diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 30 |
1 files changed, 20 insertions, 10 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index cdb18d978db..f062c6b9f1e 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -2214,6 +2214,7 @@ final_cost_nestloop(PlannerInfo *root, NestPath *path, Cost inner_run_cost = workspace->inner_run_cost; Cost inner_rescan_run_cost = workspace->inner_rescan_run_cost; double outer_matched_rows; + double outer_unmatched_rows; Selectivity inner_scan_frac; /* @@ -2226,6 +2227,7 @@ final_cost_nestloop(PlannerInfo *root, NestPath *path, * least 1, no such clamp is needed now.) */ outer_matched_rows = rint(outer_path_rows * extra->semifactors.outer_match_frac); + outer_unmatched_rows = outer_path_rows - outer_matched_rows; inner_scan_frac = 2.0 / (extra->semifactors.match_count + 1.0); /* @@ -2269,7 +2271,7 @@ final_cost_nestloop(PlannerInfo *root, NestPath *path, * of a nonempty scan. We consider that these are all rescans, * since we used inner_run_cost once already. */ - run_cost += (outer_path_rows - outer_matched_rows) * + run_cost += outer_unmatched_rows * inner_rescan_run_cost / inner_path_rows; /* @@ -2287,20 +2289,28 @@ final_cost_nestloop(PlannerInfo *root, NestPath *path, * difficult to estimate whether that will happen (and it could * not happen if there are any unmatched outer rows!), so be * conservative and always charge the whole first-scan cost once. + * We consider this charge to correspond to the first unmatched + * outer row, unless there isn't one in our estimate, in which + * case blame it on the first matched row. */ + + /* First, count all unmatched join tuples as being processed */ + ntuples += outer_unmatched_rows * inner_path_rows; + + /* Now add the forced full scan, and decrement appropriate count */ run_cost += inner_run_cost; + if (outer_unmatched_rows >= 1) + outer_unmatched_rows -= 1; + else + outer_matched_rows -= 1; /* Add inner run cost for additional outer tuples having matches */ - if (outer_matched_rows > 1) - run_cost += (outer_matched_rows - 1) * inner_rescan_run_cost * inner_scan_frac; - - /* Add inner run cost for unmatched outer tuples */ - run_cost += (outer_path_rows - outer_matched_rows) * - inner_rescan_run_cost; + if (outer_matched_rows > 0) + run_cost += outer_matched_rows * inner_rescan_run_cost * inner_scan_frac; - /* And count the unmatched join tuples as being processed */ - ntuples += (outer_path_rows - outer_matched_rows) * - inner_path_rows; + /* Add inner run cost for additional unmatched outer tuples */ + if (outer_unmatched_rows > 0) + run_cost += outer_unmatched_rows * inner_rescan_run_cost; } } else |