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• Is Java serialization a tool to shrink the memory footprint?

  - by Pentius

  Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java? Edit I'm totally aware of what serialization was intended for, but thanks anyway :-) But you know, tools can be misused. My question is, whether it is a good tool to decrease the memory usage. So what reasons can you imagine, why memory usage should increase/decrease? What will happen in most cases?

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• Generated images fail to load in browser

  - by notJim

  I've got a page on a webapp that has about 13 images that are generated by my application, which is written in the Kohana PHP framework. The images are actually graphs. They are cached so they are only generated once, but the first time the user visits the page, and the images all have to be generated, about half of the images don't load in the browser. Once the page has been requested once and images are cached, they all load successfully. Doing some ad-hoc testing, if I load an individual image in the browser, it takes from 450-700 ms to load with an empty cache (I checked this using Google Chrome's resource tracking feature). For reference, it takes around 90-150 ms to load a cached image. Even if the image cache is empty, I have the data and some of the application's startup tasks cached, so that after the first request, none of that data needs to be fetched. My questions are: Why are the images failing to load? It seems like the browser just decides not to download the image after a certain point, rather than waiting for them all to finish loading. What can I do to get them to load the first time, with an empty cache? Obviously one option is to decrease the load times, and I could figure out how to do that by profiling the app, but are there other options? As I mentioned, the app is in the Kohana PHP framework, and it's running on Apache. As an aside, I've solved this problem for now by fetching the page as soon as the data is available (it comes from a batch process), so that the images are always cached by the time the user sees them. That feels like a kludgey solution to me, though, and I'm curious about what's actually going on.

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• NetNamedPipe: varying response time when communication is idling

  - by Sven Künzler

  I have two WCF apps communicating one-way over named pipes. All is nice, except for one thing: Normally, the request/response cycle takes zero (marginal) time. However, if there was a time span of, say, half a minute without any communication, the request/response increases up to ~300-500ms. I looked around the net and I got the idea of using a heart beat/ping mechanism to keep the communication channel busy. Using trial and error I found that when doing a request each 10 seconds, the response times stay low. Starting at around 15s intervals, the "hiccup" response times begin to appear. Now I'm wondering where this phenomenon is originating from. I tried setting alle conceivable timeouts on both sides to 1 minute, but that did not help. Can anybody explain what's going on there?

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• How do you share pre-calculated data between calls to a Rails web service?

  - by Nigel Thorne

  I have a Rails app that allows users to build up a network structure and then ask questions about how to navigate around it. When adding nodes and connections these are just saved to the database. At the point you make a query of the network I calculate the shortest path from any node to any other node. Constructing this in memory takes a while (something I need to fix), but once it is there, you can instantly get the answer to any of these path questions. The question is... How do I share this network between calls to the website, so each request doesn't regenerate the paths network each time? Note: I am hosting this on apache server using passenger (mod ruby) Thoughts?

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• Better understanding of my SQL transactions

  - by Slew Poke

  I just realized that my application was needlessly making 50+ database calls per user request due to some hidden coding -- hidden in the sense that between LINQ, persistence frameworks and events it just so turned out that a huge number of calls were being made without me being aware. Is there a recommended way to analyze individual transactions going to my SQL 2008 database, preferably with some integration to my Visual Studio 2010 environment? I want to be able to 'spy' on individual transactions being made, but only for certain pieces of my code, and without making serious changes to either the code or database.

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• Unobtrusive javascript : <script> at the top or the bottom of the html code ?

  - by e-satis

  I've recently read the Yahoo manifesto Best Practices for Speeding Up Your Web Site. They recommend to put the javascript inclusion at the bottom of the HTML code when we can. But where exactly and when ? Should we put it before closing </html> or after ? And above all, when should we still put it in the <head> section ?

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• How to avoid web server traffic peak resulting from iOS Newsstand app receiving a remote notification?

  - by thomers

  I'm developing an iOS Newsstand app. If it is suspended or not running and connected to a WLAN, Newsstand apps can be triggered by a Push remote notification to download the latest issue (in our case around 100MB) in the background. I'm using Urban Airship for the delivery of the Push broadcast. I'm now worrying about many many iOS devices hitting the web server for one big download more or less at the same time, because I expect the majority of the devices will receive the notification in a very short timeframe. Instead of broadcasts to all devices, should I rather send individual notifications to batches of small groups of devices, spreading them out over a longer period of time? And/or would a CDN like Amazon Cloudfront solve that issue easier/anyway?

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• Cache layer for MVC - Model or controller?

