diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index e50664cf66b..a94d54342e4 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -42,7 +42,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.80 2002/03/01 04:09:24 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.81 2002/03/01 06:01:19 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -566,6 +566,7 @@ cost_mergejoin(Path *path, Query *root, Cost startup_cost = 0; Cost run_cost = 0; Cost cpu_per_tuple; + RestrictInfo *firstclause; double outer_rows, inner_rows; double ntuples; @@ -581,10 +582,18 @@ cost_mergejoin(Path *path, Query *root, * Estimate fraction of the left and right inputs that will actually * need to be scanned. We use only the first (most significant) * merge clause for this purpose. + * + * Since this calculation is somewhat expensive, and will be the same + * for all mergejoin paths associated with the merge clause, we cache + * the results in the RestrictInfo node. */ - mergejoinscansel(root, - (Node *) ((RestrictInfo *) lfirst(mergeclauses))->clause, - &leftscan, &rightscan); + firstclause = (RestrictInfo *) lfirst(mergeclauses); + if (firstclause->left_mergescansel < 0) /* not computed yet? */ + mergejoinscansel(root, (Node *) firstclause->clause, + &firstclause->left_mergescansel, + &firstclause->right_mergescansel); + leftscan = firstclause->left_mergescansel; + rightscan = firstclause->right_mergescansel; outer_rows = outer_path->parent->rows * leftscan; inner_rows = inner_path->parent->rows * rightscan; @@ -1099,9 +1108,9 @@ cost_qual_eval_walker(Node *node, Cost *total) * big difference.) * * The "dirty" part comes from the fact that the selectivities of multiple - * clauses are estimated independently and multiplied together. Currently, - * clauselist_selectivity can seldom do any better than that anyhow, but - * someday it might be smarter. + * clauses are estimated independently and multiplied together. Now + * clauselist_selectivity often can't do any better than that anyhow, but + * for some situations (such as range constraints) it is smarter. * * Since we are only using the results to estimate how many potential * output tuples are generated and passed through qpqual checking, it |