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From "Chen Shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-10862) LCS repair: compact tables before making available in L0
Date Thu, 09 Jun 2016 00:30:21 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15321703#comment-15321703
] 

Chen Shen commented on CASSANDRA-10862:
---------------------------------------

[~pauloricardomg]
I've done some investigation and I find it might not so easy to schedule a compaction on L0
table on reception as the only straightforward way to trigger a compaction is by submitting
a task to CompactionManager.submitBackground, and 1) it's not guaranteed to be executed according
to my knowledge 2) submitBackground need a `ColumnFamilyStore` as input, so we need either
create a new CFS, or split the compaction strategy out of CompactionManager, each of which
might need lots of work.
So instead I am doing a different tricky approach: Don't add tables to CFS until the number
of L0 sstables is smaller than a threshold. And subscribe to `SSTableListChangedNotification`
so that the `OnCompletionRunnable` could sleep and wait on notification. 
Is this a right direction? I have a commit here https://github.com/scv119/cassandra/commit/5e0c5b1da83ae7f2d2ccc382fd69c438637b2772
if you want to take a look. I'm also planing to apply this patch to our production tier to
see if this helps.
 

> LCS repair: compact tables before making available in L0
> --------------------------------------------------------
>
>                 Key: CASSANDRA-10862
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10862
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Compaction, Streaming and Messaging
>            Reporter: Jeff Ferland
>            Assignee: Chen Shen
>
> When doing repair on a system with lots of mismatched ranges, the number of tables in
L0 goes up dramatically, as correspondingly goes the number of tables referenced for a query.
Latency increases dramatically in tandem.
> Eventually all the copied tables are compacted down in L0, then copied into L1 (which
may be a very large copy), finally reducing the number of SSTables per query into the manageable
range.
> It seems to me that the cleanest answer is to compact after streaming, then mark tables
available rather than marking available when the file itself is complete.



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