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From "Aleksey Yeschenko (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-13911) IllegalStateException thrown by UPI.Serializer.hasNext() for some SELECT queries
Date Wed, 27 Sep 2017 20:13:00 GMT


Aleksey Yeschenko updated CASSANDRA-13911:
    Fix Version/s:     (was: 3.11.x)
                       (was: 3.0.x)

> IllegalStateException thrown by UPI.Serializer.hasNext() for some SELECT queries
> --------------------------------------------------------------------------------
>                 Key: CASSANDRA-13911
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Coordination
>            Reporter: Aleksey Yeschenko
>            Assignee: Aleksey Yeschenko
>             Fix For: 3.0.15, 3.11.1
> Certain combinations of rows, in presence of per partition limit (set explicitly in 3.6+
or implicitly to 1 via DISTINCT) cause {{UnfilteredPartitionIterators.Serializer.hasNext()}}
to throw {{IllegalStateException
> }}.
> Relevant code snippet:
> {code}
> // We can't answer this until the previously returned iterator has been fully consumed,
> // so complain if that's not the case.
> if (next != null && next.hasNext())
>     throw new IllegalStateException("Cannot call hasNext() until the previous iterator
has been fully consumed");
> {code}
> Since {{UnfilteredPartitionIterators.Serializer}} and {{UnfilteredRowIteratorSerializer.serializer}}
deserialize partitions/rows lazily, it is required for correct operation of the partition
iterator to have the previous partition fully consumed, so that deserializing the next one
can start from the correct position in the byte buffer. However, that condition won’t always
be satisfied, as there are legitimate combinations of rows that do not consume every row in
every partition.
> For example, look at [this dtest|].
> In case we end up with a following pattern of rows:
> {code}
> node1, partition 0 | 0
> node2, partition 0 |   x x
> {code}
> , where {{x}} and {{x}} a row tombstones for rows 1 and 2, it’s sufficient for {{MergeIterator}}
to only look at row 0 in partition from node1 and at row tombstone 1 from node2 to satisfy
the per partition limit of 1. The stopping merge result counter will stop iteration right
there, leaving row tombstone 2 from node2 unvisited and not deseiralized. Switching to the
next partition will in turn trigger the {{IllegalStateException}} because we aren’t done
> The stopping counter is behaving correctly, so is the {{MergeIterator}}. I’ll note
that simply removing that condition is not enough to fix the problem properly - it’d just
cause us to deseiralize garbage, trying to deserialize a new partition from a position in
the bytebuffer that precedes remaining rows in the previous partition.

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