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  • How to 'insert if not exists' in MySQL?

    - by warren
    I started by googling, and found this article which talks about mutex tables. I have a table with ~14 million records. If I want to add more data in the same format, is there a way to ensure the record I want to insert does not already exist without using a pair of queries (ie, one query to check and one to insert is the result set is empty)? Does a unique constraint on a field guarantee the insert will fail if it's already there? It seems that with merely a constraint, when I issue the insert via php, the script croaks.

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  • Why does Go compile quickly?

    - by Evan Kroske
    I've Googled and poked around the Go website, but I can't seem to find an explanation for Go's extraordinary build times. Are they products of the language features (or lack thereof), a highly optimized compiler, or something else? I'm not trying to promote Go; I'm just curious.

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  • Reasonably faster way to traverse a directory tree in Python?

    - by Sridhar Ratnakumar
    Assuming that the given directory tree is of reasonable size: say an open source project like Twisted or Python, what is the fastest way to traverse and iterate over the absolute path of all files/directories inside that directory? I want to do this from within Python (subprocess is allowed). os.path.walk is slow. So I tried ls -lR and tree -fi. For a project with about 8337 files (including tmp, pyc, test, .svn files): $ time tree -fi > /dev/null real 0m0.170s user 0m0.044s sys 0m0.123s $ time ls -lR > /dev/null real 0m0.292s user 0m0.138s sys 0m0.152s $ time find . > /dev/null real 0m0.074s user 0m0.017s sys 0m0.056s $ tree appears to be faster than ls -lR (though ls -R is faster than tree, but it does not give full paths). find is the fastest. Can anyone think of a faster and/or better approach? On Windows, I may simply ship a 32-bit binary tree.exe or ls.exe if necessary. Update 1: Added find

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  • Decent profiler for Windows?

    - by olliej
    Does windows have any decent sampling (eg. non-instrumenting) profilers available? Preferably something akin to Shark on MacOS, although i am willing to accept that i am going to have to pay for such a profiler on windows. I've tried the profiler in VS Team Suite and was not overly impressed, and was wondering if there were any other good ones. [Edit: Erk, i forgot to say this is for C/C++, rather than .NET -- sorry for any confusion]

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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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  • Custom session state provider needed for DB storage?

    - by subt13
    I know this question is related to many others, but please bear with me. I am trying an experiment to store all information in database tables instead of the ASP.NET session. In ASP.NET 4 one can create a custom provider for session. So, again should I implement a Custom Session-State Provider or should I just disable session (in Web.config)? Thanks! From the comments my question can be misunderstood. Hopefully this tidbit will help clarify: I don't want to store the session in the database. I want to store information in the database that you would typically store in the session. One reason why: I don't want to carry around a session on every page, especially if that page doesn't care about 90 percent of the information in the session

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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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  • fastest way to check to see if a certain index in a linq statement is null

    - by tehdoommarine
    Basic Details I have a linq statement that grabs some records from a database and puts them in a System.Linq.Enumerable: var someRecords = someRepoAttachedToDatabase.Where(p=>true); Suppose this grabs tons (25k+) of records, and i need to perform operations on all of them. to speed things up, I have to decided to use paging and perform the operations needed in blocks of 100 instead of all of the records at the same time. The Question The line in question is the line where I count the number of records in the subset to see if we are on the last page; if the number of records in subset is less than the size of paging - then that means there are no more records left. What I would like to know is what is the fastest way to do this? Code in Question int pageSize = 100; bool moreData = true; int currentPage = 1; while (moreData) { var subsetOfRecords = someRecords.Skip((currentPage - 1) * pageSize).Take(pageSize); //this is also a System.Linq.Enumerable if (subsetOfRecords.Count() < pageSize){ moreData = false;} //line in question //do stuff to records in subset currentPage++; } Things I Have Considered subsetOfRecords.Count() < pageSize subsetOfRecords.ElementAt(pageSize - 1) == null (causes out of bounds exception - can catch exception and set moreData to false there) Converting subsetOfRecords to an array (converting someRecords to an array will not work due to the way subsetOfRecords is declared - but I am open to changing it) I'm sure there are plenty of other ideas that I have missed.

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  • Slow query with unexpected scan

    - by zerkms
    Hello I have this query: SELECT * FROM SAMPLE SAMPLE INNER JOIN TEST TEST ON SAMPLE.SAMPLE_NUMBER = TEST.SAMPLE_NUMBER INNER JOIN RESULT RESULT ON TEST.TEST_NUMBER = RESULT . TEST_NUMBER WHERE SAMPLED_DATE BETWEEN '2010-03-17 09:00' AND '2010-03-17 12:00' the biggest table here is RESULT, contains 11.1M records. The left 2 tables about 1M. this query works slowly (more than 10 minutes) and returns about 800 records. executing plan shows clustered index scan over all 11M records. RESULT.TEST_NUMBER is a clustered primary key. if I change 2010-03-17 09:00 to 2010-03-17 10:00 - i get about 40 records. it executes for 300ms. and plan shows clustered index seek if i replace * in SELECT clause to RESULT.TEST_NUMBER (covered with index) - then all become fast in first case too. this points to hdd io issues, but doesn't clarifies changing plan. so, any ideas?

