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• How to profile object creation in Java?

  - by gooli

  The system I work with is creating a whole lot of objects and garbage collecting them all the time which results in a very steeply jagged graph of heap consumption. I would like to know which objects are being generated to tune the code, but I can't figure out a way to dump the heap at the moment the garbage collection starts. When I tried to initiate dumpHeap via JConsole manually at random times, I always got results after GC finished its run, and didn't get any useful data. Any notes on how to track down excessive temporary object creation are welcome.

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• MongoDB efficient dealing with embedded documents

  - by Sebastian Nowak

  I have serious trouble finding anything useful in Mongo documentation about dealing with embedded documents. Let's say I have a following schema: { _id: ObjectId, ... data: [ { _childId: ObjectId // let's use custom name so we can distinguish them ... } ] } What's the most efficient way to remove everything inside data for particular _id? What's the most efficient way to remove embedded document with particular _childId inside given _id? What's the performance here, can _childId be indexed in order to achieve logarithmic (or similar) complexity instead of linear lookup? If so, how? What's the most efficient way to insert a lot of (let's say a 1000) documents into data for given _id? And like above, can we get O(n log n) or similar complexity with proper indexing? What's the most efficient way to get the count of documents inside data for given _id?

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• In .NET which loop runs faster for or foreach

  - by Binoj Antony

  In c#/VB.NET/.NET which loop runs faster for or foreach? Ever since I read that for loop works faster than foreach a long time ago I assumed it stood true for all collections, generic collection all arrays etc. I scoured google and found few articles but most of them are inconclusive (read comments on the articles) and open ended. What would be ideal is to have each scenarios listed and the best solution for the same e.g: (just example of how it should be) for iterating an array of 1000+ strings - for is better than foreach for iterating over IList (non generic) strings - foreach is better than for Few references found on the web for the same: Original grand old article by Emmanuel Schanzer CodeProject FOREACH Vs. FOR Blog - To foreach or not to foreach that is the question asp.net forum - NET 1.1 C# for vs foreach [Edit] Apart from the readability aspect of it I am really interested in facts and figures, there are applications where the last mile of performance optimization squeezed do matter.

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• in java, which is better - three arrays of booleans or 1 array of bytes?

  - by joe_shmoe

  I know the question sounds silly, but consider this: I have an array of items and a labelling algorithm. at any point the item is in one of three states. The current version holds these states in a byte array, where 0, 1 and 2 represent the three states. alternatively, I could have three arrays of boolean - one for each state. which is better (consumes less memory) depends on how jvm (sun's version) stores the arrays - is a boolean represented by 1 bit? (p.s. don't start with all that "this is not the way OO/Java works" - I know, but here performance comes in front. plus the algorithm is simple and perfectly readable even in such form). Thanks a lot

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• Scalable way of doing self join with many to many table

  - by johnathan

  I have a table structure like the following: user id name profile_stat id name profile_stat_value id name user_profile user_id profile_stat_id profile_stat_value_id My question is: How do I evaluate a query where I want to find all users with profile_stat_id and profile_stat_value_id for many stats? I've tried doing an inner self join, but that quickly gets crazy when searching for many stats. I've also tried doing a count on the actual user_profile table, and that's much better, but still slow. Is there some magic I'm missing? I have about 10 million rows in the user_profile table and want the query to take no longer than a few seconds. Is that possible?

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• Why do a small amount of add/deletes take several seconds in EF4?

  - by TomWij

  Using the Entity Framework 4. I have created a Code First database in the past and a piece of code needs to delete and add 16 objects, this takes 6 seconds each. That's 300+ ms for each query! The deletes/adds occur in a foreach scope and there is a SaveChanges() outside the foreach. In the above image you see that each takes 6 seconds, which is 34% of the time, for 16 calls. That doesn't sound normal to me... Why is this and how can I improve the performance? If there is no solution: Are there any workarounds I can use? It would be a pain to rewrite my project...

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• How to set up a load/stress test for a web site?

  - by Ryan

  I've been tasked with stress/load testing our company web site out of the blue and know nothing about doing so. Every search I make on google for "how to load test a web site" just comes back with various companies and software to physically do the load testing. For now I'm more interested in how to actually go about setting up a load test like what I should take into account prior to load testing, what pages within my site I should be testing load against and what things I'm going to want to monitor when doing the test. Our web site is on a multi-tier system complete with a separate database server (IIS 7 Web Server, SQL Server 2000 db). I imagine I'd want to monitor both the web server and the database server for testing load however when setting up scenarios to load test the web server I'd have to use pages that query the database to see any load on the database server at the same time. Are web servers and database servers generally tested simultaneously or are they done as separate tests? As you can see I'm pretty clueless as to the whole operation so any incite as to how to go about this would be very helpful. FYI I have been tinkering with Pylot and was able to create and run a scenario against our site but I'm not sure what I should be looking for in the results or if the scenario I created is even a scenario worth measuring for our site. Thanks in advance.

