Message-ID: <1d5131fc-cd6c-4f61-8ba0-e61c518b168d@gmail.com>
Date: Fri, 4 Oct 2024 10:31:22 +0700
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: POC, WIP: OR-clause support for indexes
To: Peter Geoghegan <pg@bowt.ie>, Alexander Korotkov <aekorotkov@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alena Rybakina <a.rybakina@postgrespro.ru>,
 jian he <jian.universality@gmail.com>, Nikolay Shaplov <dhyan@nataraj.su>,
 pgsql-hackers@lists.postgresql.org, Robert Haas <robertmhaas@gmail.com>,
 pgsql-hackers@postgresql.org, Marcos Pegoraro <marcos@f10.com.br>,
 teodor@sigaev.ru, Peter Eisentraut <peter@eisentraut.org>,
 Ranier Vilela <ranier.vf@gmail.com>
References: <567ED6CA.2040504@sigaev.ru>
 <CAPpHfduFJHTNGCTFWt4GFs-E6Ts8xS5mCsKOYKBsZAmoOr8ZSA@mail.gmail.com>
 <65bfdcb6-0f0c-4d4c-a721-cb38a0ba91c7@postgrespro.ru>
 <CAPpHfdtR3cBKCSj_7dd7EDF_pa-rUUQBx3-guK6kZZ=_hSeMfg@mail.gmail.com>
 <670d1dc2-a280-4cf6-bc29-e2eafb107081@gmail.com>
 <CAPpHfdvF864n=Lzmjd2XBi9TwboZvrhRtLSt2hCP+JVUv6XKzg@mail.gmail.com>
 <CACJufxHCJvC3X8nUK-jRvRru-ZEXp16EBPADOwTGaqmOYM1Raw@mail.gmail.com>
 <fe11e5c9-877e-4306-a6a9-122125c7d2e5@postgrespro.ru>
 <93464dd6-d484-4021-b71f-e82928bf6758@gmail.com>
 <63617a30-6078-4e86-b44b-6364e04e210d@postgrespro.ru>
 <21752e9e-26fb-4665-bfcc-090bf4093e5a@postgrespro.ru>
 <CAPpHfduBA9RXa1LQAz=wFK8cGx_AaHVK_vnNqCnG4yA7KwFf7g@mail.gmail.com>
 <9ac6480d-6686-4c3a-9149-ba66df4f88ad@gmail.com>
 <CAPpHfds4wGdWQ2xx1OUKZC4ggqS6Q=cBSck9Re1ajY0ESkwcmw@mail.gmail.com>
 <CAPpHfdswA8ucBOuyf6GEn93ffC-oG7EjuvRprXx5Zc7Qdgafqw@mail.gmail.com>
 <CAH2-WznLiw20U_Tp8Otm=g7hGcfWnodM4EOGzV=F3W-EvfQDTw@mail.gmail.com>
Content-Language: en-AU
From: Andrei Lepikhov <lepihov@gmail.com>
In-Reply-To: <CAH2-WznLiw20U_Tp8Otm=g7hGcfWnodM4EOGzV=F3W-EvfQDTw@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: <https://www.postgresql.org/message-id/1d5131fc-cd6c-4f61-8ba0-e61c518b168d%40gmail.com>
Precedence: bulk

On 10/4/24 03:15, Peter Geoghegan wrote:
> On Tue, Oct 1, 2024 at 6:25 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
>> I think this patchset got much better, and it could possible be
>> committed after another round of cleanup and comment/docs improvement.
>> It would be very kind if you share your view on the decisions made in
>> this patchset.
Let me provide a standpoint to help Alexander.

The origin reason was - to avoid multiple BitmapOr, which has some 
effects at the planning stage (memory consumption, planning time) and 
execution (execution time growth). IndexScan also works better with a 
single array (especially a hashed one) than with a long list of clauses.
Another reason is that by spending some time identifying common operator 
family and variable-side clause equality, we open a way for future cheap 
improvements like removing duplicated constants.
Who knows, maybe we will be capable of using this code to improve 
cardinality estimations.

According to your proposal, we have had such casting to the common type 
in previous versions. Here, we avoid it intentionally: the general idea 
is about long lists of constants, and such casting causes questions 
about performance. Do I want it in the core? Yes, I do! But may we 
implement it a bit later to have time to probe the general method and 
see how it flies?

-- 
regards, Andrei Lepikhov