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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2021/07/26 13:13:56 UTC
[GitHub] [spark] Gabriel39 opened a new pull request #33520: [SPARK-36289]rewrite distinct count case when expressions without Expand node
Gabriel39 opened a new pull request #33520:
URL: https://github.com/apache/spark/pull/33520
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### What changes were proposed in this pull request?
Currently, RewriteDistinctAggregates rule will rewrite distinct aggregates with extra Expand node. This causes unnecessary memory waste and performance fallback for some specific aggregates(e.g. count distinct case when).
for query:
`
{{{
SELECT
cat1,
COUNT(DISTINCT CASE WHEN cond1 THEN cat2 ELSE null end) as cat2_cnt1,
COUNT(DISTINCT CASE WHEN cond2 THEN cat2 ELSE null end) as cat2_cnt2,
FROM
data
GROUP BY
key
}}}
`
Currently, we rewrite it to :
`
{{{
Aggregate(
key = ['key]
functions = [count(if (('gid = 1) and 'casewhen1) 'cat2_1 else null),
count(if (('gid = 2) and 'casewhen2) 'cat2_2 else null)]
output = ['key, 'cat2_cnt1, 'cat2_cnt2])
Aggregate(
key = ['key, 'casewhen1, 'casewhen2, 'gid]
functions = []
output = ['key, 'casewhen1, 'casewhen2, 'gid])
Expand(
projections = [('key, 'cat1, CASE WHEN cond1 THEN cat2 ELSE null END, null, 1),
('key, 'cat1, 'null, CASE WHEN cond1 THEN cat2 ELSE null END, 2)]
output = ['key, 'cat1, 'casewhen1, 'casewhen2, 'gid])
LocalTableScan [...]
}}}
`
This PR will improve performance and reduce memory waste. And query will be rewrite to:
`
if # of case when expr < 64
{{{
Aggregate(
key = ['key]
functions = [count(if (01 & 'bit_vector != 0) 0 else null),
count(if (10 & 'bit_vector != 0) 0 else null)]
output = ['key, 'cat2_cnt1, 'cat2_cnt2])
Aggregate(
key = ['key, 'cat1]
functions = [bit_or(if (cond1) 01 else 00, if (cond2) 10 else 00)]
output = ['key, 'cat1, 'bit_vector])
LocalTableScan [...]
}}}
if # of case when expr >= 64
{{{
Aggregate(
key = ['key]
functions = [count(if ('sum1 >= 1) 1 else null),
count(if ('sum2 >= 1) 1 else null)]
output = ['key, 'cat1_cnt1, 'cat1_cnt2])
Aggregate(
key = ['key, 'cat1]
functions = [sum(if (cond1) 1 else 0), sum(if (cond2) 1 else 0)]
output = ['key, 'cat1, 'sum1, 'sum2])
LocalTableScan [...]
}}}
`
### Why are the changes needed?
we can rewrite count distinct case when more efficiently
### Does this PR introduce _any_ user-facing change?
no
### How was this patch tested?
UT in RewriteDistinctAggregatesSuite
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[GitHub] [spark] github-actions[bot] closed pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
github-actions[bot] closed pull request #33520:
URL: https://github.com/apache/spark/pull/33520
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[GitHub] [spark] Gabriel39 commented on pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
Gabriel39 commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-889200948
> What is `cond2`?
@beliefer `cond1` and `cond2` are two conditions such as ` a > 1`
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[GitHub] [spark] beliefer commented on pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
beliefer commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-891492579
> > What is `cond2`?
>
> @beliefer `cond1` and `cond2` are two conditions such as ` a > 1`
It seems you should correct the description. So reviewer could understand clearly.
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[GitHub] [spark] github-actions[bot] commented on pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
github-actions[bot] commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-966714580
We're closing this PR because it hasn't been updated in a while. This isn't a judgement on the merit of the PR in any way. It's just a way of keeping the PR queue manageable.
If you'd like to revive this PR, please reopen it and ask a committer to remove the Stale tag!
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[GitHub] [spark] AmplabJenkins commented on pull request #33520: [SPARK-36289]rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
AmplabJenkins commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-886695587
Can one of the admins verify this patch?
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[GitHub] [spark] beliefer commented on pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
beliefer commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-888916658
What is `cond2`?
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[GitHub] [spark] Gabriel39 commented on pull request #33520: [SPARK-36289][SQL] Rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
Gabriel39 commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-887935948
cc @HyukjinKwon Thx :)
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[GitHub] [spark] Gabriel39 commented on pull request #33520: [SPARK-36289]rewrite distinct count case when expressions without Expand node
Posted by GitBox <gi...@apache.org>.
Gabriel39 commented on pull request #33520:
URL: https://github.com/apache/spark/pull/33520#issuecomment-886696643
cc @cloud-fan Thx :)
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