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From "Robert Coli (JIRA)" <j...@apache.org>
Subject [jira] Created: (CASSANDRA-1967) commit log replay shouldn't end with a flush
Date Tue, 11 Jan 2011 21:26:46 GMT
commit log replay shouldn't end with a flush
--------------------------------------------

                 Key: CASSANDRA-1967
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1967
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Robert Coli


(Apologies in advance if there is some very compelling reason to flush after replay, of which
I am not currently aware. ;D)

Currently, when a node restarts, the following sequence occurs :

a) commitlog is replayed
b) any memtables resulting from a) are flushed 
c) a new commitlog is opened, new memtables are switched in
... (other stuff happens)
d) node starts taking traffic

This has side effects, perhaps most seriously the potential of triggering compaction. As a
node is likely to struggle performance-wise after restarting, triggering compaction at that
time seems like something we might wish to avoid.

I propose that the sequence be :

a) commitlog is replayed
b) a new commitlog is opened, new memtables are switched in 
... (other stuff happens)
c) node starts taking traffic

Looking through the relevant code, the only code that appears to depend on this flush is at
src/java/org/apache/cassandra/db/commitlog/CommitLog.java:112 :
"
        // all old segments are recovered and deleted before CommitLog is instantiated.
        // All we need to do is create a new one.
        segments.add(new CommitLogSegment());
"

Presumably this code would have to be refactored to be aware of the currently open commitlog.

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