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From "Sylvain Lebresne (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1956) Convert row cache to row+filter cache
Date Fri, 10 Feb 2012 15:35:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13205503#comment-13205503
] 

Sylvain Lebresne commented on CASSANDRA-1956:
---------------------------------------------

bq. What about secondary indexes? I guess you'd like to be able to cache "hot" columns in
secondary indexes CF

It's a good question. Secondary indexes CF are accessed from beginning to end, using paging
potentially. Which means it's unclear to me if we can do much better than caching the whole
secondary index rows. But again, I'm good discussing that, but what I'm mainly saying is that
we can't choose the best solution unless we clearly identify the problems we are trying to
solve.
                
> 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-commiting-block-cache.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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