| From: | Dan Lynch <pyramation(at)gmail(dot)com> |
|---|---|
| To: | Noah Misch <noah(at)leadboat(dot)com> |
| Cc: | Joe Conway <mail(at)joeconway(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Isaac Morland <isaac(dot)morland(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: policies with security definer option for allowing inline optimization |
| Date: | 2021-04-06 02:51:46 |
| Message-ID: | CA+_muLFDzuxZt8DwpzouM=BHe+TOn=YsS+WQ9m7VmxzZ_uYMUw@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
This is great, thanks! It's great to have somewhere in the source to read
about the optimizer! very cool!
>
> > I suppose if the
> > get_group_ids_of_current_user() function is marked as STABLE, would the
> > optimizer cache this value for every row in a SELECT that returned
> > multiple rows?
>
> While there was a patch to implement caching, it never finished. The
> optimizer is allowed to, and sometimes does, choose plan shapes that reduce
> the number of function calls.
>
So for multiple rows, it's possible that the same query could happen for
each row? Even if it's clearly stable and only a read operation is
happening?
I suppose if the possibility exists that this could happen, perhaps using
RLS for selects is not quite "production ready"? Or perhaps if the RLS
qual/check is written well-enough, then maybe the performance hit wouldn't
be noticed?
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