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  • Using memcpy in the STL

    - by wowus
    Why does C++'s vector class call copy constructors? Why doesn't it just memcpy the underlying data? Wouldn't that be a lot faster, and remove half of the need for move semantics? I can't imagine a use case where this would be worse, but then again, maybe it's just because I'm being quite unimaginative.

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  • Save object states in .data or attr - Performance vs CSS?

    - by Neysor
    In response to my answer yesterday about rotating an Image, Jamund told me to use .data() instead of .attr() First I thought that he is right, but then I thought about a bigger context... Is it always better to use .data() instead of .attr()? I looked in some other posts like what-is-better-data-or-attr or jquery-data-vs-attrdata The answers were not satisfactory for me... So I moved on and edited the example by adding CSS. I thought it might be useful to make a different Style on each image if it rotates. My style was the following: .rp[data-rotate="0"] { border:10px solid #FF0000; } .rp[data-rotate="90"] { border:10px solid #00FF00; } .rp[data-rotate="180"] { border:10px solid #0000FF; } .rp[data-rotate="270"] { border:10px solid #00FF00; } Because design and coding are often separated, it could be a nice feature to handle this in CSS instead of adding this functionality into JavaScript. Also in my case the data-rotate is like a special state which the image currently has. So in my opinion it make sense to represent it within the DOM. I also thought this could be a case where it is much better to save with .attr() then with .data(). Never mentioned before in one of the posts I read. But then i thought about performance. Which function is faster? I built my own test following: <!DOCTYPE HTML> <html> <head> <title>test</title> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> <script type="text/javascript"> function runfirst(dobj,dname){ console.log("runfirst "+dname); console.time(dname+"-attr"); for(i=0;i<10000;i++){ dobj.attr("data-test","a"+i); } console.timeEnd(dname+"-attr"); console.time(dname+"-data"); for(i=0;i<10000;i++){ dobj.data("data-test","a"+i); } console.timeEnd(dname+"-data"); } function runlast(dobj,dname){ console.log("runlast "+dname); console.time(dname+"-data"); for(i=0;i<10000;i++){ dobj.data("data-test","a"+i); } console.timeEnd(dname+"-data"); console.time(dname+"-attr"); for(i=0;i<10000;i++){ dobj.attr("data-test","a"+i); } console.timeEnd(dname+"-attr"); } $().ready(function() { runfirst($("#rp4"),"#rp4"); runfirst($("#rp3"),"#rp3"); runlast($("#rp2"),"#rp2"); runlast($("#rp1"),"#rp1"); }); </script> </head> <body> <div id="rp1">Testdiv 1</div> <div id="rp2" data-test="1">Testdiv 2</div> <div id="rp3">Testdiv 3</div> <div id="rp4" data-test="1">Testdiv 4</div> </body> </html> It should also show if there is a difference with a predefined data-test or not. One result was this: runfirst #rp4 #rp4-attr: 515ms #rp4-data: 268ms runfirst #rp3 #rp3-attr: 505ms #rp3-data: 264ms runlast #rp2 #rp2-data: 260ms #rp2-attr: 521ms runlast #rp1 #rp1-data: 284ms #rp1-attr: 525ms So the .attr() function did always need more time than the .data() function. This is an argument for .data() I thought. Because performance is always an argument! Then I wanted to post my results here with some questions, and in the act of writing I compared with the questions Stack Overflow showed me (similar titles) And true enough, there was one interesting post about performance I read it and run their example. And now I am confused! This test showed that .data() is slower then .attr() !?!! Why is that so? First I thought it is because of a different jQuery library so I edited it and saved the new one. But the result wasn't changing... So now my questions to you: Why are there some differences in the performance in these two examples? Would you prefer to use data- HTML5 attributes instead of data, if it represents a state? Although it wouldn't be needed at the time of coding? Why - Why not? Now depending on the performance: Would performance be an argument for you using .attr() instead of data, if it shows that .attr() is better? Although data is meant to be used for .data()? UPDATE 1: I did see that without overhead .data() is much faster. Misinterpreted the data :) But I'm more interested in my second question. :) Would you prefer to use data- HTML5 attributes instead of data, if it represents a state? Although it wouldn't be needed at the time of coding? Why - Why not? Are there some other reasons you can think of, to use .attr() and not .data()? e.g. interoperability? because .data() is jquery style and HTML Attributes can be read by all... UPDATE 2: As we see from T.J Crowder's speed test in his answer attr is much faster then data! which is again confusing me :) But please! Performance is an argument, but not the highest! So give answers to my other questions please too!

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  • Threading cost - minimum execution time when threads would add speed

    - by Lukas
    I am working on a C# application that works with an array. It walks through it (meaning that at one time only a narrow part of the array is used). I am considering adding threads in it to make it perform faster (it runs on a dualcore computer). The problem is that I do not know if it would actually help, because threads cost something and this cost could easily be more than the parallel gain... So how do I determine if threading would help?

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  • ODBC vs MySQLClient

    - by Matt
    I'm currently using ODBC to connect to my MySQL database, using C#. I've been told that using the MySql Connector would be better, and faster, and not dependent on Windows. Can someone shed some light on this please? I've been unable to find anything on the net so far

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  • Is it possible to stop a javascript with Firebug without using breakpoints?

