Re: default opclass for jsonb (was Re: Call for GIST/GIN/SP-GIST opclass documentation)

On Thu, May 8, 2014 at 04:37:05PM +0200, Andres Freund wrote:
> On 2014-05-08 10:34:04 -0400, Bruce Momjian wrote:
> > On Thu, May 8, 2014 at 10:16:54AM -0400, Tom Lane wrote:
> > > > Can we hash just the values, not the keys, in jsonb_ops, and hash the
> > > > combo in jsonb_hash_ops. That would give us key-only lookups without a
> > > > recheck.
> > >
> > > No, because there's nothing in JSON limiting the length of keys, any more
> > > than values.
> > >
> > > I think the idea of hashing only keys/values that are "too long" is a
> > > reasonable compromise. I've not finished coding it (because I keep
> > > getting distracted by other problems in the code :-() but it does not
> > > look to be very difficult. I'm envisioning the cutoff as being something
> > > like 128 bytes; in practice that would mean that few if any keys get
> > > hashed, I think.
> >
> > Yes, that would be nice. Ideally we would not be doing this so close to
> > beta, but it is what it is, and if we need to break binary compatibility
> > after beta1, at least we have pg_upgrade.
>
> If we break binary compatibility pg_upgrade won't be able to help. Since
> the data files wont be, err, binary compatibile.

Oops, yeah. pg_upgrade only helps with system table changes. We would
have to require users to dump/reload any changed tables or recreate any
indexs.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +