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From "Jim Kellerman (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1421) When a region server dies, its log must be distributed to all the new servers that have been assigned its regions
Date Mon, 04 Jun 2007 22:48:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12501399
] 

Jim Kellerman commented on HADOOP-1421:
---------------------------------------

On a  clean shutdown, each region is closed by the HRegionServer.

The steps of closing a region are:
1. flush memcache to HLog
2. flush the HStores. This has the effect of creating a new HStoreFile from the memcache flush
and consequently, the HLog should be empty if the shutdown completes cleanly.

Consequently, the only case in which we need to read and split the HLog occurs when a HRegionServer
dies. Since this is only known to the master, the master can do the HLog splitting while it
is looking for the regions that the downed region server was serving.

> When a region server dies, its log must be distributed to all the new servers that have
been assigned its regions
> -----------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1421
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1421
>             Project: Hadoop
>          Issue Type: New Feature
>          Components: contrib/hbase
>            Reporter: Jim Kellerman
>            Assignee: Jim Kellerman
>
> When a region server dies, the master reallocates all the regions it was serving to other
region servers. In order for the regions to be recovered properly, the log from the old region
server must be split up into chunks that contain only the commits for a single region.
> Ideally, if a region server is assigned more than one of the old servers regions, the
log for that server would contain all the commits for all the regions it has been assigned.

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