On 03/18/2016 08:53 PM, Robert Haas wrote:
On Fri, Mar 18, 2016 at 3:29 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
Robert Haas <robertmh...@gmail.com> writes:
On Wed, Apr 29, 2015 at 12:33 PM, Tomas Vondra
<tomas.von...@2ndquadrant.com> wrote:
On 04/29/15 18:26, Tom Lane wrote:
But there are basic reasons why expression_tree_walker should not try
to deal with RestrictInfos; the most obvious one being that it's not
clear whether it should descend into both the basic and OR-clause
subtrees. Also, if a node has expression_tree_walker support then it
should logically have expression_tree_mutator support as well, but
that's got multiple issues. RestrictInfos are not supposed to be
copied once created; and the mutator couldn't detect whether their
derived fields are still valid.
OK, I do understand that. So what about pull_varnos_walker and
pull_varattnos_walker - what about teaching them about RestrictInfos?
This patch has become part 1 of many under the "multivariate
statistics vNNN" family of threads, but I guess it would be helpful if
you could opine on the reasonable-ness of this approach. I don't want
to commit anything over your objections, but this kind of tailed off
without a conclusion.
I'm up to my ears in psql at the moment, but hope to get to the
multivariate stats patch later, maybe next week.
Oh, cool.
In the meantime,
I remain of the opinion that RestrictInfo is not an expression node
and wanting expression_tree_walker to handle it is wrong. I'm
suspicious about pull_varnos; it might be all right given that we
can assume the same Vars are in both subtrees, but I still don't
really see why that one function has suddenly grown this need when
others have not.
I haven't studied the patch series in enough detail to have an
educated opinion on that.
FWIW I'm not convinced this part of the patch (matching the clauses to
the available stats, including the pull_varnos changes) is perfectly
correct either, and it's quite possible it will need reworking. But it
needs a pair of fresh eyes, I guess.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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