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  • Why are difference lists more efficient than regular concatenation?

    - by Craig Innes
    I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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  • .NET WebService IPC - Should it be done to minimise some expensive operations?

    - by Kyle
    I'm looking at a few different approaches to a problem: Client requests work, some stuff gets done, and a result (ok/error) is returned. A .NET web service definitely seems like the way to go, my only issue is that the "stuff" will involve building up and tearing down a session for each request. Does abstracting the "stuff" out to an app (which would keep a single session active, and process the request from the web service) seem like the right way to go? (and if so, what communication method) The work time is negligible, my concern is the hammering the transaction servers in question will probably get if I create/drop a session for each job. Is some form of IPC or socket based communication a feasible solution here? Thoughts/comments/experiences much appreciated. Edit: After a bit more research, it seems like hosting a WCF service in a Windows Service is probably a better way to go...

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  • Definition of Connect, Processing, Waiting in apache bench.

    - by rpatel
    When I run apache bench I get results like: Command: abs.exe -v 3 -n 10 -c 1 https://mysite Connection Times (ms) min mean[+/-sd] median max Connect: 203 213 8.1 219 219 Processing: 78 177 88.1 172 359 Waiting: 78 169 84.6 156 344 Total: 281 389 86.7 391 563 I can't seem to find the definition of Connect, Processing and Waiting. What do those numbers mean?

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  • Effecient data structure design

    - by Sway
    Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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  • Have parameters in Dao methods to get entities the most efficient way for read-only access

    - by Blankman
    Allot of my use of hibernate, at least for that data that is presented on many parts of the web application, is for read-only purposes. I want to add some parameters to my Dao methods so I can modify the way hibernate pulls the data and how it handles transactions etc. Example usage: Data on the front page of my website is displayed to the users, it is read-only, so I want to avoid any session/entity tracking that hibernate usually does. This is data that is read-only, will not be changed in this transaction, etc. What would be the most performant way to pull the data? (the code below is c#/nhibernate, I'm implementing this in java as I learn it) public IList<Article> GetArticles() { return Session.CreateCriteria(typeof(Article)) // some where cluase }

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  • C++ program runs slow in VS2008

    - by Nima
    I have a program written in C++, that opens a binary file(test.bin), reads it object by object, and puts each object into a new file (it opens the new file, writes into it(append), and closes it). I use fopen/fclose, fread and fwrite. test.bin contains 20,000 objects. This program runs under linux with g++ in 1 sec but in VS2008 in debug/release mode in 1min! There are reasons why I don't do them in batches or don't keep them in memory or any other kind of optimizations. I just wonder why it is that much slow under windows. Thanks,

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  • SQL query: how to translate IN() into a JOIN?

    - by tangens
    I have a lot of SQL queries like this: SELECT o.Id, o.attrib1, o.attrib2 FROM table1 o WHERE o.Id IN ( SELECT DISTINCT Id FROM table1, table2, table3 WHERE ... ) These queries have to run on different database engines (MySql, Oracle, DB2, MS-Sql, Hypersonic), so I can only use common SQL syntax. Here I read, that with MySql the IN statement isn't optimized and it's really slow, so I want to switch this into a JOIN. I tried: SELECT o.Id, o.attrib1, o.attrib2 FROM table1 o, table2, table3 WHERE ... But this does not take into account the DISTINCT keyword. Question: How do I get rid of the duplicate rows using the JOIN approach?

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  • NHibernate + Fluent long startup time

    - by PaRa
    Hi all, am new to NHibernate. When performing below test took 11.2 seconds (debug mode) i am seeing this large startup time in all my tests (basically creating the first session takes a tone of time) setup = Windows 2003 SP2 / Oracle10gR2 latest CPU / ODP.net 2.111.7.20 / FNH 1.0.0.636 / NHibernate 2.1.2.4000 / NUnit 2.5.2.9222 / VS2008 SP1 using System; using System.Collections; using System.Data; using System.Globalization; using System.IO; using System.Text; using System.Data; using NUnit.Framework; using System.Collections.Generic; using System.Data.Common; using NHibernate; using log4net.Config; using System.Configuration; using FluentNHibernate; [Test()] public void GetEmailById() { Email result; using (EmailRepository repository = new EmailRepository()) { results = repository.GetById(1111); } Assert.IsTrue(results != null); } public class EmailRepository : RepositoryBase { public EmailRepository():base() { } } In my RepositoryBase public T GetById(object id) { using (var session = sessionFactory.OpenSession()) using (var transaction = session.BeginTransaction()) { try { T returnVal = session.Get(id); transaction.Commit(); return returnVal; } catch (HibernateException ex) { // Logging here transaction.Rollback(); return null; } } } The query time is very small. The resulting entity is really small. Subsequent queries are fine. Its seems to be getting the first session started. Has anyone else seen something similar?

