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https://issues.apache.org/jira/browse/CASSANDRA-7168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14502981#comment-14502981
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Sylvain Lebresne commented on CASSANDRA-7168:
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bq. I'd rather just apply this as an optimization to all CL > ONE, replacing
the data/digest split that is almost certainly less useful.
I'll admit that I find this a bit scary. This means relying on the repaired
time in a way that I personally don't feel yet very comfortable with. At the
very least, I think we should preserve the option to do full data queries. And
as much as I understand the willingness to simplify the code, I would
personally be a lot more comfortable if this was living aside the existing
mechanism at first.
I can agree however than having a specific CL is weird since that really apply
to pretty much all CL. I'd be fine with adding a flag in the native protocol to
allow or disallow that feature for instance.
> 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: 3.1
>
>
> 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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