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• How does mysql define DISTINCT()

  - by goran

  AFAIK SQL defines two uses of DISTINCT keywords - SELECT DISTINCT field... and SELECT COUNT(DISTINCT field) ... However in one of web applications that I administer I've noticed performance issues on queries like SELECT DISTINCT(field1), field2, field3 ... DISTINCT() on a single column makes no sense and I am almost sure it is interpreted as SELECT DISTINCT field1, field2, field3 ... but how can I prove this? I've searched mysql site for a reference on this particular syntax but could not find any. Does anyone have a link to definition of DISTINCT() in mysql or knows about other authoritative source on this? Best

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• How do I rename a field in a structure array in MATLAB?

  - by Matthew Simoneau

  Given a structure array, how do I rename a field? For example, given the following, how do I change "bar" to "baz". clear a(1).foo = 1; a(1).bar = 'one'; a(2).foo = 2; a(2).bar = 'two'; a(3).foo = 3; a(3).bar = 'three'; disp(a) What is the best method, where "best" is a balance of performance, clarity, and generality?

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• Checking whether an object exists in StructureMap container

  - by Kevin Pang

  I'm using StructureMap to handle the creation of NHibernate's ISessionFactory and ISession. I've scoped ISessionFactory as a singleton so that it's only created once for my web app and I've scoped ISession as a hybrid so that it will only be opened once per web request. I want to make sure that at the end of each web request, I properly dispose of ISession if it was created for that web request. I figured I could put some code in my Application_EndRequest routine to first check if an ISession was created, and if so, call ISession.Dispose. My current workaround is to just open up an ISession on Application_BeginRequest then dispose of it on Application_EndRequest, but that seems somewhat wasteful in that static file requests for images and css files and whatnot will create an ISession without ever using it. I know that the overall performance hit is negligable since ISessions are very lightweight, but it's getting annoying seeing all those ISessions being created inside NHProf.

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• Optimize C# Code Fragment

  - by Eric J.

  I'm profiling some C# code. The method below is one of the most expensive ones. For the purpose of this question, assume that micro-optimization is the right thing to do. Is there an approach to improve performance of this method? Changing the input parameter to p to ulong[] would create a macro inefficiency. static ulong Fetch64(byte[] p, int ofs = 0) { unchecked { ulong result = p[0 + ofs] + ((ulong)p[1 + ofs] << 8) + ((ulong)p[2 + ofs] << 16) + ((ulong)p[3 + ofs] << 24) + ((ulong)p[4 + ofs] << 32) + ((ulong)p[5 + ofs] << 40) + ((ulong)p[6 + ofs] << 48) + ((ulong)p[7 + ofs] << 56); return result; } }

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• Out-Of-Memory while doing Core Data migration

  - by Kamchatka

  Hello, I'm migrating a CoreData model between two versions of an application. I was storing binary data as blobs in the previous version and I want to take them out of the blobs for performance. My issue is that during the migration it seems that Core Data loads everything into memory which leads to Low Memory Warnings and then to my app being killed. Apple documentation suggests the following : http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreDataVersioning/Articles/vmCustomizingTheProcess.html#//apple_ref/doc/uid/TP40005510-SW9 However, it seems to rely on the fact that the large objects are applied different mapping. In my case, all the objects are basically the same and the same mapping has to be applied to each of them. I don't see in this case how I could apply their technique. How should I handle a migration with very large objects ?

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• Service design or access to another process

  - by hotyi

  I have a cache service,it's works as .net remoting, i want to create another windows service to clean up the that cache service by transfer the objects from cache to files. because they are in separate process, is their any way i could access that cache service or do i have to expose a method from the cache service to do that clean up work? the "clean up" means i want to serialize the object from Cache to file and these saved file will be used for further process. let me explain this application more detail. the application is mainly a log service to log all the coming request and these request will be saved to db for further data mining. we have 2 design for this log system 1) use MSMQ, but seems it's performance is not good enough, we don't use it. 2) we design a cache service, each request will be saved into the cache, and we need another function to clean up the cache by serialize the object to file.

