Re: [Proposal] Global temporary tables

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(dot)stehule(at)gmail(dot)com>
wrote:

>
>
> ne 16. 2. 2020 v 16:15 odesílatel 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com>
> napsal:
>
>>
>>
>> 2020年2月15日 下午6:06，Pavel Stehule <pavel(dot)stehule(at)gmail(dot)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