_Temp; RULE1: BEGIN /*My business logic*/ END RULE2: BEGIN /*My business logic*/ END RULE3: BEGIN /*My business logic*/ END /* ... ... ... ...*/ RULE19: BEGIN /*My business logic*/ END RULE20: BEGIN /*My business logic*/ END Today I have 20 rules. It can be increase to any number in future. If I can able to use CASE statement then I have not any problem with performance, but I can't do that so I am worried about the performance of my procedure. Also one thing to be noticed that this procedure will execute very frequently by application. My questions are: Is there any way to use CASE statement in my procedure? If not, which method is best to use in my procedure to improve the performance of my code? Thanks in advance...

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• DAL Layer : EF 4.0 or Normal Data access layer with Stored Procedure

  - by Harryboy

  Hello Experts, Application : I am working on one mid-large size application which will be used as a product, we need to decide on our DAL layer. Application UI is in Silverlight and DAL layer is going to be behind service layer. We are also moving ahead with domain model, so our DB tables and domain classes are not having same structure. So patterns like Data Mapper and Repository will definitely come into picture. I need to design DAL Layer considering below mentioned factors in priority manner Speed of Development with above average performance Maintenance Future support and stability of the technology Performance Limitation : 1) As we need to strictly go ahead with microsoft, we can not use NHibernate or any other ORM except EF 4.0 2) We can use any code generation tool (Should be Open source or very cheap) but it should only generate code in .Net, so there would not be any licensing issue on per copy basis. Questions I read so many articles about EF 4.0, on outset it looks like that it is still lacking in features from NHibernate but it is considerably better then EF 1.0 So, Do you people feel that we should go ahead with EF 4.0 or we should stick to ADO .Net and use any code geneartion tool like code smith or any other you feel best Also i need to answer questions like what time it will take to port application from EF 4.0 to ADO .Net if in future we stuck up with EF 4.0 for some features or we are having serious performance issue. In reverse case if we go ahead and choose ADO .Net then what time it will take to swith to EF 4.0 Lastly..as i was going through the article i found the code only approach (with POCO classes) seems to be best suited for our requirement as switching is really easy from one technology to other. Please share your thoughts on the same and please guide on the above questions

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• Mysql Database Question about Large Columns

  - by murat

  Hi, I have a table that has 100.000 rows, and soon it will be doubled. The size of the database is currently 5 gb and most of them goes to one particular column, which is a text column for PDF files. We expect to have 20-30 GB or maybe 50 gb database after couple of month and this system will be used frequently. I have couple of questions regarding with this setup 1-) We are using innodb on every table, including users table etc. Is it better to use myisam on this table, where we store text version of the PDF files? (from memory usage /performance perspective) 2-) We use Sphinx for searching, however the data must be retrieved for highlighting. Highlighting is done via sphinx API but still we need to retrieve 10 rows in order to send it to Sphinx again. This 10 rows may allocate 50 mb memory, which is quite large. So I am planning to split these PDF files into chunks of 5 pages in the database, so these 100.000 rows will be around 3-4 million rows and couple of month later, instead of having 300.000-350.000 rows, we'll have 10 million rows to store text version of these PDF files. However, we will retrieve less pages, so again instead of retrieving 400 pages to send Sphinx for highlighting, we can retrieve 5 pages and it will have a big impact on the performance. Currently, when we search a term and retrieve PDF files that have more than 100 pages, the execution time is 0.3-0.35 seconds, however if we retrieve PDF files that have less than 5 pages, the execution time reduces to 0.06 seconds, and it also uses less memory. Do you think, this is a good trade-off? We will have million of rows instead of having 100k-200k rows but it will save memory and improve the performance. Is it a good approach to solve this problem and do you have any ideas how to overcome this problem? The text version of the data is used only for indexing and highlighting. So, we are very flexible. Thanks,

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• Access cost of dynamically created objects with dynamically allocated members

