Horton

Re: [HACKERS] Partition-wise aggregation/grouping

Rafia Sabih <rafia.sabih@enterprisedb.com>

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From: Rafia Sabih <rafia.sabih@enterprisedb.com>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Dilip Kumar <dilipbalaut@gmail.com>, David Rowley <david.rowley@2ndquadrant.com>, Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2018-02-14T06:47:37Z
Lists: pgsql-hackers

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On Tue, Feb 13, 2018 at 6:21 PM, Jeevan Chalke <
jeevan.chalke@enterprisedb.com> wrote:

>
> I see that partition-wise aggregate plan too uses parallel index, am I
> missing something?
>
>
You're right, I missed that, oops.

>
>> Q18 takes some 390 secs with patch and some 147 secs without it.
>>
>
> This looks strange. This patch set does not touch parallel or seq scan as
> such. I am not sure why this is happening. All these three queries explain
> plan shows much higher execution time for parallel/seq scan.
>
> Yeah strange it is.

> However, do you see similar behaviour with patches applied,
> "enable_partition_wise_agg = on" and "enable_partition_wise_agg = off" ?
>

I tried that for query 18, with patch and  enable_partition_wise_agg = off,
query completes in some 270 secs. You may find the explain analyse output
for it in the attached file. I noticed that on head the query plan had
parallel hash join however with patch and no partition-wise agg it is using
nested loop joins. This might be the issue.

>
> Also, does rest of the queries perform better with partition-wise
> aggregates?
>
>
As far as this setting goes, there wasn't any other query using
partition-wise-agg, so, no.

BTW, just an FYI, this experiment is on scale factor 20.

-- 
Regards,
Rafia Sabih
EnterpriseDB: http://www.enterprisedb.com/

Commits

  1. postgres_fdw: Push down partition-wise aggregation.

  2. Remove 'target' from GroupPathExtraData.

  3. Implement partition-wise grouping/aggregation.

  4. Don't pass the grouping target around unnecessarily.

  5. Determine grouping strategies in create_grouping_paths.

  6. Defer creation of partially-grouped relation until it's needed.

  7. Split create_grouping_paths into degenerate and non-degenerate cases.

  8. Pass additional arguments to a couple of grouping-related functions.

  9. Fix logic error in add_paths_to_partial_grouping_rel.

  10. Minor cleanup of code related to partially_grouped_rel.

  11. Add a new upper planner relation for partially-aggregated results.

  12. Charge cpu_tuple_cost * 0.5 for Append and MergeAppend nodes.

  13. Rename enable_partition_wise_join to enable_partitionwise_join

  14. Factor some code out of create_grouping_paths.

  15. Pad XLogReaderState's main_data buffer more aggressively.

  16. Prevent int128 from requiring more than MAXALIGN alignment.

  17. Fix DROP SUBSCRIPTION hang

  18. Inject $(ICU_LIBS) regardless of platform.

  19. Some preliminary refactoring towards partitionwise join.