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• Python urllib3 and how to handle cookie support?

  - by bigredbob

  So I'm looking into urllib3 because it has connection pooling and is thread safe (so performance is better, especially for crawling), but the documentation is... minimal to say the least. urllib2 has build_opener so something like: #!/usr/bin/python import cookielib, urllib2 cj = cookielib.CookieJar() opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cj)) r = opener.open("http://example.com/") But urllib3 has no build_opener method, so the only way I have figured out so far is to manually put it in the header: #!/usr/bin/python import urllib3 http_pool = urllib3.connection_from_url("http://example.com") myheaders = {'Cookie':'some cookie data'} r = http_pool.get_url("http://example.org/", headers=myheaders) But I am hoping there is a better way and that one of you can tell me what it is. Also can someone tag this with "urllib3" please.

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• how can I design a good architechture for a Transaction Processing System?

  - by ghedas

  I have a project that must design an architecture for it. This project is a something like a Transaction Processing system and I need to know something like this: when and where I must use synchronous and asynchronous relations between its components? If always I use synchronous relations, the amount of messages maybe become exceeded and makes problem for TP system, and on the other hand synchronous relations make lots of delay, I think a mixture of them is required! If other parameters required to considering please help me! the most nonfunctional requirements of this project are performance and availability of it. I need useful materials and suggestions for it.

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• GWT : Type of Container

  - by moorsu

  I see that there are two ways of transferring objects from server to client Use the same domain object (Contact.java) as used in the service layer. (I do not use hibernate) Use the HashMap to send the domain object field values in the form of Map with the help of BeanUtilsBean class. For multiple objects, use the List. Similary, use the Map to submit form values from client to server Is there any performance advantage for option 1 over 2?. Is there a way to hide the classname/package name that is sent to the browser if we use option 1?. thanks!.

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• SELECT INTO or Stored Procedure?

  - by Kerry

  Would this be better as a stored procedure or leave it as is? INSERT INTO `user_permissions` ( `user_id`, `object_id`, `type`, `view`, `add`, `edit`, `delete`, `admin`, `updated_by_user_id` ) SELECT `user_id`, $object_id, '$type', 1, 1, 1, 1, 1, $user_id FROM `user_permissions` WHERE `object_id` = $object_id_2 AND `type` = '$type_2' AND `admin` = 1 You can think of this with different objects, lets say you have groups and subgroups. If someone creates a subgroup, it is making everyone who had access to the parent group now also have access to the subgroup. I've never made a stored procedure before, but this looks like it might be time. This call be probably be called very often. Should I be creating a procedure or will the performance be insignificant?

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• Alternative databases to use when putting IIS Logs into a database using LogParser

  - by Robin Day

  We have run some scripts that use LogParser to dump our IIS logs into a SQL Server database. We can then query this to get simple stats on hits, usage etc. It's also good when linking it to error log databases and performance counter database to compare usage with errors, etc. Having implemented this for just one system and for the last 2-3 weeks we already have a 5GB database with around 10 million records. This is making any queries to this database quite slow and will no doubt cause storage issues if we continue to log as we are. Can anyone suggest any alternative databases that we could use for this data that would be more efficient for such logs? I'd be particularly interested in any experience of Google's BigTable or Amazon's SimbleDB. Are either of these suitable for reporting queries? COUNTs, GROUP BYs, PIVOTs?

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• Using SQL Server for WSS 3.0 instead of Windows Internal database

  - by val

  Hi Folks, There are actually two related questions: is it possible or advisable to use a full blown stand-alone SQL server for SharePoint Services WSS3.0 instead of the supplied windows internal database it comes with? The client I am working for is asking to utilize their existent SQL server for all WSS content databases to possibly minimize admin effort and improve performance. As well, would you advise to install WSS on one physical server and the content database on another server? Any gain in performace? Practicality? ect. The default is WSS and all of its databases are installed on the same single server. We don't really need a farm setup of MOSS, because the WSS capabilities are enough for our needs. Thanks, Val

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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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• Function Object in Java .

