Hans Zeller created TRAFODION-2965:
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Summary: 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
Fix For: 2.4
Here is a test case that demonstrates this:
{noformat}
update statistics for table hive.hive.time_dim on every column;
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 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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