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Add note on how to set up blockcache so we cache META blocks only and pull in DATA blocks on each access

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stack 2014-08-08 07:46:34 -07:00
parent 7335f5f87d
commit 3cff0d34c4
1 changed files with 13 additions and 0 deletions
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src/main/docbkx/book.xml
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@ -2137,6 +2137,19 @@ rs.close();
and would surely evict data that's currently in use. </para>
</listitem>
</itemizedlist>
<section xml:id="data.blocks.in.fscache">
<title>Caching META blocks only (DATA blocks in fscache)</title>
<para>An interesting setup is one where we cache META blocks only and we read DATA
blocks in on each access. If the DATA blocks fit inside fscache, this alternative
may make sense when access is completely random across a very large dataset.
To enable this setup, alter your table and for each column family
set <varname>BLOCKCACHE => 'false'</varname>. You are 'disabling' the
BlockCache for this column family only you can never disable the caching of
META blocks. Since
<link xlink:href="https://issues.apache.org/jira/browse/HBASE-4683">HBASE-4683 Always cache index and bloom blocks</link>,
we will cache META blocks even if the BlockCache is disabled.
</para>
</section>
</section>
<section
xml:id="offheap.blockcache">