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  • Using IF in T-SQL weakens or breaks execution plan caching?

    - by AnthonyWJones
    It has been suggest to me that the use of IF statements in t-SQL batches is detrimental to performance. I'm trying to find some confirmation of this assertion. I'm using SQL Server 2005 and 2008. The assertion is that with the following batch:- IF @parameter = 0 BEGIN SELECT ... something END ELSE BEGIN SELECT ... something else END SQL Server cannot re-use the execution plan generated because the next execution may need a different branch. This implies that SQL Server will eliminate one branch entirely from execution plan on the basis that for the current execution it can already determine which branch is needed. Is this really true? In addition what happens in this case:- IF EXISTS (SELECT ....) BEGIN SELECT ... something END ELSE BEGIN SELECT ... something else END where it's not possible to determine in advance which branch will be executed?

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  • Search and highlight - Client vs. Server side?

    - by OneDeveloper
    Hi everyone, I have an MVC web application that shows ~ 2000 lines "divs", and I want to make the user able to search and highlight the keywords. I tried using jQuery plugins for this but the performance was really bad and IE got almost hung! So, I was wondering if this is the best way to do it? and If am not getting a faster version I'd rather do it on the server "AJAX call" and re-render the whole lines again - this way at least the user won't feel the browser is getting hung! Any recommendations? Thanks!

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  • Google App Engine - Dealing with concurrency issues of storing an object

    - by Spines
    My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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  • Entity data field validation and part data submission

    - by pradeeptp
    I have an entity class that has 10 fields. I am using MS Validation Application block to mark all fields as mandatory (IsRequired). I am implementing a securiy feature in which during updation of the data, not all the fields in the entity class will have data. For example a few users can only view 5 fileds while others all 10 fields during updation on GUI I have the following options 1) Bring all the data for all the fields from the DB table and hide the ones not accessible to the users in GUI. I am concerned about the performance because everytime GUI will pull unncessary data. 2) Bring the data (e.g. only 5 fields) that are permissible for access/view by the user on GUI. During submit, validation block will throw exception because all fields are marked as IsRequired and only data for 5 fields are sent back to the server. I want to know if there are any other good approaches to solve problems like this. I am using .NET 3.5 Thanks.

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  • How bad is opening and closing a SQL connection for several times? What is the exact effect?

    - by Eren
    For example, I need to fill lots of DataTables with SQLDataAdapter's Fill() method: DataAdapter1.Fill(DataTable1); DataAdapter2.Fill(DataTable2); DataAdapter3.Fill(DataTable3); DataAdapter4.Fill(DataTable4); DataAdapter5.Fill(DataTable5); .... .... Even all the dataadapter objects use the same SQLConnection, each Fill method will open and close the connection unless the connection state is already open before the method call. What I want to know is how does unnecessarily opening and closing SQLConnections affect the performance of the application. How much does it need to scale to see the bad effects of this problem (100,000s of concurrent users?). In a mid-size website (daily 50000 users) does it worth bothering and searching for all the Fill() calls, keeping them together in the code and opening the connection before any Fill() call and closing afterwards?

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  • Rails/mysql SUM distinct records - optimization

    - by pepernik
    Hey. How would you optimize this SQL SELECT SUM(tmp.cost) FROM ( SELECT DISTINCT clients.id as client, countries.credits_cost AS cost FROM countries INNER JOIN clients ON clients.country_id = countries.id INNER JOIN clients_groups ON clients_groups.client_id=clients.id WHERE clients_groups.group_id IN (1,2,3,4,5,6,7,8,9) GROUP BY clients.id ) AS tmp; I'm using this example as part of my Ruby on Rails project. Note that my nested SQL (tmp) can have more then 10 milion records. You can split that in more SQLs if the performance is better. Should I add any indexes to make it quicker (i have it on IDs)?

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  • Count of memory copies in *nix systems between packet at NIC and user application?

