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[GitHub] [hive] kasakrisz opened a new pull request #2656: [draft] HIVE-24579: Incorrect Result For Groupby With Limit
kasakrisz opened a new pull request #2656:
URL: https://github.com/apache/hive/pull/2656
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[GitHub] [hive] kgyrtkirk commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kgyrtkirk commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r717361733
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
we lost the `Limit` operator from here - as a result we will be shuffling all input rows.
I think this could become more costly for larger tables than the old plan.
I don't see TopN hash enabled on the reduce operator - which could possibly save the day in this case; why did we loose that as well?
##########
File path: ql/src/test/results/clientpositive/llap/limit_pushdown.q.out
##########
@@ -1075,6 +1072,13 @@ STAGE PLANS:
Map-reduce partition columns: _col0 (type: string)
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
value expressions: _col1 (type: bigint)
+ Execution mode: vectorized, llap
+ LLAP IO: all inputs
+ Map 3
+ Map Operator Tree:
+ TableScan
+ alias: src
+ Statistics: Num rows: 500 Data size: 43500 Basic stats: COMPLETE Column stats: COMPLETE
Top N Key Operator
Review comment:
in the old plan: did we have 2 TopN key operators in this plan which are equal?
this is unrelated to this patch; but we may have an issue with its comparision - and because of that SWO is not able to simplify them
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[GitHub] [hive] kasakrisz commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kasakrisz commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r717404007
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
But we still have TopNKey operator in the Mapper (both old and new plan) it filters out the majority of the rows.
This query has the same issue like the example in the jira: it has gby with limit + aggregate function in the project:
```
SELECT src.key, sum(substr(src.value,5)) GROUP BY src.key LIMIT 5
```
If no ordering is specified we may end up with incorrect aggregations.
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[GitHub] [hive] kgyrtkirk commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kgyrtkirk commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r714118141
##########
File path: ql/src/test/results/clientpositive/llap/offset_limit_ppd_optimizer.q.out
##########
@@ -1527,41 +1530,12 @@ STAGE PLANS:
outputColumnNames: _col0, _col1
Limit
Number of rows: 20
- Offset of rows: 10
+ Offset of rows: 20
Review comment:
is this change expected?
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[GitHub] [hive] kgyrtkirk commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kgyrtkirk commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r714118141
##########
File path: ql/src/test/results/clientpositive/llap/offset_limit_ppd_optimizer.q.out
##########
@@ -1527,41 +1530,12 @@ STAGE PLANS:
outputColumnNames: _col0, _col1
Limit
Number of rows: 20
- Offset of rows: 10
+ Offset of rows: 20
Review comment:
is this change expected?
--
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[GitHub] [hive] kasakrisz commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kasakrisz commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r717404007
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
But we still have TopNKey operator in the Mapper (both old and new plan) it filters out the majority of the rows.
This query has the same issue like the example in the jira: it has gby with limit + aggregate function in the project:
```
SELECT src.key, sum(substr(src.value,5)) GROUP BY src.key LIMIT 5
```
If no ordering is specified we may end up with incorrect aggregations.
--
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[GitHub] [hive] kgyrtkirk commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kgyrtkirk commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r717361733
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
we lost the `Limit` operator from here - as a result we will be shuffling all input rows.
I think this could become more costly for larger tables than the old plan.
I don't see TopN hash enabled on the reduce operator - which could possibly save the day in this case; why did we loose that as well?
##########
File path: ql/src/test/results/clientpositive/llap/limit_pushdown.q.out
##########
@@ -1075,6 +1072,13 @@ STAGE PLANS:
Map-reduce partition columns: _col0 (type: string)
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
value expressions: _col1 (type: bigint)
+ Execution mode: vectorized, llap
+ LLAP IO: all inputs
+ Map 3
+ Map Operator Tree:
+ TableScan
+ alias: src
+ Statistics: Num rows: 500 Data size: 43500 Basic stats: COMPLETE Column stats: COMPLETE
Top N Key Operator
Review comment:
in the old plan: did we have 2 TopN key operators in this plan which are equal?
this is unrelated to this patch; but we may have an issue with its comparision - and because of that SWO is not able to simplify them
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
I missed that - most likely because the the row estimate was >100.
In that case this doesn't seem to be a problem; however we should fix the stat estimate for the TNKO - could you open a ticket?
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[GitHub] [hive] kasakrisz merged pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kasakrisz merged pull request #2656:
URL: https://github.com/apache/hive/pull/2656
--
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[GitHub] [hive] kasakrisz merged pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kasakrisz merged pull request #2656:
URL: https://github.com/apache/hive/pull/2656
--
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[GitHub] [hive] kgyrtkirk commented on a change in pull request #2656: HIVE-24579: Incorrect Result For Groupby With Limit
Posted by GitBox <gi...@apache.org>.
kgyrtkirk commented on a change in pull request #2656:
URL: https://github.com/apache/hive/pull/2656#discussion_r717408925
##########
File path: ql/src/test/results/clientpositive/llap/groupby1_limit.q.out
##########
@@ -71,33 +71,34 @@ STAGE PLANS:
mode: mergepartial
outputColumnNames: _col0, _col1
Statistics: Num rows: 316 Data size: 30020 Basic stats: COMPLETE Column stats: COMPLETE
- Limit
- Number of rows: 5
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- Reduce Output Operator
- null sort order:
- sort order:
- Statistics: Num rows: 5 Data size: 475 Basic stats: COMPLETE Column stats: COMPLETE
- TopN Hash Memory Usage: 0.1
- value expressions: _col0 (type: string), _col1 (type: double)
+ Reduce Output Operator
Review comment:
I missed that - most likely because the the row estimate was >100.
In that case this doesn't seem to be a problem; however we should fix the stat estimate for the TNKO - could you open a ticket?
--
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