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• java increase xmx dynamically at runtime

  - by Tomer

  Hi, I have a jvm server in my machine, now I want to have 2 apservers of mine sitting in same machine, however I want the standby one to have a really low amount of memory allocated with xmx because its passive, one the main server (active) goes down I want to allocate more memory to my passive server which is already up without restarting it (I have have them both having too much xmx - note they would consume memory at startup and I cant allow possibility of outOfMemory). So I want passive - low xmx once active goes down I want my passive to receive much more xmx. is there a way for me to achieve that. Thanks

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• Minimizing Java Thread Context Switching Overhead

  - by binil

  I have a Java application running on Sun 1.6 32-bit VM/Solaris 10 (x86)/Nahelem 8-core(2 threads per core). A specific usecase in the application is to respond to some external message. In my performance test environment, when I prepare and send the response in the same thread that receives the external input, I get about 50 us advantage than when I hand off the message to a separate thread to send the response. I use a ThreadPoolExecutor with a SynchronousQueue to do the handoff. In your experience what is the acceptable delay between scheduling a task to a thread pool and it getting picked up for execution? What ideas had worked for you in the past to try improve this?

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• Use of private constructor to prevent instantiation of class?

  - by cringe

  Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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• Multiple calculations on the same set of data: ruby or database?

  - by Pierre

  Hi, I have a model Transaction for which I need to display the results of many calculations on many fields for a subset of transactions. I've seen 2 ways to do it, but am not sure which is the best. I'm after the one that will have the least impact in terms of performance when data set grows and number of concurrent users increases. data[:total_before] = Transaction.where(xxx).sum(:amount_before) data[:total_after] = Transaction.where(xxx).sum(:amount_after) ... or transactions = Transaction.where(xxx) data[:total_before]= transactions.inject(0) {|s, e| s + e.amount_before } data[:total_after]= transactions.inject(0) {|s, e| s + e.amount_after } ... Which one should I choose? (or is there a 3rd, better way?) Thanks, P.

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• Is memcached a dinosaur in comparison to Redis?

  - by Industrial

  Hi everyone, I have worked quite a bit with memcached the last weeks and just found out about Redis. When I read this part of their readme, I suddenly got a warm, cozy feeling in my stomach: Redis can be used as a memcached on steroids because is as fast as memcached but with a number of features more. Like memcached, Redis also supports setting timeouts to keys so that this key will be automatically removed when a given amount of time passes. This sounds amazing. I'd also found this page with benchmarks: http://www.ruturaj.net/redis-memcached-tokyo-tyrant-mysql-comparison So, honestly - Is memcache really that old dinousaur that is a bad choice from a performance perspective when compared to this newcomer called Redis? I haven't heard lot about Redis previously, thereby the approach for my question!

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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• MySQL: Efficient Blobbing?

  - by feklee

  I'm dealing with blobs of up to - I estimate - about 100 kilo bytes in size. The data is compressed already. Storage engine: InnoDB on MySQL 5.1 Frontend: PHP (Symfony with Propel ORM) Some questions: I've read somewhere that it's not good to update blobs, because it leads to reallocation, fragmentation, and thus bad performance. Is that true? Any reference on this? Initially the blobs get constructed by appending data chunks. Each chunk is up to 16 kilo bytes in size. Is it more efficient to use a separate chunk table instead, for example with fields as below? parent_id, position, chunk Then, to get the entire blob, one would do something like: SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE parent_id = 187 The result would be used in a PHP script. Is there any difference between the types of blobs, aside from the size needed for meta data, which should be negligible.

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• CoreData and many NSArrayController

  - by unixo

  In my CoreData Application, I've an outline view on left of main window, acting as source list (like iTunes); on the right I display a proper view, based on outline selection. Each view has its components, such as table view, connected to array controller, owned by the specific view. Very often different views display same data, for example, a table view of the same entity. From a performance point of view, is better to have a single array controller per entity and share it between all views or does CoreData cache avoid memory waste?

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• How can I intercept a Tomcat request at socket level?

  - by Miguel Pardal

  Hi, I'm doing a performance study for a web application framework running on Apache Tomcat 6. I'm trying to measure the time overhead of handling HTTP requests. What I would like to do is: / // just before first request byte is read long t1 = System.nanoTime(); // request is processed... // just after final byte is written to response long t2 = System.nanoTime(); / Then I would compute the total time (t2 - t1). Is there a way to do this? Thanks for your help!

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• Adding more namespace in the code file affects performace ?