    - by Michael_73
    Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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  • GCC problem with raw double type comparisons

    - by Monomer
    I have the following bit of code, however when compiling it with GCC 4.4 with various optimization flags I get some unexpected results when its run. #include <iostream> int main() { const unsigned int cnt = 10; double lst[cnt] = { 0.0 }; const double v[4] = { 131.313, 737.373, 979.797, 731.137 }; for(unsigned int i = 0; i < cnt; ++i) { lst[i] = v[i % 4] * i; } for(unsigned int i = 0; i < cnt; ++i) { double d = v[i % 4] * i; if(lst[i] != d) { std::cout << "error @ : " << i << std::endl; return 1; } } return 0; } when compiled with: "g++ -pedantic -Wall -Werror -O1 -o test test.cpp" I get the following output: "error @ : 3" when compiled with: "g++ -pedantic -Wall -Werror -O2 -o test test.cpp" I get the following output: "error @ : 3" when compiled with: "g++ -pedantic -Wall -Werror -O3 -o test test.cpp" I get no errors when compiled with: "g++ -pedantic -Wall -Werror -o test test.cpp" I get no errors I do not believe this to be an issue related to rounding, or epsilon difference in the comparison. I've tried this with Intel v10 and MSVC 9.0 and they all seem to work as expected. I believe this should be nothing more than a bitwise compare. If I replace the if-statement with the following: if (static_cast<long long int>(lst[i]) != static_cast<long long int>(d)), and add "-Wno-long-long" I get no errors in any of the optimization modes when run. If I add std::cout << d << std::endl; before the "return 1", I get no errors in any of the optimization modes when run. Is this a bug in my code, or is there something wrong with GCC and the way it handles the double type?

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  • Validating Column Data Stored as CSV Against Another Table

    - by Jakkwylde
    I wanted to see what some suggested approaches would be to validate a field that is stored as a CSV against a table containing appropriate values. Althought it would be desired, it is NOT an option to split the CSV list into another related table. In the example data below I would be trying to capture the code 99 for widget A. Below is an example data representation. Table: Widgets WidgetName WidgetCodeList A 1, 2, 3 B 1 C 2, 3 D 99 Table: WidgetCodes WidgetCode 1 2 3 An earlier approach was to query the CSV column as rows using various string manipulations and CONNECT_BY_LEVEL however the performance was not acceptible.

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  • BDD-testing using a UI driver (e.g. Selenium for a web-application)

    - by jonathanconway
    Can BDD (Behavior Driven Design) tests be implemented using a UI driver? For example, given a web application, instead of: Writing tests for the back-end, and then more tests in Javascript for the front-end Should I: Write the tests as Selenium macros, which simulate mouse-clicks, etc in the actual browser? The advantages I see in doing it this way are: The tests are written in one language, rather than several They're focussed on the UI, which gets developers thinking outside-in They run in the real execution environment (the browser), which allows us to Test different browsers Test different servers Get insight into real-world performance Thoughts?

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  • NSMutableSet addObject question

    - by Jacob Relkin
    I've got a class that wraps around an NSMutableSet object, and I have an instance method that adds objects (using the addObject: method) to the NSMutableSet. This works well, but I'm smelling a performance hitch because inside the method i'm explicitly calling containsObject: before adding the object to the set. Three part question: Do I need to be calling containsObject: before I add an object to the set? If so, then what actual method should I be using, containsObject or containsObjectIdenticalTo:? If that is not so, what contains method gets invoked under the hood of addObject:? This is important to me because if I pass an object to containsObject: it would return true, but if I pass it to containsObjectIdenticalTo: it would return false.

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  • POS Desktop Application using DB or Localfiles ? using WPF

    - by Panindra
    I am planning to build a POS Application for my shop. I have enough knowledge to build the application using DB and also using local files( system.IO - binary files ) to store and access the data for my application. But , i have no deployment experience and confused in choosing data storing option. Database using MDF may be good option ( may ease plenty of coding ) but i don't want to have SQL server on my desktop. as i am using WPF for building , my concern is that my application may get slow due to server response and design rendering of WPF. Then i tried to use only local data (binary files) to store the data and retrive using class and objects. but this coding is taking lot of time , so in the middle of the process i struck in the dilemma of going back to Database . Please help , for performance wise whic one is better . and in Practical World ,in professional applications which one is widely using .. please give suggestions ..

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  • Should I use a hosted version of JQuery? Which one?

    - by ataylor
    Should I use a local copy of jquery, or should I link to a copy provided by Google or Microsoft? I'm primarily concerned about speed. I've heard that just pulling content from other domains can have performance advantages related to how browsers limit connections. In particular, has anyone benchmarked the speed and latency of Google vs. Microsoft vs. local? Also, do I have to agree to any conditions or licenses to link from a third-party?