  - by Tony

  I wanna implement a javascript like method in java , is this possible ? Say , I have a Person class : public class Person { private String name ; private int age ; // constructor ,accessors are omitted } And a list with Person objects: Person p1 = new Person("Jenny",20); Person p2 = new Person("Kate",22); List<Person> pList = Arrays.asList(new Person[] {p1,p2}); I wanna implement a method like this: modList(pList,new Operation (Person p) { incrementAge(Person p) { p.setAge(p.getAge() + 1)}; }); modList receives two params , one is a list , the other is the "Function object", it loops the list ,and apply this function to every element in the list. In functional programming language,this is easy , I don't know how java do this? Maybe could be done through dynamic proxy, does that have a performance trade off?

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• Who is preventing the release of Java 1.7

  - by Shawn

  I recently attended a talk by a Sun engineer Charlie Hunt regarding performance. The talk was interesting enough but one question was regarding release date of 1.7. He said it's delayed as there are parties who are refusing to sign off JSRs they own and thus preventing the 1.7 release. It apparently has something to do with the cost of determining your Sun compliance. I would be interested to know the full story if anyone knows or can point me in the right direction. What triggered my question was the amazing long release notes for 6u18. Thanks

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• Best practice for Python Assert

  - by meade

  Is there a performance or code maintenance issue with using assert as part of the standard code instead of using it just for debugging purposes? Is assert x >= 0, 'x is less then zero' and better or worse then if x < 0: raise Exception, 'x is less then zero' Also, is there anyway to set a business rule like if x < 0 raise error that is always checked with out the try, except, finally so, if at anytime throughout the code x is < 0 an error is raised, like if you set assert x < 0 at the start of a function, anywhere within the function where x becomes less then 0 an exception is raised?

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• Replication - syncronizing most of the data some of the time

  - by uncle brad

  I have some data that isn't properly "partitioned" (for lack of a better word). All inserts, processing and reporting happen on the same table. The bulk of the processing happens not long after the insert and not long after that it becomes immutable (we're talking days). I could do all inserts and processing on a new table that I replicate to the old table. When I detect that the data has become immutable I would delete the data from the new table, but I would edit the delete replication stored procedure so that the delete did not replicate. How bad an idea is this? It seems attractive at the moment (I haven't slept on it yet) because it might mitigate a performance problem with only very small changes to the application. It also seems like it might be a good way to shoot myself in the foot.

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• how to work with javascript typed arrays without using for

  - by ramesh babu

  var sendBuffer = new ArrayBuffer(4096); var dv = new DataView(sendBuffer); dv.setInt32(0, 1234); var service = svcName; for (var i = 0; i < service.length; i++) { dv.setUint8(i + 4, service.charCodeAt(i)); } ws.send(sendBuffer); how to workout this wihout using for loop. for loop decreasing performance while works with huge amount of data.

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• How to diganose an unlogged Error 500 on Apache?

  - by samuel morhaim

  We are running a very simple Symfony script, that randomly returns an Error 500. The system administrator says he can't find any trace of an Error 500 on the error logs, however using Curl or Firebug, it is obvious that an Error 500 is being returned. The script simply parses a POST request submitted to an URL on our server. We already checked for performance, memory etc but nothing seems to be the problem. How is this possible? We already enabled all debugging, logging, on Apache, PHP, etc and nothing.

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• Deleting orphans with JPA

  - by homaxto

  I have a one-to-one relation where I use CascadeType.PERSIST. This has over time build up a huge amount of child records that has not been deleted, to such an extend that it is reflected in the performance. Now I wish to add some code that cleans up the database removing all the child records that are not referenced by a parent. At the moment we are talking 400K+ records, at I need to run the code on all customer installations just to be sure they do not run into the same problem. I think the best solution would be to run a named query (because we support two databases) that deletes the necessary records, and this is where I get into problems, because how should I write it in JPQL? The result I want can be defined like the following sql statement, which unfortunaltely does not run on MySQL. DELETE FROM child c1 WHERE c1.pk NOT IN (SELECT DISTINCT p.pk FROM child c2 JOIN parent p ON p.child = c2.pk);

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• mmap() for large file I/O?

