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From "Dimitar Dimitrov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13801) CompactionManager sometimes wrongly determines that a background compaction is running for a particular table
Date Wed, 06 Dec 2017 19:32:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16280752#comment-16280752
] 

Dimitar Dimitrov commented on CASSANDRA-13801:
----------------------------------------------

It turns out that the problem does not necessarily require altering the compaction strategy.
It seems to be rooted in a potential problem with counting the CF compaction requests, that
can eventually lead to a skipped background compaction.

The wrong counting can happen if the counting multiset increment [here|https://github.com/apache/cassandra/blob/95b43b195e4074533100f863344c182a118a8b6c/src/java/org/apache/cassandra/db/compaction/CompactionManager.java#L197]
gets delayed and happens after the corresponding counting multiset decrement already happened
[here|https://github.com/apache/cassandra/blob/95b43b195e4074533100f863344c182a118a8b6c/src/java/org/apache/cassandra/db/compaction/CompactionManager.java#L284].

Here are the branches with the proposed changes, as well as a Byteman test that can be used
to demonstrate the issue.
testall results look good (3.0 and trunk each have 1 seemingly unrelated, flaky test failing).
dtest results will be added soon.

| [2.2|https://github.com/apache/cassandra/compare/cassandra-2.2...dimitarndimitrov:c13801-2.2]
| [testall|^c13801-2.2-testall.png] |
| [3.0|https://github.com/apache/cassandra/compare/cassandra-3.0...dimitarndimitrov:c13801-3.0]
| [testall|^c13801-3.0-testall.png] |
| [3.11|https://github.com/apache/cassandra/compare/cassandra-3.11...dimitarndimitrov:c13801-3.11]
| [testall|^c13801-3.11-testall.png] |
| [trunk|https://github.com/apache/cassandra/compare/trunk...dimitarndimitrov:c13801-trunk]
| [testall|^c13801-2.2-testall.png] |


> CompactionManager sometimes wrongly determines that a background compaction is running
for a particular table
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13801
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13801
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Compaction
>            Reporter: Dimitar Dimitrov
>            Assignee: Dimitar Dimitrov
>            Priority: Minor
>
> Sometimes after writing different rows to a table, then doing a blocking flush, if you
alter the compaction strategy, then run background compaction and wait for it to finish, {{CompactionManager}}
may decide that there's an ongoing compaction for that same table.
> This may happen even though logs don't indicate that to be the case (compaction may still
be running for system_schema tables).



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