Re: FIX : teach expression walker about RestrictInfo

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Apr 29, 2015 at 12:33 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)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. 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.

regards, tom lane