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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1823) Ability for Scanners to bypass the block cache
Date Thu, 10 Sep 2009 18:38:57 GMT
Ability for Scanners to bypass the block cache
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                 Key: HBASE-1823
                 URL: https://issues.apache.org/jira/browse/HBASE-1823
             Project: Hadoop HBase
          Issue Type: New Feature
          Components: client, regionserver
    Affects Versions: 0.20.0
            Reporter: Jonathan Gray
            Assignee: Jonathan Gray
             Fix For: 0.20.1, 0.21.0


There are a number of use cases where exposing the ability to not cache blocks during a scan
would be valuable.  For example, running row counts.

The LRU is scan-resistant, so it does provide some protection already, but even in that case
all you prevent is the eviction of hot blocks.  The LRU still runs many evictions and the
blocks are referenced for much longer periods of time, so this adds enormous stress to the
GC.

Compactions already do this.  This issue is about exposing that as a switch to the client-side
Scan object (will also enable it for MR jobs then).

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