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• mod_perl memory leak

  - by marghi

  Hello, I recently discovered that one of our sites has a memory leak in it, it's very strange because it happened all of the sudden. I've used GTop to measure the memory size per process and it tells me that the real value is somewhere around 65 MB (on the server) per request and and additional 5 MB shared. I tried preloading the modules in the startup.pl file a indicated in the performance tuning article for mod_perl. Nothing happened if fact the shared memory decreased down to 3.7 MB, in this situation I thought that my application is leaking memory do before any line of code got executed I measured the memory just to find out that the total value is in fact 64 MB, my questions are: Is there a default preallocation of memory for each process? Is there a configuration issue? Is mod_perl leaking memory ? Thank you very much.

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• Optimising (My)SQL Query

  - by Simon

  I usually use ORM instead of SQL and I am slightly out of touch on the different JOINs... SELECT `order_invoice`.*, `client`.*, `order_product`.*, SUM(product.cost) as net FROM `order_invoice` LEFT JOIN `client` ON order_invoice.client_id = client.client_id LEFT JOIN `order_product` ON order_invoice.invoice_id = order_product.invoice_id LEFT JOIN `product` ON order_product.product_id = product.product_id WHERE (order_invoice.date_created >= '2009-01-01') AND (order_invoice.date_created <= '2009-02-01') GROUP BY `order_invoice`.`invoice_id` The tables/ columns are logically names... it's an shop type application... the query works... it's just very very slow... I use the Zend Framework and would usually use Zend_Db_Table_Row::find(Parent|Dependent)Row(set)('TableClass') but I have to make lots of joins and I thought it'll improve performance by doing it all in one query instead of hundreds... Can I improve the above query by using more appropriate JOINs or a different implementation? Many thanks.

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• Multivalue Mysql Inserts using HibernateTemplate

  - by Langali

  I am using Spring HibernateTemplate and need to insert hundreds of records into a mysql database every second. Not sure what is the most performant way of doing it, but I am trying to see how the multi value mysql inserts do using hibernate. String query = "insert into user(age, name, birth_date) values(24, 'Joe', '2010-05-19 14:33:14'), (25, 'Joe1', '2010-05-19 14:33:14')" getHibernateTemplate().execute(new HibernateCallback(){ public Object doInHibernate(Session session) throws HibernateException, SQLException { return session.createSQLQuery(query).executeUpdate(); } }); But I get this error: 'could not execute native bulk manipulation query.' Please check your query ..... Any idea of I can use a multi value mysql insert using Hibernate? or is my query incorrect? Any other ways that I can improve the performance? I did try the saveOrUpdateAll() method, and that wasn't good enough!

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• C++ Urban Myths

  - by Neil Butterworth

  I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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• assignment vs std::swap and merging and keeping duplicates in seperate object

  - by rubenvb

  Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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• How do I calculate a good hash code for a list of strings?

  - by Ian Ringrose

  Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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• Are you using Virtual Machine as your primary development enviroment?

  - by Click Ok

  Recently I have purchased a notebook that cames with Windows Home Basic (that don't have with ASP.Net/IIS. I thought in upgrade the Windows version to one with ASP.Net/IIS, but I thought in another possibility: I have an Hard Disk Case with a 360Gb HD. I thought in create a virtual machine with Windows Ultimate (installing too ASP.Net, IIS and Visual Studio 2008) in this HD Case, then I can access my "development enviroment" in any computer that I will work on (my desktop machine and my notebook). But I was worried about the performance. I don't have experience working in Virtual Machines (I use it just to quick compatibility tests)... Are you using Virtual Machine as your primary development enviroment? What your finds? ==================== Thanks for your answers! It really did help me! I would like to know too about portability ie.: the virtual machine that I created in my laptop will work in the desktop? I will need re-activate Windows?

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• Is it possible to find out what FlashBuilder is doing during compilation?

