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Re: [Proposal] Global temporary tables

Prabhat Sahu <prabhat.sahu@enterprisedb.com>

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From: Prabhat Sahu <prabhat.sahu@enterprisedb.com>
To: 曾文旌(义从) <wenjing.zwj@alibaba-inc.com>, Pavel Stehule <pavel.stehule@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>, 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: 2020-02-21T07:45:44Z
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.

Hi,
I have started testing the "Global temporary table" feature,
from "gtt_v11-pg13.patch". Below is my findings:

-- session 1:
postgres=# create global temporary table gtt1(a int);
CREATE TABLE

-- seeeion 2:
postgres=# truncate gtt1 ;
ERROR:  could not open file "base/13585/t3_16384": No such file or directory

is it expected?

On Sun, Feb 16, 2020 at 8:53 PM Pavel Stehule <pavel.stehule@gmail.com>
wrote:

>
>
> ne 16. 2. 2020 v 16:15 odesílatel 曾文旌(义从) <wenjing.zwj@alibaba-inc.com>
> napsal:
>
>>
>>
>> 2020年2月15日 下午6:06，Pavel Stehule <pavel.stehule@gmail.com> 写道：
>>
>>
>> postgres=# insert into foo select generate_series(1,10000);
>>> INSERT 0 10000
>>> postgres=# \dt+ foo
>>>                           List of relations
>>> ┌────────┬──────┬───────┬───────┬─────────────┬────────┬─────────────┐
>>> │ Schema │ Name │ Type  │ Owner │ Persistence │  Size  │ Description │
>>> ╞════════╪══════╪═══════╪═══════╪═════════════╪════════╪═════════════╡
>>> │ public │ foo  │ table │ pavel │ session     │ 384 kB │             │
>>> └────────┴──────┴───────┴───────┴─────────────┴────────┴─────────────┘
>>> (1 row)
>>>
>>> postgres=# truncate foo;
>>> TRUNCATE TABLE
>>> postgres=# \dt+ foo
>>>                           List of relations
>>> ┌────────┬──────┬───────┬───────┬─────────────┬───────┬─────────────┐
>>> │ Schema │ Name │ Type  │ Owner │ Persistence │ Size  │ Description │
>>> ╞════════╪══════╪═══════╪═══════╪═════════════╪═══════╪═════════════╡
>>> │ public │ foo  │ table │ pavel │ session     │ 16 kB │             │
>>> └────────┴──────┴───────┴───────┴─────────────┴───────┴─────────────┘
>>> (1 row)
>>>
>>> I expect zero size after truncate.
>>>
>>> Thanks for review.
>>>
>>> I can explain, I don't think it's a bug.
>>> The current implementation of the truncated GTT retains two blocks of
>>> FSM pages.
>>> The same is true for truncating regular tables in subtransactions.
>>> This is an implementation that truncates the table without changing the
>>> relfilenode of the table.
>>>
>>>
>> This is not extra important feature - now this is little bit a surprise,
>> because I was not under transaction.
>>
>> Changing relfilenode, I think, is necessary, minimally for future VACUUM
>> FULL support.
>>
>> Not allowing relfilenode changes is the current limit.
>> I think can improve on it. But ,This is a bit complicated.
>> so I'd like to know the necessity of this improvement.
>> Could you give me more details?
>>
>
> I don't think so GTT without support of VACUUM FULL can be accepted. Just
> due consistency.
>
> Regards
>
> Pavel
>
>
>>
>> Regards
>>
>> Pavel Stehule
>>
>>
>>>
>>> Wenjing
>>>
>>>
>>> Regards
>>>
>>> Pavel
>>>
>>>
>>>>>
>>>>> Wenjing
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> >
>>>>> > --
>>>>> > Robert Haas
>>>>> > EnterpriseDB: http://www.enterprisedb.com
>>>>> > The Enterprise PostgreSQL Company
>>>>>
>>>>>
>>>
>>

-- 

With Regards,
Prabhat Kumar Sahu
EnterpriseDB: http://www.enterprisedb.com