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HBASE-6994 minor doc update about DEFAULT_ACCEPTABLE_FACTOR (Liang Xie)

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Misty Stanley-Jones 2014-10-07 13:17:05 +10:00
parent 8c3697b0d8
commit 0209e1c760
1 changed files with 8 additions and 8 deletions
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src/main/docbkx/book.xml
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@ -2262,26 +2262,26 @@ rs.close();
of time. </para>
<para>The way to calculate how much memory is available in HBase for caching is: </para>
<programlisting>
number of region servers * heap size * hfile.block.cache.size * 0.85
number of region servers * heap size * hfile.block.cache.size * 0.99
</programlisting>
<para>The default value for the block cache is 0.25 which represents 25% of the available
heap. The last value (85%) is the default acceptable loading factor in the LRU cache
heap. The last value (99%) is the default acceptable loading factor in the LRU cache
after which eviction is started. The reason it is included in this equation is that it
would be unrealistic to say that it is possible to use 100% of the available memory
since this would make the process blocking from the point where it loads new blocks.
Here are some examples: </para>
<itemizedlist>
<listitem>
<para>One region server with the default heap size (1GB) and the default block cache
size will have 217MB of block cache available.</para>
<para>One region server with the default heap size (1 GB) and the default block cache
size will have 253 MB of block cache available.</para>
</listitem>
<listitem>
<para>20 region servers with the heap size set to 8GB and a default block cache size
will have 34GB of block cache.</para>
<para>20 region servers with the heap size set to 8 GB and a default block cache size
will have 39.6 of block cache.</para>
</listitem>
<listitem>
<para>100 region servers with the heap size set to 24GB and a block cache size of 0.5
will have about 1TB of block cache.</para>
<para>100 region servers with the heap size set to 24 GB and a block cache size of 0.5
will have about 1.16 TB of block cache.</para>
</listitem>
</itemizedlist>
<para>Your data is not the only resident of the block cache. Here are others that you may have to take into account: