[jira] [Commented] (PHOENIX-6798) Eliminate unnecessary reversed scan for AggregatePlan

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-6798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17611342#comment-17611342 ] 

ASF GitHub Bot commented on PHOENIX-6798:
-----------------------------------------

comnetwork closed pull request #1510: PHOENIX-6798 Eliminate unnecessary reversed scan for AggregatePlan
URL: https://github.com/apache/phoenix/pull/1510




> Eliminate unnecessary reversed scan for AggregatePlan
> -----------------------------------------------------
>
>                 Key: PHOENIX-6798
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-6798
>             Project: Phoenix
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 5.1.2
>            Reporter: chenglei
>            Assignee: chenglei
>            Priority: Major
>
> For HBase, reversed scan is slower than normal forward scan.
> Consider following table:
> {code}
>   create table test_table  
>   (group_id integer not null, 
>     keyword varchar not null, 
>     cost integer, 
>     CONSTRAINT TEST_PK PRIMARY KEY (group_id,keyword))
> {code}
> For the following sql :
> {code}
>    select keyword,sum(cost) from test group by keyword order by keyword desc
> {code}
> The compiled {{AggregatePlan}} would set the scan for HBase as reversed scan, but that is very strange, because for this sql, {{GroupBy.isOrderPreserving}} is false, we have no need to set the scan as reversed scan because we have to hash-aggregate the scanned results from HBase in {{Coprocessor}} before sending them to client.



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