Re: POC, WIP: OR-clause support for indexes

* NOTE: returns NULL if clause is an OR or AND clause; it is the
* responsibility of higher-level routines to cope with those.
*/
static IndexClause *
match_clause_to_indexcol(PlannerInfo *root,
RestrictInfo *rinfo,
int indexcol,
IndexOptInfo *index)

the above comments need a slight change.

EXPLAIN (COSTS OFF, settings) SELECT * FROM tenk2 WHERE (thousand = 1
OR thousand = 3);
QUERY PLAN
-----------------------------------------------------------
Bitmap Heap Scan on tenk2
Recheck Cond: ((thousand = 1) OR (thousand = 3))
-> Bitmap Index Scan on tenk2_thous_tenthous
Index Cond: (thousand = ANY ('{1,3}'::integer[]))

EXPLAIN (COSTS OFF, settings) SELECT * FROM tenk2 WHERE (thousand in (1,3));
QUERY PLAN
-----------------------------------------------------------
Bitmap Heap Scan on tenk2
Recheck Cond: (thousand = ANY ('{1,3}'::integer[]))
-> Bitmap Index Scan on tenk2_thous_tenthous
Index Cond: (thousand = ANY ('{1,3}'::integer[]))

tenk2 index:
Indexes:
"tenk2_thous_tenthous" btree (thousand, tenthous)

Looking at the above cases, I found out the "Recheck Cond" is
different from "Index Cond".
I wonder why there is a difference, or if they should be the same.
then i come to:
match_orclause_to_indexcol

/*
* Finally, build an IndexClause based on the SAOP node. Use
* make_simple_restrictinfo() to get RestrictInfo with clean selectivity
* estimations because it may differ from the estimation made for an OR
* clause. Although it is not a lossy expression, keep the old version of
* rinfo in iclause->rinfo to detect duplicates and recheck the original
* clause.
*/
iclause = makeNode(IndexClause);
iclause->rinfo = rinfo;
iclause->indexquals = list_make1(make_simple_restrictinfo(root,
&saopexpr->xpr));
iclause->lossy = false;
iclause->indexcol = indexcol;
iclause->indexcols = NIL;

looking at create_bitmap_scan_plan.
I think "iclause->rinfo" itself won't be able to detect duplicates.
since the upper code would mostly use "iclause->indexquals" for comparison?

typedef struct IndexClause comments says:
"
* indexquals is a list of RestrictInfos for the directly-usable index
* conditions associated with this IndexClause. In the simplest case
* it's a one-element list whose member is iclause->rinfo. Otherwise,
* it contains one or more directly-usable indexqual conditions extracted
* from the given clause. The 'lossy' flag indicates whether the
* indexquals are semantically equivalent to the original clause, or
* represent a weaker condition.
"
should lossy be iclause->lossy be true at the end of match_orclause_to_indexcol?
since it meets the comment condition: "semantically equivalent to the
original clause"
or is the above comment slightly wrong?

in match_orclause_to_indexcol
i changed from
iclause->rinfo = rinfo;
to
iclause->rinfo = make_simple_restrictinfo(root,
&saopexpr->xpr);

as expected. now the "Recheck Cond" is same as "Index Cond"
Recheck Cond: (thousand = ANY ('{1,3}'::integer[]))
-> Bitmap Index Scan on tenk2_thous_tenthous
Index Cond: (thousand = ANY ('{1,3}'::integer[]))

I am not sure of the implication of this change.