    - by Sandra
    Is it possible with Firebug to stop a javascript with a press of a button or a keyboard shortcut instead of stopping it by setting a breakpoint? Why would I like to do this? We have a very dynamic website with lots of animations. It would be a great help if I could just stop the scripts at the moment the animation is doing something I want to inspect. That would be a lot faster than fiddling with the breakpoints.

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  • Is there a way to change the color of plots in jQuery flot without redrawing the whole chart?

    - by Sam Lee
    I have a chart that I'm drawing using flot. I want to change the colors of the data plots when someone hovers over text. Currently, I am doing this by redrawing the entire chart each time I need to highlight something. This is pretty slow (about 30 milliseconds for a simple chart, as much as 100 for a more complicated chart). Since all I want to do is change the color, is there a faster solution?

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  • How can I limit the cache used by copying so there is still memory available for other cache?

    - by Peter
    Basic situation: I am copying some NTFS disks in openSuSE. Each one is 2TB. When I do this, the system runs slow. My guesses: I believe it is likely due to caching. Linux decides to discard useful cache (eg. kde4 bloat, virtual machine disks, LibreOffice binaries, Thunderbird binaries, etc.) and instead fill all available memory (24 GB total) with stuff from the copying disks, which will be read only once, then written and never used again. So then any time I use these apps (or kde4), the disk needs to be read again, and reading the bloat off the disk again makes things freeze/hiccup. Due to the cache being gone and the fact that these bloated applications need lots of cache, this makes the system horribly slow. Since it is USB,the disk and disk controller are not the bottleneck, so using ionice does not make it faster. I believe it is the cache rather than just the motherboard going too slow, because if I stop everything copying, it still runs choppy for a while until it recaches everything. And if I restart the copying, it takes a minute before it is choppy again. But also, I can limit it to around 40 MB/s, and it runs faster again (not because it has the right things cached, but because the motherboard busses have lots of extra bandwidth for the system disks). I can fully accept a performance loss from my motherboard's IO capability being completely consumed (which is 100% used, meaning 0% wasted power which makes me happy), but I can't accept that this caching mechanism performs so terribly in this specific use case. # free total used free shared buffers cached Mem: 24731556 24531876 199680 0 8834056 12998916 -/+ buffers/cache: 2698904 22032652 Swap: 4194300 24764 4169536 I also tried the same thing on Ubuntu, which causes a total system hang instead. ;) And to clarify, I am not asking how to leave memory free for the "system", but for "cache". I know that cache memory is automatically given back to the system when needed, but my problem is that it is not reserved for caching of specific things. Question: Is there some way to tell these copy operations to limit memory usage so some important things remain cached, and therefore any slowdowns are a result of normal disk usage and not rereading the same commonly used files? For example, is there a setting of max memory per process/user/file system allowed to be used as cache/buffers?

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  • How can I load a file into a DataBag from within a Yahoo PigLatin UDF?

    - by Cervo
    I have a Pig program where I am trying to compute the minimum center between two bags. In order for it to work, I found I need to COGROUP the bags into a single dataset. The entire operation takes a long time. I want to either open one of the bags from disk within the UDF, or to be able to pass another relation into the UDF without needing to COGROUP...... Code: # **** Load files for iteration **** register myudfs.jar; wordcounts = LOAD 'input/wordcounts.txt' USING PigStorage('\t') AS (PatentNumber:chararray, word:chararray, frequency:double); centerassignments = load 'input/centerassignments/part-*' USING PigStorage('\t') AS (PatentNumber: chararray, oldCenter: chararray, newCenter: chararray); kcenters = LOAD 'input/kcenters/part-*' USING PigStorage('\t') AS (CenterID:chararray, word:chararray, frequency:double); kcentersa1 = CROSS centerassignments, kcenters; kcentersa = FOREACH kcentersa1 GENERATE centerassignments::PatentNumber as PatentNumber, kcenters::CenterID as CenterID, kcenters::word as word, kcenters::frequency as frequency; #***** Assign to nearest k-mean ******* assignpre1 = COGROUP wordcounts by PatentNumber, kcentersa by PatentNumber; assignwork2 = FOREACH assignpre1 GENERATE group as PatentNumber, myudfs.kmeans(wordcounts, kcentersa) as CenterID; basically my issue is that for each patent I need to pass the sub relations (wordcounts, kcenters). In order to do this, I do a cross and then a COGROUP by PatentNumber in order to get the set PatentNumber, {wordcounts}, {kcenters}. If I could figure a way to pass a relation or open up the centers from within the UDF, then I could just GROUP wordcounts by PatentNumber and run myudfs.kmeans(wordcount) which is hopefully much faster without the CROSS/COGROUP. This is an expensive operation. Currently this takes about 20 minutes and appears to tack the CPU/RAM. I was thinking it might be more efficient without the CROSS. I'm not sure it will be faster, so I'd like to experiment. Anyway it looks like calling the Loading functions from within Pig needs a PigContext object which I don't get from an evalfunc. And to use the hadoop file system, I need some initial objects as well, which I don't see how to get. So my question is how can I open a file from the hadoop file system from within a PIG UDF? I also run the UDF via main for debugging. So I need to load from the normal filesystem when in debug mode. Another better idea would be if there was a way to pass a relation into a UDF without needing to CROSS/COGROUP. This would be ideal, particularly if the relation resides in memory.. ie being able to do myudfs.kmeans(wordcounts, kcenters) without needing the CROSS/COGROUP with kcenters... But the basic idea is to trade IO for RAM/CPU cycles. Anyway any help will be much appreciated, the PIG UDFs aren't super well documented beyond the most simple ones, even in the UDF manual.

