Horton

Re: [Proposal] Global temporary tables

Pavel Stehule <pavel.stehule@gmail.com>

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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
Cc: Robert Haas <robertmhaas@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, 曾文旌(义从) <wenjing.zwj@alibaba-inc.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, 蔡松露(子嘉) <zijia@taobao.com>, "Cai, Le" <le.cai@alibaba-inc.com>, 萧少聪(铁庵) <shaocong.xsc@alibaba-inc.com>
Date: 2020-01-30T09:52:56Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. PageAddItemExtended(): Add LP_UNUSED assertion.

  2. Remove temporary files after backend crash

  3. Fix comment in indexing.c

  4. Fix failure to ignore leftover temp tables after a server crash.

čt 30. 1. 2020 v 10:44 odesílatel Konstantin Knizhnik <
k.knizhnik@postgrespro.ru> napsal:

>
>
> On 30.01.2020 12:23, Pavel Stehule wrote:
>
>
> Building regular index requires two kinds of lock:
>> 1. You have to lock pg_class to make changes in system catalog.
>> 2. You need to lock heap relation  to pervent concurrent updates while
>> building index.
>>
>> GTT requires 1)  but not 2).
>> Once backend inserts information about new index in system catalog, all
>> other sessions may use it. pg_class lock prevents any race condition here.
>> And building index itself doesn't affect any other backends.
>>
>
> It is true. The difference for GTT, so any other sessions have to build
> index (in your proposal) as extra operation against original plan.
>
> What is "index"?
> For most parts of Postgres it is just an entry in system catalog.
> And only executor deals with its particular implementation and content.
>
> My point is that if we process GTT index metadata in the same way as
> regular index metadata,
> then there will be no differences for the postgres between GTT and regular
> indexes.
> And we can provide the same behavior.
>

There should be a difference - index on regular table is created by one
process. Same thing is not possible on GTT. So there should be a difference
every time.

You can reduce some differences, but minimally me and Robert don't feel it
well. Starting a building index from routine, that is used for reading from
buffer doesn't look well. I can accept some stranges, but I need to have
feeling so it is necessary. I don't think so it is necessary in this case.

Regards

Pavel


> Concerning actual content of the index - it is local to the backend and it
> is safe to construct it a t any point of time (on demand).
> It depends only on private data and can not be somehow affected by other
> backends (taken in account that we preserve locking policy of regular
> tables).
>
>
> --
> Konstantin Knizhnik
> Postgres Professional: http://www.postgrespro.com
> The Russian Postgres Company
>
>