[jira] [Created] (CASSANDRA-6357) Flush memtables to seperate directory

["Patrick McFadin (JIRA)" <ji...@apache.org>]

Patrick McFadin created CASSANDRA-6357:
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             Summary: Flush memtables to seperate directory
                 Key: CASSANDRA-6357
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6357
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Patrick McFadin


Flush writers are a critical element for keeping a node healthy. When several compactions run on systems with low performing data directories, IO becomes a premium. Once the disk subsystem is saturated, write IO is blocked which will cause flush writer threads to backup. Since memtables are large blocks of memory in the JVM, too much blocking can cause excessive GC over time degrading performance. In the worst case causing an OOM.

Since compaction is running on the data directories. My proposal is to create a separate directory for flushing memtables. Potentially we can use the same methodology of keeping the commit log separate and minimize disk contention against the critical function of the flushwriter. 



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