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From "cuijianwei (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10396) The constructor of HBaseAdmin may close the shared HConnection
Date Wed, 22 Jan 2014 10:07:19 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10396?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13878481#comment-13878481

cuijianwei commented on HBASE-10396:

Thanks for your comment [~zjushch], I go through the code of HBaseAdmin in trunk. The HConnection
will be closed in HBaseAdmin#close so that fixed the problem. The code of HBaseAdmin changed
a lot between 0.94 and trunk, will we supply a patch for 0.94 to fix this problem? 

> The constructor of HBaseAdmin may close the shared HConnection 
> ---------------------------------------------------------------
>                 Key: HBASE-10396
>                 URL: https://issues.apache.org/jira/browse/HBASE-10396
>             Project: HBase
>          Issue Type: Bug
>          Components: Admin, Client
>    Affects Versions: 0.94.16
>            Reporter: cuijianwei
> HBaseAdmin has the constructor:
> {code}
>   public HBaseAdmin(Configuration c)
>   throws MasterNotRunningException, ZooKeeperConnectionException {
>     this.conf = HBaseConfiguration.create(c);
>     this.connection = HConnectionManager.getConnection(this.conf);
>     ...
> {code}
> As shown in above code, HBaseAdmin will get a cached HConnection or create a new HConnection
and use this HConnection to connect to Master. Then, HBaseAdmin will delete the HConnection
when connecting to master fail as follows:
> {code}
>     while ( true ){
>       try {
>         this.connection.getMaster();
>         return;
>       } catch (MasterNotRunningException mnre) {
>         HConnectionManager.deleteStaleConnection(this.connection);
>         this.connection = HConnectionManager.getConnection(this.conf);
>       }
> {code} 
> The above code will invoke HConnectionManager#deleteStaleConnection to delete the HConnection
from global HConnection cache. The risk is that the deleted HConnection might be sharing by
other threads, such as HTable or HTablePool. Then, these threads which sharing the deleted
HConnection will get closed HConnection exception:
> {code}
> org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation@61bc59aa
> {code}
> If users use HTablePool, the situation will become worse because closing HTable will
only return HTable to HTablePool which won't reduce the reference count of the closed HConnection.
Then, the closed HConnection will always be used before clearing HTablePool. In 0.94, some
modules such as Rest server are using HTablePool, therefore may suffer from this problem.

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