[jira] [Comment Edited] (CASSANDRA-7075) Add the ability to automatically distribute your commitlogs across all data volumes

["Benedict (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-7075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14350577#comment-14350577 ] 

Benedict edited comment on CASSANDRA-7075 at 3/6/15 5:00 PM:
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It's also worth considering if we shouldn't simply round-robin on segment advance, rather than on each mutation. If we wanted to improve the performance of batch commit log latency we could round-robin on sync also (so the next batch may potentially start committing before the prior batch has completed).

Since this is going into 3.0, and we're hoping for CASSANDRA-6696 to land then also, it might alternatively make sense to tie the two together, and write CL entries to the disk that will ultimately own the sstables. This might simplify the cognitive burden on recovery from a disk failure, since there would be no risk of partial updates being played for an owned range and queries being served from it. So no consideration would need to be given to these partial failure scenarios.


was (Author: benedict):
It's also worth considering if we shouldn't simply round-robin on segment advance, rather than on each mutation. If we wanted to improve the performance of batch commit log latency we could round-robin on sync also (so the next batch may potentially start committing before the prior batch has completed).

Since this is going into 3.0, and we're hoping for CASSANDRA-6696 to land then also, it might alternatively make sense to tie the two together, and write CL entries to the disk that will ultimately own the sstables also. This might simplify the cognitive burden on recovery from a disk failure, since there would be no risk of partial updates being played for an owned range and queries being served from it. So no consideration would need to be given to these partial failure scenarios.

> Add the ability to automatically distribute your commitlogs across all data volumes
> -----------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-7075
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7075
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Tupshin Harper
>            Assignee: Branimir Lambov
>            Priority: Minor
>              Labels: performance
>             Fix For: 3.0
>
>
> given the prevalance of ssds (no need to separate commitlog and data), and improved jbod support, along with CASSANDRA-3578, it seems like we should have an option to have one commitlog per data volume, to even the load. i've been seeing more and more cases where there isn't an obvious "extra" volume to put the commitlog on, and sticking it on only one of the jbodded ssd volumes leads to IO imbalance.



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