  - by Industrial

  Hi everyone, I am having some second thoughts about where to implement the caching part. Where is the most appropriate place to implement it, you think? Inside every model, or in the controller? Approach 1 (psuedo-code): // mycontroller.php MyController extends Controller_class { function index () { $data = $this->model->getData(); echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $data = memcached->get('data'); if (!$data) { $query->SQL_QUERY("Do query!"); } return $data; } } Approach 2: // mycontroller.php MyController extends Controller_class { function index () { $dataArray = $this->memcached->getMulti('data','data2'); foreach ($dataArray as $key) { if (!$key) { $data = $this->model->getData(); $this->memcached->set($key, $data); } } echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $query->SQL_QUERY("Do query!"); return $data; } } Thoughts: Approach 1: No multiget/multi-set. If a high number of keys would be returned, overhead would be caused. Easier to maintain, all database/cache handling is in each model Approach 2: Better performancewise - multiset/multiget is used More code required Harder to maintain Tell me what you think!

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• Tool to measure Render time

  - by Noob

  Hi Folks, Is there a tool out there to measure the actual Render time of an element(s) on a page? I don't mean download time of the resources, but the actual time the browser took to render something. I know that this time would vary based on factors on the client machine, but would still be very handy in knowing what the rendering engine takes a while to load. I would imagine this should be a useful utility since web apps are becoming pretty client heavy now. Any thoughts?

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• How to detect whether an EventWaitHandle is waiting?

  - by AngryHacker

  I have a fairly well multi-threaded winforms app that employs the EventWaitHandle in a number of places to synchronize access. So I have code similar to this: List<int> _revTypes; EventWaitHandle _ewh = new EventWaitHandle(false, EventResetMode.ManualReset); void StartBackgroundTask() { _ewh.Reset(); Thread t = new Thread(new ThreadStart(LoadStuff)); t.Start(); } void LoadStuff() { _revTypes = WebServiceCall.GetRevTypes() // ...bunch of other calls fetching data from all over the place // using the same pattern _ewh.Set(); } List<int> RevTypes { get { _ewh.WaitOne(); return _revTypes; } } Then I just call .RevTypes somewehre from the UI and it will return data to me when LoadStuff has finished executing. All this works perfectly correctly, however RevTypes is just one property - there are actually several dozens of these. And one or several of these properties are holding up the UI from loading in a fast manner. Short of placing benchmark code into each property, is there a way to see which property is holding the UI from loading? Is there a way to see whether the EventWaitHandle is forced to actually wait?

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• How expensive is a context switch? Is it better to implement a manual task switch than to rely on OS

  - by Vilx-

  The title says it all. Imagine I have two (three, four, whatever) tasks that have to run in parallel. Now, the easy way to do this would be to create separate threads and forget about it. But on a plain old single-core CPU that would mean a lot of context switching - and we all know that context switching is big, bad, slow, and generally simply Evil. It should be avoided, right? On that note, if I'm writing the software from ground up anyway, I could go the extra mile and implement my own task-switching. Split each task in parts, save the state inbetween, and then switch among them within a single thread. Or, if I detect that there are multiple CPU cores, I could just give each task to a separate thread and all would be well. The second solution does have the advantage of adapting to the number of available CPU cores, but will the manual task-switch really be faster than the one in the OS core? Especially if I'm trying to make the whole thing generic with a TaskManager and an ITask, etc?

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• finding out memory allocation hotspots in java

  - by Zamir

  Our GC is working hard and we have some pauses that we want to decrease. We have some memory allocation issues that we want to solve before or while we are tweaking with the actual JVM GC args. I would like to know which objects are making the GC sweat: is there a way to know which objects are evacuated every time the GC is working? is there a way to know which objects are moved between areas every time the GC is working? Is there a way to know which objects are in Eden area? I am working extensively with Jprofiler and Memory Analyzer. I would like to get this information on a running application in my staging environment.

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• Can serialization cause a higher memory footprint?

  - by Pentius

  Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java?

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• MySQL left outer join is slow

