2014-02-20 01:37, Tom Lane <t...@sss.pgh.pa.us>:

> Perhaps it would be acceptable to drop the btree_gist implementation
> and teach pg_upgrade to refuse to upgrade if the old database contains
> any such indexes.  I'm not sure that solves the problem, though, because
> I think pg_upgrade will still fail if the opclass is in the old database
> even though unused (because you'll get the complaint about multiple
> default opclasses anyway).  The only simple way to avoid that is to not
> have btree_gist loaded at all in the old DB, and I doubt that's an
> acceptable upgrade restriction.  It would require dropping indexes of
> the other types supported by btree_gist, which would be a pretty hard
> sell since those aren't broken.
> Really what we'd need here is for btree_gist to be upgraded to a version
> that doesn't define gist_inet_ops (or at least doesn't mark it as default)
> *before* pg_upgrading to a server version containing the proposed new
> implementation.  Not sure how workable that is.  Could we get away with
> having pg_upgrade unset the default flag in the old database?
> (Ick, but there are no very good alternatives here ...)

Upgrading btree_gist on the old installation would be almost impossible
for the majority of the users who use package managers, in my opinion.
I cannot think of a better solution than your suggestion. I can try to
prepare a patch to execute the following query on pg_upgrade before
dumping the old database, if that is the final decision.

UPDATE pg_opclass SET opcdefault = false
WHERE opcname IN ('gist_inet_ops', 'gist_cidr_ops');

> BTW, I'd not been paying any attention to this thread, but now that
> I scan through it, I think the proposal to change the longstanding
> names of the inet operators has zero chance of being accepted.
> Consistency with the names chosen for range operators is a mighty
> weak argument compared to backwards compatibility.

That is why I prepared it as a separate patch on top of the others. It is
not only consistency with the range types: <@ and @> symbols used for
containment everywhere except the inet data types, particularly on
the geometric types, arrays; cube, hstore, intaray, ltree extensions.
The patch does not just change the operator names, it leaves the old ones,
adds new operators with GiST support and changes the documentation, like
your commit ba920e1c9182eac55d5f1327ab0d29b721154277 back in 2006. I could
not find why did you leave the inet operators unchanged on that commit,
in the mailing list archives [1]. GiST support will be a promotion for
users to switch to the new operators, if we make this change with it.

This change will also indirectly deprecate the undocumented non-transparent
btree index support that works sometimes for some of the subnet inclusion
operators [2].

[1] http://www.postgresql.org/message-id/14277.1157304...@sss.pgh.pa.us

[2] http://www.postgresql.org/message-id/389.1042992...@sss.pgh.pa.us

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