Re: Change GUC hashtable to use simplehash?

On Wed, 2023-11-29 at 20:31 +0700, John Naylor wrote:
> v5-0001 puts fash-hash as-is into a new header, named in a way to
> convey in-memory use e.g. hash tables.
>
> v5-0002 does the minimal to allow dynash to use this for string_hash,
> inlined but still calling strlen.
>
> v5-0003 shows one way to do a incremental interface. It might be okay
> for simplehash with fixed length keys, but seems awkward for strings.
>
> v5-0004 shows a bytewise incremental interface, with implementations
> for dynahash (getting rid of strlen) and guc hash.

I'm trying to follow the distinctions you're making between dynahash
and simplehash -- are you saying it's easier to do incremental hashing
with dynahash, and if so, why?

If I understood what Andres was saying, the exposed hash state would be
useful for writing a hash function like guc_name_hash(). But whether we
use simplehash or dynahash is a separate question, right?

Also, while the |= 0x20 is a nice trick for lowercasing, did we decide
that it's better than my approach in patch 0004 here:

https://www.postgresql.org/message-id/27a7a289d5b8f42e1b1e79b1bcaeef3a40583bd2.camel@j-davis.com

which optimizes exact hits (most GUC names are already folded) before
trying case folding?

Regards,
Jeff Davis