diff options
Diffstat (limited to 'src/backend/optimizer/util/pathnode.c')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 8677ff20fd5..d827b4959b6 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -139,6 +139,9 @@ compare_fractional_path_costs(Path *path1, Path *path2, * total cost, we just say that their costs are "different", since neither * dominates the other across the whole performance spectrum. * + * If consider_startup is false, then we don't care about keeping paths with + * good startup cost, so we'll never return COSTS_DIFFERENT. + * * This function also includes special hacks to support a policy enforced * by its sole caller, add_path(): paths that have any parameterization * cannot win comparisons on the grounds of having cheaper startup cost, @@ -146,7 +149,8 @@ compare_fractional_path_costs(Path *path1, Path *path2, * (Unparameterized paths are more common, so we check for this case last.) */ static PathCostComparison -compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor) +compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor, + bool consider_startup) { /* * Check total cost first since it's more likely to be different; many @@ -155,7 +159,8 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor) if (path1->total_cost > path2->total_cost * fuzz_factor) { /* path1 fuzzily worse on total cost */ - if (path2->startup_cost > path1->startup_cost * fuzz_factor && + if (consider_startup && + path2->startup_cost > path1->startup_cost * fuzz_factor && path1->param_info == NULL) { /* ... but path2 fuzzily worse on startup, so DIFFERENT */ @@ -167,7 +172,8 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor) if (path2->total_cost > path1->total_cost * fuzz_factor) { /* path2 fuzzily worse on total cost */ - if (path1->startup_cost > path2->startup_cost * fuzz_factor && + if (consider_startup && + path1->startup_cost > path2->startup_cost * fuzz_factor && path2->param_info == NULL) { /* ... but path1 fuzzily worse on startup, so DIFFERENT */ @@ -177,6 +183,7 @@ compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor) return COSTS_BETTER1; } /* fuzzily the same on total cost */ + /* (so we may as well compare startup cost, even if !consider_startup) */ if (path1->startup_cost > path2->startup_cost * fuzz_factor && path2->param_info == NULL) { @@ -360,6 +367,9 @@ set_cheapest(RelOptInfo *parent_rel) * reduce the number of parameterized paths that are kept. See discussion * in src/backend/optimizer/README. * + * Another policy that is enforced here is that we only consider cheap + * startup cost to be interesting if parent_rel->consider_startup is true. + * * The pathlist is kept sorted by total_cost, with cheaper paths * at the front. Within this routine, that's simply a speed hack: * doing it that way makes it more likely that we will reject an inferior @@ -423,7 +433,8 @@ add_path(RelOptInfo *parent_rel, Path *new_path) * Do a fuzzy cost comparison with 1% fuzziness limit. (XXX does this * percentage need to be user-configurable?) */ - costcmp = compare_path_costs_fuzzily(new_path, old_path, 1.01); + costcmp = compare_path_costs_fuzzily(new_path, old_path, 1.01, + parent_rel->consider_startup); /* * If the two paths compare differently for startup and total cost, @@ -488,8 +499,10 @@ add_path(RelOptInfo *parent_rel, Path *new_path) remove_old = true; /* new dominates old */ else if (new_path->rows > old_path->rows) accept_new = false; /* old dominates new */ - else if (compare_path_costs_fuzzily(new_path, old_path, - 1.0000000001) == COSTS_BETTER1) + else if (compare_path_costs_fuzzily(new_path, + old_path, + 1.0000000001, + parent_rel->consider_startup) == COSTS_BETTER1) remove_old = true; /* new dominates old */ else accept_new = false; /* old equals or |