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From "A Markov (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-10138) Millions of compaction tasks on empty DB
Date Thu, 20 Aug 2015 12:34:45 GMT
A Markov created CASSANDRA-10138:
------------------------------------

             Summary: Millions of compaction tasks on empty DB
                 Key: CASSANDRA-10138
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10138
             Project: Cassandra
          Issue Type: Bug
         Environment: CentOS 6.5 and Cassandra 2.1.8
            Reporter: A Markov


Fresh installation of 2.1.8 Cassandra with no data in the database except systems tables becomes
unresponsive after about 5-10 minutes from the start.

Initially problem was discovered on empty cluster of 12 nodes because of the creation schema
error - script was exiting by timeout giving an error. 

Analysis of log files showed that nodes were constantly reported as DOWN and then after some
period of time UP. That was reported for multiple nodes.

Verification of the system.log file showed that nodes constantly perform GC and while doing
that all cores of the system were 100% busy which caused node disconnect after some time.

Further analysis with nodetool (tpstats option) showed us that just after 10 minutes since
clean node restart node completed more then 47M compaction tasks and had more then 12M pending.
Here is example of the output:

nodetool tpstats

Pool Name                    Active   Pending      Completed   Blocked  All time blocked
CounterMutationStage              0         0              0         0                 0
ReadStage                         0         0              0         0                 0
RequestResponseStage              0         0              0         0                 0
MutationStage                     0         0            257         0                 0
ReadRepairStage                   0         0              0         0                 0
GossipStage                       0         0              0         0                 0
CacheCleanupExecutor              0         0              0         0                 0
MigrationStage                    0         0              0         0                 0
ValidationExecutor                0         0              0         0                 0
Sampler                           0         0              0         0                 0
MemtableReclaimMemory             0         0              8         0                 0
InternalResponseStage             0         0              0         0                 0
AntiEntropyStage                  0         0              0         0                 0
MiscStage                         0         0              0         0                 0
CommitLogArchiver                 0         0              0         0                 0
MemtableFlushWriter               0         0              8         0                 0
PendingRangeCalculator            0         0              1         0                 0
MemtablePostFlush                 0         0             44         0                 0
CompactionExecutor                0  12996398       47578625         0                 0
AntiEntropySessions               0         0              0         0                 0
HintedHandoff                     0         1              2         0                 0

I am repeating myself but that was on TOTALLY EMPTY DB after 10 minutes since cassandra was
started.

I was able to repeateadly reproduce same issue and behaviour with single cassandra instance.
Issue was persistent after I did full cassandra wipe out and reinstall from repository.

I discovered that issue dissipaters if I execute
nodetool disableautocompaction

in that case system quickly (in a matter of 20-30 seconds) goes though all pending tasks and
becomes idle. If I enable autocompaction again in about 1 minute it jumps to millions of pending
tasks again.

I verified it on the save server with version of Cassandra 2.1.6 and issue was not present.

logs file do not show any ERROR messages. There were only warnings about GC events that were
taking too long.



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