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https://issues.apache.org/jira/browse/CASSANDRA-7139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14266493#comment-14266493
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Benedict commented on CASSANDRA-7139:
-------------------------------------
This is only the default. You are recommended to tune this default based on
your own system's behaviour. With modern SSDs and many cores, many concurrent
compactors is a great idea. For spinning disk setups, it can be terrible, and
we want to avoid terrible default decisions.
Either way, I suspect the problem you are encountering is entirely different,
i.e. that the default _compaction_throughput_mb_per_sec_ is 10, which would be
why you are maxing out at exactly 10MB/s.
> Default concurrent_compactors is probably too high
> --------------------------------------------------
>
> Key: CASSANDRA-7139
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7139
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Benedict
> Assignee: Jonathan Ellis
> Priority: Minor
> Fix For: 2.1 rc1
>
> Attachments: 7139.txt
>
>
> The default number of concurrent compactors is probably too high for modern
> hardware with spinning disks for storage: A modern blade can easily have 24+
> Cores, which would result in a default of 24 concurrent compactions. This not
> only increases random IO, it also keeps around a lot of obsoleted files for
> an unnecessarily long time, as each compaction keeps references to any
> possibly overlapping files that it isn't itself compacting - but these can
> have been obsoleted part way through by compactions that finished earlier. If
> you factor in the default compaction throughput rate of 16Mb/s, anything but
> a single default concurrent_compactor makes very little sense, as a single
> thread should always be able to handle 16Mb/s, will cause less interference
> with other processes, and permits obsoleted files to be immediately removed.
> See [http://imgur.com/HDqhxFp] for a graph demonstrating the result of making
> this change on a box with 24-cores and 8Tb of storage (first spike is default
> settings)
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