Horton

Re: [HACKERS] Partition-wise aggregation/grouping

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Cc: 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: 2018-02-27T18:40:14Z
Lists: pgsql-hackers 
On Tue, Feb 27, 2018 at 4:29 AM, Jeevan Chalke
<jeevan.chalke@enterprisedb.com> wrote:
> Hi Robert,
> I had a look over his provided testcase and observed that when we create a
> Gather Merge path over a cheapest partial path by sorting it explicitly as
> generate_gather_paths won't consider it, we accidentally used cheapest
> partial path from the input_rel to create a Gather Merge; instead we need a
> cheapest partial path from the partially_grouped_rel.
>
> Attached fix_aggref_in_non-agg_error.patch fixing this.

Oops.  Thanks, committed.

> test_for_aggref_in_non-agg_error.patch has a testcase reported by Rajkumar
> which I have added in a aggregates.sql.

Didn't commit this; I think that's overkill.

> While doing so, I have observed few cleanup changes, added those in
> misc_cleanup.patch.

Committed those.

> While re-basing my partitionwise aggregate changes, I observed that when we
> want to create partial aggregation paths for a child partition, we don't
> need to add Gather or Gather Merge on top of it as we first want to append
> them all and then want to stick a gather on it. So it will be better to have
> that code part in a separate function so that we can call it from required
> places.
>
> I have attached patch (create_non_partial_paths.patch) for it including all
> above fix.

I don't like that very much.  For one thing, the name
create_non_partial_paths() is not very descriptive at all.  For
another thing, it somewhat renders add_paths_to_partial_grouping_rel()
a misnomer, as that function then adds only partial paths.  I think
what you should just do is have the main patch add a test for
rel->reloptkind == RELOPT_UPPER_REL; if true, add the Gather paths; if
not, skip it.  Then it will be skipped for RELOPT_OTHER_UPPER_REL
which is what we want.

-- 
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.