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HBASE-8190 Add documentation of region merges to the book 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1461396 13f79535-47bb-0310-9956-ffa450edef68
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zjushch 2013-03-27 03:08:12 +00:00
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src/docbkx/book.xml
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@ -2176,6 +2176,28 @@ myHtd.setValue(HTableDescriptor.SPLIT_POLICY, MyCustomSplitPolicy.class.getName(
</section>
</section>
<section>
<title>Online Region Merges</title>
<para>Both Master and Regionserver participate in the event of online region merges.
Client sends merge RPC to master, then master moves the regions together to the
same regionserver where the more heavily loaded region resided, finally master
send merge request to this regionserver and regionserver run the region merges.
Similar with process of region splits, region merges run as a local transaction
on the regionserver, offlines the regions and then merges two regions on the file
system, atomically delete merging regions from META and add merged region to the META,
opens merged region on the regionserver and reports the merge to Master at last.
</para>
<para>An example of region merges in the hbase shell
<programlisting>$ hbase> merge_region 'ENCODED_REGIONNAME', 'ENCODED_REGIONNAME'
hbase> merge_region 'ENCODED_REGIONNAME', 'ENCODED_REGIONNAME', true
</programlisting>
It's an asynchronous operation and call returns immediately without waiting merge completed.
Passing 'true' as the optional third parameter will force a merge ('force' merges regardless
else merge will fail unless passed adjacent regions. 'force' is for expert use only)
</para>
</section>
<section xml:id="store">
<title>Store</title>
<para>A Store hosts a MemStore and 0 or more StoreFiles (HFiles). A Store corresponds to a column family for a table for a given region.