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• any faster alternative??

  - by kaushik

  I have to read a file from a particular line number and i know the line number say "n": i have been thinking of two choice: 1)for i in range(n) fname.readline() k=readline() print k 2)i=0 for line in fname: dictionary[i]=line i=i+1 but i want to know faster alternative as i might have to perform this on different files 20000 times. is there is any other better alternatives?? thanking u

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• Why does SQLite take such a long time to fetch the data?

  - by Derk

  I have two possible queries, both giving the result set I want. Query one takes about 30ms, but 150ms to fetch the data from the database. SELECT id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) AND EXISTS ( SELECT 1 FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) Query two takes about 3ms -this is the one I therefore prefer-, but also takes 170ms to fetch the data. SELECT ( SELECT prod2.value FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) as id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) The 170ms seems to be related to the number of rows from table featval3. After an index is used on featval3.feature IN (?,?,?,?), 151 items "remain" in featval3. Is there something obvious I am missing regarding the slow fetching? As far as I know everything is properly indexed.. I am confused because the second query only takes a blazing 3ms to run.

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• Python re module becomes 20 times slower when called on greater than 101 different regex

  - by Wiil

  My problem is about parsing log files and removing variable parts on each lines to be able to group them. For instance: s = re.sub(r'(?i)User [_0-9A-z]+ is ', r"User .. is ", s) s = re.sub(r'(?i)Message rejected because : (.*?) \(.+\)', r'Message rejected because : \1 (...)', s) I have about 120+ matching rules like those above. I have found no performances issues while searching successively on 100 different regex. But a huge slow down comes when applying 101 regex. Exact same behavior happens when replacing my rules set by for a in range(100): s = re.sub(r'(?i)caught here'+str(a)+':.+', r'( ... )', s) Got 20 times slower when putting range(101) instead. # range(100) % ./dashlog.py file.bz2 == Took 2.1 seconds. == # range(101) % ./dashlog.py file.bz2 == Took 47.6 seconds. == Why such thing is happening ? And is there any known workaround ? (Happens on Python 2.6.6/2.7.2 on Linux/Windows.)

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• when is java faster than c++ (or when is JIT faster then precompiled)?

  - by kostja

  I have heard that under certain circumstances, Java programs or rather parts of java programs are able to be executed faster than the "same" code in C++ (or other precompiled code) due to JIT optimizations. This is due to the compiler being able to determine the scope of some variables, avoid some conditionals and pull similar tricks at runtime. Could you give an (or better - some) example, where this applies? And maybe outline the exact conditions under which the compiler is able to optimize the bytecode beyond what is possible with precompiled code? NOTE : This question is not about comparing Java to C++. Its about the possibilities of JIT compiling. Please no flaming. I am also not aware of any duplicates. Please point them out if you are.

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• List of divisors of an integer n (Haskell)

  - by Code-Guru

  I currently have the following function to get the divisors of an integer: -- All divisors of a number divisors :: Integer -> [Integer] divisors 1 = [1] divisors n = firstHalf ++ secondHalf where firstHalf = filter (divides n) (candidates n) secondHalf = filter (\d -> n `div` d /= d) (map (n `div`) (reverse firstHalf)) candidates n = takeWhile (\d -> d * d <= n) [1..n] I ended up adding the filter to secondHalf because a divisor was repeating when n is a square of a prime number. This seems like a very inefficient way to solve this problem. So I have two questions: How do I measure if this really is a bottle neck in my algorithm? And if it is, how do I go about finding a better way to avoid repetitions when n is a square of a prime?

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• Speed up math code in C# by writing a C dll?

  - by Projectile Fish

  I have a very large nested for loop in which some multiplications and additions are performed on floating point numbers. for (int i = 0; i < length1; i++) { s = GetS(i); c = GetC(i); for(int j = 0; j < length2; j++) { double oldU = u[j]; u[j] = c * oldU + s * omega[i][j]; omega[i][j] = c * omega[i][j] - s * oldU; } } This loop is taking up the majority of my processing time and is a bottleneck. Would I be likely to see any speed improvements if I rewrite this loop in C and interface to it from C#?

