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HBASE-11752 Document blockcache prefetch option (Misty Stanley-Jones)

This commit is contained in:
Nick Dimiduk 2014-08-20 12:56:43 -07:00
parent 8670fb3339
commit 7d48fa698b
2 changed files with 39 additions and 6 deletions
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14
src/main/docbkx/book.xml
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@ -2134,12 +2134,14 @@ rs.close();
</section>
<section xml:id="cache.configurations">
<title>General Cache Configurations</title>
<para>Apart from the cache implementaiton itself, you can set some general
configuration options to control how the cache performs.
See <link
xlink:href="http://hbase.apache.org/devapidocs/org/apache/hadoop/hbase/io/hfile/CacheConfig.html" />.
After setting any of these options, restart or rolling restart your cluster for the
configuration to take effect. Check logs for errors or unexpected behavior.</para>
<para>Apart from the cache implementation itself, you can set some general configuration
options to control how the cache performs. See <link
xlink:href="http://hbase.apache.org/devapidocs/org/apache/hadoop/hbase/io/hfile/CacheConfig.html"
/>. After setting any of these options, restart or rolling restart your cluster for the
configuration to take effect. Check logs for errors or unexpected behavior.</para>
<para>See also <xref linkend="blockcache.prefetch"/>, which discusses a new option
introduced in <link xlink:href="https://issues.apache.org/jira/browse/HBASE-9857"
>HBASE-9857</link>.</para>
</section>
<section
xml:id="block.cache.design">

31
src/main/docbkx/performance.xml
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@ -217,6 +217,37 @@
A memory setting for the RegionServer process.
</para>
</section>
<section xml:id="blockcache.prefetch">
<title>Prefetch Option for Blockcache</title>
<para><link xlink:href="https://issues.apache.org/jira/browse/HBASE-9857">HBASE-9857</link>
adds a new option to prefetch HFile contents when opening the blockcache, if a columnfamily
or regionserver property is set. This option is available for HBase 0.98.3 and later. The
purpose is to warm the blockcache as rapidly as possible after the cache is opened, using
in-memory table data, and not counting the prefetching as cache misses. This is great for
fast reads, but is not a good idea if the data to be preloaded will not fit into the
blockcache. It is useful for tuning the IO impact of prefetching versus the time before all
data blocks are in cache. </para>
<para>To enable prefetching on a given column family, you can use HBase Shell or use the
API.</para>
<example>
<title>Enable Prefetch Using HBase Shell</title>
<screen>hbase> create 'MyTable', { NAME => 'myCF', PREFETCH_BLOCKS_ON_OPEN => 'true' }</screen>
</example>
<example>
<title>Enable Prefetch Using the API</title>
<programlisting language="java">
// ...
HTableDescriptor tableDesc = new HTableDescriptor("myTable");
HColumnDescriptor cfDesc = new HColumnDescriptor("myCF");
cfDesc.setPrefetchBlocksOnOpen(true);
tableDesc.addFamily(cfDesc);
// ...
</programlisting>
</example>
<para>See the API documentation for <link
xlink:href="https://hbase.apache.org/apidocs/org/apache/hadoop/hbase/io/hfile/CacheConfig.html"
>CacheConfig</link>.</para>
</section>
<section xml:id="perf.rs.memstore.size">
<title><varname>hbase.regionserver.global.memstore.size</varname></title>
<para>See <xref linkend="hbase.regionserver.global.memstore.size"/>.