Horton

Re: Partition-wise aggregation/grouping

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-10-17T13:43:36Z
Lists: pgsql-hackers 
On Fri, Oct 13, 2017 at 12:06 PM, Jeevan Chalke
<jeevan.chalke@enterprisedb.com> wrote:
>
While playing around with the patch I have noticed one regression with
the partial partition-wise aggregate.

I am consistently able to reproduce this on my local machine.

Scenario: Group by on non-key column and only one tuple per group.

Complete Test:
--------------------
create table t(a int,b int) partition by range(a);
create table t1 partition of t for values from (1) to (100000);
create table t2 partition of t for values from (100000) to (200000);

insert into t values (generate_series(1,199999),generate_series(1, 199999));
postgres=# explain analyze select sum(a) from t group by b;
                                                              QUERY
PLAN
--------------------------------------------------------------------------------------------------------------------------------------
 Finalize GroupAggregate  (cost=20379.55..28379.51 rows=199999
width=12) (actual time=102.311..322.969 rows=199999 loops=1)
   Group Key: t1.b
   ->  Merge Append  (cost=20379.55..25379.53 rows=199999 width=12)
(actual time=102.303..232.310 rows=199999 loops=1)
         Sort Key: t1.b
         ->  Partial GroupAggregate  (cost=10189.72..11939.70
rows=99999 width=12) (actual time=52.164..108.967 rows=99999 loops=1)
               Group Key: t1.b
               ->  Sort  (cost=10189.72..10439.72 rows=99999 width=8)
(actual time=52.158..66.236 rows=99999 loops=1)
                     Sort Key: t1.b
                     Sort Method: external merge  Disk: 1768kB
                     ->  Seq Scan on t1  (cost=0.00..1884.99
rows=99999 width=8) (actual time=0.860..20.388 rows=99999 loops=1)
         ->  Partial GroupAggregate  (cost=10189.82..11939.82
rows=100000 width=12) (actual time=50.134..102.976 rows=100000
loops=1)
               Group Key: t2.b
               ->  Sort  (cost=10189.82..10439.82 rows=100000 width=8)
(actual time=50.128..63.362 rows=100000 loops=1)
                     Sort Key: t2.b
                     Sort Method: external merge  Disk: 1768kB
                     ->  Seq Scan on t2  (cost=0.00..1885.00
rows=100000 width=8) (actual time=0.498..20.977 rows=100000 loops=1)
 Planning time: 0.190 ms
 Execution time: 339.929 ms
(18 rows)

postgres=# set enable_partition_wise_agg=off;
SET
postgres=# explain analyze select sum(a) from t group by b;
                                                            QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------
 GroupAggregate  (cost=26116.53..29616.51 rows=199999 width=12)
(actual time=139.413..250.751 rows=199999 loops=1)
   Group Key: t1.b
   ->  Sort  (cost=26116.53..26616.52 rows=199999 width=8) (actual
time=139.406..168.775 rows=199999 loops=1)
         Sort Key: t1.b
         Sort Method: external merge  Disk: 3544kB
         ->  Result  (cost=0.00..5769.98 rows=199999 width=8) (actual
time=0.674..76.392 rows=199999 loops=1)
               ->  Append  (cost=0.00..3769.99 rows=199999 width=8)
(actual time=0.672..40.291 rows=199999 loops=1)
                     ->  Seq Scan on t1  (cost=0.00..1884.99
rows=99999 width=8) (actual time=0.672..12.408 rows=99999 loops=1)
                     ->  Seq Scan on t2  (cost=0.00..1885.00
rows=100000 width=8) (actual time=1.407..11.689 rows=100000 loops=1)
 Planning time: 0.146 ms
 Execution time: 263.678 ms
(11 rows)


-- 
Regards,
Dilip Kumar
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.