Horton

Re: [HACKERS] Partition-wise aggregation/grouping

Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>

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From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
To: Jeevan Chalke <jeevan.chalke@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: 2018-03-28T13:51:06Z
Lists: pgsql-hackers 
On Tue, Mar 27, 2018 at 2:43 PM, Jeevan Chalke
<jeevan.chalke@enterprisedb.com> wrote:

>>          else if (IS_UPPER_REL(foreignrel))
>>          {
>>              PgFdwRelationInfo *ofpinfo;
>> -            PathTarget *ptarget =
>> root->upper_targets[UPPERREL_GROUP_AGG];
>> +            PathTarget *ptarget = fpinfo->grouped_target;
>>
>> I think we need an assert there to make sure that the upper relation is a
>> grouping relation. That way any future push down will notice it.
>
>
> 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.

>
>>
>>
>> -                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.



>>
>> +    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.

-- 
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.