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  • What does "Computing additional info" mean?

    - by JesperE
    Eclipse Helios periodically starts running a job which displays "Computing additional info". During this time, Eclipse is very sluggish, bordering on unusable. What does this job do? Can I shut it off? I just hope that someone in the JDT team comes to sense and gets rid of it, make it go faster, or at the very least change it to something meaningful.

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  • Jruby rspec to be run parallely

    - by Priyank
    Hi. Is there something like Spork for Jruby too? We want to parallelize our specs to run faster and pre-load the classes while running the rake task; however we have not been able to do so. Since our project is considerable in size, specs take about 15 minutes to complete and this poses a serious challenge to quick turnaround. Any ideas are more than welcome. Cheers

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  • mysql datetime performance

    - by praksant
    Hi, since in mysql datetime field is represented as string (i'm not sure how it works internally), wouldn't be from performance point of view faster to store date as unix timestamp? I don't need to use any mysql native date functions, i'm going for performance of sorting and selecting data. if there was an index for that column, would be difference between int and datetime? Thank you

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  • Java NIO Servlet to File

    - by Gandalf
    Is there a way (without buffering the whole Inputstream) to take the HttpServletRequest from a Java Servlet and write it out to a file using all NIO? Is it even worth trying? Will it be any faster reading from a normal java.io stream and writing to a java.nio Channel or do they both really need to be pure NIO to see a benefit? Thanks.

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  • Performance of looping over an Unboxed array in Haskell

    - by Joey Adams
    First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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  • Algorithm for multiple word matching in a text, count the number of every matched word

    - by 66
    I have noticed that it has solutions for matching multiple words in a given text, such as below: http://stackoverflow.com/questions/1099985/algorithm-for-multiple-word-matching-in-text If I want to know exactly the number of appearances of each matched word in the text, my solution is like this: step 1: using ac-algorithm to obtain the maching words; step 2: count the number of each word obtained in step 1 is there a faster way? Thx~

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  • Fastest way to check array items existence in mySQL table

    - by Enrique
    User writes a series of tags (, separated) and posts the form. I build an array containing the tags and delete dupes with array_unique() php function. I'm thinking of doing: go through the array with foreach($newarray as $item) { ... } check each $item for existence in the tags mySQL table if item does not exists, insert into tags table Is there a FASTER or MORE OPTIMUM way for doing this?

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  • what does process geometry mean?

    - by wenlujon
    from ARM DDI 01001, there is a term: process geometry, does it mean the chip size? Caches and write buffers to improve average system performance are now commonplace in ARM® memory systems. Core clock rates have increased at a faster rate than memory access times over recent years. This factor, and smaller process geometries, the economics of on-chip memory, and system power constraints have encouraged the use of caches to meet growing system demands. thanks.

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  • Fastest way to compute a "Visual" checksum of an image

    - by ensnare
    I'm looking to create an ID system for cataloging images. I can't use md5() since that will change if I alter the EXIF tags of the image. I am currently using the SHA1 checksum computed by imagemagick. It works perfectly, but it's really, really slow on larger images (~15 seconds on a quad-core xeon for a 21 megapixel JPG). Are there any other "visual" methods of uniquely identifying an image that would be faster? Thank you.

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  • Silverlight or MVC for Web Development

    - by jhorback
    I was just wondering about the opinions out there. What do you think promotes faster development times for a web application? Silverlight or .Net MVC? And could Silverlight be a replacement for a true http web application? Feel free to rant or give as much details as necessary.

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  • How to find subgroups statistics in pandas?

    - by user2808117
    I am grouping a DataFrame using multiple columns (e.g., columns A, B - my_df.groupby(['A','B']) ), is there a better (less lines of code, faster) way of finding how many rows are in each subgroup and how many subgroups are there in total? at the moment I am using: def get_grp_size(grp): grp['size'] = len(grp) return grp my_df = my_df.groupby(['A','B']).apply(get_grp_size) my_df[['A','B','size']].drop_duplicates().size

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  • Required help to Increase the performance of the MySQL query

    - by Joseph
    Hi all, I am using a following query in MySQl for fetching data from a table. Its taking too long because the conditional check within the aggregate function.Please help how to make it faster SELECT testcharfield ,SUM(IF (Type = 'pi',quantity, 0)) AS OB ,SUM(IF (Type = 'pe',quantity, 0)) AS CB FROM Table1 WHERE sequenceID = 6107 GROUP BY testcharfield

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