From: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
---|---|
To: | "Andrey V(dot) Lepikhov" <a(dot)lepikhov(at)postgrespro(dot)ru>, Teodor Sigaev <teodor(at)sigaev(dot)ru> |
Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: POC: GROUP BY optimization |
Date: | 2022-03-29 00:48:50 |
Message-ID: | 44472925-f6c6-e8de-6f72-0451458532c4@enterprisedb.com |
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Thread: | |
Lists: | pgsql-hackers |
Hi,
Here's a rebased/improved version of the patch, with smaller parts
addressing various issues. There are seven parts:
0001 - main part, just rebased
0002 - replace the debug GUC options with a single GUC to disable the
optimization if needed
0003 - minor code cleanup, removal of unnecessary variable
0004 - various comment fixes (rewordings, typos, ...)
0005 - a minor code simplification, addressing FIXMEs from 0004
0006 - adds the new GUC to the docs
0007 - demonstrates plan changes with a disabled optimization
The first 6 parts should be squashed and committed at one, I only kept
them separate for clarity. The 0007 is merely a demonstration of the new
GUC and that it disables the optimization.
> Agree. Because it is a kind of automation we should allow user to switch
> it off in the case of problems or manual tuning.
> > Also, I looked through this patch. It has some minor problems:
> 1. Multiple typos in the patch comment.
I went through the comments and checked all of them for grammar mistakes
and typos using a word processor, so hopefully that should be OK. But
maybe there's still something wrong.
> 2. The term 'cardinality of a key' - may be replace with 'number of
> duplicates'?
No, cardinality means "number of distinct values", so "duplicates" would
be wrong. And I think "cardinality" is well established term, so I think
it's fine.
BTW I named the GUC enable_group_by_reordering, I wonder if it should be
named differently, e.g. enable_groupby_reordering? Opinions?
regards
--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
Attachment | Content-Type | Size |
---|---|---|
0001-Optimize-order-of-GROUP-BY-keys-20220328.patch | text/x-patch | 102.1 KB |
0002-fixup-rework-GUC-options-20220328.patch | text/x-patch | 7.6 KB |
0003-fixup-minor-code-cleanup-20220328.patch | text/x-patch | 1.8 KB |
0004-fixup-comments-cleanup-type-fixes-and-rewor-20220328.patch | text/x-patch | 21.9 KB |
0005-fixup-minor-simplification-20220328.patch | text/x-patch | 1.3 KB |
0006-fixup-add-GUC-to-docs-20220328.patch | text/x-patch | 1.3 KB |
0007-demonstrate-disabled-optimization-20220328.patch | text/x-patch | 15.9 KB |
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