Horton

Re: Partition-wise aggregation/grouping

Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>

View thread View on postgr.es
From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
To: David Rowley <david.rowley@2ndquadrant.com>
Cc: Jeevan Chalke <jeevan.chalke@enterprisedb.com>, Rajkumar Raghuwanshi <rajkumar.raghuwanshi@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-10-10T10:00:02Z
Lists: pgsql-hackers 
On Tue, Oct 10, 2017 at 1:31 PM, David Rowley
<david.rowley@2ndquadrant.com> wrote:
>
> I don't think there's any need to invent any new GUC. You could just
> divide cpu_tuple_cost by something.
>
> I did a quick benchmark on my laptop to see how much Append really
> costs, and with the standard costs the actual cost seems to be about
> cpu_tuple_cost / 2.4. So probably cpu_tuple_cost / 2 might be
> realistic. create_set_projection_path() does something similar and
> brincostestimate() does some similar magic and applies 0.1 *
> cpu_operator_cost to the total cost.
>
>
> # -- How does that compare to the cpu_tuple_cost?
> # select current_Setting('cpu_tuple_cost')::float8 / 0.00416630302337493743;
>     ?column?
> ----------------
>  2.400209476818
> (1 row)
>
> Maybe it's worth trying with different row counts to see if the
> additional cost is consistent, but it's probably not worth being too
> critical here.
>

This looks good to me. I think it should be a separate, yet very small patch.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database 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.