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https://issues.apache.org/jira/browse/CASSANDRA-21406?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aleksey Yeschenko updated CASSANDRA-21406:
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Reviewers: Aleksey Yeschenko
Status: Review In Progress (was: Patch Available)
> CEP-45: Prevent dropping journal segments referenced by partially reconciled
> sstables
> -------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21406
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21406
> Project: Apache Cassandra
> Issue Type: New Feature
> Components: Consistency/Coordination
> Reporter: Aleksey Yeschenko
> Assignee: Francisco Guerrero
> Priority: Normal
>
> When we partially seal a shard, a replica that was down during the
> sealing will need to filter out minority writes it had belonging to the sealed
> shard from its sstables when it comes back online.
> Fully reconciled (and marked as repaired) sstables should remain as they are.
> Partially reconciled (unrepaired) sstables, if they contain any minority
> mutations, need to be dropped and rebuilt from the mutation journal. The
> replacing sstable will need to include all the fully reconciled mutations,
> plus any unreconciled mutations that are safe to keep (i.e., *not* minority
> mutations outside of the sealed mutation ID sets).
> To make this possible, we must change our journal segment dropping logic.
> Currently, we deem a segment droppable if every mutation it contains has been
> fully reconciled. However, to rebuild a partially reconciled sstable, we must
> ensure that all the reconciled mutations in such an sstable can still be read
> from the journal. So, we must prevent the dropping of any segment we might
> still need in the future to rebuild a partially reconciled sstable, even if
> every mutation in that segment has been fully reconciled.
> The criteria for marking a segment as droppable must change. Currently, a
> journal segment is droppable if all of the following conditions are met:
> 1. The segment doesn't need replay - every affected memtable has been flushed
> to disk as an sstable (a current condition)
> 2. Every mutation in the segment has been durably reconciled by all peers (a
> current condition)
> In the future, a journal segment will be droppable once the following
> conditions have been met:
> 1. The segment doesn't need replay - every affected memtable has been flushed
> to disk as an sstable (a current condition)
> 2. No partially reconciled sstables reference *any* mutations in the segment
> (*new condition*)
> The most sensible way to implement the new restriction is to lean on
> `StatsMetadata.commitLogIntervals`. We'll keep track of the relationships
> between sstables and the journal segments that feed into them, and once all
> sstables with ties to a given journal segment have been promoted to repaired
> (fully reconciled), we'll drop the segment. In other words, we can treat
> journal segments as refcounted, with each tied sstable representing one
> reference.
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