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https://issues.apache.org/jira/browse/CASSANDRA-19870?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benedict Elliott Smith updated CASSANDRA-19870:
-----------------------------------------------
Resolution: Fixed
Status: Resolved (was: Triage Needed)
> Accord: DefaultProgressLog
> --------------------------
>
> Key: CASSANDRA-19870
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19870
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Accord
> Reporter: Benedict Elliott Smith
> Priority: Normal
> Attachments: ci_summary-1.html, ci_summary.html, result_details.tar.gz
>
>
> Redesign progress mechanisms to be memory efficient, use fewer messages and
> to resolve dependency chains promptly.
> The SimpleProgressLog had a number of problems:
> # It polled for progress with no attempt to determine whether progress could
> realistically be made, so:
> ## as the number of pending transactions grew, the proportion of useful work
> dropped (as many would be unable to make progress without earlier
> transactions completing)
> ## each transaction in the chain could recover only on average 1/2 poll
> interval behind the last transaction to complete
> # It requested full transaction state from every replica on each attempt
> # It maintained a lot of in-memory state
> # Polling happened en-masse, allowing for little per-transaction control
> We also separately maintained fairly expensive per-command listener state
> that negatively affected our command loading and caching.
> The new DefaultProgressLog makes use of several new features: LocalListeners,
> RemoteListeners, Timers and Await messages.
> - LocalListeners provide a memory-efficient collection for managing each
> CommandStore’s transaction listeners, with dedicated record keeping for
> inter-transaction relationships.
> - RemoteListeners provide a mechanism for request/response pairs that may be
> separated by longer than the normal Cassandra message timeout, and require
> minimal state on sender and recipient. This permits replicas to cheaply
> update their local state machine as soon as distributed information becomes
> available.
> The DefaultProgressLog tracks each transaction with separate timers to handle
> per-transaction scheduling, backoff etc, and a succinct state machine. To
> reduce overhead correspondence is preferentially limited to a handful of
> replicas, and limited to the home shard where appropriate.
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