diff options
Diffstat (limited to 'src/backend/optimizer/path/joinpath.c')
| -rw-r--r-- | src/backend/optimizer/path/joinpath.c | 40 |
1 files changed, 36 insertions, 4 deletions
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 5d595ce2151..d5e2506d7a0 100644 --- a/src/backend/optimizer/path/joinpath.c +++ b/src/backend/optimizer/path/joinpath.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.114 2008/01/01 19:45:50 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.115 2008/01/09 20:42:27 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -34,7 +34,8 @@ static void hash_inner_and_outer(PlannerInfo *root, RelOptInfo *joinrel, List *restrictlist, JoinType jointype); static Path *best_appendrel_indexscan(PlannerInfo *root, RelOptInfo *rel, RelOptInfo *outer_rel, JoinType jointype); -static List *select_mergejoin_clauses(RelOptInfo *joinrel, +static List *select_mergejoin_clauses(PlannerInfo *root, + RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel, List *restrictlist, @@ -69,7 +70,8 @@ add_paths_to_joinrel(PlannerInfo *root, * disable if it's a full join. */ if (enable_mergejoin || jointype == JOIN_FULL) - mergeclause_list = select_mergejoin_clauses(joinrel, + mergeclause_list = select_mergejoin_clauses(root, + joinrel, outerrel, innerrel, restrictlist, @@ -883,7 +885,8 @@ best_appendrel_indexscan(PlannerInfo *root, RelOptInfo *rel, * currently of interest. */ static List * -select_mergejoin_clauses(RelOptInfo *joinrel, +select_mergejoin_clauses(PlannerInfo *root, + RelOptInfo *joinrel, RelOptInfo *outerrel, RelOptInfo *innerrel, List *restrictlist, @@ -937,6 +940,35 @@ select_mergejoin_clauses(RelOptInfo *joinrel, continue; /* no good for these input relations */ } + /* + * Insist that each side have a non-redundant eclass. This + * restriction is needed because various bits of the planner expect + * that each clause in a merge be associatable with some pathkey in a + * canonical pathkey list, but redundant eclasses can't appear in + * canonical sort orderings. (XXX it might be worth relaxing this, + * but not enough time to address it for 8.3.) + * + * Note: it would be bad if this condition failed for an otherwise + * mergejoinable FULL JOIN clause, since that would result in + * undesirable planner failure. I believe that is not possible + * however; a variable involved in a full join could only appear + * in below_outer_join eclasses, which aren't considered redundant. + * + * This case *can* happen for left/right join clauses: the + * outer-side variable could be equated to a constant. Because we + * will propagate that constant across the join clause, the loss of + * ability to do a mergejoin is not really all that big a deal, and + * so it's not clear that improving this is important. + */ + cache_mergeclause_eclasses(root, restrictinfo); + + if (EC_MUST_BE_REDUNDANT(restrictinfo->left_ec) || + EC_MUST_BE_REDUNDANT(restrictinfo->right_ec)) + { + have_nonmergeable_joinclause = true; + continue; /* can't handle redundant eclasses */ + } + result_list = lappend(result_list, restrictinfo); } |