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  • mysql statement with nested SELECT - how to improve performance

    - by ernie
    This statement appears inefficient because only one one out of 10 records are selected and only 1 of 100 entries contain comments. What can I do to improve it ? $query = "SELECT A,B,C, (SELECT COUNT(*) FROM comments WHERE comments.nid = header_file.nid) as my_comment_count FROM header_file Where A = 'admin' " edit: I want header records even if no comments are found.

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  • Javascript fine grain performance tweaking

    - by thermal7
    I have been writing my first jQuery plugin and struggling to find a means to time how long different pieces of code take to run. I can use firebug and console.time/profile. However, it seems that because my code executes so fast I get no results with profile and with time it spits out 0ms. (http://stackoverflow.com/questions/2690697/firebug-profiling-issue-no-activity-to-profile/2690846#2690846) Is there a way to get the time at a greater level of detail that milliseconds in javascript?

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  • Delphi Performance: Case Versus If

    - by Andreas Rejbrand
    I guess there might be some overlapping with previous SO questions, but I could not find a Delphi-specific question on this topic. Suppose that you want to check if an unsigned 32-bit integer variable "MyAction" is equal to any of the constants ACTION1, ACTION2, ... ACTIONn, where n is - say 1000. I guess that, besides being more elegant, case MyAction of ACTION1: {code}; ACTION2: {code}; ... ACTIONn: {code}; end; if much faster than if MyAction = ACTION1 then // code else if MyAction = ACTION2 then // code ... else if MyAction = ACTIONn then // code; I guess that the if variant takes time O(n) to complete (i.e. to find the right action) if the right action ACTIONi has a high value of i, whereas the case variant takes a lot less time (O(1)?). Am I correct that switch is much faster? Am I correct that the time required to find the right action in the switch case actually is independent of n? I.e. is it true that it does not really take any longer to check a million cases than to check 10 cases? How, exactly, does this work?

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  • HTTPS request to a specific load-balanced virtual host (using Shibboleth for SSO)?

    - by Gary S. Weaver
    In one environment, we have three servers load balanced that have a single Tomcat instance on each, fronted by two different Apache virtual hosts. Each of those two virtual hosts (served by all three servers) has its own different load balancer. Internally, the first host (we'll call it barfoo) is served by port 443 (HTTPS) with its cert and the second host (we'll call it foobar) is served by port 1443 (HTTPS). When you hit foobar, it goes to the load balancer which is using IP affinity for that host, so you can easily test login/HTTPS on one of the servers serving foobar, but not the others (because you keep getting that server for the lifetime of the LB session, iirc). In addition, each of the servers are using Shibboleth v2 for authN/SSO, using mod_shib (iirc). So, a normal request to foobar hits the LB, is directed to the 3rd server (and will do that from then on for as long as the LB session lasts), then Apache, then to the Shibboleth SP which looks at the request, makes you login via negotiation with the Shibboleth IdP, then you hit Apache again which in turn hits Tomcat, renders, and returns the response. (I'm leaving out some steps there.) We'd like to hit one of the individual servers (foobar-03.acme.org which we'll say has IP 1.2.3.4) via HTTPS (skipping the load balancer), so we at first try putting this in /etc/hosts: 1.2.3.4 foobar.acme.org But since foobar.acme.org is a secondary virtual host running on 1443, it attempts to get barfoo.acme.org rather than foobar.acme.org at port 1443 and see that the cert for barfoo.acme.org is invalid for this case since it doesn't match the request's host, foobar.acme.org. I thought an ssh tunnel might be easy enough, so I tried: ssh -L 7777:foobar-03.acme.org:1443 [email protected] I tried just hitting https://localhost:7777/webappname in a browser, but when the Shibboleth login is over, it again tries to redirect to barfoo.acme.org, which is the default host for 443, and we get into an infinite redirect loop. I then tried setting up an SSH tunnel with privileged port 443 locally going to 443 of foobar-03.acme.org as the hostname for that virtual host: sudo ssh -L 443:foobar-03.acme.org:1443 [email protected] I also edited /etc/hosts to add: 127.0.0.1 foobar.acme.org This finally worked and I was able to get the browser to hit the individual HTTPS host at https://foobar.acme.org/webappname, bypassing the load balancer. This was a bit of a pain and wouldn't work for everyone, due to the requirement to use the local 443 port and ssh to the server. Is there an easier way to browse to and log into an individual host in this case?