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• iPhone Image Resources, ICO vs PNG, app bundle filesize

  - by Jasarien

  My application has a collection of around 1940 icons that are used throughout. They're currently in ICO and new images provided to me come in ICO format too. I have noticed that they contain a 16x16 and 32x32 representation of each icon in one file. Each file is roughly 4KB in filesize (as reported by finder, but ls reports that they vary from being ~1000 bytes to 5000 bytes) A very small number of these icons only contain the 32x32 representation, and as a result are only around 700 bytes in size. Currently I am bundling these icons with my application and they are inflating the size of the app a bit more than I would like. Altogether, the images total just about 25.5MB. Xcode must do some kind of compression because the resulting app bundle is about 12.4MB. Compressing this further into a ZIP (as it would be when submitted to the App Store), results in a final file of 5.8MB. I'm aware that the maximum limit for over the air App Store downloads has been raised to 20MB since the introduction of the iPad (I'm not sure if that extends to iPhone apps as well as iPad apps though, if not the limit would be 10MB). My worry is that new icons are going to be added (sometimes up to 10 icons per week), and will continue to inflate the app bundle over time. What is the best way to distribute these icons with my app? Things I've tried and not had much success with: Converting the icons from ICO to PNG: I tried this in the hopes that the pngcrush utility would help out with the filesize. But it appears that it doesn't make much of a difference between a normal PNG and a crushed png (I believe it just optimises the image for display on the iPhone's GPU rather than compress it's size). Also in going from ICO to PNG actually increased the size of the icon file... Zipping the images, and then uncompressing them on first run. While this did reduce the overall image sizes, I found that the effort needed to unzip them, copy them to the documents folder and ensure that duplication doesn't happen on upgrades was too much hassle to be worth the benefit. Also, on original and 3G iPhones unzipping and copying around 25MB of images takes too long and creates a bad experience... Things I've considered but not yet tried: Instead of distributing the icons within the app bundle, host them online, and download each icon on demand (it depends on the user's data as to which icons will actually be displayed and when). Issues with this is that bandwidth costs money, and image downloads will be bandwidth intensive. However, my app currently has a small userbase of around 5,500 users (of which I estimate around 1500 to be active based on Flurry stats), and I have a huge unused bandwidth allowance with my current hosting package. So I'm open to thoughts on how to solve this tricky issue.

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• No improvement in speed when using Ehcache with Hibernate

  - by paddydub

  I'm getting no improvement in speed when using Ehcache with Hibernate Here are the results I get when i run the test below. The test is reading 80 Stop objects and then the same 80 Stop objects again using the cache. On the second read it is hitting the cache, but there is no improvement in speed. Any idea's on what I'm doing wrong? Speed Test: First Read: Reading stops 1-80 : 288ms Second Read: Reading stops 1-80 : 275ms Cache Info: elementsInMemory: 79 elementsInMemoryStore: 79 elementsInDiskStore: 0 JunitCacheTest public class JunitCacheTest extends TestCase { static Cache stopCache; public void testCache() { ApplicationContext context = new ClassPathXmlApplicationContext("beans-hibernate.xml"); StopDao stopDao = (StopDao) context.getBean("stopDao"); CacheManager manager = new CacheManager(); stopCache = (Cache) manager.getCache("ie.dataStructure.Stop.Stop"); //First Read for (int i=1; i<80;i++) { Stop toStop = stopDao.findById(i); } //Second Read for (int i=1; i<80;i++) { Stop toStop = stopDao.findById(i); } System.out.println("elementsInMemory " + stopCache.getSize()); System.out.println("elementsInMemoryStore " + stopCache.getMemoryStoreSize()); System.out.println("elementsInDiskStore " + stopCache.getDiskStoreSize()); } public static Cache getStopCache() { return stopCache; } } HibernateStopDao @Repository("stopDao") public class HibernateStopDao implements StopDao { private SessionFactory sessionFactory; @Transactional(readOnly = true) public Stop findById(int stopId) { Cache stopCache = JunitCacheTest.getStopCache(); Element cacheResult = stopCache.get(stopId); if (cacheResult != null){ return (Stop) cacheResult.getValue(); } else{ Stop result =(Stop) sessionFactory.getCurrentSession().get(Stop.class, stopId); Element element = new Element(result.getStopID(),result); stopCache.put(element); return result; } } } ehcache.xml <cache name="ie.dataStructure.Stop.Stop" maxElementsInMemory="1000" eternal="false" timeToIdleSeconds="5200" timeToLiveSeconds="5200" overflowToDisk="true"> </cache> stop.hbm.xml <class name="ie.dataStructure.Stop.Stop" table="stops" catalog="hibernate3" mutable="false" > <cache usage="read-only"/> <comment></comment> <id name="stopID" type="int"> <column name="STOPID" /> <generator class="assigned" /> </id> <property name="coordinateID" type="int"> <column name="COORDINATEID" not-null="true"> <comment></comment> </column> </property> <property name="routeID" type="int"> <column name="ROUTEID" not-null="true"> <comment></comment> </column> </property> </class> Stop public class Stop implements Comparable<Stop>, Serializable { private static final long serialVersionUID = 7823769092342311103L; private Integer stopID; private int routeID; private int coordinateID; }