  - by justkevin

  I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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• Dealing with Windows line-endings in Python

  - by Adam Nelson

  I've got a 700MB XML file coming from a Windows provider. As one might expect, the line endings are '\r\n' (or ^M in vi). What is the most efficient way to deal with this situation aside from getting the supplier to send over '\n' :-) Use os.linesep Use rstrip() (requiring opening the file ... which seems crazy) Using Universal newline support is not standard on my Mac Snow Leopard - so isn't an option. I'm open to anything that requires Python 2.6+ but it needs to work on Snow Leopard and Ubuntu 9.10 with minimal external requirements. I don't mind a small performance penalty but I am looking for the standard best way to deal with this.

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• GetHashCode Method reliability in Silverlight/WP7.1

  - by abhinav

  I am attempting to hash and keep(the hash) an object of type IEnumerable<anotherobject> which has about a 1000 entries. I'll be generating another such object, but this time I'd like to check for any changes in the values of the entries using the hash codes of the two objects. Basically, I was wondering if GetHashCode() is apt for this, both from a performance perspective and reliability perspective (getting different values for different object values and same values for same object values, always). If I have to override it, what would be a good way to do so, does it always depend on the type of anotherobject and what Equals means when comparing two anotherobjects? Is there a generic way to do it? This concern is because my object can be quite big.

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• Emulating a transaction-safe SEQUENCE in MySQL

  - by Michael Pliskin

  We're using MySQL with InnoDB storage engine and transactions a lot, and we've run into a problem: we need a nice way to emulate Oracle's SEQUENCEs in MySQL. The requirements are: - concurrency support - transaction safety - max performance (meaning minimizing locks and deadlocks) We don't care if some of the values won't be used, i.e. gaps in sequence are ok. There is an easy way to archieve that by creating a separate InnoDB table with a counter, however this means it will take part in transaction and will introduce locks and waiting. I am thinking to try a MyISAM table with manual locks, any other ideas or best practices?

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• CakePHP repeats same queries

  - by Rytis

  I have a model structure: Category hasMany Product hasMany Stockitem belongsTo Warehouse, Manufacturer. I fetch data with this code, using containable to be able to filter deeper in the associated models: $this->Category->find('all', array( 'conditions' => array('Category.id' => $category_id), 'contain' => array( 'Product' => array( 'Stockitem' => array( 'conditions' => array('Stockitem.warehouse_id' => $warehouse_id), 'Warehouse', 'Manufacturer', ) ) ), ) ); Data structure is returned just fine, however, I get multiple repeating queries like, sometimes hundreds of such queries in a row, based on dataset. SELECT `Warehouse`.`id`, `Warehouse`.`title` FROM `beta_warehouses` AS `Warehouse` WHERE `Warehouse`.`id` = 2 Basically, when building data structure Cake is fetching data from mysql over and over again, for each row. We have datasets of several thousand rows, and I have a feeling that it's going to impact performance. Is it possible to make it cache results and not repeat same queries?

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• how do copyright permission systems for content hosting sites work?

  - by zebraman

  I am wondering about subscription sites that host content, like recorded performances from concerts. I'm sure there is a tangle of copyright permissions that must be granted for these video/audio files to be hosted. For example, if a band plays a cover of another band's song, permission must be obtained from not only the band that performed, but the band that owns the song. Perhaps even from the venue that hosted the performance, to record the video and post the content. I am curious how websites that host content like this work. How might an automated copyright system work to keep track of who has ownership of certain performances and obtain permission from said owners to record and post their content.

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• Conceptually, how does replay work in a game?

  - by SnOrfus

  I was kind of curious as to how replay might be implemented in a game. Initially, I thought that there would be just a command list of every player/ai action that was taken in the game, and it then 're-plays' the game and lets the engine render as usual. However, I have looked at replays in FPS/RTS games, and upon careful inspection even things like the particles and graphical/audible glitches are consistent (and those glitches are generally *in*consistent). So How does this happen. In fixed camera angle games I though it might just write every frame of the whole scene to a stream that gets stored and then just replays the stream back, but that doesn't seem like enough for games that allow you to pause and move the camera around. You'd have to store the locations of everything in the scene at all points in time (No?). So for things like particles, that's a lot of data to push which seems like a significant draw on the game's performance whilst playing.

