Re: simplehash: tb->sizemask = 0

Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> I'm a bit puzzled by this code in SH_COMPUTE_PARAMETERS:

> if (tb->size == SH_MAX_SIZE)
> tb->sizemask = 0;
> else
> tb->sizemask = tb->size - 1;

> Doesn't that mean that with SH_MAX_SIZE we end up with sizemask being 0
> (i.e. no bits set)?

Yeah, which is very obviously broken: for one thing, the Asserts
in SH_NEXT/SH_PREV would surely go off.

(Why are those assertions, anyway, and not test-and-elog?
I do not think an assertion failure is a suitable way to
report "hash table full".)

> I don't think we're building hash tables with 2^32 buckets, though.

What this proves is that nobody has ever tested the behavior at
SH_MAX_SIZE. I would suggest building a test version with that
set small enough to be conveniently reachable, and then exercising
the behavior as the limit is approached and reached.

regards, tom lane