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  • Jmeter- HTTP Cache Manager, Unable to cache everything what it is being cached by Browser

    - by chinmay brahma
    I used HTTP Chache Manager to Cache files which are being cached in browser. I am successful of doing it for some of the pages. Number of files being cached in Jmeter is equal to Number of files being cached by browser. But in some cases : I found number files being cached is lesser than the files being cached by browser. Using Jmeter I found only 5 files are being cached but in real browser 12 files are getting cached. Thanks in advance

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  • Stored procedure optimization

    - by George Zacharia
    Hi, i have a stored procedure which takes lot of time to execure .Can any one suggest a better approch so that the same result set is achived. ALTER PROCEDURE [dbo].[spFavoriteRecipesGET] @USERID INT, @PAGENUMBER INT, @PAGESIZE INT, @SORTDIRECTION VARCHAR(4), @SORTORDER VARCHAR(4),@FILTERBY INT AS BEGIN DECLARE @ROW_START INT DECLARE @ROW_END INT SET @ROW_START = (@PageNumber-1)* @PageSize+1 SET @ROW_END = @PageNumber*@PageSize DECLARE @RecipeCount INT DECLARE @RESULT_SET_TABLE TABLE ( Id INT NOT NULL IDENTITY(1,1), FavoriteRecipeId INT, RecipeId INT, DateAdded DATETIME, Title NVARCHAR(255), UrlFriendlyTitle NVARCHAR(250), [Description] NVARCHAR(MAX), AverageRatingId FLOAT, SubmittedById INT, SubmittedBy VARCHAR(250), RecipeStateId INT, RecipeRatingId INT, ReviewCount INT, TweaksCount INT, PhotoCount INT, ImageName NVARCHAR(50) ) INSERT INTO @RESULT_SET_TABLE SELECT FavoriteRecipes.FavoriteRecipeId, Recipes.RecipeId, FavoriteRecipes.DateAdded, Recipes.Title, Recipes.UrlFriendlyTitle, Recipes.[Description], Recipes.AverageRatingId, Recipes.SubmittedById, COALESCE(users.DisplayName,users.UserName,Recipes.SubmittedBy) As SubmittedBy, Recipes.RecipeStateId, RecipeReviews.RecipeRatingId, COUNT(RecipeReviews.Review), COUNT(RecipeTweaks.Tweak), COUNT(Photos.PhotoId), dbo.udfGetRecipePhoto(Recipes.RecipeId) AS ImageName FROM FavoriteRecipes INNER JOIN Recipes ON FavoriteRecipes.RecipeId=Recipes.RecipeId AND Recipes.RecipeStateId <> 3 LEFT OUTER JOIN RecipeReviews ON RecipeReviews.RecipeId=Recipes.RecipeId AND RecipeReviews.ReviewedById=@UserId AND RecipeReviews.RecipeRatingId= ( SELECT MAX(RecipeReviews.RecipeRatingId) FROM RecipeReviews WHERE RecipeReviews.ReviewedById=@UserId AND RecipeReviews.RecipeId=FavoriteRecipes.RecipeId ) OR RecipeReviews.RecipeRatingId IS NULL LEFT OUTER JOIN RecipeTweaks ON RecipeTweaks.RecipeId = Recipes.RecipeId AND RecipeTweaks.TweakedById= @UserId LEFT OUTER JOIN Photos ON Photos.RecipeId = Recipes.RecipeId AND Photos.UploadedById = @UserId AND Photos.RecipeId = FavoriteRecipes.RecipeId AND Photos.PhotoTypeId = 1 LEFT OUTER JOIN users ON Recipes.SubmittedById = users.UserId WHERE FavoriteRecipes.UserId=@UserId GROUP BY FavoriteRecipes.FavoriteRecipeId, Recipes.RecipeId, FavoriteRecipes.DateAdded, Recipes.Title, Recipes.UrlFriendlyTitle, Recipes.[Description], Recipes.AverageRatingId, Recipes.SubmittedById, Recipes.SubmittedBy, Recipes.RecipeStateId, RecipeReviews.RecipeRatingId, users.DisplayName, users.UserName, Recipes.SubmittedBy; WITH SortResults AS ( SELECT ROW_NUMBER() OVER ( ORDER BY CASE WHEN @SORTDIRECTION = 't' AND @SORTORDER='a' THEN TITLE END ASC, CASE WHEN @SORTDIRECTION = 't' AND @SORTORDER='d' THEN TITLE END DESC, CASE WHEN @SORTDIRECTION = 'r' AND @SORTORDER='a' THEN AverageRatingId END ASC, CASE WHEN @SORTDIRECTION = 'r' AND @SORTORDER='d' THEN AverageRatingId END DESC, CASE WHEN @SORTDIRECTION = 'mr' AND @SORTORDER='a' THEN RecipeRatingId END ASC, CASE WHEN @SORTDIRECTION = 'mr' AND @SORTORDER='d' THEN RecipeRatingId END DESC, CASE WHEN @SORTDIRECTION = 'd' AND @SORTORDER='a' THEN DateAdded END ASC, CASE WHEN @SORTDIRECTION = 'd' AND @SORTORDER='d' THEN DateAdded END DESC ) RowNumber, FavoriteRecipeId, RecipeId, DateAdded, Title, UrlFriendlyTitle, [Description], AverageRatingId, SubmittedById, SubmittedBy, RecipeStateId, RecipeRatingId, ReviewCount, TweaksCount, PhotoCount, ImageName FROM @RESULT_SET_TABLE WHERE ((@FILTERBY = 1 AND SubmittedById= @USERID) OR ( @FILTERBY = 2 AND (SubmittedById <> @USERID OR SubmittedById IS NULL)) OR ( @FILTERBY <> 1 AND @FILTERBY <> 2)) ) SELECT RowNumber, FavoriteRecipeId, RecipeId, DateAdded, Title, UrlFriendlyTitle, [Description], AverageRatingId, SubmittedById, SubmittedBy, RecipeStateId, RecipeRatingId, ReviewCount, TweaksCount, PhotoCount, ImageName FROM SortResults WHERE RowNumber BETWEEN @ROW_START AND @ROW_END print @ROW_START print @ROW_END SELECT @RecipeCount=dbo.udfGetFavRecipesCount(@UserId) SELECT @RecipeCount AS RecipeCount SELECT COUNT(Id) as FilterCount FROM @RESULT_SET_TABLE WHERE ((@FILTERBY = 1 AND SubmittedById= @USERID) OR (@FILTERBY = 2 AND (SubmittedById <> @USERID OR SubmittedById IS NULL)) OR (@FILTERBY <> 1 AND @FILTERBY <> 2)) END

