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Re: [Proposal] Global temporary tables

Konstantin Knizhnik <k.knizhnik@postgrespro.ru>

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From: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
To: Pavel Stehule <pavel.stehule@gmail.com>
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: 2020-01-30T10:02:18Z
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.


On 30.01.2020 12:52, Pavel Stehule wrote:
>
>
> čt 30. 1. 2020 v 10:44 odesílatel Konstantin Knizhnik 
> <k.knizhnik@postgrespro.ru <mailto: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.

Metadata of GTT index is also created by one process. And actual content 
of the index is not interesting for most parts of Postgres.

>
> 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.

Sorry, but "don't feel it well", "doesn't look well" looks more 
likeliterary criticism rather than code review;)
Yes, I agree that it is unnatural to call btindex from _bt_getbuf. But 
what can go wrong here?

-- 
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company