  - by Boatzart

  I'm creating a utility in C++ to be run on Linux which can convert videos to a proprietary format. The video frames are very large (up to 16 megapixels), and we need to be able to seek directly to exact frame numbers, so our file format uses libz to compress each frame individually, and append the compressed data onto a file. Once all frames are finished being written, a journal which includes meta data for each frame (including their file offsets and sizes) is written to the end of the file. I'm currently using ifstream and ofstream to do the file i/o, but I am looking to optimize as much as possible. I've heard that mmap() can increase performance in a lot of cases, and I'm wondering if mine is one of them. Our files will be in the tens to hundreds of gigabytes, and although writing will always be done sequentially, random access reads should be done in constant time. Any thoughts as to whether I should investigate this further, and if so does anyone have any tips for things to look out for? Thanks!

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• logging in scala

  - by IttayD

  In Java, the standard idiom for logging is to create a static variable for a logger object and use that in the various methods. In Scala, it looks like the idiom is to create a Logging trait with a logger member and mixin the trait in concrete classes. This means that each time an object is created it calls the logging framework to get a logger and also the object is bigger due to the additional reference. Is there an alternative that allows the ease of use of "with Logging" while still using a per-class logger instance? EDIT: My question is not about how one can write a logging framework in Scala, but rather how to use an existing one (log4j) without incurring an overhead of performance (getting a reference for each instance) or code complexity. Also, yes, I want to use log4j, simply because I'll use 3rd party libraries written in Java that are likely to use log4j.

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• What is the best solution to do Reporting on Object data for .NET ?

  - by Peter Fox

  Hi, Our projects are using objects as the data source to reports. Our business layer is returning single objects or IEnumerable. Our reports (quite complex) need to display value-type properties of the object, and its related objects. Typical case would be, from a List, display a master report with category data, then a subreport with data for each Product inside each Category, then a subreport for each Part of each Product, and so on. Reporting from the database is not an option for us. We have tried so far - Reporting Services : works but have to mess around with the XML definition of the report to define the datasource classes, very hard to work with if you use an object datasource, architecturally not too clean - Telerik Reports : quite nice (esp., nice architecture) but seems to have problems with complex reports (master/sub), does not give great paging control, rumored to have performance/crash problems (immature product). Does anyone know a good reporting solution that can be integrated in an ASP.NET application and works well with objects as datasources ?

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• MSSQL choosing row (from group) with max value

  - by sriehl

  I have a large database and am putting together a report of the data. I have aggregated and summed the data from many tables to get two tables that look like the following. id | code | value id | code | value 13 | AA | 0.5 13 | AC | 2.0 13 | AB | 1.0 14 | AB | 1.5 14 | AA | 2.0 13 | AA | 0.5 15 | AB | 0.5 15 | AB | 3.0 15 | AD | 1.5 15 | AA | 1.0 I need to get a list of id's, with the code (sumed from both tables) with the largest value. 13 | AC 14 | AA 15 | AB There are 4-6 thousand records and it is not possible to change the original tables. I'm not too worried about performance as I only need to run it a few times a year.

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• Database EAV model, record listing as per search

  - by Shyam Sunder Verma

  I am building a dynamic application. I have three tables : ( EAV model style) 1: Items ( ItemId, ItemName) 2: Fields (FieldId, FieldName) 3: Field Values ( ItemID, FieldId, Value) Can you tell me how to write SINGLE query to get starting 20 records from ALL items where FieldId=4 is equal to TRUE. Expected Result : Columns = ItemID | Name | Field1 | Field2 | Field3 Each Row= ItemId | ItemName| Value1 | Value2 | Value3 Important concerns : 1: Number of fields per item are not known 2: I need one to write ONE query. 3: Query will be running on 100K records, so performance is concern. 4: I am using MySQL 5.0, so need solution for MYSQL Should I denormalize the tables if above query is not possible at all ? Any advice ?

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