-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 James,
On 6/17/14, 2:21 PM, James H. H. Lampert wrote: > We launch Tomcat from a CL program, with a command front-end, and > currently we have the defaults set to 512M for the minimum heap > space, and 2048M for the maximum, running 7.0.47 or 7.0.54, and > using the JVM at /QOpenSys/QIBM/ProdData/JavaVM/jdk60/32bit. > > Any recommendations about heap size, particularly with bigger > boxes? It really all comes down to your application's requirements. Generally speaking, if you are going to have a large maximum heap size (e.g. 2GiB versus 0.5GiB), then you are better off just allocating the whole heap at JVM launch by setting Xms=Xms. That way, the heap never has to be re-sized and you'll avoid the delays associated with that resizing. Once the JVM has allocated heap space, it won't give it back to the OS, so eventually, if you need it, you're going to take the whole heap anyway. GC pauses are proportional to the number of live objects in the newer heap spaces (e.g. eden) that get promoted to the older heap spaces. If you generate a lot of garbage, it's okay: the GC isn't working much harder to handle a large heap than a small heap. If you generate lots of long-lived objects at startup, they will quickly be tenured. So the question is how your heap gets used. It's the high- and medium-longevity objects that really dictate how much heap space you need. If you have very few long-lived objects (e.g. life of the JVM process) then session objects are likely to dominate your heap. That means that required heap space will be dictated by your user load (and average session size). If you don't have sessions, or you have very modest ones, then you really don't have much to worry about. Having a large heap means that GC will run less often all things being equal. Less GC activity means a faster process overall. So, if most objects are dying on the eden heap, then having a large heap can be advantageous: you'll get fewer GC pauses leading to higher overall performance. You should really do some performance testing on your application with different heap configurations and see what happens. Remember to have a realistic load profile for testing. Simply logging-in over and over again probably isn't enough. ;) - -chris -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: GPGTools - http://gpgtools.org Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIcBAEBCAAGBQJToI8HAAoJEBzwKT+lPKRYiD8QALILc2aDVC48Kmtok+PYaGdQ AO7sy3dwUYVGDlEHVM220UAVPSXxXMN1021qZkRJ50jEzFBUI6DnYXnslFh7WkpM k8xuvTB6JO40L8gizLSQOPe5zDQm9Gyl0KGJ5ax6FBEiUSUN9x0t7eAdLNKdLXxi 3VRlqgv6C1GmUQCzFeHhrTvSfFxzVguIU+onhhw9W/o06rcBYBgAGomk8lATPwUy Yvr7trGsYaTUtagdBhZg/dv0eUwi3M+TDoEBY0U0avyogA3Ez7Icawr6b+AqqYzq u+RMSY7CEfqtnLGHl/GiW8hfT5y20W0fJ1gBJW0NOolykAVUn9nybE2GiXvV+mRr wzSAYuq71VS6yGhirzKEEu+jZ2qaKuLRxIzmO/rjmyTy4fZZN5jw9zTckhhG/2K6 LlbubXSY6MD6riD5l3bBLmbK9j03zlK2zSFvL0adkVzJcqljQACdgngpkEaAmIup EuMrCvKZVNWkOdsfHbtQZlBSwG72cg8SXN1o76DEZhIdtWttSX9LPvVfaYHDFhii XMd/IT++Q8LkjqmTkJHHfWAJYSAZf24l6PoCYTrmjxf2TB1yaF41rlAQcgrcAWiE 0qfGzh2IkxI7I0+tpoi3dbHvCEqjPDkNxQtV+IbmO58rKzl5e5vyMdTsGLF7K+h8 NK/r1/nxLLF9/Dl5QB2X =bS51 -----END PGP SIGNATURE----- --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