  - by Ryan Doherty

  Hi, hoping to get some help with this query, I've worked at it for a while now and can't get it any faster: SELECT date, count(id) as 'visits' FROM dates LEFT OUTER JOIN visits ON (dates.date = DATE(visits.start) and account_id = 40 ) WHERE date >= '2010-12-13' AND date <= '2011-1-13' GROUP BY date ORDER BY date ASC That query takes about 8 seconds to run. I've added indexes on dates.date, visits.start, visits.account_id and visits.start+visits.account_id and can't get it to run any faster. Table structure (only showing relevant columns in visit table): create table visits ( `id` int(11) NOT NULL AUTO_INCREMENT, `account_id` int(11) NOT NULL, `start` DATETIME NOT NULL, `end` DATETIME NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; CREATE TABLE `dates` ( `date` date NOT NULL, PRIMARY KEY (`date`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; dates table contains all days from 2010-1-1 to 2020-1-1 (~3k rows). visits table contains about 400k rows dating from 2010-6-1 to yesterday. I'm using the date table so the join will return 0 visits for days there were no visits. Results I want for reference: +------------+--------+ | date | visits | +------------+--------+ | 2010-12-13 | 301 | | 2010-12-14 | 356 | | 2010-12-15 | 423 | | 2010-12-16 | 332 | | 2010-12-17 | 346 | | 2010-12-18 | 226 | | 2010-12-19 | 213 | | 2010-12-20 | 311 | | 2010-12-21 | 273 | | 2010-12-22 | 286 | | 2010-12-23 | 241 | | 2010-12-24 | 149 | | 2010-12-25 | 102 | | 2010-12-26 | 174 | | 2010-12-27 | 258 | | 2010-12-28 | 348 | | 2010-12-29 | 392 | | 2010-12-30 | 395 | | 2010-12-31 | 278 | | 2011-01-01 | 241 | | 2011-01-02 | 295 | | 2011-01-03 | 369 | | 2011-01-04 | 438 | | 2011-01-05 | 393 | | 2011-01-06 | 368 | | 2011-01-07 | 435 | | 2011-01-08 | 313 | | 2011-01-09 | 250 | | 2011-01-10 | 345 | | 2011-01-11 | 387 | | 2011-01-12 | 0 | | 2011-01-13 | 0 | +------------+--------+ Thanks in advance for any help!

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• what can cause large discrepancy between minor GC time and total pause time?

  - by cxcg

  We have a latency-sensitive application, and are experiencing some GC-related pauses we don't fully understand. We occasionally have a minor GC that results in application pause times that are much longer than the reported GC time itself. Here is an example log snippet: 485377.257: [GC 485378.857: [ParNew: 105845K-621K(118016K), 0.0028070 secs] 136492K-31374K(1035520K), 0.0028720 secs] [Times: user=0.01 sys=0.00, real=1.61 secs] Total time for which application threads were stopped: 1.6032830 seconds The total pause time here is orders of magnitude longer than the reported GC time. These are isolated and occasional events: the immediately preceding and succeeding minor GC events do not show this large discrepancy. The process is running on a dedicated machine, with lots of free memory, 8 cores, running Red Hat Enterprise Linux ES Release 4 Update 8 with kernel 2.6.9-89.0.1EL-smp. We have observed this with (32 bit) JVM versions 1.6.0_13 and 1.6.0_18. We are running with these flags: -server -ea -Xms512m -Xmx512m -XX:+UseConcMarkSweepGC -XX:NewSize=128m -XX:MaxNewSize=128m -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCApplicationStoppedTime -XX:-TraceClassUnloading Can anybody offer some explanation as to what might be going on here, and/or some avenues for further investigation?

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• MySQL Single Query Benchmarking Strategies

  - by Pepper

  Hello, I have a slow mySQL query in my application that I need to re-write. The problem is, it's only slow on my production server and only when it's not cached. The first time I run it, it will take 12 seconds, then anytime after that it'll be 500 milliseconds. Is there an easy way to test this query without it hitting the query cache so I can see the results of my refactoring? Thanks!

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• Java reduce CPU usage

  - by steve

  Greets- We gots a few nutters in work who enjoy using while(true) { //Code } in their code. As you can imagine this maxes out the CPU. Does anyone know ways to reduce the CPU utilization so that other people can use the server as well. The code itself is just constantly polling the internet for updates on sites. Therefore I'd imagine a little sleep method would greatly reduce the the CPU usage. Also all manipulation is being done in String objects (Java) anyone know how much StringBuilders would reduce the over head by? Thanks for any pointers

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• Does table columns increase select statement execution time

  - by paokg4

  I have 2 tables, same structure, same rows, same data but the first has more columns (fields). For example: I select the same 3 fields from both of them (SELECT a,b,c FROM mytable1 and then SELECT a,b,c FROM mytable2) I've tried to run those queries on 100,000 records (for each table) but at the end I got the same execution time (0.0006 sec) Do you know if the number of the columns (and in the end the size of the one table is bigger than the other) has to do something with the query execution time?

