Understanding the CMS Collector
CMS has three basic operations:
▪ CMS collects the young generation (stopping all application threads).
▪ CMS runs a concurrent cycle to clean data out of the old generation.
▪ If necessary, CMS performs a full GC.
A CMS collection of the young generation appears in Figure 6-4 .
Figure 6-4. Young collection performed by CMS
A CMS young collection is very similar to a throughput young collection: data is moved
from eden into one survivor space and into the old generation.
The GC log entry for CMS is also similar:
89.853: [GC 89.853: [ParNew: 629120K->69888K(629120K), 0.1218970 secs]
1303940K->772142K(2027264K), 0.1220090 secs]
[Times: user=0.42 sys=0.02, real=0.12 secs]
The size of the young generation is presently 629 MB; after collection, 69 MB of it remains
(in a survivor space). Similarly, the size of the entire heap is 2,027 MB—772 MB of which is