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From "Maryann Xue (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (PHOENIX-2601) Query result is incorrect when both index hint and limit are used
Date Sat, 16 Jan 2016 03:40:39 GMT

     [ https://issues.apache.org/jira/browse/PHOENIX-2601?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Maryann Xue resolved PHOENIX-2601.
----------------------------------
    Resolution: Fixed

> Query result is incorrect when both index hint and limit are used
> -----------------------------------------------------------------
>
>                 Key: PHOENIX-2601
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2601
>             Project: Phoenix
>          Issue Type: Bug
>    Affects Versions: 4.4.0
>         Environment: Linux
>            Reporter: Simon Lee
>            Assignee: Maryann Xue
>             Fix For: 4.7.0
>
>         Attachments: PHOENIX-2601.patch
>
>
> Query result is incorrect when both index hint and limit are used.
> To reproduce the problem,
> 1. Create an HBase table with a column family. The column family has 4 columns (a1, a2,
a3, a4). Create an index on (a1, a2).
> 2. Populate the table with the following data
> {code}
> a1  a2     a3      a4
> --  -----  -----   -----
> 1   Small  Red     USA
> 1   Small  Yellow  UK
> 1   Small  Green   China
> {code}
> 3. Run the following Phoenix queries, and the query results are correct.
> {code}
> select a1, a2, a3, a4 from table where a1 = '1' and a2 = 'Small' ;
> {code}
> Three rows are returned as expected
> {code}
> select a1, a2, a3, a4 from table where a1 = '1' and a2 = 'Small' and a3 = "Yellow" limit
1;
> {code}
> One row is returned as expected
> {code}
> select /*+ INDEX(add_index_hint_here) */ a1, a2, a3, a4 from table where a1 = '1' and
a2 = 'Small' and a3 = "Yellow";
> {code}
> One row is returned as expected
> 4. However, with the combination of index hint and limit clause, the query result is
incorrect.
> {code}
> select /*+ INDEX(add_index_hint_here) */ a1, a2, a3, a4 from table where a1 = '1' and
a2 = 'Small' and a3 = "Yellow" limit 1;
> {code}
> Zero row is returned. The expected result is 1 row (i.e. the second row in the example).
> *The explain plan of the problematic query* 
> {code}
> +------------------------------------------+
> |                   PLAN                   |
> +------------------------------------------+
> | CLIENT 11-CHUNK PARALLEL 1-WAY ... MY_TABLE |
> |     SERVER FILTER BY A.A3 = 'Yellow' |
> | CLIENT 1 ROW LIMIT                       |
> |     SKIP-SCAN-JOIN TABLE 0               |
> |         CLIENT 1-CHUNK SERIAL 1-WAY RANGE SCAN OVER MY_INDEX [[52,48,48,45,69,79,84,45,48,48,57],23]
|
> |             SERVER FILTER BY FIRST KEY ONLY |
> |             SERVER 1 ROW LIMIT           |
> |         CLIENT 1 ROW LIMIT               |
> |     DYNAMIC SERVER FILTER BY ("MY_ROW_KEY") IN (($148.$150, $1 |
> |     JOIN-SCANNER 1 ROW LIMIT             |
> +------------------------------------------+
> {code}
>  It looks like the query plan uses the index first.  Although all three rows match the
index (a1 = '1' and 'a2 = 'Small'), but the intermediate result only has the first row due
the "limit 1" clause. In this case, the intermediate result has one row (a3 = 'Red'). Then
the query engine tries to apply the (a3 = 'Yellow') to the intermediate result, and get zero
row as the final result.



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