  - by user343547

  I'm building an application which will have dynamic allocated objects of type A each with a dynamically allocated member (v) similar to the below class class A { int a; int b; int* v; }; where: The memory for v will be allocated in the constructor. v will be allocated once when an object of type A is created and will never need to be resized. The size of v will vary across all instances of A. The application will potentially have a huge number of such objects and mostly need to stream a large number of these objects through the CPU but only need to perform very simple computations on the members variables. Could having v dynamically allocated could mean that an instance of A and its member v are not located together in memory? What tools and techniques can be used to test if this fragmentation is a performance bottleneck? If such fragmentation is a performance issue, are there any techniques that could allow A and v to allocated in a continuous region of memory? Or are there any techniques to aid memory access such as pre-fetching scheme? for example get an object of type A operate on the other member variables whilst pre-fetching v. If the size of v or an acceptable maximum size could be known at compile time would replacing v with a fixed sized array like int v[max_length] lead to better performance? The target platforms are standard desktop machines with x86/AMD64 processors, Windows or Linux OSes and compiled using either GCC or MSVC compilers.

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• Combining cache methods - memcache/disk based

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• MSBuild script fails but produces no errors

  - by Kate

  I have a MSBuild script that I am executing through TeamCity. One of the tasks that is runs is from Xheo DeploxLX CodeVeil which obfuscates some DLLs. The task I am using is called VeilProject. I have run the CodeVeil Project through the interface manually and it works correctly, so I think I can safely assume that the actual obfuscate process is ok. This task used to take around 40 minutes and the rest of the MSBuild file executed perfectly and finished without errors. For some reason this task is now taking 1hr 20 minutes or so to execute. Once the VeilProject task is finished the output from the task says it completely successfully, however the MSBuild script fails at this point. I have a task directly after the VeilProject task and it does not get outputted. Using diagnostic output from MSBUild I can see the following: My questions are: Would it be possible that the MSBuild script has timed out? Once the task has completed it is after a certain timeout period so it just fails? Why would the build fail with no errors and no warnings? [05:39:06]: [Target "Obfuscate"] Finished. [05:39:06]: [Target "Obfuscate"] Saving exception map [05:49:21]: [Target "Obfuscate"] Ended at 11/05/2010 05:49:21, ~1 hour, 48 minutes, 6 seconds [05:49:22]: [Target "Obfuscate"] Done. [05:49:51]: MSBuild output: Ended at 11/05/2010 05:49:21, ~1 hour, 48 minutes, 6 seconds (TaskId:8) Done. (TaskId:8) Done executing task "VeilProject" -- FAILED. (TaskId:8) Done building target "Obfuscate" in project "AMK_Release.proj.teamcity.patch.tcprojx" -- FAILED.: (TargetId:12) Done Building Project "C:\Builds\Scripts\AMK_Release.proj.teamcity.patch.tcprojx" (All target(s)) -- FAILED. Project Performance Summary: 6535484 ms C:\Builds\Scripts\AMK_Release.proj.teamcity.patch.tcprojx 1 calls 6535484 ms All 1 calls Target Performance Summary: 156 ms PreClean 1 calls 266 ms SetBuildVersionNumber 1 calls 2406 ms CopyFiles 1 calls 6532391 ms Obfuscate 1 calls Task Performance Summary: 16 ms MakeDir 2 calls 31 ms TeamCitySetBuildNumber 1 calls 31 ms Message 1 calls 62 ms RemoveDir 2 calls 234 ms GetAssemblyIdentity 1 calls 2406 ms Copy 1 calls 6528047 ms VeilProject 1 calls Build FAILED. 0 Warning(s) 0 Error(s) Time Elapsed 01:48:57.46 [05:49:52]: Process exit code: 1 [05:49:55]: Build finished

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• Web Shop Schema - Document Db

