Dmytro Astapov <dastapov@gmail.com> writes:
> As the subject implies, I am observing that
> current_user/session_user/current_database/current_schema, when used as an
> argument for pl/pgsql function, could affect execution plans of unrelated
> queries inside that pl/pgsql function -- because they seemingly affect
> collation for other arguments (I am not 100% sure about this last claim,
> but the observed effects suggest that this might be the case).
This is expected behavior. Those functions return type "name" not
"text", and "name" is considered to have C collation. Then, in
a call such as
select_test('1',current_user);
that is the only source of collation in the expression and so
select_test is invoked with an input collation of "C", rather
than whatever the database's default is.
The most robust solution probably is to write
explain select *
from tbl
where id = id_to_update COLLATE "default"
regards, tom lane