  - by Harikrishna

  If we imports more namespace in the code file(cs file) then it affects on perfomance ? Like we should add namespace in the cs file as needed. That is adding more namespace in the cs file affects performance ? Like using System; using System.Data.Sql; using System.Collections.Generic; using System.Data; using System.IO; using System.Linq; using System.Text.RegularExpressions; using System.Windows.Forms; using System.Xml; using System.Data.SqlClient; using System.ComponentModel;

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• Django: How/Where to store a value for a session without unnecessary DB hits

  - by GerardJP

  Hi all, I have an extended userprofile with AUTH_PROFILE_MODULE (ref: http://tinyurl.com/yhracqq) I would like to set a user.is_guru() method similar to user.is_active(). This would results for al views (or rather templates) to e.g. disable/enable certain user messages, displaying of widgets, etc. The boolean is stored in the extended user profile model, but I want to avoid hitting the DB for every view. So the questions is .. Do I use a context_processor, a template tag, session_dict or what have you to, possible cached, store this info for the duration of the users visit. Note: I dont have performance issues, so it's definitely filed under premature optimization. I just want to avoid generating extra work in the future :). Any pointers are very welcome. Thanx and greetz! Gerard.

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• What is the fastest way to compare 2 rows in SQL?

  - by Swoosh

  I have 2 different databases. Upon changing something in the big one (i don't have access to), i get some rows imported in my databases in a similar HUGE table. I have a job checking for records in this table, and if any, execute a stored procedure, process and delete from table. Performance. (Huge amount of data) I would like to know what is the fastest way to know if something has changed using let's say 2 imported rows with 100 columns each. Don't have FK-s, don't need. Chances are, that even though I have records in my table, nothing has actually changed. Also. Let's say there is actually changed something. Is it possible for example to check only for changes inside datetime columns? Thanks

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• How taxing would a game map grid be to a web browser?

  - by Vilx-

  Suppose we're making a strategy game (think Civilization) in a web browser. The game has a visible map portion - say 30x30 squares. Each square is 30x30px and has several overlaid images - the terrain, resources, units, roads, etc. The classical way of drawing this would be with a huge <table> where each cell would contain absolutely positioned images. It would probably be rendered in Javascript to reduce traffic. But it's still several thousand images and a huge table. Can the browser take it? Will the performance not drop below any acceptable limits? Alternatively I could keep a pre-rendered map image with as many overlays as possible, but that would be more work, I think.

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• How is fseek() implemented in the filesystem?

  - by pajton

  This is not a pure programming question, however it impacts the performance of programs using fseek(), hence it is important to know how it works. A little disclaimer so that it doesn't get closed. I am wondering how efficient it is to insert data in the middle of the file. Supposing I have a file with 1MB data and then I insert something at the 512KB offset. How efficient would that be compared to appending my data at the end of the file? Just to make the example complete lets say I want to insert 16KB of data. I understand the answer varies depending on the filesystem, however I assume that the techniques used in common filesystems are quite similar and I just want to get the right notion of it.

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• JQuery Optimization: Is there any way to speed up the rendering of the FlexSelect control?

  - by Sephrial

  Greetings, I am new to jQuery, and I have a performance problem with the FlexSelect control where it takes about 5 seconds to render the dropdown control (in the renderDropdown() function). The dropdown list contains about 5000 element. I believe all the runtime is attributed to the following block of code: var list = this.dropdownList.html(""); $.each(this.results, function() { list.append($("<li/>").html(this.name)); }); Question: Are there any alternatives that would build this list of elements in a more inefficient manner?

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• Improving WPF memory usage

  - by Krishna

  Hello developers Is there any way you can store the UI state to disk when a WPF form has been minimised. I have a complex GUI with few Tab Controls and it consumes quite a bit of memory which is kept allocated when the application is not active. I was hoping one of you may have got this working along the lines (or similar) Application Active User does work, plays with UI - enters some information in the text boxes and moves around the tabs User minimises the form to work with other applications On Minimise, Save the current state to the disk and dispose the root tabcontrol On Activiate, build the root tabcontrol from the disk and add to the controls collection Before I divein to do this, I thought it will help me if I ask this question here. Please let me know your thoughts

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• NoSQL for concurrent reads/writes

  - by Mickael Marrache

  After getting some performance issues for an application using a MySQL database, I'm thinking of using NoSQL solutions. My architecture is as follows: One application receives messages from the network at a high throughput (i.e. 50000 messages/sec). Each message is stored in the DB, so it's important for the write rate to be as fast as the arrival rate. Then, I also have some PHP pages that accesses the DB to get the data stored by the other application. It's important for me that the retrieved data is as relevant as possible (i.e. not old data, let's say not more than 5 seconds old). Also, the data is not critical, so I don't need any security mechanism to avoid losing the data. I see there are a lot of NoSQL solutions, but I don't know if they are all relevant. Could you please provide me some directions. Thanks

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• How do I ensure GUI responsiveness when using OpenCL on the display GPU?

  - by pauldoo

  In my relatively short time learning OpenCL I frequently see my application cause the operating system UI to become significantly less responsive (several seconds for a window to respond to a drag for example). I have encountered this problem on Windows Vista and Mac OS X both with NVidia GPUs. What can I do when using OpenCL on the same GPU as the display to ensure that my application does not significantly degrade the UI responsiveness like this? Also, can this be done without taking needless performance losses within my application? (Ie, if the user is not doing some UI intensive task then I would not expect my application to run any slower than it does now.) I understand that any answers will be very platform specific (where platform includes OS/GPU/driver combo).

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