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https://issues.apache.org/jira/browse/TRAFODION-2965?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hans Zeller closed TRAFODION-2965.
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Resolution: Fixed
> Hash partial groupby does not report a row count in operator statistics
> -----------------------------------------------------------------------
>
> Key: TRAFODION-2965
> URL: https://issues.apache.org/jira/browse/TRAFODION-2965
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-exe
> Affects Versions: 2.0-incubating
> Environment: any
> Reporter: Hans Zeller
> Assignee: Hans Zeller
> Priority: Major
> Fix For: 2.3
>
>
> Here is a test case that demonstrates this:
> {noformat}
> update statistics for table hive.hive.time_dim on every column;
> control query shape groupby(exchange(groupby(exchange(groupby(scan)))));
> prepare s from
> select count(distinct t_time_id) from hive.hive.time_dim;
> explain options 'f' s;
> execute s;
> get statistics for qid current default;
> {noformat}
> The actual statistics show a "0" as the row count (ActRowsUsed) for the
> lowest EX_HASH_GRBY with id 2:
> {noformat}
> LC RC Id PaId ExId Frag TDB Name DOP Dispatches
> OperCpuTime EstRowsUsed ActRowsUsed ActDataUsed
> Details
> 13 . 14 . 8 0 EX_ROOT 1 2
> 37 0 1 8 3658
> 12 . 13 14 7 0 EX_SORT_GRBY 1 5
> 61 1 1 8
> 11 . 12 13 6 0 EX_SPLIT_TOP 1 8
> 171 1 4 32
> 10 . 11 12 6 0 EX_SEND_TOP 4 16
> 3,389 1 4 64
> 9 . 10 11 6 2 EX_SEND_BOTTOM 4 12
> 683 1 4 64
> 8 . 9 10 6 2 EX_SPLIT_BOTTOM 4 19
> 597 1 4 32
> 833874
> 7 . 8 9 5 2 EX_SORT_GRBY 4 2,259
> 289,200 1 4 32
> 6 . 7 8 4 2 EX_HASH_GRBY 4 2,259
> 394,235 1451 86,400 2,765,059,200 0|0|0
> 5 . 6 7 3 2 EX_SPLIT_TOP 4 2,211
> 51,034 110007 86,400 2,765,059,200
> 4 . 5 6 3 2 EX_SEND_TOP 8 2,436
> 98,125 110007 86,400 2,766,528,000
> 3 . 4 5 3 3 EX_SEND_BOTTOM 8 10,658
> 196,714 110007 86,400 2,766,528,000
> 2 . 3 4 3 3 EX_SPLIT_BOTTOM 2 2,663
> 95,246 110007 86,400 2,765,059,200
> 1547521
> 1 . 2 3 2 3 EX_HASH_GRBY 2 4,521
> 303,319 55003.5 0 0
> . . 1 2 1 3 EX_HDFS_SCAN 2 2,650
> 952,242 116085 86,400 2,765,059,200
> HIVE.HIVE.TIME_DIM|86400|5288324
> {noformat}
> The reason is that the hash groupby reports its row count in the BMO stats.
> However, a partial hash groupby is not considered a BMO (Big Memory
> Operator), so no rowcount gets reported. The fix is to increment the rowcount
> in the generic stats entry that is present in both partial and full groupby
> operators.
>
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