Date: Fri, 9 May 2014 16:32:01 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
 Gavin Flower <GavinFlower@archidevsys.co.nz>,
 "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: <20140509143201.GF30231@awork2.anarazel.de>
References: <57E8AA44-F816-45F2-BB61-5A854FFB0A97@justatheory.com>
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 <536C550F.50108@archidevsys.co.nz> <18360.1399633457@sss.pgh.pa.us>
 <20140509135336.GC23254@momjian.us>
 <20140509142648.GD23254@momjian.us>
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On 2014-05-09 10:26:48 -0400, Bruce Momjian wrote:
> On Fri, May  9, 2014 at 09:53:36AM -0400, Bruce Momjian wrote:
> > On Fri, May  9, 2014 at 07:04:17AM -0400, Tom Lane wrote:
> > > Gavin Flower <GavinFlower@archidevsys.co.nz> writes:
> > > > On 09/05/14 15:34, Bruce Momjian wrote:
> > > >> Looks good.  I was thinking the jsonb_ops name could remain unchanged
> > > >> and the jsonb_hash_ops could be called jsonb_combo_ops as it combines
> > > >> the key and value into a single index entry.
> > > 
> > > > If you have 'jsonb_combo_ops' - then surely 'jsonb_op' should be called 
> > > > 'jsonb_xxx_ops', where the 'xxx' distinguishes that from 
> > > > 'jsonb_combo_ops'?  I guess, if any appropriate wording of 'xxx' was too 
> > > > cumbersome, then it would be worse.
> > > 
> > > Yeah, I'm disinclined to change the opclass names now.  It's not apparent
> > > to me that "combo" is a better choice than "hash" for the second opclass.
> > 
> > Well, if we are optionally hashing json_ops for long strings, what does
> > jsonb_hash_ops do uniquely with hashing?  Does it always hash, while
> > json_ops optionally hashes?  Is that the distinguishing characteristic? 
> > It seemed the _content_ of the indexed value was more important, rather
> > than the storage method.
> 
> Also, are people going to think that jsonb_hash_ops creates a hash
> index, which is not crash safe, even though it is a GIN index?  Do we
> have this "hash" confusion anywhere else?

The operator class has to be specified after the USING GIN in CREATE
INDEX so I think that rest is neglegible.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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