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https://issues.apache.org/jira/browse/CASSANDRA-13747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aleksey Yeschenko updated CASSANDRA-13747:
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Status: Open (was: Patch Available)
> Fix short read protection
> -------------------------
>
> Key: CASSANDRA-13747
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13747
> Project: Cassandra
> Issue Type: Bug
> Components: Coordination
> Reporter: Aleksey Yeschenko
> Assignee: Aleksey Yeschenko
> Fix For: 3.0.x, 3.11.x
>
>
> {{ShortReadRowProtection.moreContents()}} expects that by the time we get to
> that method, the global post-reconciliation counter was already applied to
> the current partition. However, sometimes it won’t get applied, and the
> global counter continues counting with {{rowInCurrentPartition}} value not
> reset from previous partition, which in the most obvious case would trigger
> the assertion we are observing - {{assert
> !postReconciliationCounter.isDoneForPartition();}}. In other cases it’s
> possible because of this lack of reset to query a node for too few extra
> rows, causing unnecessary SRP data requests.
> Why is the counter not always applied to the current partition?
> The merged {{PartitionIterator}} returned from {{DataResolver.resolve()}} has
> two transformations applied to it, in the following order:
> {{Filter}} - to purge non-live data from partitions, and to discard empty
> partitions altogether (except for Thrift)
> {{Counter}}, to count and stop iteration
> Problem is, {{Filter}} ’s {{applyToPartition()}} code that discards empty
> partitions ({{closeIfEmpty()}} method) would sometimes consume the iterator,
> triggering short read protection *before* {{Counter}} ’s
> {{applyToPartition()}} gets called and resets its {{rowInCurrentPartition}}
> sub-counter.
> We should not be consuming iterators until all transformations are applied to
> them. For transformations it means that they cannot consume iterators unless
> they are the last transformation on the stack.
> The linked branch fixes the problem by splitting {{Filter}} into two
> transformations. The original - {{Filter}} - that does filtering within
> partitions - and a separate {{EmptyPartitionsDiscarder}}, that discards empty
> partitions from {{PartitionIterators}}. Thus {{DataResolve.resolve()}}, when
> constructing its {{PartitionIterator}}, now does merge first, then applies
> {{Filter}}, then {{Counter}}, and only then, as its last (third)
> transformation - the {{EmptyPartitionsDiscarder}}. Being the last one
> applied, it’s legal for it to consume the iterator, and triggering
> {{moreContents()}} is now no longer a problem.
> Fixes: [3.0|https://github.com/iamaleksey/cassandra/commits/13747-3.0],
> [3.11|https://github.com/iamaleksey/cassandra/commits/13747-3.11],
> [4.0|https://github.com/iamaleksey/cassandra/commits/13747-4.0]. dtest
> [here|https://github.com/iamaleksey/cassandra-dtest/commits/13747].
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