Re: [HACKERS] Partition-wise aggregation/grouping

On Tue, Mar 27, 2018 at 2:43 PM, Jeevan Chalke
<jeevan(dot)chalke(at)enterprisedb(dot)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