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  • Fastest XML parser for small, simple documents in Java

    - by Varkhan
    I have to objectify very simple and small XML documents (less than 1k, and it's almost SGML: no namespaces, plain UTF-8, you name it...), read from a stream, in Java. I am using JAXP to process the data from my stream into a Document object. I have tried Xerces, it's way too big and slow... I am using Dom4j, but I am still spending way too much time in org.dom4j.io.SAXReader. Does anybody out there have any suggestion on a faster, more efficient implementation, keeping in mind I have very tough CPU and memory constraints? [Edit 1] Keep in mind that my documents are very small, so the overhead of staring the parser can be important. For instance I am spending as much time in org.xml.sax.helpers.XMLReaderFactory.createXMLReader as in org.dom4j.io.SAXReader.read [Edit 2] The result has to be in Dom format, as I pass the document to decision tools that do arbitrary processing on it, like switching code based on the value of arbitrary XPaths, but also extracting lists of values packed as children of a predefined node. [Edit 3] In any case I eventually need to load/parse the complete document, since all the information it contains is going to be used at some point. (This question is related to, but different from, http://stackoverflow.com/questions/373833/best-xml-parser-for-java )

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  • What's the good of IDE's auto generated @override annotation ?

    - by Tony
    I am using eclipse , when I use shortcut to generate override implementations , there is an override annotation up there , I am using JDK 6 , this is all right , but under JDK 5 this annotation will cause an error, so I want to ask , if this annotation is completely useless ? Will compiler do some kind of optimization using this annotation ?

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  • Quickest way to compare a bunch of array or list of values.

    - by zapping
    Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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  • How can I most accurately calculate the execution time of an ASP.NET page while also displaying it o

    - by henningst
    I want to calculate the execution time of my ASP.NET pages and display it on the page. Currently I'm calculating the execution time using a System.Diagnostics.Stopwatch and then store the value in a log database. The stopwatch is started in OnInit and stopped in OnPreRenderComplete. This seems to be working quite fine, and it's giving a similar execution time as the one shown in the page trace. The problem now is that I'm not able to display the execution time on the page because the stopwatch is stopped too late in the life cycle. What is the best way to do this?

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  • mySQL & Relational databases: How to handle sharding/splitting on application level?

    - by Industrial
    Hi everybody, I have thought a bit about sharding tables, since partitioning cannot be done with foreign keys in a mySQL table. Maybe there's an option to switch to a different relational database that features both, but I don't see that as an option right now. So, the sharding idea seems like a pretty decent thing. But, what's a good approach to do this on a application level? I am guessing that a take-off point would be to prefix tables with a max value for the primary key in each table. Something like products_4000000 , products_8000000 and products_12000000. Then the application would have to check with a simple if-statement the size of the id (PK) that will be requested is smaller then four, eight or twelve million before doing any actual database calls. So, is this a step in the right direction or are we doing something really stupid?

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  • C++ code which is slower than its C equivalent?

    - by user997112
    Are there any aspects to the C++ programming language where the code is known to be slower than the equivalent C language? Obviously this would be excluding the OO features like virtual functions and vtable features etc. I am wondering whether, when you are programming in a latency-critical area (and you aren't worried about OO features) whether you could stick with basic C++ or would C be better?

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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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  • Which is more efficient regular expression?

    - by Vagnerr
    I'm parsing some big log files and have some very simple string matches for example if(m/Some String Pattern/o){ #Do something } It seems simple enough but in fact most of the matches I have could be against the start of the line, but the match would be "longer" for example if(m/^Initial static string that matches Some String Pattern/o){ #Do something } Obviously this is a longer regular expression and so more work to match. However I can use the start of line anchor which would allow an expression to be discarded as a failed match sooner. It is my hunch that the latter would be more efficient. Can any one back me up/shoot me down :-)

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  • Fastest implementation of the frac function in C#

    - by user349937
    I would like to implement a frac function in C# (just like the one in hsl here http://msdn.microsoft.com/en-us/library/bb509603%28VS.85%29.aspx) but since it is for a very processor intensive application i would like the best version possible. I was using something like public float Frac(float value) { return value - (float)Math.Truncate(value); } but I'm having precision problems, for example for 2.6f it's returning in the unit test Expected: 0.600000024f But was: 0.599999905f I know that I can convert to decimal the value and then at the end convert to float to obtain the correct result something like this: public float Frac(float value) { return (float)((decimal)value - Decimal.Truncate((decimal)value)); } But I wonder if there is a better way without resorting to decimals...

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  • How to speed this kind of for-loop?

    - by wok
    I would like to compute the maximum of translated images along the direction of a given axis. I know about ordfilt2, however I would like to avoid using the Image Processing Toolbox. So here is the code I have so far: imInput = imread('tire.tif'); n = 10; imMax = imInput(:, n:end); for i = 1:(n-1) imMax = max(imMax, imInput(:, i:end-(n-i))); end Is it possible to avoid using a for-loop in order to speed the computation up, and, if so, how?

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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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  • Cache JSP based on URL parameter

    - by Satheesh
    I have a jsp file pageshow.jsp and the parameter id, Is there any way to cache the jsp file in server-side based on the url parameter Requesting page pageshow.jsp?id=100 get from cache instead of building from server Requesting page pageshow.jsp?id=200 get from cache instead of building from server Above two pages should have different cache content since their parameter are different This may avoid the rebuilding the jsp file in server side and also decrease the server load

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  • How does CouchDB perform for a regularly updated dataset?

    - by Ritesh M Nayak
    I am planning on using CouchDB on a project. But as the querying mechanism involves writing views (which are a lot like indexes on regular RDMBMS's) I was wondering, if the document database keeps getting updated a lot ( a write heavy database) would CouchDB perform well compared to a regular RDBMS? Or do we have to compact/re-index the system occasionally to make it perform faster?

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  • Cuboid inside generic polyhedron

    - by DOFHandler
    I am searching for an efficient algorithm to find if a cuboid is completely inside or completely outside or (not-inside and not-outside) a generic (concave or convex) polyhedron. The polyhedron is defined by a list of 3D points and a list of facets. Each facet is defined by the subset of the contour points ordinated such as the right-hand normal points outward the solid. Any suggestion? Thank you

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