Horton

Re: [HACKERS] Partition-wise aggregation/grouping

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Jeevan Chalke <jeevan.chalke@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: 2017-12-01T19:08:34Z
Lists: pgsql-hackers 
On Fri, Dec 1, 2017 at 7:41 AM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:
> This code creates plans where there are multiple Gather nodes under an Append
> node.

We should avoid that.  Starting and stopping workers is inefficient,
and precludes things like turning the Append into a Parallel Append.

> AFAIU, the workers assigned to one gather node can be reused until that
> Gather node finishes. Having multiple Gather nodes under an Append mean that
> every worker will be idle from the time that worker finishes the work till the
> last worker finishes the work.

No, workers will exit as soon as they finish.  They don't hang around idle.

> index b422050..1941468 100644
> --- a/src/tools/pgindent/typedefs.list
> +++ b/src/tools/pgindent/typedefs.list
> @@ -2345,6 +2345,7 @@ UnlistenStmt
>  UnresolvedTup
>  UnresolvedTupData
>  UpdateStmt
> +UpperPathExtraData
>  UpperRelationKind
>  UpperUniquePath
>  UserAuth
>
> Do we commit this file as part of the feature?

Andres and I regularly commit such changes; Tom rejects them.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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.