HConnectionManager.HBASE_INSTANCES leaks TableServers
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Key: HBASE-2027
URL: https://issues.apache.org/jira/browse/HBASE-2027
Project: Hadoop HBase
Issue Type: Bug
Affects Versions: 0.20.0
Reporter: Dave Latham
Assignee: Dave Latham
Fix For: 0.20.3, 0.21.0
HConnectionManager.HBASE_INSTANCES is a WeakHashMap from HBaseConfiguration to
TableServers. However, each TableServers has a strong reference back to the
HBaseConfiguration key so they are never freed. (See note at
http://java.sun.com/javase/6/docs/api/java/util/WeakHashMap.html :
"Implementation note: The value objects in a WeakHashMap are held by ordinary
strong references. Thus care should be taken to ensure that value objects do
not strongly refer to their own keys, either directly or indirectly, since that
will prevent the keys from being discarded.")
Moreover, HBaseConfiguration implements hashCode() but not equals() so
identical HBaseConfiguration objects each get their own TableServers object.
We had a long running HBase client process that was creating new HTable()
objects, each creating a new HBaseConfiguration() and thus a new TableServers
object. It eventually went OOM, and gave a heap dump indicating 360 MB of data
retained by HBASE_INSTANCES.
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