Re: Change GUC hashtable to use simplehash?

On Wed, Nov 22, 2023 at 12:00 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>
> On Tue, 2023-11-21 at 16:42 +0700, John Naylor wrote:
> > The strlen call required for hashbytes() is not free.
>
> Should we have a hash_string() that's like hash_bytes() but checks for
> the NUL terminator itself?
>
> That wouldn't be inlinable, but it would save on the strlen() call. It
> might benefit some other callers?

We do have string_hash(), which...calls strlen. :-)

Thinking some more, I'm not quite comfortable with the number of
places in these patches that have to know about the pre-downcased
strings, or whether we need that in the first place. If lower case is
common enough to optimize for, it seems the equality function can just
check strict equality on the char and only on mismatch try downcasing
before returning false. Doing our own function would allow the
compiler to inline it, or at least keep it on the same page. Further,
the old hash function shouldn't need to branch to do the same
downcasing, since hashing is lossy anyway. In the keyword hashes, we
just do "*ch |= 0x20", which downcases letters and turns undercores to
DEL. I can take a stab at that later.