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From "Dave Latham (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HBASE-2027) HConnectionManager.HBASE_INSTANCES leaks TableServers
Date Thu, 03 Dec 2009 01:31:20 GMT

     [ https://issues.apache.org/jira/browse/HBASE-2027?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Dave Latham updated HBASE-2027:
-------------------------------

    Attachment: 2027-branch.20.patch

Here's a patch for 0.20 that changes the WeakHashMap to use WeakReference's to the TableServers
for values and adds an equals method to HBaseConfiguration so that identical configs will
share the same TableServers instead of each getting their own.  Also corrects the javadoc
for HBaseConfiguration.hashCode().

> HConnectionManager.HBASE_INSTANCES leaks TableServers
> -----------------------------------------------------
>
>                 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
>
>         Attachments: 2027-branch.20.patch
>
>
> 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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