I just created sections in the SGML manual chapters about GIST, GIN, and
SP-GIST to hold documentation about the standard opclasses provided for
them:
http://www.postgresql.org/docs/devel/static/gist-builtin-opclasses.html
http://www.postgresql.org/docs/devel/static/gin-builtin-opclasses.html
http://www.postgresql.org/docs/devel/static/spgist-builtin-opclasses.html
We never had any well-defined place to discuss such opclasses before,
but I think it's past time we did. I envision these sections as places to
document, for example, the difference between the two jsonb gin opclasses.
I put this text in about that:
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?
For the moment what's there is mostly just tables of the core opclasses
and the operators they support. If anyone can think of specific additions
that should be there, please send in patches.
(BTW, I didn't worry about btree and hash because they don't have such
a wide variety of opclass behaviors.)
regards, tom lane