Re: [Proposal] Global temporary tables

Hi,
I have started testing the "Global temporary table" feature,
That's great, I see hope.
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?

Oh ,this is a bug, I fixed it.

Wenjing

On Sun, Feb 16, 2020 at 8:53 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com <mailto: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 <mailto: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 <mailto: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 <http://www.enterprisedb.com/>
>> > The Enterprise PostgreSQL Company
>>
>

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