diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 87 | ||||
| -rw-r--r-- | src/include/optimizer/pathnode.h | 3 |
2 files changed, 58 insertions, 32 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 56de8fc370a..1ea89ff54c9 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -3578,17 +3578,42 @@ create_limit_path(PlannerInfo *root, RelOptInfo *rel, /* * Adjust the output rows count and costs according to the offset/limit. - * This is only a cosmetic issue if we are at top level, but if we are - * building a subquery then it's important to report correct info to the - * outer planner. - * - * When the offset or count couldn't be estimated, use 10% of the - * estimated number of rows emitted from the subpath. - * - * XXX we don't bother to add eval costs of the offset/limit expressions - * themselves to the path costs. In theory we should, but in most cases - * those expressions are trivial and it's just not worth the trouble. */ + adjust_limit_rows_costs(&pathnode->path.rows, + &pathnode->path.startup_cost, + &pathnode->path.total_cost, + offset_est, count_est); + + return pathnode; +} + +/* + * adjust_limit_rows_costs + * Adjust the size and cost estimates for a LimitPath node according to the + * offset/limit. + * + * This is only a cosmetic issue if we are at top level, but if we are + * building a subquery then it's important to report correct info to the outer + * planner. + * + * When the offset or count couldn't be estimated, use 10% of the estimated + * number of rows emitted from the subpath. + * + * XXX we don't bother to add eval costs of the offset/limit expressions + * themselves to the path costs. In theory we should, but in most cases those + * expressions are trivial and it's just not worth the trouble. + */ +void +adjust_limit_rows_costs(double *rows, /* in/out parameter */ + Cost *startup_cost, /* in/out parameter */ + Cost *total_cost, /* in/out parameter */ + int64 offset_est, + int64 count_est) +{ + double input_rows = *rows; + Cost input_startup_cost = *startup_cost; + Cost input_total_cost = *total_cost; + if (offset_est != 0) { double offset_rows; @@ -3596,16 +3621,16 @@ create_limit_path(PlannerInfo *root, RelOptInfo *rel, if (offset_est > 0) offset_rows = (double) offset_est; else - offset_rows = clamp_row_est(subpath->rows * 0.10); - if (offset_rows > pathnode->path.rows) - offset_rows = pathnode->path.rows; - if (subpath->rows > 0) - pathnode->path.startup_cost += - (subpath->total_cost - subpath->startup_cost) - * offset_rows / subpath->rows; - pathnode->path.rows -= offset_rows; - if (pathnode->path.rows < 1) - pathnode->path.rows = 1; + offset_rows = clamp_row_est(input_rows * 0.10); + if (offset_rows > *rows) + offset_rows = *rows; + if (input_rows > 0) + *startup_cost += + (input_total_cost - input_startup_cost) + * offset_rows / input_rows; + *rows -= offset_rows; + if (*rows < 1) + *rows = 1; } if (count_est != 0) @@ -3615,19 +3640,17 @@ create_limit_path(PlannerInfo *root, RelOptInfo *rel, if (count_est > 0) count_rows = (double) count_est; else - count_rows = clamp_row_est(subpath->rows * 0.10); - if (count_rows > pathnode->path.rows) - count_rows = pathnode->path.rows; - if (subpath->rows > 0) - pathnode->path.total_cost = pathnode->path.startup_cost + - (subpath->total_cost - subpath->startup_cost) - * count_rows / subpath->rows; - pathnode->path.rows = count_rows; - if (pathnode->path.rows < 1) - pathnode->path.rows = 1; + count_rows = clamp_row_est(input_rows * 0.10); + if (count_rows > *rows) + count_rows = *rows; + if (input_rows > 0) + *total_cost = *startup_cost + + (input_total_cost - input_startup_cost) + * count_rows / input_rows; + *rows = count_rows; + if (*rows < 1) + *rows = 1; } - - return pathnode; } diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h index 3a803b3fd00..5b577c12eca 100644 --- a/src/include/optimizer/pathnode.h +++ b/src/include/optimizer/pathnode.h @@ -265,6 +265,9 @@ extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath, Node *limitOffset, Node *limitCount, int64 offset_est, int64 count_est); +extern void adjust_limit_rows_costs(double *rows, + Cost *startup_cost, Cost *total_cost, + int64 offset_est, int64 count_est); extern Path *reparameterize_path(PlannerInfo *root, Path *path, Relids required_outer, |