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HBASE-4091 book.xml - description of block cache in arch, description of inMemory in schema creation 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1151747 13f79535-47bb-0310-9956-ffa450edef68
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Michael Stack 2011-07-28 06:34:56 +00:00
parent d6c0338415
commit aaad75743a
1 changed files with 24 additions and 3 deletions
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src/docbkx/book.xml
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@ -261,6 +261,17 @@ admin.enableTable(table);
that includes versioning. Take that into consideration when making your design, as well as block size for the ColumnFamily.
</para>
</section>
<section xml:id="cf.in.memory">
<title>
In-Memory ColumnFamilies
</title>
<para>ColumnFamilies can optionally be defined as in-memory. Data is still persisted to disk, just like any other ColumnFamily.
In-memory blocks have the highest priority in the <xref linkend="block.cache" />, but it is not a guarantee that the entire table
will be in memory.
</para>
<para>See <link xlink:href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html">HColumnDescriptor</link> for more information.
</para>
</section>
</chapter>
@ -984,10 +995,20 @@ HTable table2 = new HTable(conf2, "myTable");</programlisting>
</para>
</section>
</section> <!-- store -->
<section xml:id="block.cache">
<title>Block Cache</title>
<para>The Block Cache contains three levels of block priority to allow for scan-resistance and in-memory ColumnFamilies. A block is added with an in-memory
flag if the containing ColumnFamily is defined in-memory, otherwise a block becomes a single access priority. Once a block is accessed again, it changes to multiple access.
This is used to prevent scans from thrashing the cache, adding a least-frequently-used element to the eviction algorithm. Blocks from in-memory ColumnFamilies
are the last to be evicted.
</para>
<para>
For more information, see the <link xlink:href="http://hbase.apache.org/xref/org/apache/hadoop/hbase/io/hfile/LruBlockCache.html">LruBlockCache source</link>
</para>
</section>
</section>
<section xml:id="wal">
<title >Write Ahead Log (WAL)</title>