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  • Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

    - by Kaleb Brasee
    I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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  • Should I use a global var or call the function every time? C++

    - by extintor
    Im using: bool GetOS(LPTSTR pszOS) { OSVERSIONINFOEX osve; BOOL bOsVersionInfoEx; ZeroMemory(&osve, sizeof(OSVERSIONINFOEX)); osve.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX); if( !(bOsVersionInfoEx = GetVersionEx ((OSVERSIONINFO *) &osve)) ) return false; TCHAR buf[80]; StringCchPrintf( buf, 80, TEXT("%u.%u.%u.%u"), osve.dwPlatformId, osve.dwMajorVersion, osve.dwMinorVersion, osve.dwBuildNumber); StringCchCat(pszOS, BUFSIZE, buf); return true; } to get the windows version, and I am planning to use pszOS every a few minutes, Should I use pszOS as a global var or call GetOS() every time? What's the best option from a performance point of view.

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  • Why are gettimeofday() intervals occasionally negative?

    - by Andres Jaan Tack
    I have an experimental library whose performance I'm trying to measure. To do this, I've written the following: struct timeval begin; gettimeofday(&begin, NULL); { // Experiment! } struct timeval end; gettimeofday(&end, NULL); // Print the time it took! std::cout << "Time: " << 100000 * (end.tv_sec - begin.tv_sec) + (end.tv_usec - begin.tv_usec) << std::endl; Occasionally, my results include negative timings, some of which are nonsensical. For instance: Time: 226762 Time: 220222 Time: 210883 Time: -688976 What's going on?

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  • What could be adding "Pragma:no-cache" to my response Headers? (Apache, PHP)

    - by Daniel Magliola
    I have a website whose maintenance I've inherited, which is a big hairy mess. One of the things i'm doing is improving performance. Among other things, I'm adding Expires headers to images. Now, there are some images that are served through a PHP file, and I notice that they do have the Expires header, but they also get loaded every time. Looking at Response Headers, I see this: Expires Wed, 15 Jun 2011 18:11:55 GMT Cache-Control no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma no-cache Which obviously explains the problem. Now, i've looked all over the code base, and it doesn't say "pragma" anywhere. .htaccess doesn't seem to have anything related either. Any ideas who could be setting those "pragma" (and "cache-control") headers, and how I can avoid it? Thanks! Daniel

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  • Best way to daemonize Java application on Linux

    - by SyBer
    Hi. While I found this question being answered here on SW several times, I didn't find a concluding answer what is the best approach. I'm not looking to use any external wrapper, as I found them launching the java process under a nice level lower then themselves which potentially lowers the performance, so it seems only the shell methods are left. I so far found 3 different shell methods: start-stop-daemon RedHat daemon init.d function nohup on start / disown after start What you people are using, and can recommend as the most reliable method? Thanks.

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  • Screen capture during testing

    - by Edwward
    This is an application for reviewing performance tests. Simple in concept, tricky to describe. Picture: 1) Recording interactions with a WPF program so the inputs can be played back. 2) Playing the inputs back while doing a continuous screen capture. 3) Capturing wall time as well as continuous CPU percentages during playback. 4) Repeating steps (2) and (3) lots of times. 5) Writing the relevant stuff out to files/db. 6) Reading it and putting it all in a fancy UI for easy review/analysis. The killer for me is (2). I could use some guidance on a good, possibly commercial, screen capture SDK. I would also welcome the news that my whole problem already has a solution. And of course any thoughts on the overall idea would also be great. Thanks. Ed

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  • RewriteRule in htaccess in subdirectory

    - by Jay
    Windows server, running Apache. In my Apache conf, I have AllowOverride None for the root of a site and then I have a subdirectory set to AllowOverride All: <Directory /> AllowOverride None </Directory> <Directory "/safe/"> AllowOverride All </Directory> However, when I try to set up a rewrite rule in the subdirectory's htaccess file, nothing happens, I just get a 404 page not found error. Example: RewriteEngine On RewriteRule (.*) /blah?test=$1 [R=302,NC,NE,L] Rwewriting URLs are working fine from the root via the Apache conf. I don't understand why the rule is ignored. I don't want to do the URL re-writing within the conf because for this case I may need to be changing the redirects constantly and don't want to reload the server every time a change is made. I also don't want to affect server performance by enabling htaccess files site-wide, just in the subdirectory I need it.

