[jira] [Commented] (CASSANDRA-5519) Reduce index summary memory use for cold sstables

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

    [ https://issues.apache.org/jira/browse/CASSANDRA-5519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13726788#comment-13726788 ] 

Tyler Hobbs commented on CASSANDRA-5519:
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An initial idea for the implementation:

Based on the recent (last 15m?) read rate (reads/sec), periodically down-sample the summary for SSTables which fall below the mean rate.  The down-sampling rate could use a sliding scale based on the ratio of the mean to that SSTable's rate.  As a example basic implementation, keep X% of the samples, where {{X = max(25, min(100, 100 * (rate / mean_rate)))}}, so the coldest SSTables keep only 25% of the samples in memory.

Presenting a way for the user to tune this (other than a simple on/off) is a little trickier.  Perhaps make the min (default 25%) adjustable?  Or start down-sampling at a configurable point (the default is the mean)?  Those could also be automatically adjusted based on memory pressure.
                
> Reduce index summary memory use for cold sstables
> -------------------------------------------------
>
>                 Key: CASSANDRA-5519
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5519
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Jonathan Ellis
>            Priority: Minor
>             Fix For: 2.0.1
>
>


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