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From "Sammy Yu (JIRA)" <>
Subject [jira] Created: (CASSANDRA-418) SSTable generation clash during compaction
Date Thu, 03 Sep 2009 01:51:32 GMT
SSTable generation clash during compaction

                 Key: CASSANDRA-418
             Project: Cassandra
          Issue Type: Bug
    Affects Versions: 0.5
            Reporter: Sammy Yu
            Assignee: Sammy Yu
             Fix For: 0.5

We found that one of our node started getting timeouts for get_slice.  Looking further we
found that the CFS.ssTables_ references a SStable doesn't exist on the file system.

Walking down the log we see that the sstable in question 6038 is being compacted onto itself
(in terms of filename file wise it is written to -tmp):
system.log.2009-09-01: INFO [MINOR-COMPACTION-POOL:1] 2009-09-01 23:50:07,553
(line 1067) Compacting 
system.log.2009-09-01: INFO [MINOR-COMPACTION-POOL:1] 2009-09-01 23:51:43,727
(line 1209) Compacted to
/mnt/var/cassandra/data/Digg/FriendActions-6038-Data.db.  0/1010269806 bytes for 9482/9373
keys read/written.  Time: 96173ms.

It appears the generation number is generated by looking at the lowest number in the list
of files to be compacted and adding 1.  In this scenario it is 6037+1=6038.
The code in CFS.doFileCompaction will remove the key and add the key back and remove the key
again, hence the error we were seeing.

Should the generation number be generated via another way or should we update doFileCompaction
to be smarter?

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