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• Designing a table to store EXIF data

  - by rafale

  I'm looking to get the best performance out of querying a table containing EXIF data. The queries in question will only search the EXIF data for the specified strings and return the row index on a match. With that said, would it better to store the EXIF data in a table with separate columns for each of the tags, or would storing all of the tags in a single column as one long delimited string suit me just as well? There are around 115 EXIF tags I'll be storing, and each record would be around 1500 to 2000 chars in length if concatenated into a single string.

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• Why should I use an N-Tier Approach When using an SqlDatasource is ALOT EASIER ?

  - by The_AlienCoder

  When it comes to web development I have always tried to work SMART not HARD. So for along time My Aproach to interacting with databases in my AspNet projects has been this : 1) Create my stored procedures 2) Drag an SQLDatasource control on my aspx page 3) Bind a DataList Control to my SQLDatasource 4) Insert, Update & Delete by using my Datalist or programmatically using built in SQLDatasource methods e.g MySqlDataSource.InsertParameters["author"].DefaultValue = TextBox1.Text; MySqlDataSource.Insert(); Recently however I got a relatively easy web project. So I decided to employ a 3-tier Model...But I got exhausted halfway and just didnt seem worth it ! It seemed like I was working too HARD for a project that could have been easily accomplished by a couple of SqlDataSource Controls. So Why Is the N-Tier Model better than my Approach? Has it anything to do with performance? What are the advantages of the ObjectDataSource control over the SqlDataSource Control?

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• Implementing Tagging using Core Data on the iPhone

  - by Jonathan Penn

  I have an application that uses CoreData and I'm trying to figure out the best way to implement tagging and filtering by tag. For my purposes, if I was doing this in raw SQLite I would only need three tables, tags, item_tags and of course my items table. Then filtering would be as simple as joining between the three tables where only items are related to the given tags. Quite straightforward. But, is there a way to do this in CoreData and utilizing NSFetchedResultsController? It doesn't seem that NSPredicate give you the ability to filter through joins. NSPredicate's aren't full SQL anyway so I'm probably barking up the wrong tree there. I'm trying to avoid reimplementing my app using SQLite without CoreData since I'm enjoying the performance CoreData gives me in other areas. Yes, I did consider (and built a test implementation) diving into the raw SQLite that CoreData generates, but that's not future proof and I want to avoid that, too. Has anyone else tried to tackle tagging/filtering with CoreData in a UITableView with NSFetchedResultsController

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• What are some "mental steps" a developer must take to begin moving from SQL to NO-SQL (CouchDB, Fath

  - by Byron Sommardahl

  I have my mind firmly wrapped around relational databases and how to code efficiently against them. Most of my experience is with MySQL and SQL. I like many of the things I'm hearing about document-based databases, especially when someone in a recent podcast mentioned huge performance benefits. So, if I'm going to go down that road, what are some of the mental steps I must take to shift from SQL to NO-SQL? If it makes any difference in your answer, I'm a C# developer primarily (today, anyhow). I'm used to ORM's like EF and Linq to SQL. Before ORMs, I rolled my own objects with generics and datareaders. Maybe that matters, maybe it doesn't. Here are some more specific: How do I need to think about joins? How will I query without a SELECT statement? What happens to my existing stored objects when I add a property in my code? (feel free to add questions of your own here)

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• PostgreSQL: How to index all foreign keys?

  - by biggusjimmus

  I am working with a large PostgreSQL database, and I are trying to tune it to get more performance. Our queries and updates seem to be doing a lot of lookups using foreign keys. What I would like is a relatively simple way to add Indexes to all of our foreign keys without having to go through every table (~140) and doing it manually. In researching this, I've come to find that there is no way to have Postgres do this for you automatically (like MySQL does), but I would be happy to hear otherwise there, too.

