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https://issues.apache.org/jira/browse/CASSANDRA-21791?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Blake Eggleston updated CASSANDRA-21791:
----------------------------------------
    Test and Documentation Plan: ci
                         Status: Patch Available  (was: Open)

PR: https://github.com/apache/cassandra/pull/5282

> CEP-45 - improve tracked read coordination
> ------------------------------------------
>
>                 Key: CASSANDRA-21791
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-21791
>             Project: Apache Cassandra
>          Issue Type: Bug
>          Components: Consistency/Coordination
>            Reporter: Blake Eggleston
>            Assignee: Blake Eggleston
>            Priority: Normal
>
> The tracked read coordinator currently waits for all peers to send it both 
> their initial summaries and their acknowledgement that they’ve received any 
> mutations they were missing. This is the network equivalent of running read 
> repair for every read. This patch improves read completion by:
> * Not waiting for sync acks from nodes we know are up to date. We know which 
> writes each peer is missing from their initial summary, if we can see that 
> they’re not behind, we no longer wait for them to send sync acknowledgements.
> * Sending per-peer sync acks. Peers currently wait to receive all mutations 
> they’re missing from all other peers before notifying the coordinator. This 
> send an ack per-peer
> * Accounting for mutations received between local summary creation and remove 
> summary receipt
> * Eager quorum completion - both of these improvements allow us to be more 
> intelligent about how we decide we’ve reached quorum. If a quorum exists that 
> we can satisfy immediately (for instance, 1/3 non data nodes is reporting a 
> mutation none of the other peers have seen, we can skip syncing and returning 
> that mutation while preserving monotonicity)



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