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From "Kannan Muthukkaruppan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3327) For increment workloads, retain memstores in memory after flushing them
Date Thu, 09 Dec 2010 20:12:03 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3327?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969919#action_12969919
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Kannan Muthukkaruppan commented on HBASE-3327:
----------------------------------------------

Typo:
I think this scheme helps more than the ICV case.
meant to say:
I think this scheme helps more than just the ICV case.


> 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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