  - by Maxem

  I'd like to evaluate a document db, probably mongo db in an ASP.Net MVC web shop. A little reasoning at the beginning: There are about 2 million products. The product model would be pretty bad for rdbms as there'd be many different kinds of products with unique attributes. For example, there'd be books which have isbn, authors, title, pages etc as well as dvds with play time, directors, artists etc and quite a few more types. In the end, I'd have about 9 different products with a combined column count (counting common columns like title only once) of about 70 to 100 whereas each individual product has 15 columns at most. The three commonly used ways in RDBMS would be: EAV model which would have pretty bad performance characteristics and would make it either impractical or perform even worse if I'd like to display the author of a book in a list of different products (think start page, recommended products etc.). Ignore the column count and put it all in the product table: Although I deal with somewhat bigger databases (row wise), I don't have any experience with tables with more than 20 columns as far as performance is concered but I guess 100 columns would have some implications. Create a table for each product type: I personally don't like this approach as it complicates everything else. C# Driver / Classes: I'd like to use the NoRM driver and so far I think i'll try to create a product dto that contains all properties (grouped within detail classes like book details, except for those properties that should be displayed on list views etc.). In the app I'll use BookBehavior / DvdBehaviour which are wrappers around a product dto but only expose the revelent Properties. My questions now: Are my performance concerns with the many columns approach valid? Did I overlook something and there is a much better way to do it in an RDBMS? Is MongoDb on Windows stable enough? Does my approach with different behaviour wrappers make sense?

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• Using memory-based cache together with conventional cache

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• Using memcache together with conventional cache

  - by Industrial

  Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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• Interchange structured data between Haskell and C

  - by Eonil

  First, I'm a Haskell beginner. I'm planning integrating Haskell into C for realtime game. Haskell does logic, C does rendering. To do this, I have to pass huge complexly structured data (game state) from/to each other for each tick (at least 30 times per second). So the passing data should be lightweight. This state data may laid on sequential space on memory. Both of Haskell and C parts should access every area of the states freely. In best case, the cost of passing data can be copying a pointer to a memory. In worst case, copying whole data with conversion. I'm reading Haskell's FFI(http://www.haskell.org/haskellwiki/FFICookBook#Working_with_structs) The Haskell code look specifying memory layout explicitly. I have a few questions. Can Haskell specify memory layout explicitly? (to be matched exactly with C struct) Is this real memory layout? Or any kind of conversion required? (performance penalty) If Q#2 is true, Any performance penalty when the memory layout specified explicitly? What's the syntax #{alignment foo}? Where can I find the document about this? If I want to pass huge data with best performance, how should I do that? *PS Explicit memory layout feature which I said is just C#'s [StructLayout] attribute. Which is specifying in-memory position and size explicitly. http://www.developerfusion.com/article/84519/mastering-structs-in-c/ I'm not sure Haskell has matching linguistic construct matching with fields of C struct.

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• Using EhCache for session.createCriteria(...).list()

  - by James Smith

  I'm benchmarking the performance gains from using a 2nd level cache in Hibernate (enabling EhCache), but it doesn't seem to improve performance. In fact, the time to perform the query slightly increases. The query is: session.createCriteria(MyEntity.class).list(); The entity is: @Entity @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE) public class MyEntity { @Id @GeneratedValue private long id; @Column(length=5000) private String data; //---SNIP getters and setters--- } My hibernate.cfg.xml is: <!-- all the normal stuff to get it to connect & map the entities plus:--> <property name="hibernate.cache.region.factory_class"> net.sf.ehcache.hibernate.EhCacheRegionFactory </property> The MyEntity table contains about 2000 rows. The problem is that before adding in the cache, the query above to list all entities took an average of 65 ms. After the cache, they take an average of 74 ms. Is there something I'm missing? Is there something extra that needs to be done that will increase performance?

