[jira] [Created] (CASSANDRA-10352) Paging with DISTINCT and IN can throw ClassCastException

["Sylvain Lebresne (JIRA)" <ji...@apache.org>]

Sylvain Lebresne created CASSANDRA-10352:
--------------------------------------------

             Summary: Paging with DISTINCT and IN can throw ClassCastException
                 Key: CASSANDRA-10352
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10352
             Project: Cassandra
          Issue Type: Bug
            Reporter: Sylvain Lebresne
            Assignee: Sylvain Lebresne
             Fix For: 2.1.x


The ctor of {{SliceQueryPager}} has the following code:
{noformat}
        if (state != null)
        {
            // The only case where this could be a non-CellName Composite is if it's Composites.EMPTY, but that's not
            // valid for PagingState.cellName, so we can safely cast to CellName.
            lastReturned = (CellName) cfm.comparator.fromByteBuffer(state.cellName);
            restoreState(state.remaining, true);
        }
{noformat}
The assumption that we can only get a {{CellName}} is invalid however. When using a {{MultiPartitionPager}} (so when the query has a {{IN}} on the partition key), it's possible for a page to stop at the end of one of the underlying pager, and for that pager to be exhausted. If that's the case, the {{PagingState}} returned will have the partition key of the next key to retrieve, but a {{null}} cellname (since we haven't started to query that next key). When the next page is queried, that {{PagingState}} will trigger a {{ClassCastException}}.

The [following dtest|https://github.com/pcmanus/cassandra-dtest/commit/b98a112fc22f92aa965d2068345c708ae43b8a85] reproduces this problem.



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