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: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.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: 2018-03-29T13:01:01Z
Lists: pgsql-hackers

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On Wed, Mar 28, 2018 at 7:21 PM, Ashutosh Bapat <
ashutosh.bapat@enterprisedb.com> wrote:

> On Tue, Mar 27, 2018 at 2:43 PM, Jeevan Chalke
> <jeevan.chalke@enterprisedb.com> wrote:
>
> > I am not sure on what we should Assetrt here. Note that we end-up here
> only
> > when doing grouping, and thus I don't think we need any Assert here.
> > Let me know if I missed anything.
>
> Since we are just checking whether it's an upper relation and directly
> using root->upper_targets[UPPERREL_GROUP_AGG], I thought we could add
> an assert to verify that it's really the grouping rel we are dealing
> with. But I guess, we can't really check that from given relation. But
> then for a grouped rel we can get its target from RelOptInfo. So, we
> shouldn't need to root->upper_targets[UPPERREL_GROUP_AGG]. Am I
> missing something? For other upper relations we do not set the target
> yet but then we could assert that there exists one in the grouped
> relation.
>

Yes. We fetch target from the grouped_rel itself.
Added Assert() per out off-list discussion.


>
> >
> >>
> >>
> >> -                get_agg_clause_costs(root, (Node *)
> >> root->parse->havingQual,
> >> +                get_agg_clause_costs(root, fpinfo->havingQual,
> >>                                       AGGSPLIT_SIMPLE, &aggcosts);
> >>              }
> >> Should we pass agg costs as well through GroupPathExtraData to avoid
> >> calculating it again in this function?
> >
> >
> > Adding an extra member in GroupPathExtraData just for FDW does not look
> good
> > to me.
> > But yes, if we do that, then we can save this calculation.
> > Let me know if its OK to have an extra member for just FDW use, will
> prepare
> > a separate patch for that.
>
> I think that should be fine. A separate patch would be good, so that a
> committer can decide whether or not to include it.
>

Attached patch 0003 for this.


>
>
> >>
> >> +    Node       *havingQual;
> >> I am wondering whether we could use remote_conds member for storing
> this.
> >
> >
> > This havingQual is later checked for shippability and classified into
> > pushable and non-pushable quals and stored in remote_conds and
> local_conds
> > respectively.
> > Storing it directly in remote_conds and then splitting it does not look
> good
> > to me.
> > Also, remote_conds is list of RestrictInfo nodes whereas havingQual is
> not.
> > So using that for storing havingQual does not make sense. So better to
> have
> > a separate member in PgFdwRelationInfo.
>
> Ah sorry, I was wrong about remote_conds. remote_conds and local_conds
> are basically the conditions on the relation being pushed down.
> havingQuals are conditions on a grouped relation so treating them like
> baserestrictinfo or join conditions looks more straight forward,
> rather than having a separate member in PgFdwRelationInfo. So, remote
> havingQuals go into remote_conds and local havingQuals go to
> local_conds.
>

OK. Agree.
In this version, I have not added anything in PgFdwRelationInfo.
Having qual is needed at two places; (1) in foreign_grouping_ok() to check
shippability, so passed this translated HAVING qual as a parameter to it,
and (2) estimating aggregates costs in estimate_path_cost_size(); there we
can use havingQual from root itself as costs won't change for parent and
child.
Thus no need of storing a havingQual in PgFdwRelationInfo.

Thanks


--
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>



-- 
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.