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From "gaojinchao (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5202) NPE during Master failover in master.AssignmentManager.regionOnline()
Date Mon, 16 Jan 2012 04:15:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13186681#comment-13186681

gaojinchao commented on HBASE-5202:

The root reason of this issue is some region server register lately.

when one region server without META/ROOT registers atfer "rebuildUserRegions" finished. The
regions in this one will be opened twice.

> NPE during Master failover in master.AssignmentManager.regionOnline()
> ---------------------------------------------------------------------
>                 Key: HBASE-5202
>                 URL: https://issues.apache.org/jira/browse/HBASE-5202
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.90.6
>            Reporter: Eugene Koontz
>            Assignee: Eugene Koontz
>         Attachments: HBASE-5202.patch, testMasterFailoverWithSlowRS.txt
> The following NPE can occur during master failover:
> {code}
> 2012-01-15 17:45:00,314 FATAL [Master:1;ip-10-166-123-193.us-west-1.compute.internal:36708]
master.HMaster(944): Unhandled exception. Starting shutdown.
> java.lang.NullPointerException
>         at org.apache.hadoop.hbase.master.AssignmentManager.regionOnline(AssignmentManager.java:724)
>         at org.apache.hadoop.hbase.master.AssignmentManager.processFailover(AssignmentManager.java:214)
>         at org.apache.hadoop.hbase.master.HMaster.finishInitialization(HMaster.java:396)
>         at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:279)
>         at java.lang.Thread.run(Thread.java:636)
> {code}
> This is caused by regionOnline() being passed a null serverInfo (its second parameter).

> The AssignmentManager's processFailover() method is passing a null to regionOnline()
because the value that regionOnline is passing, hsi, is set as:
> {code}
> hsi = this.serverManager.getHServerInfo(this.catalogTracker.getMetaLocation());
> {code}
> and
> {code}
> hsi = this.serverManager.getHServerInfo(this.catalogTracker.getRootLocation());
> {code}
> getHServerInfo() is defined as:
> {code}
>   public HServerInfo getHServerInfo(final HServerAddress hsa) {
>     synchronized(this.onlineServers) {
>       // TODO: This is primitive.  Do a better search.
>       for (Map.Entry<String, HServerInfo> e: this.onlineServers.entrySet()) {
>         if (e.getValue().getServerAddress().equals(hsa)) {
>           return e.getValue();
>         }
>       }
>     }
>     return null;
>   }
> {code}
> This will return null if the onlineServers map does not yet have a value corresponding
to the key supplied by the catalogTracker's getRootLocation() or getMetaLocation(). 
> Since the catalogTracker uses zookeeper to establish the server locations of {{-ROOT-}}
and {{.META.}}, while the onlineServers map is set according to the these servers' registering
with the master, there can be an inconsistency between the catalogTracker and the onlineServers
if either of these regionservers is online with respect to zookeeper, but haven't yet registered
with the master (perhaps due to a high latency network between the master and the regionserver).
> The attached testMasterFailoverWithSlowRS.txt patch can be used to modify TestMasterFailover
to cause this NPE. 
> The proposed fix (provided along with the above test in a separate attachment) is for
the master to use the new verifyMetaTablesAreUp() to wait for both of the servers named by
the catalog tracker's getRootLocation() and getMetaLocation() to register with the master
before the master can continue with failover.

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