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• Preventing a heavy process from sinking in the swap file

  - by eran

  Our service tends to fall asleep during the nights on our client's server, and then have a hard time waking up. What seems to happen is that the process heap, which is sometimes several hundreds of MB, is moved to the swap file. This happens at night, when our service is not used, and others are scheduled to run (DB backups, AV scans etc). When this happens, after a few hours of inactivity the first call to the service takes up to a few minutes (consequent calls take seconds). I'm quite certain it's an issue of virtual memory management, and I really hate the idea of forcing the OS to keep our service in the physical memory. I know doing that will hurt other processes on the server, and decrease the overall server throughput. Having that said, our clients just want our app to be responsive. They don't care if nightly jobs take longer. I vaguely remember there's a way to force Windows to keep pages on the physical memory, but I really hate that idea. I'm leaning more towards some internal or external watchdog that will initiate higher-level functionalities (there is already some internal scheduler that does very little, and makes no difference). If there were a 3rd party tool that provided that kind of service is would have been just as good. I'd love to hear any comments, recommendations and common solutions to this kind of problem. The service is written in VC2005 and runs on Windows servers.

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• Coding Practices which enable the compiler/optimizer to make a faster program.

  - by EvilTeach

  Many years ago, C compilers were not particularly smart. As a workaround K&R invented the register keyword, to hint to the compiler, that maybe it would be a good idea to keep this variable in an internal register. They also made the tertiary operator to help generate better code. As time passed, the compilers matured. They became very smart in that their flow analysis allowing them to make better decisions about what values to hold in registers than you could possibly do. The register keyword became unimportant. FORTRAN can be faster than C for some sorts of operations, due to alias issues. In theory with careful coding, one can get around this restriction to enable the optimizer to generate faster code. What coding practices are available that may enable the compiler/optimizer to generate faster code? Identifying the platform and compiler you use, would be appreciated. Why does the technique seem to work? Sample code is encouraged. Here is a related question [Edit] This question is not about the overall process to profile, and optimize. Assume that the program has been written correctly, compiled with full optimization, tested and put into production. There may be constructs in your code that prohibit the optimizer from doing the best job that it can. What can you do to refactor that will remove these prohibitions, and allow the optimizer to generate even faster code? [Edit] Offset related link

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• Which memory related Tomcat JVM startup parameters are worth tuning?

  - by knorv

  I'm trying to understand the fine art of tuning Tomcat memory settings. In this quest I have the following three questions: Which memory related JVM startup parameters are worth setting when running Tomcat? Why? What are useful rule-of-thumbs when fine-tuning the memory settings for a Tomcat installation? How do you monitor the memory consumption of your live Tomcat installation?

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• A solution for the slow diff in (Tortoise)SVN?

  - by Michal Czardybon

  I often do code review in the following way: Open the SVN log Select a revision Double click on a file... ...and wait See the changes Goto 2 or 3 or finish The 4th step is very annoying. Do you know a solution for this?

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• How to cast an array to an array with another primitive type

  - by Martijn Courteaux

  Hi, Can someone complete the code on an easy way? float[] floats = {...}; // create an array // Now I want to create a new array of ints from the arrays floats int[] ints = ????; I know I can simply cast element by element to a new array. But is it possible on an easier way? Thanks

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• Cocoa - does CGDataProviderCopyData() actually copy the bytes? Or just the pointer?

  - by jtrim

  I'm running that method in quick succession as fast as I can, and the faster the better, so obviously if CGDataProviderCopyData() is actually copying the data byte-for-byte, then I think there must be a faster way to directly access that data...it's just bytes in memory. Anyone know for sure if CGDataProviderCopyData() actually copies the data? Or does it just create a new pointer to the existing data?

