Re: Memory question

From:

Eric Sosman <Eric.Sosman@sun.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 03 May 2007 14:38:53 -0400

Message-ID:

<1178217534.384895@news1nwk>

Martin Gregorie wrote On 05/03/07 13:45,:

[... processing mail with large attachments ...]
Very much to my surprise nothing barfed, though when its processing the
larger mails things slow do down as it starts swapping like mad. I've
watched what's going on via the top utility. The assigned memory
eventually peaks out at 400 MB and then declines, ending the run at
around 208 MB. Releasing the memory surprised me. I had GC monitoring on
at one point and the memory release was connected with the most drastic
garbage collection modes.

By "assigned memory" do you mean the process' total
virtual memory, or the subset resident in physical RAM?
The former only shrinks by explicit action on the part
of the program ("Dear O/S: Take back your mink!"), while
the latter will fluctuate upwards and downwards as the
system responds to changing demands for memory.

It's certainly possible that the JVM explicitly
releases virtual memory under some conditions, but few
applications find it worthwhile to do so. If there's
a substantial amount of memory managed via JNI (maybe
plugins for the attachments?), that's perhaps a more
likely memory-releaser.

--
Eric.Sosman@sun.com