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  • Efficient way to delete a line from a text file (C#)

    - by Valentin Vasilyev
    Hello. I need to delete a certain line from a text file. What is the most efficient way of doing this? File can be potentially large(over million records). Thank you. UPDATE: below is the code I'm currently using, but I'm not sure if it is good. internal void DeleteMarkedEntries() { string tempPath=Path.GetTempFileName(); using (var reader = new StreamReader(logPath)) { using (var writer = new StreamWriter(File.OpenWrite(tempPath))) { int counter = 0; while (!reader.EndOfStream) { if (!_deletedLines.Contains(counter)) { writer.WriteLine(reader.ReadLine()); } ++counter; } } } if (File.Exists(tempPath)) { File.Delete(logPath); File.Move(tempPath, logPath); } }

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  • How to find the worst performing queries in MS SQL Server 2008?

    - by Thomas Bratt
    How to find the worst performing queries in MS SQL Server 2008? I found the following example but it does not seem to work: SELECT TOP 5 obj.name, max_logical_reads, max_elapsed_time FROM sys.dm_exec_query_stats a CROSS APPLY sys.dm_exec_sql_text(sql_handle) hnd INNER JOIN sys.sysobjects obj on hnd.objectid = obj.id ORDER BY max_logical_reads DESC Taken from: http://www.sqlservercurry.com/2010/03/top-5-costly-stored-procedures-in-sql.html

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  • Why the difference in speed?

    - by AngryHacker
    Consider this code: function Foo(ds as OtherDLL.BaseObj) dim lngRowIndex as long dim lngColIndex as long for lngRowIndex = 1 to ubound(ds.Data, 2) for lngColIndex = 1 to ds.Columns.Count Debug.Print ds.Data(lngRowIndex, lngColIndex) next next end function OK, a little context. Parameter ds is of type OtherDLL.BaseObj which is defined in a referenced ActiveX DLL. ds.Data is a variant 2-dimensional array (one dimension carries the data, the other one carries the column index. ds.Columns is a Collection of columns in 'ds.Data`. Assuming there are at least 400 rows of data and 25 columns, this code takes about 15 seconds to run on my machine. Kind of unbelievable. However if I copy the variant array to a local variable, so: function Foo(ds as OtherDLL.BaseObj) dim lngRowIndex as long dim lngColIndex as long dim v as variant v = ds.Data for lngRowIndex = 1 to ubound(v, 2) for lngColIndex = 1 to ds.Columns.Count Debug.Print v(lngRowIndex, lngColIndex) next next end function the entire thing processes in barely any noticeable time (basically close to 0). Why?

