Re: Locking question

=?UTF-8?B?VG9yc3RlbiBGw7ZydHNjaA==?= <torsten.foertsch@gmx.net> writes:
> given a query like this:

> select *
>   from account a
>  cross join lateral (
>        select rate
>          from exchange
>         where target='USD'
>           and source=a.currency
>         order by date desc
>         limit 1) e
>  where a.id=19
>    for update;

> If I understand the documentation correctly, both rows, the one from
> exchange and the one from account are locked, right?

A look at the plan for this suggests that all rows returned by the
sub-select will end up row-locked (whether or not they actually join
to "a").  Note the LockRows node in the sub-select.

> However, if I create a SQL function like this: [ no locking happens ]

FOR UPDATE locking doesn't propagate into functions.  For a moment
I felt like this was a planner bug, but really it isn't: the locking
would certainly not have propagated into a non-inlined function, so
if the planner were to make it happen when inlining, that would make
inlining change the semantics, which it should not.

            regards, tom lane