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https://issues.apache.org/jira/browse/CASSANDRA-20222?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benedict Elliott Smith updated CASSANDRA-20222:
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Resolution: Fixed
Status: Resolved (was: Triage Needed)
> Accord: Fast and Medium path protocol optimisations
> ---------------------------------------------------
>
> Key: CASSANDRA-20222
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20222
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Accord
> Reporter: Benedict Elliott Smith
> Priority: Normal
>
> Protocol optimisations:
> - Privileged coordinator. If the coordinator is a replica we can reduce our
> quorum sizes by including the coordinator's vote.
> - with deps: if we include coordinator's preaccept deps we can reliably
> reduce quorum size by 1, at the expense of recovery sometimes requiring
> additional phases and waiting for future txns
> - with only vote: if we only include the vote we can avoid any additional
> recovery phases or waiting for future txns, but can reduce our quorum size
> for only some configurations
> - Medium path. If t=t0 at a simple majority we can take just two rounds.
> - with additional phase: on recovery, earlier txns must wait for medium
> path to be disabled (or committed) so we do not accidentally recover a
> transaction that won't be witnessed
> - with unstable deps: on slow path commit, deps not found in accept as
> committed as unstable and do not affect recovery decisions for earlier
> transactions
> Also improve:
> - Recovery of await conditions simply recalculates the rejects flag rather
> than restarting to ensure faster forward progress
> - refactor Command hierarchy
> - tweak: don't save Writes for non-write transactions
> Also fix:
> - isOutOfRange when invoked from callback for some txn < Committed
> - handle loadingPruned that is pre-bootstrap on update to bootstrappedAt
> - journal replay can overwrite in memory state loaded for a command not yet
> replayed
> - subtle ordering bug in LatestDeps.mergeProposal
> - fix occasional class initialisation order bug
> - handle race condition on learning of topology
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