Re: PATCH: index-only scans with partial indexes

Hello, Tomas. my cerebral cortext gets squeezed by jumping from
parser to planner.

At Wed, 24 Feb 2016 01:13:22 +0100, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote in <56CCF5A2(dot)5040702(at)2ndquadrant(dot)com>
> Hi,
>
> On 12/06/2015 11:48 PM, Tomas Vondra wrote:
> > /*
> > * Frequently, there will be no partial indexes, so first check to
> > * make sure there's something useful to do here.
> > */
> > have_partial = false;
> > foreach(lc, rel->indexlist)
> > {
> > IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
> >
> > /*
> > * index rinfos are the same to baseristrict infos for non-partial
> > * indexes
> > */
> > index->indrinfos = rel->baserestrictinfo;
> >
> > if (index->indpred == NIL)
> > continue; /* ignore non-partial indexes */
> >
> > if (index->predOK)
> > continue; /* don't repeat work if already proven OK */
> >
> > have_partial = true;
> > break;
> > }
>
> Attached is a v6 of the patch, which is actually the version submitted
> by Kyotaro-san on 2015/10/8 rebased to current master and with two
> additional changes.

This relies on the fact I believe that no indexrelinfos are
shared among any two baserels. Are you OK with that?

> Firstly, I've removed the "break" from the initial foreach loop in
> check_partial_indexes(). As explained in the previous message, I
> believe this was a bug in the patch.

I agreed. The break is surely a bug. (the regression didn't find
it though..)

> Secondly, I've tried to improve the comments to explain a bit better
> what the code is doing.

In check_partial_indexes, the following commnet.

> /*
> * Update restrictinfo for this index by excluding clauses that
> * are implied by the index predicates. We first quickly check if
> * there are any implied clauses, and if we found at least one
> * we do the actual work. This way we don't need the construct
> * a copy of the list unless actually needed.
> */

Is "need the construct" a mistake of "need to construct" ?

match_restriction_clauses_to_index is called only from
create_index_paths, and now the former doesn't use its first
parameter rel. We can safely remove the useless parameter.

- match_restriction_clauses_to_index(RelOptInfo *rel, IndexOptInfo *index,
- IndexClauseSet *clauseset)
+ match_restriction_clauses_to_index(IndexOptInfo *index,
+ IndexClauseSet *clauseset)

I find no other problem and have no objection to this. May I mark
this "Ready for committer" after fixing them?

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center