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https://issues.apache.org/jira/browse/PHOENIX-4287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16225583#comment-16225583
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Samarth Jain commented on PHOENIX-4287:
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There is some level of duplication but the generation of estimates when
statsParallelization is off is relatively simpler. We only need to intersect
scan stop and start key with guideposts and not worry about region boundaries
and everything else which the code in getParallelScans() does. My previous
attempt at using the existing code to generate estimates and not generate
intra-region scans failed miserably. I will sync with you offline to see if
what we can do to reuse the existing code.
> Incorrect aggregate query results when stats are disable for parallelization
> ----------------------------------------------------------------------------
>
> Key: PHOENIX-4287
> URL: https://issues.apache.org/jira/browse/PHOENIX-4287
> Project: Phoenix
> Issue Type: Bug
> Affects Versions: 4.12.0
> Environment: HBase 1.3.1
> Reporter: Mujtaba Chohan
> Assignee: Samarth Jain
> Labels: localIndex
> Fix For: 4.12.1
>
> Attachments: PHOENIX-4287.patch, PHOENIX-4287_v2.patch
>
>
> With {{phoenix.use.stats.parallelization}} set to {{false}}, aggregate query
> returns incorrect results when stats are available.
> With local index and stats disabled for parallelization:
> {noformat}
> explain select count(*) from TABLE_T;
> +-------------------------------------------------------------------------------------------------------+-----------------+----------------+-----------+
> | PLAN
> | EST_BYTES_READ | EST_ROWS_READ | EST_INFO |
> +-------------------------------------------------------------------------------------------------------+-----------------+----------------+-----------+
> | CLIENT 0-CHUNK 332170 ROWS 625043899 BYTES PARALLEL 0-WAY RANGE SCAN OVER
> TABLE_T [1] | 625043899 | 332170 | 150792825 |
> | SERVER FILTER BY FIRST KEY ONLY
> | 625043899 | 332170 | 150792825 |
> | SERVER AGGREGATE INTO SINGLE ROW
> | 625043899 | 332170 | 150792825 |
> +-------------------------------------------------------------------------------------------------------+-----------------+----------------+-----------+
> select count(*) from TABLE_T;
> +-----------+
> | COUNT(1) |
> +-----------+
> | 0 |
> +-----------+
> {noformat}
> Using data table
> {noformat}
> explain select /*+NO_INDEX*/ count(*) from TABLE_T;
> +--------------------------------------------------------------------------------------------------+-----------------+----------------+----------------+
> | PLAN
> | EST_BYTES_READ | EST_ROWS_READ | EST_INFO_TS |
> +--------------------------------------------------------------------------------------------------+-----------------+----------------+----------------+
> | CLIENT 2-CHUNK 332151 ROWS 438492470 BYTES PARALLEL 1-WAY FULL SCAN OVER
> TABLE_T | 438492470 | 332151 | 1507928257617 |
> | SERVER FILTER BY FIRST KEY ONLY
> | 438492470 | 332151 | 1507928257617 |
> | SERVER AGGREGATE INTO SINGLE ROW
> | 438492470 | 332151 | 1507928257617 |
> +--------------------------------------------------------------------------------------------------+-----------------+----------------+----------------+
> select /*+NO_INDEX*/ count(*) from TABLE_T;
> +-----------+
> | COUNT(1) |
> +-----------+
> | 14 |
> +-----------+
> {noformat}
> Without stats available, results are correct:
> {noformat}
> explain select /*+NO_INDEX*/ count(*) from TABLE_T;
> +----------------------------------------------------------------------+-----------------+----------------+--------------+
> | PLAN |
> EST_BYTES_READ | EST_ROWS_READ | EST_INFO_TS |
> +----------------------------------------------------------------------+-----------------+----------------+--------------+
> | CLIENT 2-CHUNK PARALLEL 1-WAY FULL SCAN OVER TABLE_T | null |
> null | null |
> | SERVER FILTER BY FIRST KEY ONLY | null
> | null | null |
> | SERVER AGGREGATE INTO SINGLE ROW | null
> | null | null |
> +----------------------------------------------------------------------+-----------------+----------------+--------------+
> select /*+NO_INDEX*/ count(*) from TABLE_T;
> +-----------+
> | COUNT(1) |
> +-----------+
> | 333327 |
> +-----------+
> {noformat}
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