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• Measuring debug vs release of ASP.NET applications

  - by Alex Angas

  A question at work came up about building ASP.NET applications in release vs debug mode. When researching further (particularly on SO), general advice is that setting <compilation debug="true"> in web.config has a much bigger impact. Has anyone done any testing to get some actual numbers about this? Here's the sort of information I'm looking for (which may give away my experience with testing such things): Execution time | Debug build | Release build -------------------+---------------+--------------- Debug web.config | average 1 | average 2 Retail web.config | average 3 | average 4 Max memory usage | Debug build | Release build -------------------+---------------+--------------- Debug web.config | average 1 | average 2 Retail web.config | average 3 | average 4 Output file size | Debug build | Release build -------------------+---------------+--------------- | size 1 | size 2

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• Why are compilers so stupid?

  - by martinus

  I always wonder why compilers can't figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit complex. For example, this code takes about 6 seconds on my computer to print the value zero (using java 1.6): int x = 0; for (int i = 0; i < 100 * 1000 * 1000 * 1000; ++i) { x += x + x + x + x + x; } System.out.println(x); It is totally obvious that x is never changed so no matter how often you add 0 to itself it stays zero. So the compiler could in theory replace this with System.out.println(0). Or even better, this takes 23 seconds: public int slow() { String s = "x"; for (int i = 0; i < 100000; ++i) { s += "x"; } return 10; } First the compiler could notice that I am actually creating a string s of 100000 "x" so it could automatically use s StringBuilder instead, or even better directly replace it with the resulting string as it is always the same. Second, It does not recognize that I do not actually use the string at all, so the whole loop could be discarded! Why, after so much manpower is going into fast compilers, are they still so relatively dumb? EDIT: Of course these are stupid examples that should never be used anywhere. But whenever I have to rewrite a beautiful and very readable code into something unreadable so that the compiler is happy and produces fast code, I wonder why compilers or some other automated tool can't do this work for me.

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• Is it true "JavaScript files are not reliably cached by browsers, CSS files are"

  - by metal-gear-solid

  as mentioned on this site Note that while JavaScript files are not reliably cached by browsers, CSS files are. http://www.websiteoptimization.com/speed/tweak/http/

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• Is there a lightweight datagrid alternative in Flex ?

  - by Wayne

  What is the most performant way of displaying a table of data in Flex? Are there alternatives to the native Flex Datagrid Component? Alternatives that are noted for their rendering speed? Are there other ways to display a table? I have a datagrid with roughly 70 lines and 7 columns of simple text data. This is currently created and loaded in memory. This is being refreshed rapidly (about 800 msec) and there is a slight lag in other animations when it is rendering the table... So I am trying to cut down this render time.

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• web service filling gridview awfully slow, as is paging/sorting

  - by nat

  Hi I am making a page which calls a web service to fill a gridview this is returning alot of data, and is horribly slow. i ran the svcutil.exe on the wsdl page and it generated me the class and config so i have a load of strongly typed objects coming back from each request to the many service functions. i am then using LINQ to loop around the objects grabbing the necessary information as i go, but for each row in the grid i need to loop around an object, and grab another list of objects (from the same request) and loop around each of them.. 1 to many parent object child one.. all of this then gets dropped into a custom datatable a row at a time.. hope that makes sense.... im not sure there is any way to speed up the initial load. but surely i should be able to page/sort alot faster than it is doing. as at the moment, it appears to be taking as long to page/sort as it is to load initially. i thought if when i first loaded i put the datasource of the grid in the session, that i could whip it out of the session to deal with paging/sorting and the like. basically it is doing the below protected void Page_Load(object sender, EventArgs e) { //init the datatable //grab the filter vars (if there are any) WebServiceObj WS = WSClient.Method(args); //fill the datatable (around and around we go) foreach (ParentObject po in WS.ReturnedObj) { var COs = from ChildObject c in WS.AnotherReturnedObj where c.whatever.equals(...) ...etc foreach(ChildObject c in COs){ myDataTable.Rows.Add(tlo.this, tlo.that, c.thisthing, c.thatthing, etc......); } } grdListing.DataSource = myDataTable; Session["dt"] = myDataTable; grdListing.DataBind(); } protected void Listing_PageIndexChanging(object sender, GridViewPageEventArgs e) { grdListing.PageIndex = e.NewPageIndex; grdListing.DataSource = Session["dt"] as DataTable; grdListing.DataBind(); } protected void Listing_Sorting(object sender, GridViewSortEventArgs e) { DataTable dt = Session["dt"] as DataTable; DataView dv = new DataView(dt); string sortDirection = " ASC"; if (e.SortDirection == SortDirection.Descending) sortDirection = " DESC"; dv.Sort = e.SortExpression + sortDirection; grdListing.DataSource = dv.ToTable(); grdListing.DataBind(); } am i doing this totally wrongly? or is the slowness just coming from the amount of data being bound in/return from the Web Service.. there are maybe 15 columns(ish) and a whole load of rows.. with more being added to the data the webservice is querying from all the time any suggestions / tips happily received thanks