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  • Checking server load with PHP and taking appropriate action

    - by teehoo
    Hi, I'm creating a project in which a server receives operations from clients to apply to a local server document. The server and client both share the same document and therefore each message the client sends contains an MD5 hash, which the server compares to after generating its own hash to ensure the server and client documents are synchronized. My question is, if the server is overloaded, could I somehow detect this in PHP, which would in turn let me decide whether I want to execute the hash generation function or not? Perhaps in the scenario defined, this is not a perfect use-case, but I'm interested in this approach in general.

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  • Cassandra performance slow down with counter column

    - by tubcvt
    I have a cluster (4 node ) and a node have 16 core and 24 gb ram: 192.168.23.114 datacenter1 rack1 Up Normal 44.48 GB 25.00% 192.168.23.115 datacenter1 rack1 Up Normal 44.51 GB 25.00% 192.168.23.116 datacenter1 rack1 Up Normal 44.51 GB 25.00% 192.168.23.117 datacenter1 rack1 Up Normal 44.51 GB 25.00% We use about 10 column family (counter column) to make some system statistic report. Problem on here is that When i set replication_factor of this keyspace from 1 to 2 (contain 10 counter column family ), all cpu of node increase from 10% ( when use replication factor=1) to --- 90%. :( :( who can help me work around that :( . why counter column consume too much cpu time :(. thanks all

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  • How to test my GAE site for performance

    - by Sergey Basharov
    I am building a GAE site that uses AJAX/JSON for almost all its tasks including building the UI elements, all interactions and client-server requests. What is a good way to test it for highloads so that I could have some statistics about how much resources 1000 average users per some period of time would take. I think I can create some Python functions for this purpose. What can you advise? Thanks.

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  • How significant are JPA lazy loading performance benefits?

    - by Robert
    I understand that this is highly specific to the concrete application, but I'm just wondering what's the general opinion, or at least some personal experiences on the issue. I have an aversion towards the 'open session in view' pattern, so to avoid it, I'm thinking about simply fetching everything small eagerly, and using queries in the service layer to fetch larger stuff. Has anyone used this and regretted it? And is there maybe some elegant solution to lazy loading in the view layer that I'm not aware of?

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  • What performance overhead do IoC containers involve?

    - by Sosh
    Hi, Loose coupling is wonderful of course, but I have often wondered what overhead wiring up dynamically using an IoC container (for example Castle Windsor) has over a tightly coupled system? I know that a detailed answer would depend on what the IoC was being used for, but I'm really just trying to get a feel for the magnitude of effort involved in the IoC work. Does anyone have any stats or other resources regarding this? Thanks

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  • Java Collection performance question

    - by Shervin
    I have created a method that takes two Collection<String> as input and copies one to the other. However, I am not sure if I should check if the collections contain the same elements before I start copying, or if I should just copy regardless. This is the method: /** * Copies from one collection to the other. Does not allow empty string. * Removes duplicates. * Clears the too Collection first * @param target * @param dest */ public static void copyStringCollectionAndRemoveDuplicates(Collection<String> target, Collection<String> dest) { if(target == null || dest == null) return; //Is this faster to do? Or should I just comment this block out if(target.containsAll(dest)) return; dest.clear(); Set<String> uniqueSet = new LinkedHashSet<String>(target.size()); for(String f : target) if(!"".equals(f)) uniqueSet.add(f); dest.addAll(uniqueSet); } Maybe it is faster to just remove the if(target.containsAll(dest)) return; Because this method will iterate over the entire collection anyways.

