Thread Count supported by JVM on various OSs

Problem Statement:  On increasing our JBoss heap-size to 2GB from 1GB, JBoss was crashing every 30-60 mins.

On further analysis, it was found that the issue here was with number of threads.

Solution:

> Well, best solution is to check why your application is creating so many threads. You can check out thread-dumps for the same or use some profiling tool to find out what all threads are created by your application and if you can do something about it at application level.

> Second solution is to go for thread-pooling.

> Third solution, you can tune JVM thread stack space.

Of course, ideally, all the 3 solutions should be used. However, third one is the quickest one to start with.

Tuning JVM thread stack space:

Every thread created in a Java program has its own stack space outside the heap. So if you look at the OS report on the memory used by your JVM, you may notice that it is more than what -Xmx parameter specifies.

Default value of this stack size varies based on JVM version and OS version ranging up to 2MB.

Normally 128k is enough for all the applications. If your application requires more stack space, you will get StackOverflowError at some-point, so you need to observer application logs for this error.

You can assign thread-stack-space value with JVM option –Xss. (e.g. –Xss128k)

Following is the result of a sample program that I executed to find how many threads can be created with different stack-space (Xss) values.

(Please note: The results will be different on 64-bit system)

Important points to note:

1. For same "Thread-Stack-Size (Xss)" value, supported thread-count increases as we reduce max-heap-size
2. For same "Max-Heap-Size (Xmx)" value, supported thread-count increases as we reduce thread-stack-size

OS (32-bit)	Java-Version	Max-Heap-Size	Thread-Stack-Size	Thread-count
RHEL	1.5	1024m	Default	3636
RHEL	1.5	1250m	Default	3196
RHEL	1.5	1536m	Default	2632
RHEL	1.5	1750m	Default	2206
RHEL	1.5	2g	Default	1615
RHEL	1.5	1024m	128k	13947
RHEL	1.5	1250m	128k	12245
RHEL	1.5	1536m	128k	10083
RHEL	1.5	1750m	128k	8466
RHEL	1.5	2g	128k	6215
RHEL	1.5	1024m	256k	7183
RHEL	1.5	1250m	256k	6301
RHEL	1.5	1536m	256k	5190
RHEL	1.5	1750m	256k	4365
RHEL	1.5	2g	256k	3198
WinXP	1.5	1024m	Default	3388
WinXP	1.5	1250m	Default	2495
WinXP	1.5	1536m	Default	NA*
WinXP	1.5	1750m	Default	NA*
WinXP	1.5	2g	Default	NA*
WinXP	1.5	1024m	128k	3388
WinXP	1.5	1250m	128k	2495
WinXP	1.5	1536m	128k	NA*
WinXP	1.5	1750m	128k	NA*
WinXP	1.5	2g	128k	NA*
WinXP	1.5	1024m	256k	855
WinXP	1.5	1250m	256k	631
WinXP	1.5	1536m	256k	NA*
WinXP	1.5	1750m	256k	NA*
WinXP	1.5	2g	256k	NA*

*NA – My machine does not have enough memory to allocate to JVM

Cheers,

Sarang