Re: Why must AUTOCOMMIT be ON to do txn control in plpgsql procedure?

Hello, Bryn.

At Tue, 6 Aug 2019 15:18:51 -0700, Bryn Llewellyn <bryn@yugabyte.com> wrote in <EE6D19C1-1CA6-424B-91AC-63A1A64A5921@yugabyte.com>

Here’s how I’ve tried to describe what I see for p2() with AUTOCOMMIT ON for myself:

1. my call p2() starts a txn.

2. However, during the execution of the proc, the usual autocommit behavior is programmatically turned off by explicit PostgreSQL code.

3. Other explicit PostgreSQL code makes “start transaction” inside a proc simply cause a runtime error under all circumstances. However, txns can be ended by “commit” or “rollback”. And new ones can be started—but only implicitly by executing a SQL statement that, as a top level SQL, would start a txn.

In-procedure transaction control premises that no transaction is
active before calling the procedure.

https://www.postgresql.org/docs/11/sql-call.html

If CALL is executed in a transaction block, then the called
procedure cannot execute transaction control
statements. Transaction control statements are only allowed if
CALL is executed in its own transaction.

With AUTOCOMMIT=off, implicit BEGIN is invoked just before
CALLing p2() if no transaction is active. Thus p2() is always
called having a transaction active, which inhibits in-procedure
transaction control.

I'm not sure why you want to turn AUTOCOMNIT off, but even with
AUTOCOMMIT on, explict BEGIN prevents per-command COMMIT as you
perhaps know.

https://www.postgresql.org/docs/11/app-psql.html

When on (the default), each SQL command is automatically
committed upon successful completion. To postpone commit in
this mode, you must enter a BEGIN or START TRANSACTION SQL
command.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center