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  • Performance of C# method polymorphism with generics

    - by zildjohn01
    I noticed in C#, unlike C++, you can combine virtual and generic methods. For example: using System.Diagnostics; class Base { public virtual void Concrete() {Debug.WriteLine("base concrete");} public virtual void Generic<T>() {Debug.WriteLine("base generic");} } class Derived : Base { public override void Concrete() {Debug.WriteLine("derived concrete");} public override void Generic<T>() {Debug.WriteLine("derived generic");} } class App { static void Main() { Base x = new Derived(); x.Concrete(); x.Generic<PerformanceCounter>(); } } Given that any number of versions of Generic<T> could be instantiated, it doesn't look like the standard vtbl approach could be used to resolve method calls, and in fact it's not. Here's the generated code: x.Concrete(); mov ecx,dword ptr [ebp-8] mov eax,dword ptr [ecx] call dword ptr [eax+38h] x.Generic<PerformanceCounter>(); push 989A38h mov ecx,dword ptr [ebp-8] mov edx,989914h call 76A874F1 mov dword ptr [ebp-4],eax mov ecx,dword ptr [ebp-8] call dword ptr [ebp-4] The extra code appears to be looking up a dynamic vtbl according to the generic parameters, and then calling into it. Has anyone written about the specifics of this implementation? How well does it perform compared to the non-generic case?

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  • Performance Problem with Clojure Array

    - by dbyrne
    This piece of code is very slow. Execution from the slime-repl on my netbook takes a couple minutes. Am I doing something wrong? (def test-array (make-array Integer/TYPE 400 400 3)) (doseq [x (range 400), y (range 400), z (range 3)] (aset test-array x y z 0))

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  • Predicting performance for an iPhone/iPod Touch App

    - by Avizz
    I don't have an iPhone Developer Program Account yet and will be getting one in the next couple of days. Can instruments be used with the simulator to give a rough estimate on how well my app may perform? Using instruments I checked and fixed all the leaks it was detecting, and it appears that my memory usage maxes out at about 5.77mb. Is there any other tests I could perform with instruments to judge how well my app would perform? I realize there is no way other then the actual device to get a definite answer, it would be nice to get an estimate.

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  • Visual Studio 2008 awful performance

    - by Nima
    Hi, I have ported a piece of C++ code, that works out of core, from Linux(Ubuntu) to Windows(Vista) and I realized that it works about 50times slower on VS2008! I removed all the out of core parts and now I just have a piece of code that has nothing to do with the hard disk. I set compiler parameters to O2 in Project Properties but still get about 10times slower than g++ in linux! Does anybody have an idea why it is this much slower under VS? I really appreciate any kind of hint! Thanks,

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  • Performance with timestamp conditions

    - by Tim Whitlock
    Which of the following is faster, or are they equivalent? (grabbing recent most records from a TIMESTAMP COLUMN) SELECT UNIX_TIMESTAMP(`modified`) stamp FROM `some_table` HAVING stamp > 127068799 ORDER BY stamp DESC or SELECT UNIX_TIMESTAMP(`modified`) stamp FROM `some_table` WHERE UNIX_TIMESTAMP(`modified`) > 127068799 ORDER BY `modified` DESC or even another combination?

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  • weird performance in C++ (VC 2010)

