Horton

Re: [HACKERS] Partition-wise aggregation/grouping

Jeevan Chalke <jeevan.chalke@enterprisedb.com>

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From: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
To: Rafia Sabih <rafia.sabih@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: 2018-02-13T12:51:14Z
Lists: pgsql-hackers 
On Tue, Feb 13, 2018 at 12:37 PM, Rafia Sabih <rafia.sabih@enterprisedb.com>
wrote:

>
> I was testing this patch for TPC-H benchmarking and came across following
> results,
>

Thanks Rafia for testing this with TPC-H benchmarking.


>
> Q1 completes in 229 secs with patch and in 66 secs without it. It looks
> like with this patch the time of parallel seq scan itself is elevated for
> some of the partitions. Notice for partitions, lineitem_3, lineitem_7,
> lineitem_10, and linietem_5 it is some 13 secs which was somewhere around 5
> secs on head.
>

> Q6 completes in some 7 secs with patch and it takes 4 secs without it.
> This is mainly caused because with the new parallel append, the parallel
> operator below it (parallel index scan in this case) is not used, however,
> on head it was the append of all the parallel index scans, which was saving
> quite some time.
>

I see that partition-wise aggregate plan too uses parallel index, am I
missing something?


>
> 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.

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

Also, does rest of the queries perform better with partition-wise
aggregates?


>
> The experimental setup for these tests is as follows,
> work_mem = 500MB
> shared_buffers = 10GB
> effective_cache_size = 4GB
> seq_page_cost = random+page_cost = 0.01
> enable_partition_wise_join = off
>
> Partitioning info:
> Total 10 partitions on tables - lineitem and orders each with partitioning
> key being l_orderkey and o_orderkey respectively.
>
> Please find the attached file for explain analyse outputs of each of the
> reported query.
> --
> Regards,
> Rafia Sabih
> EnterpriseDB: http://www.enterprisedb.com/
>



-- 
Jeevan Chalke
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

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.