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Posted to commits@cassandra.apache.org by "Jonathan Ellis (JIRA)" <ji...@apache.org> on 2013/08/12 20:14:52 UTC
[jira] [Issue Comment Deleted] (CASSANDRA-5850) change
gc_grace_seconds default to 28 days
[ https://issues.apache.org/jira/browse/CASSANDRA-5850?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Jonathan Ellis updated CASSANDRA-5850:
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Comment: was deleted
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Your support ticket concerning '[jira] [Commented] (CASSANDRA-5850) change gc_grace_seconds default to 28 days' can be viewed here: https://support.bluebox.net/tickets/21BA55
The submission as we received it:
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[ https://issues.apache.org/jira/browse/CASSANDRA-5850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13737018#comment-13737018 ]
Mike Heffner commented on CASSANDRA-5850:
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"repair often fails" => Should the focus be on fixing those scenarios?
We often set this value to zero for the append-only CFs to keep our tombstone load at a minimum, but it took us a while to come to this solution. How about improving documentation around gc_grace_seconds for when it makes sense to increase/decrease the default?
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> change gc_grace_seconds default to 28 days
> ------------------------------------------
>
> Key: CASSANDRA-5850
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5850
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0 beta 2
> Reporter: Robert Coli
> Priority: Trivial
> Attachments: gc_grace_seconds_to_2419200_seconds_aka_28_days.patch
>
>
> Current default for gc_grace_seconds is 10 days. Attached patch changes all instances of this 10 day default to 28 days.
> Rationale :
> - 10 days is arbitrary, there is nothing special about the current value
> - human societies do not operate on cycles which are a multiple of 10 days, they operate on a cycle of 7 day weeks
> - operators must run repair once every gc_grace_seconds, and with typical data sizes (and compaction/streaming throttling) this might run for a significant fraction of 10 days
> - repair often fails, and detecting and working around that failure might also take a significant fraction of 10 days
> - repair is the heaviest operation one can run on a cassandra cluster and operators are therefore motivated to run it ~3x less frequently by default
> - the worst case impact is keeping data around for 18 days longer than the previous default, and this only occurs in CFs which actually take DELETE operation
> - 28 days is an even multiple of 7 days and easily comprehensible as a default time in which to schedule repair
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