Need some help understanding the MATLAB `cat` command in high dimensions
- by Runner
The commands
a = magic(3);
b = pascal(3);
c = cat(4,a,b);
produce a 3-by-3-by-1-by-2 array.
Why is the result 3-3-1-2 when the dimension is 4?
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High Runtime for Dictionary.Add for a large amount of items
- by aaginor
Hi folks, I have a C#-Application that stores data from a TextFile in a Dictionary-Object. The amount of data to be stored can be rather large, so it takes a lot of time inserting the entries. With many items in the Dictionary it gets even worse, because of the resizing of internal array, that stores the data for the Dictionary. So I initialized the Dictionary with the amount of items that will be added, but this has no impact on speed. Here is my function: private Dictionary<IdPair, Edge> AddEdgesToExistingNodes(HashSet<NodeConnection> connections) { Dictionary<IdPair, Edge> resultSet = new Dictionary<IdPair, Edge>(connections.Count); foreach (NodeConnection con in connections) { ... resultSet.Add(nodeIdPair, newEdge); } return resultSet; } In my tests, I insert ~300k items. I checked the running time with ANTS Performance Profiler and found, that the Average time for resultSet.Add(...) doesn't change when I initialize the Dictionary with the needed size. It is the same as when I initialize the Dictionary with new Dictionary(); (about 0.256 ms on average for each Add). This is definitely caused by the amount of data in the Dictionary (ALTHOUGH I initialized it with the desired size). For the first 20k items, the average time for Add is 0.03 ms for each item. Any idea, how to make the add-operation faster? Thanks in advance, FrankRead the article
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linq: SQL performance on high loaded web applications
- by Alex
I started working with linq to SQL several weeks ago. I got really tired of working with SQL server directly through the SQL queries (sqldatareader, sqlcommand and all this good stuff). After hearing about linq to SQL and mvc I quickly moved all my projects to these technologies. I expected linq to SQL work slower but it suprisongly turned out to be pretty fast, primarily because I always forgot to close my connections when using datareaders. Now I don't have to worry about it. But there's one problem that really bothers me. There's one page that's requested thousands of times a day. The system gets data in the beginning, works with it and updates it. Primarily the updates are ++ @ -- (increase and decrease values). I used to do it like this UPDATE table SET value=value+1 WHERE ID=@I'd It worked with no problems obviously. But with linq to SQL the data is taken in the beginning, moved to the class, changed and then saved. Stats.registeredusers++; Db.submitchanges(); Let's say there were 100 000 users. Linq will say "let it be 100 001" instead of "let it be increased by 1". But if there value of users has already been increased (that happens in my site all the time) then linq will be like oops, this value is already 100 001. Whatever I'll throw an exception" You can change this behavior so that it won't throw an exception but it still will not set the value to 100 002. Like I said, it happened with me all the time. The stas value was increased twice a second on average. I simply had to rewrite this chunk of code with classic ado net. So my question is how can you solve the problem with linqRead the article
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CSS font-size causing the last line to be too high
- by tster
OK, I have a list (<ul>) then inside each <li> element I have an <a...> Here are all the applicable CSS items to the <a> tag .search_area li a { font-size:11px; } sResCntr li { list-style-type:none; } body { font-family:Arial; } Everything looked great, until I put that font-size:11px in there. The problem is that the hyperlinks wrap to multiple lines within the list (which is fine). But when I decrease the font-size, the last line of the hyperlink always has a larger gap between it and the line above it than the other lines. All the other lines look good, but the last line looks like it is 1.5 spaced or something. I have adjusted the line-height property, but always the last line is larger than the rest. If you need a demo to look at to see what I mean, I can arrange it when I get home.Read the article
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High performance querying - Suggestions please
- by Alex Takitani
Supposing that I have millions of user profiles, with hundreds of fields (name, gender, preferred pet and so on...). You want to make searches on profiles. Ex.:All profiles that has age between x and y, loves butterflies, hates chocolate.... With database would you choose? Suppose that You have a Facebook like load. Speed is a must. Open Source preferred. I've read a lot about Cassandra, HBase, Mongo, Mysql... I just can't decide.....Read the article
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WinForms notifyicon high dpi
- by Dubila
in my c# application (2.0 framework) I'm using notifyicon. I set the icon to an ico file that contains 16X16 and 32X32 icons. when I change the DPI to 150% in win7 the icon looks the 16X16 icon. it looks with very low resolution.Read the article
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OpenGL: Textured Primitives + High Framerate
- by James D
Short version: What's the best practice going forward for efficiently rendering large numbers of independent texture-mapped, lighted 2D/3D primitives (circles, rects, etc.) in OpenGL? For example: a typical particle system using billboarded quads/triangles, point sprites, or whatever other technique, with blending. Because after reading this thread on the messiness of OpenGL versioning/deprecation I'm starting to have my doubts. My specific question is not the ABCs of displaying primitives in OpenGL, but rather how to do so efficiently in post-deprecation (or pre-deprecation) OpenGL, in a way that's going to be compatible with a wide range of commodity hardware and in a way that's not going to break or itself get deprecated, five years down the line. Thanks!Read the article
