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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1597) Prevent unnecessary caching of blocks during compactions
Date Wed, 01 Jul 2009 05:02:47 GMT
Prevent unnecessary caching of blocks during compactions
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                 Key: HBASE-1597
                 URL: https://issues.apache.org/jira/browse/HBASE-1597
             Project: Hadoop HBase
          Issue Type: Bug
    Affects Versions: 0.20.0
            Reporter: Jonathan Gray
             Fix For: 0.20.0


When running any kind of compaction, we read every block of every storefile being compacted
into the block cache.

We would like to reuse any already cached blocks, if available, but otherwise we should not
bog down the LRU with unnecessary blocks.

This is not as bad as it was with the old LRU because the latest LRU implementation (HBASE-1460)
is scan-resistant.  This ensures that we are not causing massive eviction of the blocks that
are being read multiple times or from in-memory tables.  However, this does add to the GC-woes
of an import because each block gets further referenced, and for longer periods of time. 
There is also overhead in running the LRU evictions.

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