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  • SQL Server 2008: If Multiple Values Set In Other Mutliple Values Set

    - by AJH
    In SQL, is there anyway to accomplish something like this? This is based off a report built in SQL Server Report Builder, where the user can specify multiple text values as a single report parameter. The query for the report grabs all of the values the user selected and stores them in a single variable. I need a way for the query to return only records that have associations to EVERY value the user specified. -- Assume there's a table of Elements with thousands of entries. -- Now we declare a list of properties for those Elements to be associated with. create table #masterTable ( ElementId int, Text varchar(10) ) insert into #masterTable (ElementId, Text) values (1, 'Red'); insert into #masterTable (ElementId, Text) values (1, 'Coarse'); insert into #masterTable (ElementId, Text) values (1, 'Dense'); insert into #masterTable (ElementId, Text) values (2, 'Red'); insert into #masterTable (ElementId, Text) values (2, 'Smooth'); insert into #masterTable (ElementId, Text) values (2, 'Hollow'); -- Element 1 is Red, Coarse, and Dense. Element 2 is Red, Smooth, and Hollow. -- The real table is actually much much larger than this; this is just an example. -- This is me trying to replicate how SQL Server Report Builder treats -- report parameters in its queries. The user selects one, some, all, -- or no properties from a list. The written query treats the user's -- selections as a single variable called @Properties. -- Example scenario 1: User only wants to see Elements that are BOTH Red and Dense. select e.* from Elements e where (@Properties) --ideally a set containing only Red and Dense in (select Text from #masterTable where ElementId = e.Id) --ideally a set containing only Red, Coarse, and Dense --Both Red and Dense are within Element 1's properties (Red, Coarse, Dense), so Element 1 gets returned, but not Element 2. -- Example scenario 2: User only wants to see Elements that are BOTH Red and Hollow. select e.* from Elements e where (@Properties) --ideally a set containing only Red and Hollow in (select Text from #masterTable where ElementId = e.Id) --Both Red and Hollow are within Element 2's properties (Red, Smooth, Hollow), so Element 2 gets returned, but not Element 1. --Example Scenario 3: User only picked the Red option. select e.* from Elements e where (@Properties) --ideally a set containing only Red in (select Text from #masterTable where ElementId = e.Id) --Red is within both Element 1 and Element 2's properties, so both Element 1 and Element 2 get returned. The above syntax doesn't actually work because SQL doesn't seem to allow multiple values on the left side of the "in" comparison. Error that returns: Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. Am I even on the right track here? Sorry if the example looks long-winded or confusing.

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  • Website content hosted with Google. Good or bad?

    - by user305052
    I recently decided to host my styles.css and various scripts on Google Docs and link them into my website. I also have all my images hosted through Picasa so that they too will load much faster and consistently across users. My site has most of its traffic from Japan, Africa, and South America, so I assume there will be a performance boost for my users since my server is hosted in Hong Kong. I (in Canada) have measured my load times to be half of what they used to be. Basically it's a free CDN for my personal stuff. I'm not too sure about all of this yet, so here's my question: what are the caveats of this setup?

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  • Reading ResultSet from multiple threads

    - by superdario
    Hello, In the database, I have a definition table that is read from the application once upon starting. This definition table rarely changes, so it makes sense to read it once and restart the application every time it changes. However, after the table is read (put into a ResultSet), it will be read by multiple handlers running in their own threads. How do you suggest to accomplish this? My idea was to populate a CachedRowSet, and then create a copy of this set (through the createCopy() method) for each handler every time a new request comes. Do you think this is wise? Does this offer a good performance? Thanks.

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  • MySQL: Get unique values across multiple columns in alphabetical order

    - by RuCh
    Hey everyone, If my table looks like this: id | colA | colB | colC =========================== 1 | red | blue | yellow 2 | orange | red | red 3 | orange | blue | cyan What SELECT query do I run such that the results returned are: blue, cyan, orange, red, yellow Basically, I want to extract a collective list of distinct values across multiple columns and return them in alphabetical order. I am not concerned with performance optimization, because the results are being parsed to an XML file that will serve as a cache (database is hardly updated). So even a dirty solution would be fine. Thanks for any help!

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  • How to: Inline assembler in C++ (under Visual Studio 2010)

    - by toxic shock
    I'm writing a performance-critical, number-crunching C++ project where 70% of the time is used by the 200 line core module. I'd like to optimize the core using inline assembly, but I'm completely new to this. I do, however, know some x86 assembly languages including the one used by GCC and NASM. All I know: I have to put the assembler instructions in _asm{} where I want them to be. Problem: I have no clue where to start. What is in which register at the moment my inline assembly comes into play?

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