From: Alexey Kondratov <a.kondratov@postgrespro.ru>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Andrey V. Lepikhov <a.lepikhov@postgrespro.ru>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: PostgreSQL-Dev <pgsql-hackers@postgresql.org>
Subject: Re: [POC] Fast COPY FROM command for the table with foreign partitions
Date: Tue, 08 Sep 2020 18:34:31 +0300
Message-ID: <d3fbf3bc93b7bcd99ff7fa9ee41e0e20@postgrespro.ru> (raw)
In-Reply-To: <CA+HiwqHhdBcYRxhUUK7FRSWoQxe8met8fDvN=fhooH9x5dU35A@mail.gmail.com>
References: <ae25e79e-6122-720e-1349-fb832c6021df@postgrespro.ru>
<CA+HiwqH2ehGurL9bYUydXBxVUH6aHN5yXXxESAOs9O6-f_+Qeg@mail.gmail.com>
<cf1e92eb-9a8e-f5c1-f0cc-598882f1e546@postgrespro.ru>
<CA+HiwqHRqG8X9W6-v-E6d0nw1k6aC7QSMk-SOvv4puOjWsQMmA@mail.gmail.com>
<9a65d03b-250f-b086-5a3c-541d8e2de30d@postgrespro.ru>
<CA+HiwqE6M4mwH=CDOKmy5DUHRDP-knLdAfmCh+GW7D59s3QDRg@mail.gmail.com>
<CA+HiwqHtQaZp_t5M3z1+M0T9zd=0s3r_oOmi9TxHDdyW0_cxvg@mail.gmail.com>
<ab62d228-cf9a-e517-8667-7df1184adf2a@postgrespro.ru>
<CA+HiwqG1o5BDi0Hx6Uoxteyra2FbiSvaN4Fzs-i0pfKo1Zp_fg@mail.gmail.com>
<CA+HiwqHT9UFhVHyKsavL5u=iVdW9k92pHHN=FYL0sEysGtvYsw@mail.gmail.com>
<20200907072651.GF4867@paquier.xyz>
<19ba27e7-ee1e-9117-68ad-fd609b5763ca@postgrespro.ru>
<CA+HiwqEoSMpzMhzz1Dv7qFsFtzG71t5Wrgy4F+MoVUVR_5HdDQ@mail.gmail.com>
<0c67618c2e43b1dccb260dd6f90eeac2@postgrespro.ru>
<CA+HiwqHhdBcYRxhUUK7FRSWoQxe8met8fDvN=fhooH9x5dU35A@mail.gmail.com>
On 2020-09-08 17:00, Amit Langote wrote:
> Hi Alexey,
>
> On Tue, Sep 8, 2020 at 6:29 PM Alexey Kondratov
> <a.kondratov@postgrespro.ru> wrote:
>> On 2020-09-08 10:34, Amit Langote wrote:
>> > Any thoughts on the taking out the refactoring changes out of the main
>> > patch as I suggested?
>> >
>>
>> +1 for splitting the patch. It was rather difficult for me to
>> distinguish changes required by COPY via postgres_fdw from this
>> refactoring.
>>
>> Another ambiguous part of the refactoring was in changing
>> InitResultRelInfo() arguments:
>>
>> @@ -1278,6 +1280,7 @@ InitResultRelInfo(ResultRelInfo *resultRelInfo,
>> Relation resultRelationDesc,
>> Index resultRelationIndex,
>> Relation partition_root,
>> + bool use_multi_insert,
>> int instrument_options)
>>
>> Why do we need to pass this use_multi_insert flag here? Would it be
>> better to set resultRelInfo->ri_usesMultiInsert in the
>> InitResultRelInfo() unconditionally like it is done for
>> ri_usesFdwDirectModify? And after that it will be up to the caller
>> whether to use multi-insert or not based on their own circumstances.
>> Otherwise now we have a flag to indicate that we want to check for
>> another flag, while this check doesn't look costly.
>
> Hmm, I think having two flags seems confusing and bug prone,
> especially if you consider partitions. For example, if a partition's
> ri_usesMultiInsert is true, but CopyFrom()'s local flag is false, then
> execPartition.c: ExecInitPartitionInfo() would wrongly perform
> BeginForeignCopy() based on only ri_usesMultiInsert, because it
> wouldn't know CopyFrom()'s local flag. Am I missing something?
No, you're right. If someone want to share a state and use ResultRelInfo
(RRI) for that purpose, then it's fine, but CopyFrom() may simply
override RRI->ri_usesMultiInsert if needed and pass this RRI further.
This is how it's done for RRI->ri_usesFdwDirectModify.
InitResultRelInfo() initializes it to false and then
ExecInitModifyTable() changes the flag if needed.
Probably this is just a matter of personal choice, but for me the
current implementation with additional argument in InitResultRelInfo()
doesn't look completely right. Maybe because a caller now should pass an
additional argument (as false) even if it doesn't care about
ri_usesMultiInsert at all. It also adds additional complexity and feels
like abstractions leaking.
Regards
--
Alexey Kondratov
Postgres Professional https://www.postgrespro.com
Russian Postgres Company
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To: pgsql-hackers@postgresql.org
Cc: a.kondratov@postgrespro.ru, amitlangote09@gmail.com, a.lepikhov@postgrespro.ru, michael@paquier.xyz, ashutosh.bapat@2ndquadrant.com, ashutosh.bapat.oss@gmail.com, etsuro.fujita@gmail.com
Subject: Re: [POC] Fast COPY FROM command for the table with foreign partitions
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