Re: [COMMITTERS] pgsql: Fix an O(N^2) problem in foreign key references.

Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> Would it make sense to remove the only the few oldest entries, instead
> of all of them? As is, I think this causes a storm of reloads every
> once in a while, if the number of FKs in the system is large enough.
> Maybe on a cache hit we could push the entry to the head of the list,
> and then remove N entries from the back of the list when the threshold
> is reached.

Sure, there's room for optimization of that sort, although I think we
could do with some evidence that it's actually helpful. I believe that
under "production" workloads InvalidateConstraintCacheCallBack won't
get called much at all, so the problem's moot.

(FWIW, it might take less code to put the recently-used entries at the
back of the list. Then the loop in InvalidateConstraintCacheCallBack
could just invalidate/delete entries if either they're targets, or
the current list length exceeds the threshold.)

regards, tom lane