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From "Nikolai Grigoriev (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-6496) Endless L0 LCS compactions
Date Tue, 17 Dec 2013 03:01:08 GMT
Nikolai Grigoriev created CASSANDRA-6496:
--------------------------------------------

             Summary: Endless L0 LCS compactions
                 Key: CASSANDRA-6496
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6496
             Project: Cassandra
          Issue Type: Bug
          Components: Core
         Environment: Cassandra 2.0.3, Linux, 6 nodes, 5 disks per node
            Reporter: Nikolai Grigoriev


I have first described the problem here: http://stackoverflow.com/questions/20589324/cassandra-2-0-3-endless-compactions-with-no-traffic

I think I have really abused my system with the traffic (mix of reads, heavy updates and some
deletes). Now after stopping the traffic I see the compactions that are going on endlessly
for over 4 days.

For a specific CF I have about 4700 sstable data files right now.  The compaction estimates
are logged as "[3312, 4, 0, 0, 0, 0, 0, 0, 0]". sstable_size_in_mb=256.  3214 files are about
256Mb (+/1 few megs), other files are smaller or much smaller than that. No sstables are larger
than 256Mb. What I observe is that LCS picks 32 sstables from L0 and compacts them into 32
sstables of approximately the same size. So, what my system is doing for last 4 days (no traffic
at all) is compacting groups of 32 sstables into groups of 32 sstables without any changes.
Seems like a bug to me regardless of what did I do to get the system into this state...




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