diff options
Diffstat (limited to 'src/backend/optimizer/path/joinpath.c')
| -rw-r--r-- | src/backend/optimizer/path/joinpath.c | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 7d2872065ba..f5e9b1e987e 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 1.105 2006/07/14 14:52:20 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.106 2006/08/17 17:06:37 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -542,8 +542,11 @@ match_unsorted_outer(PlannerInfo *root, * Look for presorted inner paths that satisfy the innersortkey list * --- or any truncation thereof, if we are allowed to build a * mergejoin using a subset of the merge clauses. Here, we consider - * both cheap startup cost and cheap total cost. Ignore - * inner_cheapest_total, since we already made a path with it. + * both cheap startup cost and cheap total cost. We can ignore + * inner_cheapest_total on the first iteration, since we already made + * a path with it --- but not on later iterations with shorter + * sort keys, because then we are considering a different situation, + * viz using a simpler mergejoin to avoid a sort of the inner rel. */ num_sortkeys = list_length(innersortkeys); if (num_sortkeys > 1 && !useallclauses) @@ -568,7 +571,8 @@ match_unsorted_outer(PlannerInfo *root, trialsortkeys, TOTAL_COST); if (innerpath != NULL && - innerpath != inner_cheapest_total && + (innerpath != inner_cheapest_total || + sortkeycnt < num_sortkeys) && (cheapest_total_inner == NULL || compare_path_costs(innerpath, cheapest_total_inner, TOTAL_COST) < 0)) @@ -603,7 +607,8 @@ match_unsorted_outer(PlannerInfo *root, trialsortkeys, STARTUP_COST); if (innerpath != NULL && - innerpath != inner_cheapest_total && + (innerpath != inner_cheapest_total || + sortkeycnt < num_sortkeys) && (cheapest_startup_inner == NULL || compare_path_costs(innerpath, cheapest_startup_inner, STARTUP_COST) < 0)) |