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• C++ Program performs better when piped

  - by ET1 Nerd

  I haven't done any programming in a decade. I wanted to get back into it, so I made this little pointless program as practice. The easiest way to describe what it does is with output of my --help codeblock: ./prng_bench --help ./prng_bench: usage: ./prng_bench $N $B [$T] This program will generate an N digit base(B) random number until all N digits are the same. Once a repeating N digit base(B) number is found, the following statistics are displayed: -Decimal value of all N digits. -Time & number of tries taken to randomly find. Optionally, this process is repeated T times. When running multiple repititions, averages for all N digit base(B) numbers are displayed at the end, as well as total time and total tries. My "problem" is that when the problem is "easy", say a 3 digit base 10 number, and I have it do a large number of passes the "total time" is less when piped to grep. ie: command ; command |grep took : ./prng_bench 3 10 999999 ; ./prng_bench 3 10 999999|grep took .... Pass# 999999: All 3 base(10) digits = 3 base(10). Time: 0.00005 secs. Tries: 23 It took 191.86701 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. An average of 0.00019 secs & 99 tries was needed to find each one. It took 159.32355 secs & 99947208 tries to find 999999 repeating 3 digit base(10) numbers. If I run the same command many times w/o grep time is always VERY close. I'm using srand(1234) for now, to test. The code between my calls to clock_gettime() for start and stop do not involve any stream manipulation, which would obviously affect time. I realize this is an exercise in futility, but I'd like to know why it behaves this way. Below is heart of the program. Here's a link to the full source on DB if anybody wants to compile and test. https://www.dropbox.com/s/6olqnnjf3unkm2m/prng_bench.cpp clock_gettime() requires -lrt. for (int pass_num=1; pass_num<=passes; pass_num++) { //Executes $passes # of times. clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time start_time = timetodouble(temp_time); //convert time to double, store as start_time for(i=1, tries=0; i!=0; tries++) { //loops until 'comparison for' fully completes. counts reps as 'tries'. <------------ for (i=0; i<Ndigits; i++) //Move forward through array. | results[i]=(rand()%base); //assign random num of base to element (digit). | /*for (i=0; i<Ndigits; i++) //---Debug Lines--------------- | std::cout<<" "<<results[i]; //---a LOT of output.---------- | std::cout << "\n"; //---Comment/decoment to disable/enable.*/ // | for (i=Ndigits-1; i>0 && results[i]==results[0]; i--); //Move through array, != element breaks & i!=0, new digits drawn. -| } //If all are equal i will be 0, nested for condition satisfied. -| clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &temp_time); //get time draw_time = (timetodouble(temp_time) - start_time); //convert time to dbl, subtract start_time, set draw_time to diff. total_time += draw_time; //add time for this pass to total. total_tries += tries; //add tries for this pass to total. /*Formated output for each pass: Pass# ---: All -- base(--) digits = -- base(10) Time: ----.---- secs. Tries: ----- (LINE) */ std::cout<<"Pass# "<<std::setw(width_pass)<<pass_num<<": All "<<Ndigits<<" base("<<base<<") digits = " <<std::setw(width_base)<<results[0]<<" base(10). Time: "<<std::setw(width_time)<<draw_time <<" secs. Tries: "<<tries<<"\n"; } if(passes==1) return 0; //No need for totals and averages of 1 pass. /* It took ----.---- secs & ------ tries to find --- repeating -- digit base(--) numbers. (LINE) An average of ---.---- secs & ---- tries was needed to find each one. (LINE)(LINE) */ std::cout<<"It took "<<total_time<<" secs & "<<total_tries<<" tries to find " <<passes<<" repeating "<<Ndigits<<" digit base("<<base<<") numbers.\n" <<"An average of "<<total_time/passes<<" secs & "<<total_tries/passes <<" tries was needed to find each one. \n\n"; return 0;

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• Using scanf() in C++ programs is faster than using cin ?

  - by zeroDivisible

  Hello, I don't know if this is true, but when I was reading FAQ on one of the problem providing sites, I found something, that poke my attention: Check your input/output methods. In C++, using cin and cout is too slow. Use these, and you will guarantee not being able to solve any problem with a decent amount of input or output. Use printf and scanf instead. Can someone please clarify this? Is really using scanf() in C++ programs faster than using cin something ? If yes, that is it a good practice to use it in C++ programs? I thought that it was C specific, though I am just learning C++...

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• Syncing Data to Remote Services, Best Practices for Caching?

