Summary

Add an option to write a gzip compressed heap dump via the GC.heap_dump diagnostic command.

Problem

With ever increasing heap sizes, the creation of heap dumps takes long and uses more space.

Solution

Add an option to directly write a gzipped heap dump via the diagnostic command GC.heap_dump. Since the deflate mechanism used in the gzip format is relatively slow, the compression is done in parallel.

When writing to a slow backing store, compression can lead to faster writing of the heap dump. And in practically all cases a compression rate of about 3 or more should be achieved.

The diagnostic command can be accessed via the jcmd tool. An example would be:

jcmd <pid|main class> GC.heap_dump -gz=4 dump.hprof.gz

This would trigger a gzip compressed heap dump of the specified VM, using a compression level of 4.

For a discussion of alternative solutions see https://mail.openjdk.java.net/pipermail/serviceability-dev/2020-February/030369.html

Specification

Add an integer option called gz to the GC.heap_dump diagnostic command. If it is specified, it will enable the gzip compression of the written heap dump. The supplied value is the compression level. It can range from 1 (fastest) to 9 (slowest, but best compression). The recommended level is 1.