Horton

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: 2020-01-30T09:44:39Z
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 12:23, 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.

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