On 28 March 2011 02:57, Sonam Chauhan <son...@gmail.com> wrote: > Hello JMeter users: Just wanted some feedback on a formula for max. active > threads and some thoughts on errors when running tests with lots of threads. > > > > Someone recently asked a question about JMeter running out of memory when > creating new threads (the “cannot create native thread” error). > > > > I came up with this formula for maximum active threads in a thread group > with a simple ramp > > > > *maximum active threads* = average thread lifetime * total threads/ramp > period > > > Does this look right? The way I understand the formula is it finds the total > threads created by the time the first threads start terminating. Since > threads now terminate at the same rate they are being added by the ramp, > this is a steady-state figure - the “high water mark” of active threads. >
If some threads last longer than others, the maximum may be more. > > As for memory usage, each thread uses heap memory and stack memory. Total > heap memory usage limits are defined in the JMeter run script by the ‘Xms’ > (min.) and ‘Xmx’ (max.) flags. Stack memory usage is a fixed memory > allocation per thread -- it can be changed by the ‘Xss’ parameter (but its > best left alone in my experience) > > > > A 32-bit JVM running on a 32-bit OS can occupy 2 GB of RAM at most. As some > RAM is taken up by the JVM runtime itself, a JMeter instance can really > access only 1.5 -1.7 GB of RAM – the sum of both the heap and stack usage > fit into this. So we do need to be careful about allocating too much heap. > Lets assume *Xms* is set to *1.5 GB *and the test has a high water mark of > 500 active threads. The JVM will probably run out of memory creating > threads… even though there could be plenty of heap left unused, 500 threads > require about 180 MB of stack (for a 32 bit JVM), and this will cause the > test to probably generate a “cannot create native thread” error at some > point. The maximum number of thread depends very much on the test plan. I just created a test with 2000 threads, rampup 200, loop forever. Currently running at over 6500 samples per second. This is on WinXP with 2GB memory, Intel Core 2 1.67GZ with Eclipse and various other applications running. But the test only contains a single Java Request sampler and a Summary Listener. --------------------------------------------------------------------- To unsubscribe, e-mail: jmeter-user-unsubscr...@jakarta.apache.org For additional commands, e-mail: jmeter-user-h...@jakarta.apache.org