  - by viatropos

  I want to be able to publish events to Eventbrite, Eventful, and Google Calendar for my Google Apps. Each service has slightly different properties for events... I will be syncing many other things too, such as users with Google Contacts and MailChimp, Documents with Google Docs and some other services, etc... So I'm wondering, what is the recommended way of retrieving the data for the end user so that it's reasonably maintainable and optimized? Here are the things I'm thinking that I'm having trouble with: My App keeps a central database of all the models (Event, Document, User, Form, etc.), and whenever Admin creates an object (e.g. create through Eventbrite or through our Admin panel), we sync them and store a copy in our local database. When User goes to the site /events, App retrieves the events from the database. Read Events from a target feed, such as the Eventbrite or Eventful feed, and scrap the local database. Basically, I'm wondering, if we're storing all of the data on a remote service, do we really need to have a local database copy of the data? When would we need to have a local database, when wouldn't we?

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• How to set up a load/stress test for a web site?

  - by Ryan

  I've been tasked with stress/load testing our company web site out of the blue and know nothing about doing so. Every search I make on google for "how to load test a web site" just comes back with various companies and software to physically do the load testing. For now I'm more interested in how to actually go about setting up a load test like what I should take into account prior to load testing, what pages within my site I should be testing load against and what things I'm going to want to monitor when doing the test. Our web site is on a multi-tier system complete with a separate database server (IIS 7 Web Server, SQL Server 2000 db). I imagine I'd want to monitor both the web server and the database server for testing load however when setting up scenarios to load test the web server I'd have to use pages that query the database to see any load on the database server at the same time. Are web servers and database servers generally tested simultaneously or are they done as separate tests? As you can see I'm pretty clueless as to the whole operation so any incite as to how to go about this would be very helpful. FYI I have been tinkering with Pylot and was able to create and run a scenario against our site but I'm not sure what I should be looking for in the results or if the scenario I created is even a scenario worth measuring for our site. Thanks in advance.

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• Does variable = null set it for garbage collection

  - by manyxcxi

  Help me settle a dispute with a coworker: Does setting a variable or collection to null in Java aid in garbage collection and reducing memory usage? If I have a long running program and each function may be iteratively called (potentially thousands of times): Does setting all the variables in it to null before returning a value to the parent function help reduce heap size/memory usage?

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• Objective - C, fastest way to show sequence of images in UIImageView

  - by Almas Adilbek

  I have hundreds of images, which are frame images of one animation (24 images per second). Each image size is 1024x690. My problem is, I need to make smooth animation iterating each image frame in UIImageView. I know I can use animationImages of UIImageView. But it crashes, because of memory problem. Also, I can use imageView.image = [UIImage imageNamed:@""] that would cache each image, so that the next repeat animation will be smooth. But, caching a lot of images crashed app. Now I use imageView.image = [UIImage imageWithContentsOfFile:@""], which does not crash app, but doesn't make animation so smooth. Maybe there is a better way to make good animation of frame images? Maybe I need to make some preparations, in order to somehow achieve better result. I need your advices. Thank you!

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• Multi-threaded random_r is slower than single threaded version.

  - by Nixuz

  The following program is essentially the same the one described here. When I run and compile the program using two threads (NTHREADS == 2), I get the following run times: real 0m14.120s user 0m25.570s sys 0m0.050s When it is run with just one thread (NTHREADS == 1), I get run times significantly better even though it is only using one core. real 0m4.705s user 0m4.660s sys 0m0.010s My system is dual core, and I know random_r is thread safe and I am pretty sure it is non-blocking. When the same program is run without random_r and a calculation of cosines and sines is used as a replacement, the dual-threaded version runs in about 1/2 the time as expected. #include <pthread.h> #include <stdlib.h> #include <stdio.h> #define NTHREADS 2 #define PRNG_BUFSZ 8 #define ITERATIONS 1000000000 void* thread_run(void* arg) { int r1, i, totalIterations = ITERATIONS / NTHREADS; for (i = 0; i < totalIterations; i++){ random_r((struct random_data*)arg, &r1); } printf("%i\n", r1); } int main(int argc, char** argv) { struct random_data* rand_states = (struct random_data*)calloc(NTHREADS, sizeof(struct random_data)); char* rand_statebufs = (char*)calloc(NTHREADS, PRNG_BUFSZ); pthread_t* thread_ids; int t = 0; thread_ids = (pthread_t*)calloc(NTHREADS, sizeof(pthread_t)); /* create threads */ for (t = 0; t < NTHREADS; t++) { initstate_r(random(), &rand_statebufs[t], PRNG_BUFSZ, &rand_states[t]); pthread_create(&thread_ids[t], NULL, &thread_run, &rand_states[t]); } for (t = 0; t < NTHREADS; t++) { pthread_join(thread_ids[t], NULL); } free(thread_ids); free(rand_states); free(rand_statebufs); } I am confused why when generating random numbers the two threaded version performs much worse than the single threaded version, considering random_r is meant to be used in multi-threaded applications.

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