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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-6812) Iterative Memtable->SSTable Replacement
Date Thu, 06 Mar 2014 20:53:56 GMT
Benedict created CASSANDRA-6812:
-----------------------------------

             Summary: Iterative Memtable->SSTable Replacement
                 Key: CASSANDRA-6812
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6812
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Benedict
             Fix For: 3.0


In an ideal world we wouldn't flush any memtable until we were almost completely out of room.
The problem with this approach (and in fact whenever we currently *do* run out of room) is
that flushing an entire memtable is a slow process, and so write latencies spike dramatically
during this interval.

The solution to this is, in principle, quite straight forward: As we write chunks of the new
sstable and its index, open them up immediately for reading, and free the memory associated
with the portion of the file that has been written so that it can be reused immediately for
writing. This way whilst latency will increase for the duration of the flush, the max latency
experienced during this time should be no greater than the time taken to flush a few chunks,
which should still be on the order of milliseconds, not seconds.

This depends on CASSANDRA-6689 and CASSANDRA-6694, so that we can reclaim arbitrary portions
of the allocated memory prior to a complete flush.



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