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From "Karthik Ranganathan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-3327) For increment workloads, retain memstores in memory after flushing them
Date Thu, 09 Dec 2010 19:10:03 GMT
For increment workloads, retain memstores in memory after flushing them

                 Key: HBASE-3327
                 URL: https://issues.apache.org/jira/browse/HBASE-3327
             Project: HBase
          Issue Type: Improvement
          Components: regionserver
            Reporter: Karthik Ranganathan

This is an improvement based on our observation of what happens in an increment workload.
The working set is typically small and is contained in the memstores. 
1. The reason the memstores get flushed is because the number of wal logs limit gets hit.

2. This in turn triggers compactions, which evicts the block cache. 
3. Flushing of memstore and eviction of the block cache causes disk reads for increments coming
in after this because the data is no longer in memory.

We could solve this elegantly by retaining the memstores AFTER they are flushed into files.
This would mean we can quickly populate the new memstore with the working set of data from
memory itself without having to hit disk. We can throttle the number of such memstores we
retain, or the memory allocated to it. In fact, allocating a percentage of the block cache
to this would give us a huge boost.

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