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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2027) HConnectionManager.HBASE_INSTANCES leaks TableServers
Date Sat, 05 Dec 2009 21:12:20 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12786503#action_12786503
] 

stack commented on HBASE-2027:
------------------------------

@Dave Grand.  My uninformed notion is that the way this HBASE_INSTANCES stuff works is broke.
 A static map will always be problematic.  I can understand that in the one JVM you might
want differently configured connections but keying with the HBC instance seems off.  Table
name might be better but then what if you wanted differently configured connections to the
same table?  Would that even make sense?  Thanks for looking into this.

> 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-LRU.patch, 2027.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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