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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4292) Per-disk I/O queues
Date Wed, 25 Jul 2012 20:19:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422574#comment-13422574
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Jonathan Ellis commented on CASSANDRA-4292:
-------------------------------------------

bq. Directory is chosen based on available space in both queue and disk.

We still want to prioritize disks that have no tasks yet, since ipos are a bigger bottleneck
than space, in general.

So specifically, we want to prioritize in order of:

# enough space for the new sstable (boolean)
# zero tasks (boolean)
# total free space (long)

We may want to test changing #2 to ordering by task count...  both have pros and cons.
                
> Per-disk I/O queues
> -------------------
>
>                 Key: CASSANDRA-4292
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4292
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Yuki Morishita
>             Fix For: 1.2
>
>         Attachments: 4292-v2.txt, 4292.txt
>
>
> As noted in CASSANDRA-809, we have a certain amount of flush (and compaction) threads,
which mix and match disk volumes indiscriminately.  It may be worth creating a tight thread
-> disk affinity, to prevent unnecessary conflict at that level.
> OTOH as SSDs become more prevalent this becomes a non-issue.  Unclear how much pain this
actually causes in practice in the meantime.

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