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From "Vijay (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1956) Convert row cache to row+filter cache
Date Wed, 18 Apr 2012 20:50:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13256949#comment-13256949
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Vijay commented on CASSANDRA-1956:
----------------------------------

Hi Jonathan, When user requests X1,Y1 we cache the block from (Start->X1-Position ->Y1-Position)
+ N.... with block size being configurable. (it should similar to the page cache and if there
is a write on the block the whole block is marked dirty and next fetch will go to the FS).
there is a configurable block size when set high enough will cache the whole row (like the
existing cache). The logic around it is kind of what the patch has....

We can also use column indexes (if needed) and caching data within it, but the simple may
be is to start from the column requested and cache blocks (else updating them cache without
invalidating the whole row is going to be hard).
                
> 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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