Re: Strange row locking - question

Vaclav Kulakovsky <vaclav.kulakovsky@definity.cz> writes:
> When I update row in table with foring key, referenced row is locked. I
> can see it in log file:

> DEBUG:  query: update entry set sometext = 'aaa' where id = 1;
> DEBUG:  query: SELECT 1 FROM ONLY "languages" WHERE "id" = $1 FOR UPDATE
> OF "languages"

> When I execute update second time I receive only this:

> query: update entry set sometext = 'aaa' where id = 1;

> Referenced row is locked only first time ? This behavior looks me little
> bit strange. Can anybody explain it ?

You are not seeing the RI query get *executed*, only get *parsed*.
After the first time through, the RI code re-uses a cached query plan.
Since it's not fed through the parser again, no log message.

plpgsql shows similar behavior, BTW.  Some day it might be an idea to
make these things a little more debugging-friendly by having them emit
suitable log messages when they re-execute cached plans.

            regards, tom lane