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  • SQL Server uncorrelated subquery very slow

    - by brianberns
    I have a simple, uncorrelated subquery that performs very poorly on SQL Server. I'm not very experienced at reading execution plans, but it looks like the inner query is being executed once for every row in the outer query, even though the results are the same each time. What can I do to tell SQL Server to execute the inner query only once? The query looks like this: select * from Record record0_ where record0_.RecordTypeFK='c2a0ffa5-d23b-11db-9ea3-000e7f30d6a2' and ( record0_.EntityFK in ( select record1_.EntityFK from Record record1_ join RecordTextValue textvalues2_ on record1_.PK=textvalues2_.RecordFK and textvalues2_.FieldFK = '0d323c22-0ec2-11e0-a148-0018f3dde540' and (textvalues2_.Value like 'O%' escape '~') ) )

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  • [N]Hibernate: view-like fetching properties of associated class

    - by chiccodoro
    (Felt quite helpless in formulating an appropriate title...) In my C# app I display a list of "A" objects, along with some properties of their associated "B" objects and properties of B's associated "C" objects: A.Name B.Name B.SomeValue C.Name Foo Bar 123 HelloWorld Bar Hello 432 World ... To clarify: A has an FK to B, B has an FK to C. (Such as, e.g. BankAccount - Person - Company). I have tried two approaches to load these properties from the database (using NHibernate): A fast approach and a clean approach. My eventual question is how to do a fast & clean approach. Fast approach: Define a view in the database which joins A, B, C and provides all these fields. In the A class, define properties "BName", "BSomeValue", "CName" Define a hibernate mapping between A and the View, whereas the needed B and C properties are mapped with update="false" insert="false" and do actually stem from B and C tables, but Hibernate is not aware of that since it uses the view. This way, the listing only loads one object per "A" record, which is quite fast. If the code tries to access the actual associated property, "A.B", I issue another HQL query to get B, set the property and update the faked BName and BSomeValue properties as well. Clean approach: There is no view. Class A is mapped to table A, B to B, C to C. When loading the list of A, I do a double left-join-fetch to get B and C as well: from A a left join fetch a.B left join fetch a.B.C B.Name, B.SomeValue and C.Name are accessed through the eagerly loaded associations. The disadvantage of this approach is that it gets slower and takes more memory, since it needs to created and map 3 objects per "A" record: An A, B, and C object each. Fast and clean approach: I feel somehow uncomfortable using a database view that hides a join and treat that in NHibernate as if it was a table. So I would like to do something like: Have no views in the database. Declare properties "BName", "BSomeValue", "CName" in class "A". Define the mapping for A such that NHibernate fetches A and these properties together using a join SQL query as a database view would do. The mapping should still allow for defining lazy many-to-one associations for getting A.B.C My questions: Is this possible? Is it [un]artful? Is there a better way?

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  • how to optimize an oracle query that has to_char in where clause for date

    - by panorama12
    I have a table that contains about 49403459 records. I want to query the table on a date range. say 04/10/2010 to 04/10/2010. However, the dates are stored in the table as format 10-APR-10 10.15.06.000000 AM (time stamp). As a result. When I do: SELECT bunch,of,stuff,create_date FROM myTable WHERE TO_CHAR (create_date,'MM/DD/YYYY)' >= '04/10/2010' AND TO_CHAR (create_date, 'MM/DD/YYYY' <= '04/10/2010' I get 529 rows but in 255.59 seconds! which is because I guess I am doing to_char on EACH record. However, When I do SELECT bunch,of,stuff,create_date FROM myTable WHERE create_date >= to_date('04/10/2010','MM/DD/YYYY') AND create_date <= to_date('04/10/2010','MM/DD/YYYY') then I get 0 results in 0.14 seconds. How can I make this query fast and still get valid (529) results?? At this point I can not change indexes. Right now I think index is created on create_date column

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  • querying huge database table takes too much of time in mysql

