[jira] [Created] (CASSANDRA-10010) Paging on DISTINCT queries repeats result when first row in partition changes

["Tyler Hobbs (JIRA)" <ji...@apache.org>]

Tyler Hobbs created CASSANDRA-10010:
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             Summary: Paging on DISTINCT queries repeats result when first row in partition changes
                 Key: CASSANDRA-10010
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10010
             Project: Cassandra
          Issue Type: Bug
          Components: Core
            Reporter: Tyler Hobbs
            Assignee: Benjamin Lerer
            Priority: Minor
             Fix For: 2.1.x, 2.2.x


When paging, we always check new pages to see if they start with the same row that the previous page ended with, and if so, we trim that row to avoid duplicates.  With {{DISTINCT}} queries, we only fetch the first row in each partition.  If that row happens to change (it's deleted, or another row is inserted at the front of the partition) in between fetching the two pages, our check for a matching row will fail, resulting in a duplicate row being returned.

It seems like the correct fix is to handle {{DISTINCT}} queries specially and only check to see if the partition key matches the last returned one instead checking that the rows match.



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