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High performance querying - Sugestions please
- by Alex Takitani
Supposing that I have millions of user profiles, with hundreds of fields (name, gender, preferred pet and so on...). With database would You choose? Suppose that You have a Facebook like load. Speed is a must. Open Source preferred. I've read a lot about Cassandra, HBase, Mongo, Mysql... I just can't decide.....Read the article
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high cpu in IIS
- by Miki Watts
Hi all. I'm developing a POS application that has a local database on each POS computer, and communicates with the server using WCF hosted in IIS. The application has been deployed in several customers for over a year now. About a week ago, we've started getting reports from one of our customers that the server that the IIS is hosted on is very slow. When I've checked the issue, I saw the application pool with my process rocket to almost 100% cpu on an 8 cpu server. I've checked the SQL Activity Monitor and network volume, and they showed no significant overload beyond what we usually see. When checking the threads in Process Explorer, I saw lots of threads repeatedly calling CreateApplicationContext. I've tried installing .Net 2.0 SP1, according to some posts I found on the net, but it didn't solve the problem and replaced the function calls with CLRCreateManagedInstance. I'm about to capture a dump using adplus and windbg of the IIS processes and try to figure out what's wrong. Has anyone encountered something like this or has an idea which directory I should check ? p.s. The same version of the application is deployed in another customer, and there it works just fine. I also tried rolling back versions (even very old versions) and it still behaves exactly the same. Edit: well, problem solved, turns out I've had an SQL query in there that didn't limit the result set, and when the customer went over a certain number of rows, it started bogging down the server. Took me two days to find it, because of all the surrounding noise in the logs, but I waited for the night and took a dump then, which immediately showed me the query.Read the article
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CEIL is one too high for exact integer divisions
- by Synetech
This morning I lost a bunch of files, but because the volume they were one was both internally and externally defragmented, all of the information necessary for a 100% recovery is available; I just need to fill in the FAT where required. I wrote a program to do this and tested it on a copy of the FAT that I dumped to a file and it works perfectly except that for a few of the files (17 out of 526), the FAT chain is one single cluster too long, and thus cross-linked with the next file. Fortunately I know exactly what the problem is. I used ceil in my EOF calculation because even a single byte over will require a whole extra cluster: //Cluster is the starting cluster of the file //Size is the size (in bytes) of the file //BPC is the number of bytes per cluster //NumClust is the number of clusters in the file //EOF is the last cluster of the file’s FAT chain DWORD NumClust = ceil( (float)(Size / BPC) ) DWORD EOF = Cluster + NumClust; This algorithm works fine for everything except files whose size happens to be exactly a multiple of the cluster size, in which case they end up being one cluster too much. I thought about it for a while but am at a loss as to a way to do this. It seems like it should be simple but somehow it is surprisingly tricky. What formula would work for files of any size?Read the article
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Partitioning requests in code among several servers
- by Jacques René Mesrine
I have several forum servers (what they are is irrelevant) which stores posts from users and I want to be able to partition requests among these servers. I'm currently leaning towards partitioning them by geographic location. To improve the locality of data, users will be separated into regions e.g. North America, South America and so on. Is there any design pattern on how to implement the function that maps the partioning property to the server, so that this piece of code has high availability and would not become a single point of failure ? f( Region ) -> Server IPRead the article
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Implementing a scalable and high-performing web app
- by Christopher McCann
I have asked a few questions on here before about various things relating to this but this is more of a consolidation question as I would like to check I have got the gist of everything. I am in the middle of developing a social media web app and although I have a lot of experience coding in Java and in PHP I am trying things a bit different this time. I have modularised each component of the application. So for example one component of the application allows users to private message each other and I have split this off into its own private messaging service. I have also created a user data service the purpose of which is to return data about the user for example their name, address, age etc etc from the database. Their is also another service, the friends service, which will work off the neo4j database to create a social graph. My reason for doing all this is to allow me up to update seperate modules when I need to - so while they mostly all run off MySQL right now I could move one to Cassandra later if I thought it approriate. The actual code of the web app is really just used for the final construction. The modules behind it dont really follow any strict REST or SOAP protocol. Basically each method on our API is turned into a PHP procedural script. This then may make calls to other back-end code which tends to be OO. The web app makes CURL requests to these pages and POSTs data to them or GETs data from them. These pages then return JSON where data is required. I'm still a little mixed up about how I actually identify which user is logged in at that moment. Do I just use sessions for that? Like if we called the get-messages.php script which equates to the getMessages() method for that user - returning all the private messages for that user - how would the back-end code know which user it is as posting the users ID to the script would not be secure. Anyone could do that and get all the messages. So I thought I would use sessions for it. Am I correct on this? Can anyone spot any other problems with what I am doing here? ThanksRead the article
