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• C++ Vector at/[] operator speed

  - by sub

  In order to give functions the option to modify the vector I can't do curr = myvec.at( i ); doThis( curr ); doThat( curr ); doStuffWith( curr ); But I have to do: doThis( myvec.at( i ) ); doThat( myvec.at( i ) ); doStuffWith( myvec.at( i ) ); (as the answers of my other question pointed out) I'm going to make a hell lot of calls to myvec.at() then. How fast is it, compared to the first example using a variable to store the result? Is there a different option for me? Can I somehow use pointers? When it's getting serious there will be thousands of calls to myvec.at() per second. So every little performance-eater is important.

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• What is the most "database independent" way of creating a variable length text field in a database

  - by Thibaut Colar

  I want to create a text field in the database, with no specific size (it will store text of length unknown in some case) - the particular text are serialized simple object (~ JSON) What is the most database independent way to do this : - a varchar with no size specified (don't think all db support this) - a 'text' field, this seems to be common, but I don't believe it's a standard - a blob or other object of that kind ? - a varchar of a a very large size (that's inefficient and wastes disk space probably) - Other ? I'm using JDBC, but I'd like to use something that is supported in most DB (oracle, mysql, postgresql, derby, HSQL, H2 etc...) Thanks.

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• c++ Sorting a vector based on values of other vector, or what's faster?

  - by pollux

  Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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• Take advantage of multiple cores executing SQL statements

  - by willvv

  I have a small application that reads XML files and inserts the information on a SQL DB. There are ~ 300 000 files to import, each one with ~ 1000 records. I started the application on 20% of the files and it has been running for 18 hours now, I hope I can improve this time for the rest of the files. I'm not using a multi-thread approach, but since the computer I'm running the process on has 4 cores I was thinking on doing it to get some improvement on the performance (although I guess the main problem is the I/O and not only the processing). I was thinking on using the BeginExecutingNonQuery() method on the SqlCommand object I create for each insertion, but I don't know if I should limit the max amount of simultaneous threads (nor I know how to do it). What's your advice to get the best CPU utilization? Thanks

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• Likelihood of IOError during print vs. write

  - by jkasnicki

  I recently encountered an IOError writing to a file on NFS. There wasn't a disk space or permission issue, so I assume this was just a network hiccup. The obvious solution is to wrap the write in a try-except, but I was curious whether the implementation of print and write in Python make either of the following more or less likely to raise IOError: f_print = open('print.txt', 'w') print >>f_print, 'test_print' f_print.close() vs. f_write = open('write.txt', 'w') f_write.write('test_write\n') f_write.close() (If it matters, specifically in Python 2.4 on Linux).

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• SQL Server, fetching data from multiple joined tables. Why is slow?

  - by user562192

  I have problem with performance when retrieving data from SQL Server. My sql query looks something like this: SELECT table_1.id, table_1.value, table_2.id, table_2.value,..., table_20.id, table_20.value From table_1 INNER JOIN table_2 ON table_1.id = table_2.table_1_id INNER JOIN table_3 ON table_2.id = table_3.table_2_id... WHERE table_1.row_number BETWEEN 1 AND 20 So, I am fetching 20 results. This query takes about 5 seconds to execute. When I select only table_1.id, it returns results instantly. Because of that, I guess that problem is not in JOINs, it is in retrieving data from multiple tables. Any suggestions how I would speed up this query?

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• Go, AppEngine: How to structure templates for application

  - by laslowh

  How are people handling the use of templates in their Go-based AppEngine applications? Specifically, I'm looking for a project structure that affords the following: Hierarchical (directory) structure of templates and partial templates Allow me to use HTML tools/editors on my templates (embedding template text in xxx.go files makes this difficult) Automatic reload of template text when on dev server Potential stumbling blocks are: template.ParseGlob() will not traverse recursively. For performance reasons it has been recommended not to upload your templates as raw text files (because those text files reside on different servers than executing code). Please note that I am not looking for a tutorial/examples of the use of the template package. This is more of an app structure question. That being said, if you have code that solves the above problems, I would love to see it. Thanks in advance.

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• Fast comparison of char arrays?

  - by StackedCrooked

  I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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• Breaking One Big Graphic of MutablePaths into CAShapeLayers

  - by StackOverFlowRider

  I have a class called GraphicView that takes a Graphic object and draws it in its drawRect method. This Graphic object is basically an array of mutablePaths that comprise an icon that I want drawn. For performance and other issues, I was thinking of taking this icon that is comprised of mutablePaths, and dividing it into a bunch of CAShapeLayers. I'm wondering is this possible? Considering the points for the mutablePaths of the icon are all interwoven together (ie the icon was initially an SVG file that I converted to code), is it possible to divide different parts of the icon into CAShapeLayers, and reassemble them all together when assigning to the views layer? If so how would it be done? If I assign them as sublayers to a CALayer or CAShapeLayer, will it understand to mesh them all together?

