[jira] [Commented] (CASSANDRA-3762) AutoSaving KeyCache and System load time improvements.

["Jonathan Ellis (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-3762?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13256793#comment-13256793 ] 

Jonathan Ellis commented on CASSANDRA-3762:
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bq. If we want to see the optimal solution for all the use cases i think we have to go for the alternative where we can save the Keycache position to the disk and read it back and what ever is missing let it fault fill.

I like this idea.  If you have a lot of rows (i.e., a large index) then this is the only thing that's going to save you from doing random i/o.

The only downside I see is the question of how much churn your sstables will experience between save, and load.  If you have a small data set that is constantly being overwritten for instance, you could basically invalidate the whole cache.  But, it's quite possible that just reducing cache save period is adequate to address this.
                
> AutoSaving KeyCache and System load time improvements.
> ------------------------------------------------------
>
>                 Key: CASSANDRA-3762
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3762
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.2
>            Reporter: Vijay
>            Assignee: Vijay
>            Priority: Minor
>             Fix For: 1.2
>
>         Attachments: 0001-SavedKeyCache-load-time-improvements.patch
>
>
> CASSANDRA-2392 saves the index summary to the disk... but when we have saved cache we will still scan through the index to get the data out.
> We might be able to separate this from SSTR.load and let it load the index summary, once all the SST's are loaded we might be able to check the bloomfilter and do a random IO on fewer Index's to populate the KeyCache.

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