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From "Benjamin Lerer (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-10010) Paging on DISTINCT queries repeats result when first row in partition changes
Date Wed, 27 Jan 2016 09:38:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-10010?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15118932#comment-15118932
] 

Benjamin Lerer edited comment on CASSANDRA-10010 at 1/27/16 9:37 AM:
---------------------------------------------------------------------

|[utest-2.2|http://cassci.datastax.com/view/Dev/view/blerer/job/blerer-10010-testall/]|[dtest-2.2|http://cassci.datastax.com/view/Dev/view/blerer/job/blerer-10010-dtest/]

The problem seems to be only affecting range queries. The patch makes sure that for distinct
range queries only the partition keys are compared and not the rows.

PR for the DTest is [here|https://github.com/riptano/cassandra-dtest/pull/774]. It adds some
testing for multi partition queries to the original test of [~thobbs]


was (Author: blerer):
|[utest|http://cassci.datastax.com/view/Dev/view/blerer/job/blerer-10010-testall/]|[dtest|http://cassci.datastax.com/view/Dev/view/blerer/job/blerer-10010-dtest/]

The problem seems to be only affecting range queries. The patch makes sure that for distinct
range queries only the partition keys are compared and not the rows.

PR for the DTest is [here|https://github.com/riptano/cassandra-dtest/pull/774]. It adds some
testing for multi partition queries to the original test of [~thobbs]

> 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
>            Reporter: Tyler Hobbs
>            Assignee: Benjamin Lerer
>            Priority: Minor
>             Fix For: 2.1.x, 2.2.x
>
>         Attachments: 10010-2.2.txt
>
>
> 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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