Re: [Proposal] Global temporary tables

> 2020年3月16日 下午5:04，Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> 写道：
>
>
>
> po 16. 3. 2020 v 9:58 odesílatel tushar <tushar(dot)ahuja(at)enterprisedb(dot)com <mailto:tushar(dot)ahuja(at)enterprisedb(dot)com>> napsal:
> Hi Wenjing,
>
> I have created a global table on X session but i am not able to drop from Y session ?
>
> X session - ( connect to psql terminal )
> postgres=# create global temp table foo(n int);
> CREATE TABLE
> postgres=# select * from foo;
> n
> ---
> (0 rows)
>
>
> Y session - ( connect to psql terminal )
> postgres=# drop table foo;
> ERROR: can not drop relation foo when other backend attached this global temp table
>
> Table has been created so i think - user should be able to drop from another session as well without exit from X session.
>
> By the original design GTT was not modifiable until is used by any session. Now, you cannot to drop normal table when this table is used.
>
> It is hard to say what is most correct behave and design, but for this moment, I think so protecting table against drop while it is used by other session is the best behave.
>
> Maybe for next release we can introduce DROP TABLE x (FORCE) - like we have for DROP DATABASE. This behave is very similar.
I agree with that.

Wenjing

>
> Pavel
>
>
> regards,
>
> On 3/16/20 1:35 PM, 曾文旌(义从) wrote:
>>
>>
>>> 2020年3月16日 下午2:23，Prabhat Sahu <prabhat(dot)sahu(at)enterprisedb(dot)com <mailto:prabhat(dot)sahu(at)enterprisedb(dot)com>> 写道：
>>>
>>> Hi Wenjing,
>>> Please check the below scenario, where the Foreign table on GTT not showing records.
>>>
>>> postgres=# create extension postgres_fdw;
>>> CREATE EXTENSION
>>> postgres=# do $d$
>>> begin
>>> execute $$create server fdw foreign data wrapper postgres_fdw options (host 'localhost',dbname 'postgres',port '$$||current_setting('port')||$$')$$;
>>> end;
>>> $d$;
>>> DO
>>> postgres=# create user mapping for public server fdw;
>>> CREATE USER MAPPING
>>>
>>> postgres=# create table lt1 (c1 integer, c2 varchar(50));
>>> CREATE TABLE
>>> postgres=# insert into lt1 values (1,'c21');
>>> INSERT 0 1
>>> postgres=# create foreign table ft1 (c1 integer, c2 varchar(50)) server fdw options (table_name 'lt1');
>>> CREATE FOREIGN TABLE
>>> postgres=# select * from ft1;
>>> c1 | c2
>>> ----+-----
>>> 1 | c21
>>> (1 row)
>>>
>>> postgres=# create global temporary table gtt1 (c1 integer, c2 varchar(50));
>>> CREATE TABLE
>>> postgres=# insert into gtt1 values (1,'gtt_c21');
>>> INSERT 0 1
>>> postgres=# create foreign table f_gtt1 (c1 integer, c2 varchar(50)) server fdw options (table_name 'gtt1');
>>> CREATE FOREIGN TABLE
>>>
>>> postgres=# select * from gtt1;
>>> c1 | c2
>>> ----+---------
>>> 1 | gtt_c21
>>> (1 row)
>>>
>>> postgres=# select * from f_gtt1;
>>> c1 | c2
>>> ----+----
>>> (0 rows)
>>>
>>> --
>>
>> I understand that postgre_fdw works similar to dblink.
>> postgre_fdw access to the table requires a new connection.
>> The data in the GTT table is empty in the newly established connection.
>> Because GTT shares structure but not data between connections.
>>
>> Try local temp table:
>> create temporary table ltt1 (c1 integer, c2 varchar(50));
>>
>> insert into ltt1 values (1,'gtt_c21');
>>
>> create foreign table f_ltt1 (c1 integer, c2 varchar(50)) server fdw options (table_name 'ltt1');
>>
>> select * from ltt1;
>> c1 | c2
>> ----+---------
>> 1 | gtt_c21
>> (1 row)
>>
>> select * from l_gtt1;
>> ERROR: relation "l_gtt1" does not exist
>> LINE 1: select * from l_gtt1;
>>
>>
>> Wenjing
>>
>>
>>> With Regards,
>>> Prabhat Kumar Sahu
>>> EnterpriseDB: http://www.enterprisedb.com <http://www.enterprisedb.com/>
>>
>
> --
> regards,tushar
> EnterpriseDB https://www.enterprisedb.com/ <https://www.enterprisedb.com/>
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