Re: Performance issue when we use policies for Row Level Security along with functions

"Gopisetty, Ramesh" <rameshg2(at)illinois(dot)edu> writes:
> Policy
> create policy policy_sel on test FOR SELECT to ram1 USING ( testkey in (f_sel_policy_test(testkey)) );
> Going to a Sequential scan instead of index scan. Hence, performance issue.

> If i replace the policy with stright forward without function then it chooses the index. Not sure how i can implement with the function.
> create policy policy_sel on test FOR SELECT to ram1 USING ( testkey in ('COMMON',current_setting('ctx_ng'||'.'||'ctx_key_fil')));

" testkey in ('COMMON',current_setting('ctx_ng'||'.'||'ctx_key_fil')) "
is an indexable condition on testkey, because it compares testkey to
a constant (or at least, a value that's fixed for the life of the query).

" testkey in (f_sel_policy_test(testkey)) "
is not an indexable condition on anything, because there are variables
on both sides of the condition. So there's no fixed value that the
index can search on.

If you intend f_sel_policy_test() to be equivalent to the other condition,
why are you passing it an argument it doesn't need?

As Luis noted, there's also the problem that an indexable condition
can't be volatile. I gather that SYS_CONTEXT ends up being a probe
of some GUC setting, which means that marking the function IMMUTABLE
would be a lie, but you ought to be able to mark it STABLE.

regards, tom lane