Re: [Proposal] Global temporary tables - Mailing list pgsql-hackers

2020年3月16日 下午4:58，tushar <tushar.ahuja@enterprisedb.com> 写道：

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.

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.sahu@enterprisedb.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

-- 
regards,tushar
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