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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• How to handle huge table ?

  - by misha-moroshko

  I would like to display to user a table which contains ~500,000 rows. The table should be calculated based on a file (i.e. the table is known at the beginning, and does not change). I guess that building the HTML text of this table is not a good idea in terms of memory performance. So how can I build such table ? I would like user to be able to scroll the table using a vertical scroll bar. Is it possible to build on the fly only the visible part of the table ? I'm afraid to see delays because of this. Is it a better idea to use server side programming rather than Javascript ? Any advise would be appreciated.

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• Why I should use an N-Tier Approach When using an SqlDatasource is ALOT EASIER ?

  - by The_AlienCoder

  When it comes to web development I have always tried to work SMART not HARD. So for along time My Aproach to interacting with databases in my AspNet projects has been this : 1) Create my stored procedures 2) Drag an SQLDatasource control on my aspx page 3) Bind a DataList Control to my SQLDatasource 4) Insert, Update & Delete by using my Datalist or programmatically using built in SQLDatasource methods e.g MySqlDataSource.InsertParameters["author"].DefaultValue = TextBox1.Text; MySqlDataSource.Insert(); Recently however I got a relatively easy web project. So I decided to employ a 3-tier Model...But I got exhausted halfway and just didnt seem worth it ! It seemed like I was working too HARD for a project that could have been easily accomplished by a couple of SqlDataSource Controls. So Why Is the N-Tier Model better than my Approach? Has it anything to do with performance? What are the advantages of the ObjectDataSource control over the SqlDataSource Control?

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• user buffer after doing 'write' to file opened with O_DIRECT

  - by user1868481

  I'm using the O_DIRECT flag to write to the disk directly from the user buffer. But as far as I understand, Linux doesn't guarantee that after this call, the data is written. It just writes directly from the user buffer to the physical device using DMA or anything else... Therefore, I don't understand if I can write to the user buffer after the call to 'write' function. I'm sure that example code will help to understand my question: char *user_buff = malloc(...); /* assume it is aligned as needed */ fd = open(..., O_DIRECT); write(fd, ...) memset(user_buff, 0, ...) Is the last line (memset) legal? Is writing to the user buffer valid that is maybe used by DMA to transfer data to the device?

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• java-maven2: How to include the a jar as depedency in pom so that I will be able to access test clas

  - by flavour-of-bru

  Hi, I have a set of functional jars(more than 3) that tests my source code. These jars just contains test classes and assisting asserter classes. I am creating a new performance jar that would import all the functional tests from these jars so that all can be run simultaneously. But when I include them as test dependencies in pom of current jar, what all I get to see is the classes in src/main/java. How can I include these functional jars as dependent jars so that I can also reference classes in src/test/java. In other words, how do I reference the test classes in other jars. In what way should I include the dependency as. Thanks for your support.

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• Is it a problem if i query again and again to SQL Server 2005 and 2000?

  - by learner

  Window app i am constructing is for very low end machines (Celeron with max 128 RAM). From the following two approaches which one is the best (I don't want that application becomes memory hog for low end machines):- Approach One:- Query the database Select GUID from Table1 where DateTime <= @givendate which is returning me more than 300 thousands records (but only one field i.e. GUID - 300 thousands GUIDs). Now running a loop to achieve next process of this software based on GUID. Second Approach:- Query the database Select Top 1 GUID from Table1 where DateTime <= @givendate with top 1 again and again until all 300 thousands records done. It will return me only one GUID at a time, and I can do my next step of operation. What do you suggest which approach will use the less Memory Resources?? (Speed / performance is not the issue here).

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• Database design: one huge table or separate tables?

  - by littlegreen

  Currently I am designing a database for use in our company. We are using SQL Server 2008. The database will hold data gathered from several customers. The goal of the database is to acquire aggregate benchmark numbers over several customers. Recently, I have become worried with the fact that one table in particular will be getting very big. Each customer has approximately 20.000.000 rows of data, and there will soon be 30 customers in the database (if not more). A lot of queries will be done on this table. I am already noticing performance issues and users being temporarily locked out. My question, will we be able to handle this table in the future, or is it better to split this table up into smaller tables for each customer?

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• Getting \ building latest NHibernate build

  - by Alex Yakunin

  I'd like to get the latest NHibernate build or build it by my own. The build available at SourceForge is dated by Nov 2009, although I see there was a lot of activity later, especially related to LINQ development. So what is the best option? I can: Get the latest source code and try to build it. Are there any instructions for this? Get one of latest builds shared by someone else. Are there any people maintaining such builds? Please note, that I'm not interested in 8-month old builds - I need the latest code for tests (LINQ, performance). I know there is a similar question, but it looks like top answers there are outdated.