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MySQL Rank Not Matching High Score in Table
- by boddie
While making a game the MySQL call to get the top 10 is as follows: SELECT username, score FROM userinfo ORDER BY score DESC LIMIT 10 This seems to work decently enough, but when paired with a call to get a individual player's rank the numbers may be different if the player has a tied score with other players. The call to get the players rank is as follows: SELECT (SELECT COUNT(*) FROM userinfo ui WHERE (ui.score, ui.username) >= (uo.score, uo.username)) AS rank FROM userinfo uo WHERE username='boddie'; Example results from first call: +------------+-------+ | username | score | +------------+-------+ | admin | 4878 | | test3 | 3456 | | char | 785 | | test2 | 456 | | test1 | 253 | | test4 | 78 | | test7 | 0 | | boddie | 0 | | Lz | 0 | | char1 | 0 | +------------+-------+ Example results from second call +------+ | rank | +------+ | 10 | +------+ As can be seen, the first call ranks the player at number 8 on the list, but the second call puts him at number 10. What changes or what can I do to make these calls give matching results? Thank you in advance for any help!Read the article
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Tuning JVM (GC) for high responsive server application
- by elgcom
I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?Read the article
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How to display many SVGs in Java with high performance
- by Oak
What I want My goal is to be able to display a large number of SVG images on a single drawing area in Java, each with its own translation/rotation/scale values. I'm looking for the simplest solution allowing this, optionally even using OpenGL to speed things up. What I've Tried My initial naive approach was to use SVGSalamander to draw directly on a JPanel, but the performance was pathetic. I poked around around and learned that I should do something like manually convert each SVG into a BufferedImage created with createCompatibleImage, then do the transformations I want, then draw it using double buffering. I ran into some troubles here, and before I continued I tried looking for frameworks to simplify things. What I've Looked At I've been a bit overwhelmed by the available options, which is why I'm turning to SO for help. I've looked at: Cairo (with Glitz maybe?) Libart - not sure if this actually supports SVGs FengGUI Slick - looks promising but a bit of an overkill But couldn't decide what is best for me to start working with, and I hope someone here as experience with any of these doing similar things.Read the article
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Stuttering animation in iPhone OpenGL ES although fps is high
- by guymic
I am building a 2d OpenGL es application For iPad it displays a background texture and numerous textures on top of it which are always in motion. Every frame their location is recalculated based on time delta and speed and the entire thing is being rendered at 60 fps successfully, but still as the movement speed of the sprites raises, thing look stuttering. Any ideas? Are there inherit problems with what I'm doing? Are there known design patterns for smooth animation?Read the article
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High concurrent request server in ruby
- by WedTM
I'm trying to write a simple server that will grab an mp3 file from rackspace cloudfiles, and stream it to a client over HTTP. The server must be able to stream to multiple clients simultaneously, however, I'm finding it difficult to come up with a viable solution. Anyone have some ideas?Read the article
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High precision event timer
- by rahul jv
#include "target.h" #include "xcp.h" #include "LocatedVars.h" #include "osek.h" /** * This task is activated every 10ms. */ long OSTICKDURATION; TASK( Task10ms ) { void XCP_FN_TYPE Xcp_CmdProcessor( void ); uint32 startTime = GetQueryPerformanceCounter(); /* Trigger DAQ for the 10ms XCP raster. */ if( XCPEVENT_DAQ_OVERLOAD & Xcp_DoDaqForEvent_10msRstr() ) { ++numDaqOverload10ms; } /* Update those variables which are modified every 10ms. */ counter16 += slope16; /* Trigger STIM for the 10ms XCP raster. */ if( enableBypass10ms ) { if( XCPEVENT_MISSING_DTO & Xcp_DoStimForEvent_10msRstr() ) { ++numMissingDto10ms; } } duration10ms = (uint32)( ( GetQueryPerformanceCounter() - startTime ) / STOPWATCH_TICKS_PER_US ); } What would be the easiest (and/or best) way to synchronise to some accurate clock to call a function at a specific time interval, with little jitter during normal circumstances, from C++? I am working on WINDOWS operating system now. The above code is for RTAS OSEK but I want to call a function at a specific time interval for windows operating system. Could anyone assist me in c++ language ??Read the article
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Appropriate high level language to deal with binary data
- by fortran