    - by Vijay
    Hi all, I am running sql queries on a mysql db table that has 110Mn+ unique records for whole day. Problem: Whenever I run any query with "where" clause it takes at least 30-40 mins. Since I want to generate most of data on the next day, I need access to whole db table. Could you please guide me to optimize / restructure the deployment model? Site description: mysql Ver 14.12 Distrib 5.0.24, for pc-linux-gnu (i686) using readline 5.0 4 GB RAM, Dual Core dual CPU 3GHz RHEL 3 my.cnf contents : [root@reports root]# cat /etc/my.cnf [mysqld] datadir=/data/mysql/data/ socket=/tmp/mysql.sock sort_buffer_size = 2000000 table_cache = 1024 key_buffer = 128M myisam_sort_buffer_size = 64M # Default to using old password format for compatibility with mysql 3.x # clients (those using the mysqlclient10 compatibility package). old_passwords=1 [mysql.server] user=mysql basedir=/data/mysql/data/ [mysqld_safe] err-log=/data/mysql/data/mysqld.log pid-file=/data/mysql/data/mysqld.pid [root@reports root]# DB table details: CREATE TABLE `RAW_LOG_20100504` ( `DT` date default NULL, `GATEWAY` varchar(15) default NULL, `USER` bigint(12) default NULL, `CACHE` varchar(12) default NULL, `TIMESTAMP` varchar(30) default NULL, `URL` varchar(60) default NULL, `VERSION` varchar(6) default NULL, `PROTOCOL` varchar(6) default NULL, `WEB_STATUS` int(5) default NULL, `BYTES_RETURNED` int(10) default NULL, `RTT` int(5) default NULL, `UA` varchar(100) default NULL, `REQ_SIZE` int(6) default NULL, `CONTENT_TYPE` varchar(50) default NULL, `CUST_TYPE` int(1) default NULL, `DEL_STATUS_DEVICE` int(1) default NULL, `IP` varchar(16) default NULL, `CP_FLAG` int(1) default NULL, `USER_LOCATE` bigint(15) default NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=200000000; Thanks in advance! Regards,

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  • Can this loop be sped up in pure Python?

    - by Noctis Skytower
    I was trying out an experiment with Python, trying to find out how many times it could add one to an integer in one minute's time. Assuming two computers are the same except for the speed of the CPUs, this should give an estimate of how fast some CPU operations may take for the computer in question. The code below is an example of a test designed to fulfill the requirements given above. This version is about 20% faster than the first attempt and 150% faster than the third attempt. Can anyone make any suggestions as to how to get the most additions in a minute's time span? Higher numbers are desireable. EDIT: This experiment is being written in Python 3.1 and is 15% faster than the fourth speed-up attempt. def start(seconds): import time, _thread def stop(seconds, signal): time.sleep(seconds) signal.pop() total, signal = 0, [None] _thread.start_new_thread(stop, (seconds, signal)) while signal: total += 1 return total if __name__ == '__main__': print('Testing the CPU speed ...') print('Relative speed:', start(60))

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  • Sql Server 2000 Stored Procedure Prevent Parallelism or something?

    - by user187305
    I have a huge disgusting stored procedure that wasn't slow a couple months ago, but now is. I barely know what this thing does and I am in no way interested in rewriting it. I do know that if I take the body of the stored procedure and then declare/set the values of the parameters and run it in query analyzer that it runs more than 20x faster. From the internet, I've read that this is probably due to a bad cached query plan. So, I've tried running the sp with "WITH RECOMPILE" after the EXEC and I've also tried putting the "WITH RECOMPLE" inside the sp, but neither of those helped even a little bit. When I look at the execution plan of the sp vs the query, the biggest difference is that the sp has "Parallelism" operations all over the place and the query doesn't have any. Can this be the cause of the difference in speeds? Thank you, any ideas would be great... I'm stuck.

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  • C#/WPF FileSystemWatcher on every extension on every path

    - by BlueMan
    I need FileSystemWatcher, that can observing same specific paths, and specific extensions. But the paths could by dozens, hundreds or maybe thousand (hope not :P), the same with extensions. The paths and ext are added by user. Creating hundreds of FileSystemWatcher it's not good idea, isn't it? So - how to do it? Is it possible to watch/observing every device (HDDs, SD flash, pendrives, etc.)? Will it be efficient? I don't think so... . Every changing Windows log file, scanning file by antyvirus program - it could realy slow down my program with SystemWatcher :(

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  • Should I aim for fewer HTTP requests or more cacheable CSS files?

    - by Jonathan Hanson
    We're being told that fewer HTTP requests per page load is a Good Thing. The extreme form of that for CSS would be to have a single, unique CSS file per page, with any shared site-wide styles duplicated in each file. But there's a trade off there. If you have separate shared global CSS files, they can be cached once when the front page is loaded and then re-used on multiple pages, thereby reducing the necessary size of the page-specific CSS files. So which is better in real-world practice? Shorter CSS files through multiple discrete CSS files that are cacheable, or fewer HTTP requests through fewer-but-larger CSS files?

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