Re: hash_create API changes (was Re: speedup tidbitmap patch: hash BlockNumber)

I wrote:
> However, there's another way we could attack this,
> which is to invent a new hash option flag bit that says "pick a suitable
> hash function for me, assuming that all bits of the specified key size are
> significant". So instead of

> ctl.keysize = sizeof(...);
> ctl.entrysize = sizeof(...);
> ctl.hash = tag_hash;
> tab = hash_create("...", ..., &ctl,
> HASH_ELEM | HASH_FUNCTION);

> you'd write

> ctl.keysize = sizeof(...);
> ctl.entrysize = sizeof(...);
> tab = hash_create("...", ..., &ctl,
> HASH_ELEM | HASH_BLOBS);

> which would save some code space and is arguably cleaner than the
> current approach of specifying some support functions and not others.

Here's a proposed patch along this line. I left in oid_hash (in the
form of a macro) so that this does not cause any API break for existing
third-party modules. However, no callers in our own code directly
refer to tag_hash or oid_hash anymore.

regards, tom lane