Hi, I need to write a small tool that parses a textual input and generates some binary encoded data. I would prefer to stay away from C and the like, in favour of a higher level, (optionally) safer, more expressive and faster to develop language. My language of choice for this kind of tasks usually is Python, but for this case dealing with binary raw data can be problematic if one isn't very careful with the numbers being promoted to bignums, sign extensions and such. Ideally I would like to have records with named bitfields that are portable to be serialised in a consistent manner. (I know that there's a strong point in doing it in a language I already master, although it isn't optimal, but I think this could be a good opportunity to learn something new). Thanks.Read the article
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Higher speed options for executing very large (20 GB) .sql file in MySQL
- by Jonogan
My firm was delivered a 20+ GB .sql file in reponse to a request for data from the gov't. I don't have many options for getting the data in a different format, so I need options for how to import it in a reasonable amount of time. I'm running it on a high end server (Win 2008 64bit, MySQL 5.1) using Navicat's batch execution tool. It's been running for 14 hours and shows no signs of being near completion. Does anyone know of any higher speed options for such a transaction? Or is this what I should expect given the large file size? ThanksRead the article
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Dynamically generating high performance functions in clojure
- by mikera
I'm trying to use Clojure to dynamically generate functions that can be applied to large volumes of data - i.e. a requirement is that the functions be compiled to bytecode in order to execute fast, but their specification is not known until run time. e.g. suppose I specify functions with a simple DSL like: (def my-spec [:add [:multiply 2 :param0] 3]) I would like to create a function compile-spec such that: (compile-spec my-spec) Would return a compiled function of one parameter x that returns 2x+3. What is the best way to do this in Clojure?Read the article
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Best Method For High Data Availability for SQL Server
- by omatase
I have a web service that runs 24/7. Periodically it needs to refresh its database with data from another web service. There is a lot of data. It's tens of thousands of rows. (no, I don't mean this is a lot of data for SQL Server, just trying to point out that I expect it to take some time to come down the pipe from the other web service) The data refresh can take between 5 and 10 minutes. The actual data update portion of that is between 1 and 2 minutes. This means the service would be down for all intents and purposes when consumers would be requesting this type of data. I would like to implement a system where data is always available. The only thing that comes to mind is some type of system where I maintain two separate databases. I populate the inactive one, swapping it to active before populating the other one. I'm not sure I know the best way to do this. My current ideas just revolve around two sets of the schema in a single database (using views to access the active set) or two databases each with the same schema. The application would rotate between the two databases. Any suggestions from someone who has done something like this before?Read the article
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What happens if a message is rolled back in MQ?
- by Manglu
Hi, I receive a message from a WebSPhere MQ queue. I try to process and if i receive some exceptions i want to rollback the message to the MQ Queue. I have no problems in doing the same. What happens to the message? Does it go to the bottom of the queue? If i try and pull a message from the queue would i receive the same message that i rolledback? What is the behaviour likely to be? I want to know this behaviour typically in a high volume Queue scenario? Appreciate any inputs. Thanks, MangluRead the article
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C# - High Quality Byte Array Conversion of Images
- by Lijo
Hi Team, I am converting images to byte array and storing in a text file using the following code. I am retrieving them successfully as well. My concern is that the quality of the retrieved image is not up to the expectation. Is there a way to have better conversion to byte array and retrieving? I am not worried about the space conception. Please share your thoughts. string plaintextStoringLocation = @"D:\ImageSource\Cha5.txt"; string bmpSourceLocation = @"D:\ImageSource\Cha50.bmp"; ////Read image Image sourceImg = Image.FromFile(bmpSourceLocation); ////Convert to Byte[] byte[] clearByteArray = ImageToByteArray(sourceImg); ////Store it for future use (in plain text form) StoreToLocation(clearByteArray, plaintextStoringLocation); //Read from binary byte[] retirevedImageBytes = ReadByteArrayFromFile(plaintextStoringLocation); //Retrieve from Byte[] Image destinationImg = ByteArrayToImage(retirevedImageBytes); //Display Image pictureBox1.Image = destinationImg; Thanks LijoRead the article
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Developing a high-performance, scalable Comet application
- by Rob
Well, the title says most of it. I'm looking to develop a chat application that will hopefully become something more, and currently I'm considering my options for what I should build it on top of. I've taken a look at Tornado with Redis as my primary option - Tornado, being a Comet server, is perfect for long polling to retrieve the messages on Redis, which I have the intention of using as both a persistent data store, as well as a message queue with its nifty subpub features. However, I've also heard good things about Django, RabbitMQ, MongoDB and Orbited. JavaScript isn't a big problem for me, so Orbited's JavaScript support isn't too much of a boon. Really, I'd probably be happy to develop on the route I've chosen for myself, but if there are any gaping deficiencies in my plan, I'd like some kind person to point them out before I find I've wasted months on this.Read the article
