对Join的成本计算的调用路径：
make_one_rel
->make_rel_from_joinlist
->standard_join_search
-> join_search_one_level
-> make_join_rel
-> add_paths_to_joinrel
->hash_inner_and_outer
->try_hashjoin_path
->initial_cost_hashjoin
在make_join_rel函数中，有如下的代码：
RelOptInfo * make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2) { ... /* * Consider paths using each rel as both outer and inner. Depending on * the join type, a provably empty outer or inner rel might mean the join * is provably empty too; in which case throw away any previously computed * paths and mark the join as dummy. (We do it this way since it's * conceivable that dummy-ness of a multi-element join might only be * noticeable for certain construction paths.) * * Also, a provably constant-false join restriction typically means that * we can skip evaluating one or both sides of the join. We do this by * marking the appropriate rel as dummy. For outer joins, a * constant-false restriction that is pushed down still means the whole * join is dummy, while a non-pushed-down one means that no inner rows * will join so we can treat the inner rel as dummy. * * We need only consider the jointypes that appear in join_info_list, plus * JOIN_INNER. */ switch (sjinfo->jointype) { case JOIN_INNER: fprintf(stderr,"JOIN_INNER \n"); if (is_dummy_rel(rel1) || is_dummy_rel(rel2) || restriction_is_constant_false(restrictlist, false)) { mark_dummy_rel(joinrel); break; } add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_INNER, sjinfo, restrictlist); add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_INNER, sjinfo, restrictlist); break; case JOIN_LEFT: ... break; case JOIN_FULL: ... break; case JOIN_SEMI: ... break; case JOIN_ANTI: ... break; ... } ... }
