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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7168) Add repair aware consistency levels
Date Tue, 06 May 2014 20:06:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13991065#comment-13991065
] 

Benedict commented on CASSANDRA-7168:
-------------------------------------

It seems like a pretty reasonable idea - the coordinator (if an owner of the range) could
simply issue a special quorum request for all data since the local repairedAt time (which
would include all deletedcolumns as is, instead of filtering them), which would rule out any
races on repair overlaps

However aggregations are most likely some way off, so I'm not sure this buys us much in the
near-term?

> Add repair aware consistency levels
> -----------------------------------
>
>                 Key: CASSANDRA-7168
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7168
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: T Jake Luciani
>              Labels: performance
>             Fix For: 3.0
>
>
> With CASSANDRA-5351 and CASSANDRA-2424 I think there is an opportunity to avoid a lot
of extra disk I/O when running queries with higher consistency levels.  
> Since repaired data is by definition consistent and we know which sstables are repaired,
we can optimize the read path by having a REPAIRED_QUORUM which breaks reads into two phases:
>  
>   1) Read from one replica the result from the repaired sstables. 
>   2) Read from a quorum only the un-repaired data.
> For the node performing 1) we can pipeline the call so it's a single hop.
> In the long run (assuming data is repaired regularly) we will end up with much closer
to CL.ONE performance while maintaining consistency.
> Some things to figure out:
>   - If repairs fail on some nodes we can have a situation where we don't have a consistent
repaired state across the replicas.  
>   



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