    - by raicuandi
    Hello, I have this loop written in C++, that compiled with MSVC2010 takes a long time to run. (300ms) for (int i=0; i<h; i++) { for (int j=0; j<w; j++) { if (buf[i*w+j] > 0) { const int sy = max(0, i - hr); const int ey = min(h, i + hr + 1); const int sx = max(0, j - hr); const int ex = min(w, j + hr + 1); float val = 0; for (int k=sy; k < ey; k++) { for (int m=sx; m < ex; m++) { val += original[k*w + m] * ds[k - i + hr][m - j + hr]; } } heat_map[i*w + j] = val; } } } It seemed a bit strange to me, so I did some tests then changed a few bits to inline assembly: (specifically, the code that sums "val") for (int i=0; i<h; i++) { for (int j=0; j<w; j++) { if (buf[i*w+j] > 0) { const int sy = max(0, i - hr); const int ey = min(h, i + hr + 1); const int sx = max(0, j - hr); const int ex = min(w, j + hr + 1); __asm { fldz } for (int k=sy; k < ey; k++) { for (int m=sx; m < ex; m++) { float val = original[k*w + m] * ds[k - i + hr][m - j + hr]; __asm { fld val fadd } } } float val1; __asm { fstp val1 } heat_map[i*w + j] = val1; } } } Now it runs in half the time, 150ms. It does exactly the same thing, but why is it twice as quick? In both cases it was run in Release mode with optimizations on. Am I doing anything wrong in my original C++ code?

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  • Usual hibernate performance pitfall

    - by Antoine Claval
    Hi, We have just finish to profile our application. ( she's begin to be slow ). the problem seems to be "in hibernate". It's a legacy mapping. Who work's, and do it's job. The relational shema behind is ok too. But some request are slow as hell. So, we would appreciate any input on common and usual mistake made with hibernate who end up with slow response. Exemple : Eager in place of Lazy can change dramaticly the response time....

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  • Improve SQL Server 2005 Query Performance

    - by user366810
    I have a course search engine and when I try to do a search, it takes too long to show search results. You can try to do a search here http://76.12.87.164/cpd/testperformance.cfm At that page you can also see the database tables and indexes, if any. I'm not using Stored Procedures - the queries are inline using Coldfusion. I think I need to create some indexes but I'm not sure what kind (clustered, non-clustered) and on what columns. Thanks

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  • How do I load PersistentDocuments into the same window

    - by Brad Stone
    I want to open NSPersistentDocuments and load them into the same window one at a time. I'm almost there but missing some steps. Hopefully someone can help me. I have a few saved documents on the hard drive. On launch my app opens to an untitled NSPersistentDocument and creates a separate NSWindowController. When I press the button to load file 1 off the hard drive the data appears in the fields but two things are wrong that I can see: 1) changing the data doesn't make the document dirty 2) choosing save updates the persistentstore (I know this because when I open the file again I see the changes) but I get an error: +entityForName: could not locate an NSManagedObjectModel for entity name 'Book' Here's my code which is in the WindowController that was launched initially with the untitled document. This code isn't perfect. For example, I know I should processPendingChanges and save the current doc before I load the new one. This is test code to try to get over this hurdle. - (IBAction)newBookTwo:(id)sender { NSDocumentController *dc = [NSDocumentController sharedDocumentController]; NSURL *url = [NSURL fileURLWithPath:[@"~/Desktop/File 2.binary" stringByExpandingTildeInPath]]; NSError *error; MainWindowDocument *thisDoc = [dc openDocumentWithContentsOfURL:url display:NO error:&error]; [self setDocument:thisDoc]; [self setManagedObjectContext:[thisDoc managedObjectContext]]; } Thanks!

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  • Indirect load of type fails in PowerShell

    - by Dan
    When invoking [System.Configuration.ConfigurationManager]::GetSection("MySection") from within a PowerShell prompt, it throws an exception because the assembly containing the type represented by "MySection" in the app config is unable to be loaded. However, I have previously loaded the assembly containing that type, and I am even able to instantiate the type directly using 'new-object'. How is the ConfigurationManager resolving types such that the assemblies already loaded into the PowerShell app domain are not visible to it?

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  • Java: Calculate distance between a large number of locations and performance

    - by Ally
    I'm creating an application that will tell a user how far away a large number of points are from their current position. Each point has a longitude and latitude. I've read over this article http://www.movable-type.co.uk/scripts/latlong.html and seen this post http://stackoverflow.com/questions/837872/calculate-distance-in-meters-when-you-know-longitude-and-latitude-in-java There are a number of calculations (50-200) that need carried about. If speed is more important than the accuracy of these calculations, which one is best?

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