Hello everybody:
Sorry for disturbing.
I experience the prepared statement of postgresql via psql and have one question:
In terminal A:
I prepared:
postgres=# prepare test(int) AS
postgres-# select * from customers c where c.cust_id = $1;
PREPARE
postgres=#
Then run:
postgres=# execute test(3);
cust_id | cust_name
---------+-----------
3 | Taylor
(1 row)
postgres=#
In the terminal A , I can found the statement prepared via pg_prepared_statements:
postgres=# select * from pg_prepared_statements;
name | statement | prepare_time | parameter_types | from_sql
------+-------------------------------------------------+-------------------------------+-----------------+----------
test | prepare test(int) AS +| 2013-06-14 15:58:22.796369+08 | {integer} | t | select * from customers c where c.cust_id = $1; | | |
(1 row)
postgres=#
But in terminal B, I can't see the above statement:
postgres=# select * from pg_prepared_statements;
name | statement | prepare_time | parameter_types | from_sql
------+-----------+--------------+-----------------+----------
(0 rows)
postgres=#
Even when I run execute in term B, It failed:
postgres=# execute test(3);
ERROR: prepared statement "test" does not exist
postgres=#
So I can draw a conclusion:
Prepared statement is only for use in the same session at which it has been executed.
It can not be shared via multiple sessions.
That is, when in some special situations ,
if I have to use mulitple connections between client applicaiton and postgresql database,
I must consider this point if I want to get benifit from prepared statements.
So I am now thinking about the reason that prepared statement can not cross over sessions.
Maybe it is because of MVCC control? So in order to make it simple, the prepared statement is in one session range?
Thanks!