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• Detecting and reloading updated application parameters at runtime

  - by VeeKayBee

  I am working on an ASP.NET web application(using .NET 4.5 and C#).The application deals with lot of units (for measuring like KG,Litre,KM etc). So based on the selected unit we have to implement some allowed range.This values can be configured without much effort. We identified two solutions for this Keeping a configuration xml. Suppose the values in xml, does it requires an iisreset or any other thing which can take the site down for some time, if we are changing the xml file to change some validation. Keeping in Db, then use SQL dependency caching. So an update to DB can reflect the caching values.SO i believe if we change the values, it will update the cache. How much complex is this and does it effect the performance ? It will be great helpful, if we have some other method to achieve this. Thanks in advance.

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• [Symfony] Admin generator and i18n

  - by David

  I have read lots of questions about i18n, but I haven't found any about performance. I have a simple backend app listing the contents of an ads table. These ads have a category, that is translated in some languages (it's defined as i18n in the Doctrine schema). So, when I add a "table_method" in my generator.yml to include de Category table, it reduces the number of queries, but there are yet some of them referencing i18n translation tables. So, if I add the category Translation table to the query, it reduces even more the queries BUT it increases the processing time considerably. Why this time penalty? Just because of the translation table? And why isn't the filter using this method to avoid so many translation queries as well? I mean, if I want to filter by category, it is making one query per category to include the translation table. Why??

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• parsing/matching string occurrence in C

  - by David

  I have the following string: const char *str = "\"This is just some random text\" 130 28194 \"Some other string\" \"String 3\"" I would like to get the the integer 28194 of course the integer varies, so I can't do strstr("20194"). So I was wondering what would be a good way to get that part of the string? I was thinking to use #include <regex.h> which I already have a procedure to match regexp's but not sure how the regexp in C will look like using the POSIX style notation. [:alpha:]+[:digit:] and if performance will be an issue. Or will it be better using strchr,strstr? Any ideas will be appreciate it

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• What factors could cause the scalability issue on a 10-core CPU?

  - by JackWM

  I am tuning the performance of parallel Java programs. And want to check the impacts from the Architecture. I'm look into the Intel 10-core CPU, Intel(R) Xeon(R) CPU E7-L8867. I found my program only scales up to 5 cores. What could be the causes? I'm considering the Architecture effects. e.g. memory contention? More specifically, Are the 10 cores symmetric to each other? How many memory controllers does it have?

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• Managing Data Prefetching and Dependencies with .NET Typed Datasets

  - by Derek Morrison

  I'm using .NET typed datasets on a project, and I often get into situations where I prefetch data from several tables into a dataset and then pass that dataset to several methods for processing. It seems cleaner to let each method decide exactly which data it needs and then load the data itself. However, several of the methods work with the same data, and I want the performance benefit of loading data in the beginning only once. My problem is that I don't know of a good way or pattern to use for managing dependencies (I want to be sure I load all the data that I'm going to need for each class/method that will use the dataset). Currently, I just end up looking through the code for the various classes that will use the dataset to make sure I'm loading everything appropriately. What are good approaches or patterns to use in this situation? Am I doing something fundamentally wrong? Although I'm using typed datasets, this seems like it would be a common situation where prefetching data is used. Thanks!

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• Interview Question: .Any() vs if (.Length > 0) for testing if a collection has elements

  - by Chris

  In a recent interview I was asked what the difference between .Any() and .Length > 0 was and why I would use either when testing to see if a collection had elements. This threw me a little as it seems a little obvious but feel I may be missing something. I suggested that you use .Length when you simply need to know that a collection has elements and .Any() when you wish to filter the results. Presumably .Any() takes a performance hit too as it has to do a loop / query internally.

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