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https://issues.apache.org/jira/browse/CASSANDRA-11432?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15238141#comment-15238141
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Dikang Gu commented on CASSANDRA-11432:
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[~iamaleksey], I did more tests, and I think it's very likely related to the
small files generated during repair.
Before I ran the repair, this is the distribution of sstables in each level,
SSTables in each level: [1, 14/10, 146/100, 20, 0, 0, 0, 0, 0]
After I ran the repair for a while, the distribution became:
SSTables in each level: [3651/4, 14/10, 145/100, 20, 0, 0, 0, 0, 0]
So it looks like that repair generated so many small files, and since
CounterMutation needs to do a read before write, so the operation timed out.
[~iamaleksey], does it make sense? Any suggestions about how to fix it? Thanks!
> Counter values become under-counted when running repair.
> --------------------------------------------------------
>
> Key: CASSANDRA-11432
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11432
> Project: Cassandra
> Issue Type: Bug
> Reporter: Dikang Gu
> Assignee: Aleksey Yeschenko
>
> We are experimenting Counters in Cassandra 2.2.5. Our setup is that we have 6
> nodes, across three different regions, and in each region, the replication
> factor is 2. Basically, each nodes holds a full copy of the data.
> We are writing to cluster with CL = 2, and reading with CL = 1.
> When are doing 30k/s counter increment/decrement per node, and at the
> meanwhile, we are double writing to our mysql tier, so that we can measure
> the accuracy of C* counter, compared to mysql.
> The experiment result was great at the beginning, the counter value in C* and
> mysql are very close. The difference is less than 0.1%.
> But when we start to run the repair on one node, the counter value in C*
> become much less than the value in mysql, the difference becomes larger than
> 1%.
> My question is that is it a known problem that the counter value will become
> under-counted if repair is running? Should we avoid running repair for
> counter tables?
> Thanks.
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