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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-8635) STCS cold sstable omission does not handle overwrites without reads
Date Tue, 20 Jan 2015 23:36:35 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14284610#comment-14284610
] 

Tyler Hobbs edited comment on CASSANDRA-8635 at 1/20/15 11:36 PM:
------------------------------------------------------------------

If we have to release 2.1.3 without a proper fix, I suggest disabling this behavior unless
a {{-D}} flag is present.  We could re-enable it in 2.1.4.

Also, for any affected users, this is also a valid workaround:

{noformat}
ALTER TABLE <tablename> WITH compaction = {'class': 'SizeTieredCompactionStrategy',
'min_threshold': '4', 'max_threshold': '32', 'cold_reads_to_omit': 0.0};
{noformat}


was (Author: thobbs):
If we have to release 2.1.4 without a proper fix, I suggest disabling this behavior unless
a {{-D}} flag is present.  We could re-enable it in 2.1.5.

Also, for any affected users, this is also a valid workaround:

{noformat}
ALTER TABLE <tablename> WITH compaction = {'class': 'SizeTieredCompactionStrategy',
'min_threshold': '4', 'max_threshold': '32', 'cold_reads_to_omit': 0.0};
{noformat}

> STCS cold sstable omission does not handle overwrites without reads
> -------------------------------------------------------------------
>
>                 Key: CASSANDRA-8635
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8635
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Tyler Hobbs
>            Assignee: Marcus Eriksson
>            Priority: Critical
>             Fix For: 2.1.3
>
>
> In 2.1, STCS may omit cold SSTables from compaction (CASSANDRA-6109).  If data is regularly
overwritten or deleted (but not enough to trigger a single-sstable tombstone purging compaction),
data size on disk may continuously grow if:
> * The table receives very few reads
> * The reads only touch the newest SSTables
> Basically, if the overwritten data is never read and there aren't many tombstones, STCS
has no incentive to compact the sstables.  We should take sstable overlap into consideration
as well as coldness to address this case.



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