Re: simplehash: tb->sizemask = 0

On 2017-11-27 22:53:41 -0500, Tom Lane wrote:
> 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.

That's obviously wrong. Not sure how that happened. I might have had it
as a shift at first?

> (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".)

There's a test and elog during insert. Adding actual branches into
SH_NEXT/SH_PREV seems like a bad idea.

Will test a fix.

Greetings,

Andres Freund