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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-3451) Secondary index and query using distinct: LIMIT doesn't return the first rows
Date Mon, 07 Nov 2016 17:17:58 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-3451?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15644761#comment-15644761
] 

James Taylor commented on PHOENIX-3451:
---------------------------------------

When the index is used, the final sort is not being done:
{code}
0: jdbc:phoenix:> explain SELECT DISTINCT entity_id, score FROM test.test2 WHERE organization_id
= 'org2' AND container_id IN ( 'container1','container2','container3' ) ORDER BY score DESC
LIMIT 2;
+--------------------------------------------------------------------------------------------------------------------------------------------------------+
|                                                                          PLAN          
                                                               |
+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| CLIENT 1-CHUNK PARALLEL 1-WAY SKIP SCAN ON 3 KEYS OVER TEST.TEST_SCORE2 ['org2         
 ','container1     '] - ['org2           ','container3     ']  |
|     SERVER FILTER BY FIRST KEY ONLY                                                    
                                                               |
|     SERVER AGGREGATE INTO DISTINCT ROWS BY ["ENTITY_ID", "SCORE"] LIMIT 2 GROUPS       
                                                               |
| CLIENT MERGE SORT                                                                      
                                                               |
| CLIENT 2 ROW LIMIT                                                                     
                                                               |
+--------------------------------------------------------------------------------------------------------------------------------------------------------+
{code}

If the query is hinted to not use the index, the output is fine:
{code}
0: jdbc:phoenix:> explain SELECT /*+ NO_INDEX */ DISTINCT entity_id, score FROM test.test2
WHERE organization_id = 'org2' AND container_id IN ( 'container1','container2','container3'
) ORDER BY score DESC LIMIT 2;
+--------------------------------------------------------------------------------------------------------------------------------------------------+
|                                                                       PLAN             
                                                         |
+--------------------------------------------------------------------------------------------------------------------------------------------------+
| CLIENT 1-CHUNK PARALLEL 1-WAY SKIP SCAN ON 3 KEYS OVER TEST.TEST2 ['org2           ','container1
    '] - ['org2           ','container3     ']  |
|     SERVER AGGREGATE INTO DISTINCT ROWS BY [ENTITY_ID, SCORE]                          
                                                         |
| CLIENT MERGE SORT                                                                      
                                                         |
| CLIENT TOP 2 ROWS SORTED BY [SCORE DESC]                                               
                                                         |
+--------------------------------------------------------------------------------------------------------------------------------------------------+
{code}

Do you need that index, [~jpalmert]? For the above query, it's not buying you anything.

Also, do you know about the FIRST_VALUE aggregate function:  https://phoenix.apache.org/language/functions.html#first_value,
as this may help you.

> Secondary index and query using distinct: LIMIT doesn't return the first rows
> -----------------------------------------------------------------------------
>
>                 Key: PHOENIX-3451
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-3451
>             Project: Phoenix
>          Issue Type: Bug
>    Affects Versions: 4.8.0
>            Reporter: Joel Palmert
>
> This may be related to PHOENIX-3452 but the behavior is different so filing it separately.
> Steps to repro:
> CREATE TABLE IF NOT EXISTS TEST.TEST (
>     ORGANIZATION_ID CHAR(15) NOT NULL,
>     CONTAINER_ID CHAR(15) NOT NULL,
>     ENTITY_ID CHAR(15) NOT NULL,
>     SCORE DOUBLE,
>     CONSTRAINT TEST_PK PRIMARY KEY (
>         ORGANIZATION_ID,
>         CONTAINER_ID,
>         ENTITY_ID
>     )
> ) VERSIONS=1, MULTI_TENANT=TRUE, REPLICATION_SCOPE=1, TTL=31536000;
> CREATE INDEX IF NOT EXISTS TEST_SCORE ON TEST.TEST (CONTAINER_ID, SCORE DESC, ENTITY_ID
DESC);
> UPSERT INTO test.test VALUES ('org2','container2','entityId6',1.1);
> UPSERT INTO test.test VALUES ('org2','container1','entityId5',1.2);
> UPSERT INTO test.test VALUES ('org2','container2','entityId4',1.3);
> UPSERT INTO test.test VALUES ('org2','container1','entityId3',1.4);
> UPSERT INTO test.test VALUES ('org2','container3','entityId7',1.35);
> UPSERT INTO test.test VALUES ('org2','container3','entityId8',1.45);
> EXPLAIN
> SELECT DISTINCT entity_id, score
> FROM test.test
> WHERE organization_id = 'org2'
> AND container_id IN ( 'container1','container2','container3' )
> ORDER BY score DESC
> LIMIT 2
> OUTPUT
> entityId5    1.2
> entityId3    1.4
> The expected out out would be
> entityId8    1.45
> entityId3    1.4
> You will get the expected output if you remove the secondary index from the table or
remove distinct from the query.
> As described in PHOENIX-3452 if you run the query without the LIMIT the ordering is not
correct. However, the 2first results in that ordering is still not the onces returned by the
limit clause, which makes me think there are multiple issues here and why I filed both separately.
The rows being returned are the ones assigned to container1. It looks like Phoenix is first
getting the rows from the first container and when it finds that to be enough it stops the
scan. What it should be doing is getting 2 results for each container and then merge then
and then limit again.



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