Re: PATCH: index-only scans with partial indexes

Hello, This is a (maybe) committer-ready patch of a Tomas
Vondra's project.

This patch applies on the current master and passes make check.

This is to exclude some base-estrict clauses that are implied by
index predicates on index scans on partial indexes.

First, this patch adds a new member indexrinfos to IndexOptInfo,
which usually has the same value with baserestrictinfo of the
parent RelOptInfo and cost_index() uses this instead of
RelOptInfo.baserestrictinfo.

For partial indexes, the clauses implied by the index predicates
are removed from the indexrinfos, so that the result plan for
scans on such indexes won't contain such restrictions. Such
restrictions commonly become filter quals that are nothing but a
useless work to do, so this will improve the performance of some
index scans on partial indexes.

The largest part of the extra cost of the additional work would
be the cost of predicate_implied_by() on all clauses of
baserectrictinfo and indpred of every IndexOptInfos. The extra
work is done in check_partial_indexes() for all index scans on
partial indexes.

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center