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Date: Wed, 4 Jan 2012 21:37:39 +0000 (UTC)
From: "Daniel Doubleday (Commented) (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-1956) Convert row cache to row+filter
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    [ https://issues.apache.org/jira/browse/CASSANDRA-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13179909#comment-13179909 ] 

Daniel Doubleday commented on CASSANDRA-1956:
---------------------------------------------

bq. users can optimize that themselves by using "select *" instead of "select x" and "select y"

I guess it's not totally atypical right now to model data in a way that it fits the current caching scheme. I.e. we have UserData rows with around 10 columns and around 50 - 100k row size. All of them are read during one session at a different time. With the proposed new caching scheme we have the choice to either create 10x cache misses and a lot more objects to gc. Or load the entire row everywhere.
                
> Convert row cache to row+filter cache
> -------------------------------------
>
>                 Key: CASSANDRA-1956
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1956
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>            Assignee: Vijay
>            Priority: Minor
>             Fix For: 1.2
>
>         Attachments: 0001-1956-cache-updates-v0.patch, 0001-re-factor-row-cache.patch, 0001-row-cache-filter.patch, 0002-1956-updates-to-thrift-and-avro-v0.patch, 0002-add-query-cache.patch
>
>
> Changing the row cache to a row+filter cache would make it much more useful. We currently have to warn against using the row cache with wide rows, where the read pattern is typically a peek at the head, but this usecase would be perfect supported by a cache that stored only columns matching the filter.
> Possible implementations:
> * (copout) Cache a single filter per row, and leave the cache key as is
> * Cache a list of filters per row, leaving the cache key as is: this is likely to have some gotchas for weird usage patterns, and it requires the list overheard
> * Change the cache key to "rowkey+filterid": basically ideal, but you need a secondary index to lookup cache entries by rowkey so that you can keep them in sync with the memtable
> * others?

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