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• Hashtable is that fast

  - by Costa

  Hi s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]. Is the hash function of the java string, I assume the rest of languages is similar or close to this implementation. If we have hash-Table and a list of 50 elements. each element is 7 chars ABCDEF1, ABCDEF2, ABCDEF3..... ABCDEFn If each bucket of hashtable contains 5 strings (I think this function will make it one string per bucket, but let us assume it is 5). If we call col.Contains("ABCDEFn"); // will do 6 comparisons and discover the difference on the 7th. The hash-table will take around 70 operations (multiplication and additions) to get the hashcode and to compare with 5 strings in bucket. and BANG it found. For list it will take around 300 comparisons to find it. for the case that there is only 10 elements, the list will take around 70 operations but the Hashtable will take around 50 operations. and note that hashtable operations are more time consuming (it is multiplications). I conclude that HybirdDictionary in .Net probably is the best choice for that most cases that require Hashtable with unknown size, because it will let me use a list till the list becomes more than 10 elements. still need something like HashSet rather than a Dictionary of keys and values, I wonder why there is no HybirdSet!! So what do u think? Thanks

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Faster way to clone.

  - by AngryHacker

  I am trying to optimize a piece of code that clones an object: #region ICloneable public object Clone() { MemoryStream buffer = new MemoryStream(); BinaryFormatter formatter = new BinaryFormatter(); formatter.Serialize(buffer, this); // takes 3.2 seconds buffer.Position = 0; return formatter.Deserialize(buffer); // takes 2.1 seconds } #endregion Pretty standard stuff. The problem is that the object is pretty beefy and it takes 5.4 seconds (according ANTS Profiler - I am sure there is the profiler overhead, but still). Is there a better and faster way to clone?

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• MSSQL Server high CPU and I/O activity database tuning

  - by zapping

  Our application tends to be running very slow recently. On debugging and tracing found out that the process is showing high cpu cycles and SQL Server shows high I/O activity. Can you please guide as to how it can be optimised? The application is now about an year old and the database file sizes are not very big or anything. The database is set to auto shrink. Its running on win2003, SQL Server 2005 and the application is a web application coded in c# i.e vs2005

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• How to delete duplicate/aggregate rows faster in a file using Java (no DB)

  - by S. Singh

  I have a 2GB big text file, it has 5 columns delimited by tab. A row will be called duplicate only if 4 out of 5 columns matches. Right now, I am doing dduping by first loading each coloumn in separate List , then iterating through lists, deleting the duplicate rows as it encountered and aggregating. The problem: it is taking more than 20 hours to process one file. I have 25 such files to process. Can anyone please share their experience, how they would go about doing such dduping? This dduping will be a throw away code. So, I was looking for some quick/dirty solution, to get job done as soon as possible. Here is my pseudo code (roughly) Iterate over the rows i=current_row_no. Iterate over the row no. i+1 to last_row if(col1 matches //find duplicate && col2 matches && col3 matches && col4 matches) { col5List.set(i,get col5); //aggregate } Duplicate example A and B will be duplicate A=(1,1,1,1,1), B=(1,1,1,1,2), C=(2,1,1,1,1) and output would be A=(1,1,1,1,1+2) C=(2,1,1,1,1) [notice that B has been kicked out]

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• advantages of Zend_Db_Table vs raw (My)SQL?

  - by sunwukung

  Currently working on a new Zend application and developing the Model. Having worked with Zend_Db_Table before, I opted to replace references in the Model to the Table API with a custom SQL script to take care of data access duties. Now I'm looking at developing a new application/domain model, and I wanted to get some feedback from people re: their experiences with Zend_Db API vs raw SQL, and use cases where it would be preferable to use the API. From a project perspective, the DB platform is unlikely to change from MySQL - so it doesn't need to be particularly abstract - and I assume writing a custom SQL API will be more performant than the assorted classes the Zend DB API requires.

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