Ryan Brush created HBASE-6322:
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Summary: Unnecessary creation of finalizers in HTablePool
Key: HBASE-6322
URL: https://issues.apache.org/jira/browse/HBASE-6322
Project: HBase
Issue Type: Bug
Components: client
Affects Versions: 0.94.0, 0.92.1, 0.92.0
Reporter: Ryan Brush
>From a mailing list question:
While generating some load against a library that makes extensive use of
HTablePool in 0.92, I noticed that the largest heap consumer was
java.lang.ref.Finalizer. Digging in, I discovered that HTablePool's
internal PooledHTable extends HTable, which instantiates a
ThreadPoolExecutor and supporting objects every time a pooled HTable is
retrieved. Since ThreadPoolExecutor has a finalizer, it and its
dependencies can't get garbage collected until the finalizer runs. The
result is by using HTablePool, we're creating a ton of objects to be
finalized that are stuck on the heap longer than they should be, creating
our largest source of pressure on the garbage collector. It looks like
this will also be a problem in 0.94 and trunk.
The easy fix is just to have PooledHTable implement HTableInterface (rather
than subclass HTable), but this does break a unit test that explicitly checks
that PooledHTable implements HTable -- I can only assume this test is there for
some historical passivity reason.
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