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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5907) Leveled compaction may cause overlap in L1 when L0 compaction get behind
Date Tue, 20 Aug 2013 22:57:52 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13745585#comment-13745585
] 

Jonathan Ellis commented on CASSANDRA-5907:
-------------------------------------------

Hmm.  I don't follow what the linked line has to do with the problem.  (Quite possibly there
are multiple problems.)  It looks to me like the bug is that the max-sstables short circuit
here

{code}
                if (candidates.size() > MAX_COMPACTING_L0)
                {
                    // limit to only the MAX_COMPACTING_L0 oldest candidates
                    candidates = new HashSet<SSTableReader>(ageSortedSSTables(candidates).subList(0,
MAX_COMPACTING_L0));
                    break;
                }
{code}

can chop out some of the overlapping stuff from L1 that we added to {{candidates}} in the
previous loop.  (In which case it shouldn't be necessary to have multiple parallel compactions
to cause trouble.)
                
> Leveled compaction may cause overlap in L1 when L0 compaction get behind
> ------------------------------------------------------------------------
>
>                 Key: CASSANDRA-5907
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5907
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Yuki Morishita
>            Assignee: Yuki Morishita
>            Priority: Minor
>             Fix For: 1.2.9
>
>
> 1.2 makes LCS run parallel, though if L0 compaction get far behind and concurrent compactions
at L0 where each compaction holds maximum number of SSTable to compact at L0(32), it will
likely cause overlap in L1. There will be ERROR log as follows:
> {code}
> ERROR [CompactionExecutor:30] 2013-08-19 17:54:29,648 LeveledManifest.java (line 244)
At level 1, SSTableReader(path='xxx-Data.db') [DecoratedKey(204853724659241194183955214890519,
30303132343830), DecoratedKey(69227335985728660912035125310473966323, 30393537373332)] overlaps
SSTableReader(path='xxx-Data.db') [DecoratedKey(217896711032704014921095870827202, 30333635363932),
DecoratedKey(71430242198281555888954138354238066233, 30333035343132)].  This is caused by
a bug in Cassandra 1.1.0 .. 1.1.3.  Sending back to L0.  If you have not yet run scrub, you
should do so since you may also have rows out-of-order within an sstable
> {code}
> We should send back compacted SSTables to L0 when compacting max SSTables at L0. Also,
the above error message is confusing, at version 1.2, we can reduce to WARNing level without
mentioning scrub.
> C* 2.0 performs Size-Tiered compaction on L0 when it has max SSTables and sends back
compacted SSTable to L0, so I think we don't need to fix this on 2.0.

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