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• Which is the 'correct' way to do this (if statement)

  - by frinkz

  I've got plenty of these lying around, and I'm wondering if I'm going to face any trouble - or performance problems. I have method A: MyClass monkey; ... if(monkey != null) { ... } Or method B: boolean hasMonkey; //This is set to TRUE when monkey is not null MyClass monkey; ... if(hasMonkey) { ... } On a functional level, they both do the same thing. Right now, I'm using method A. Is that a bad way of doing things? Which is going to perform better?

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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• how to create english language dictionary application with python (django)?

  - by sintaloo

  Hi All, I would like to create an online dictionary application by using python (or with django). It will be similar to http://dictionary.reference.com/. My question is (1) Are there any existing open source python package or modules or application which implements this functionality that I can use or study from? (2) If the answer to the first question is NO. which algorithm should I follow to create such web application? Can I simply use the python built-in dictionary object for this job? so that the dictionary object's key will be the english word and the value will be the explanation. is this OK in term of performance? OR Do I have to create my own Tree Object to speed up the search? or any existing package which handles this job properly? Thank you very much.

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• Java : VolatileImage slower than BufferedImage.

  - by Norswap

  I'm making a game in java and in used BufferedImages to render content to the screen. I had performance issues on low end machines where the game is supposed to run, so I switched to VolatileImage which are normally faster. Except they actually slow the whole thing down. The images are created with GraphicsConfiguration.createCompatibleVolatileImage(...) and are drawn to the screen with Graphics.drawImage(...) (follow link to see which one specifically). They are drawn upon a Canvas using double buffering. Does someone has an idea of what is going wrong here ?

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• Serialze an Object to a String

  - by Vaccano

  I have the following method to save an Object to a file: // Save an object out to the disk public static void SerializeObject<T>(this T toSerialize, String filename) { XmlSerializer xmlSerializer = new XmlSerializer(toSerialize.GetType()); TextWriter textWriter = new StreamWriter(filename); xmlSerializer.Serialize(textWriter, toSerialize); textWriter.Close(); } I confess I did not write it (I only converted it to a extension method that took a type parameter). Now I need it to give the xml back to me as a string (rather than save it to a file). I am looking into it, but I have not figured it out yet. I thought this might be really easy for someone familiar with these objects. If not I will figure it out eventually.

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• Caching in Ruby Gem, possibly not using Rails

  - by corprew

  I am rewriting an existing Ruby Gem to include caching. This is for a gem that is relatively commonly used, and accesses a large amount of static data on a web service. Currently, I have a small number of gem users doing a large number of accesses to the service that under normal conditions would be swamping / downing the service, and we're going to put the gem up on github for general consumption. Right now, users can choose between using the rails cache mechanism, a simple disk cache, or no cache. What is best practice for letting people choose what cache to use like this (being able to use this outside of rails is a priority so i can't just bail to the underlying caching mechanism)? I'm looking for suggestions/examples for configuration and interface, especially. Thanks for your suggestions

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• Multiple column foreign key contraints

  - by eugene4968

  I want to setup table constraints for the following scenario and I’m not sure how to do it or if it’s even possible in SQL Server 2005. I have three tables A,B,C. C is a child of B. B will have a optional foreign key(may be null) referencing A. For performance reasons I also want table C to have the same foreign key reference to table A. The constraint on table C should be that C must reference its parent (B) and also have the same foreign key reference to A as its parent. Anyone have any thoughts on how to do this?

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• ASP SaveToDisk method takes an incredible amount of time

  - by burnt_hand

  This is a method in ASP Classic that saves a file to disk. It takes a very long time but I'm not sure why. Normally, I wouldn't mind so much, but the files it handles are pretty large so need this needs to faster than 100kB a second save. Seriously slow. (old legacy system, band aid fix till it gets replaced...) Public Sub SaveToDisk(sPath) Dim oFS, oFile Dim nIndex If sPath = "" Or FileName = "" Then Exit Sub If Mid(sPath, Len(sPath)) <> "\" Then sPath = sPath & "\" '" Set oFS = Server.CreateObject("Scripting.FileSystemObject") If Not oFS.FolderExists(sPath) Then Exit Sub Set oFile = oFS.CreateTextFile(sPath & FileName, True) For nIndex = 1 to LenB(FileData) oFile.Write Chr(AscB(MidB(FileData,nIndex,1))) Next oFile.Close End Sub I'm asking because there are plenty of WTF's in this code so I'm fighting those fires while getting some help on these ones.

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