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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Commented] (PHOENIX-951) Don't push LIMIT as PageFilter for joins
Date Mon, 28 Apr 2014 00:44:14 GMT


ASF GitHub Bot commented on PHOENIX-951:

Github user JamesRTaylor commented on a diff in the pull request:
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/coprocessor/
    @@ -106,7 +113,7 @@ private void processResults(List<Cell> result, boolean hasLimit)
throws IOExcept
    -        if (hasLimit)
    +        if (hasBatchLimit)
                 throw new UnsupportedOperationException("Cannot support join operations in
scans with limit");
    --- End diff --
    When can this exception occur? Is this the case where a nested join query has a limit,
and do we have a test case for this?

> Don't push LIMIT as PageFilter for joins
> ----------------------------------------
>                 Key: PHOENIX-951
>                 URL:
>             Project: Phoenix
>          Issue Type: Bug
>    Affects Versions: 3.0.0, 4.0.0
>            Reporter: James Taylor
>            Assignee: Maryann Xue
>            Priority: Minor
> When a join has a limit, you can't push the limit through a PageFilter since you might
not get a match when you join the LHS to the RHS. I think ideally you'd want to push the LIMIT
to the ScanRegionObserver (or GroupedAggregateRegionObserver) and then stop the inner scan
when the limit is reached. There's a similar optimize for a GROUP BY that has a LIMIT with

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