On Mon, Apr 05, 2021 at 07:51:46PM -0700, Dan Lynch wrote: > > > 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?
Yes. The caching patch thread gives some example queries: https://postgr.es/m/flat/CABRT9RA-RomVS-yzQ2wUtZ%3Dm-eV61LcbrL1P1J3jydPStTfc6Q%40mail.gmail.com > I suppose if the possibility exists that this could happen, perhaps using > RLS for selects is not quite "production ready"? I would not draw that conclusion. > Or perhaps if the RLS > qual/check is written well-enough, then maybe the performance hit wouldn't > be noticed? Yes.
