Re: [HACKERS] Partition-wise aggregation/grouping

From: Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Partition-wise aggregation/grouping
Date: 2018-02-27 09:29:18
Message-ID: CAM2+6=X9kxQoL2ZqZ00E6asBt9z+rfyWbOmhXJ0+8fPAyMZ9Jg@mail.gmail.com
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Hi Robert,

On Mon, Feb 26, 2018 at 8:03 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

>
> Committed after incorporating your other fixes and updating the
> optimizer README.
>

Thanks Robert.

Off-list Rajkumar has reported an issue. When we have enable_hashagg set to
false, and Gather Merge path is chosen, it ended-up in an error saying
"ERROR: Aggref found in non-Agg plan node".

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

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

---

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.

Thanks

> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>

--
Jeevan Chalke
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

Attachment Content-Type Size
fix_aggref_in_non-agg_error.patch text/x-patch 643 bytes
test_for_aggref_in_non-agg_error.patch text/x-patch 4.0 KB
misc_cleanup.patch text/x-patch 1.6 KB
create_non_partial_paths.patch text/x-patch 2.7 KB

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