From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@heroku.com>
cc: pgsql-hackers@postgresql.org, pgsql-docs@postgresql.org
Subject: Re: Call for GIST/GIN/SP-GIST opclass documentation
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Comments: In-reply-to Peter Geoghegan <pg@heroku.com>
 message dated "Tue, 08 Apr 2014 14:03:46 -0700"
Date: Tue, 08 Apr 2014 17:34:01 -0400
Message-ID: <28589.1396992841@sss.pgh.pa.us>
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Peter Geoghegan <pg@heroku.com> writes:
> On Tue, Apr 8, 2014 at 1:41 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Of the two operator classes for type jsonb, jsonb_ops is the
>> default. jsonb_hash_ops supports fewer operators but will work with
>> larger indexed values than jsonb_ops can support.
>> 
>> Is that accurate?  Do we need to say more?

> Well, I'm not sure that it's worth noting there, but as you probably
> already know jsonb_hash_ops will perform a lot better than the default
> GIN opclass, and will have much smaller indexes. FWIW I think that the
> size limitation is overblown, and performance is in fact the
> compelling reason to prefer jsonb_hash_ops, although it's probably
> incongruous to explain the issues that way in this section of the
> docs. It probably suffices that that is covered in the "JSON Types"
> section.

Well, the subtext is whether we should move that discussion to this
new section.  I think there is some comparable discussion in the
full-text-indexing chapter, too.

(BTW, wasn't there some discussion of changing our minds about which
one is the default?  We already have one bug report complaining about
jsonb_ops' size restriction, so that seems to be evidence in favor
of changing ...)

			regards, tom lane


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