Date: Thu, 8 May 2014 10:40:12 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Andres Freund <andres@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "David E. Wheeler" <david@justatheory.com>,
 Greg Stark <stark@mit.edu>, Robert Haas <robertmhaas@gmail.com>,
 Heikki Linnakangas <hlinnakangas@vmware.com>,
 Andrew Dunstan <andrew@dunslane.net>, Peter Geoghegan <pg@heroku.com>,
 "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: default opclass for jsonb (was Re: Call for
 GIST/GIN/SP-GIST opclass documentation)
Message-ID: <20140508144012.GQ30817@momjian.us>
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 <20140506201048.GI30817@momjian.us>
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 <20140506212020.GK30817@momjian.us>
 <57E8AA44-F816-45F2-BB61-5A854FFB0A97@justatheory.com>
 <28554.1399414853@sss.pgh.pa.us>
 <20140508134701.GO30817@momjian.us> <5819.1399558614@sss.pgh.pa.us>
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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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +


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