Reading Verbose GC Output

To enable verbose GC output use the follwing java options when starting the JVM:

-verbose:gc

The output looks like this (and can vary slightly from different version of the JVM):

 
[GC 46336K->3775K(129664K), 0.2158256 secs]

This line represents a partial GC, as can been seen by the first part of the line:

[GC

if this GC had been a full GC, the first part of the output would be:

[Full GC

The other fields are as follows:

46336K->3775K 

-- size before and after the GC

(129664K) 

-- total available space, not counting the space in perm

0.2158256 secs

-- time the GC took

Another example, this time with a Full GC:

[Full GC 20260K->13975K(129792K), 0.5393601 secs]

20260K->13975K

-- size before and after the GC

(129664K)

-- total available space, not counting the space in perm

0.5393601 secs

-- time the GC took

Time stamps can be added to the output by adding the following option to the Java options:

-verbose:gc -XX:+PrintGCTimeStamps

which prints a time stamp at the beginning of the line, relative to the time the JVM was started, in seconds

127.720: [Full GC 20260K->13975K(129792K), 0.5393601 secs]
176.532: [GC 56794K->17083K(129792K), 0.1041413 secs]