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• I need a fast runtime expression parser

  - by Chris Lively

  I need to locate a fast, lightweight expression parser. Ideally I want to pass it a list of name/value pairs (e.g. variables) and a string containing the expression to evaluate. All I need back from it is a true/false value. The types of expressions should be along the lines of: varA == "xyz" and varB==123 Basically, just a simple logic engine whose expression is provided at runtime. UPDATE At minimum it needs to support ==, !=, , =, <, <= Regarding speed, I expect roughly 5 expressions to be executed per request. We'll see somewhere in the vicinity of 100/requests a second. Our current pages tend to execute in under 50ms. Usually there will only be 2 or 3 variables involved in any expression. However, I'll need to load approximately 30 into the parser prior to execution. UPDATE 2012/11/5 Update about performance. We implemented nCalc nearly 2 years ago. Since then we've expanded it's use such that we average 40+ expressions covering 300+ variables on post backs. There are now thousands of post backs occurring per second with absolutely zero performance degradation. We've also extended it to include a handful of additional functions, again with no performance loss. In short, nCalc met all of our needs and exceeded our expectations.

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• lapply slower than for-loop when used for a BiomaRt query. Is that expected?

  - by ptocquin

  I would like to query a database using BiomaRt package. I have loci and want to retrieve some related information, let say description. I first try to use lapply but was surprise by the time needed for the task to be performed. I thus tried a more basic for-loop and get a faster result. Is that expected or is something wrong with my code or with my understanding of apply ? I read other posts dealing with *apply vs for-loop performance (Here, for example) and I was aware that improved performance should not be expected but I don't understand why performance here is actually lower. Here is a reproducible example. 1) Loading the library and selecting the database : library("biomaRt") athaliana <- useMart("plants_mart_14") athaliana <- useDataset("athaliana_eg_gene",mart=athaliana) 2) Querying the database : loci <- c("at1g01300", "at1g01800", "at1g01900", "at1g02335", "at1g02790", "at1g03220", "at1g03230", "at1g04040", "at1g04110", "at1g05240" ) I create a function for the use in lapply : foo <- function(loci) { getBM("description","tair_locus",loci,athaliana) } When I use this function on the first element : > system.time(foo(cwp_loci[1])) utilisateur système écoulé 0.020 0.004 1.599 When I use lapply to retrieve the data for all values : > system.time(lapply(loci, foo)) utilisateur système écoulé 0.220 0.000 16.376 I then created a new function, adding a for-loop : foo2 <- function(loci) { for (i in loci) { getBM("description","tair_locus",loci[i],athaliana) } } Here is the result : > system.time(foo2(loci)) utilisateur système écoulé 0.204 0.004 10.919 Of course, this will be applied to a big list of loci, so the best performing option is needed. I thank you for assistance. EDIT Following recommendation of @MartinMorgan Simply passing the vector loci to getBM greatly improves the query efficiency. Simpler is better. > system.time(lapply(loci, foo)) utilisateur système écoulé 0.236 0.024 110.512 > system.time(foo2(loci)) utilisateur système écoulé 0.208 0.040 116.099 > system.time(foo(loci)) utilisateur système écoulé 0.028 0.000 6.193

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• Phonegap: Will my mobile app 'feel' faster or slower once ported to phonegap?

  - by user15872

  So I'm designing everything in mobile Safari and I know that phonegap is essentially a stripped webview but... Question: Will my application will run better in phonegap? (revised below) a)I imagine my navigation and core app will load faster as the scripts and images are on the hard drive. Is this True? b)I assume since they've been working on it for 2 years now that they may have made some optimizations to make it quicker than just an average safari window. Is this true? (Assuming both html5/js/css code bases are pretty much the same and app is running on iOS.) Update: Sorry, I meant to compare apples to slightly different apples. Question 1 revised: Will my app see any performance benefits running with in a phonegap environment vs standard mobile safari? (compare mobile - to mobile) 1b) In what ways, other than loading time has phonegap optimized performance over standard mobile safari? Follow ups: 1) Are there any pitfalls, other than large libraries, that may cause phonegap to suffer a serious performance hit vs stand mobile safari? 2) Can I mix native and webview rendering? (i.e the top half of my app is rendered in with html/css/js and the bottom half native)

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