java - Heap dump's total size more than the used heap/perm gem -
i'm analyzing memory usage of tool using visualvm + visualgc. noticed wasn't expecting exposes misunderstanding of mine concerning jvm , heap dumps.
to give full context, application profiling lookup of huge blob of serialized printing size of using jamm. after that, app sits there , waits until aborted.
using visualvm, see heap usage growing expected. once operation complete , app sitting there sleeping, trigger gc (or rather, multiple gcs, carried away clicking button) using visualvm.
- the used heap @ point
1,849,825,472 bytes
, permgem used space25,864,448 bytes
. at point, perform heap dump takes while but, when heap dump completes, used heap still
1,944,542,296 bytes
permgen same @25,892,800 bytes
.here's punch: heap dump shows total bytes count of
2,299,816,089
.
what explain such discrepancy? repeated experiments few times , i'm getting same results.
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