diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 67 |
1 files changed, 50 insertions, 17 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 1246f87830d..7c8d4b63c07 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -19,7 +19,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.50 2000/01/26 05:56:34 momjian Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.51 2000/02/07 04:40:59 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -447,22 +447,26 @@ cost_hashjoin(Path *outer_path, } /* - * set_rel_rows_width - * Set the 'rows' and 'width' estimates for the given base relation. + * set_baserel_size_estimates + * Set the size estimates for the given base relation. * - * 'rows' is the estimated number of output tuples (after applying - * restriction clauses). - * 'width' is the estimated average output tuple width in bytes. + * The rel's targetlist and restrictinfo list must have been constructed + * already. + * + * We set the following fields of the rel node: + * rows: the estimated number of output tuples (after applying + * restriction clauses). + * width: the estimated average output tuple width in bytes. */ void -set_rel_rows_width(Query *root, RelOptInfo *rel) +set_baserel_size_estimates(Query *root, RelOptInfo *rel) { /* Should only be applied to base relations */ Assert(length(rel->relids) == 1); rel->rows = rel->tuples * restrictlist_selectivity(root, - rel->restrictinfo, + rel->baserestrictinfo, lfirsti(rel->relids)); Assert(rel->rows >= 0); @@ -470,28 +474,56 @@ set_rel_rows_width(Query *root, RelOptInfo *rel) } /* - * set_joinrel_rows_width - * Set the 'rows' and 'width' estimates for the given join relation. + * set_joinrel_size_estimates + * Set the size estimates for the given join relation. + * + * The rel's targetlist must have been constructed already, and a + * restriction clause list that matches the given component rels must + * be provided. + * + * Since there is more than one way to make a joinrel for more than two + * base relations, the results we get here could depend on which component + * rel pair is provided. In theory we should get the same answers no matter + * which pair is provided; in practice, since the selectivity estimation + * routines don't handle all cases equally well, we might not. But there's + * not much to be done about it. (Would it make sense to repeat the + * calculations for each pair of input rels that's encountered, and somehow + * average the results? Probably way more trouble than it's worth.) + * + * We set the same relnode fields as set_baserel_size_estimates() does. */ void -set_joinrel_rows_width(Query *root, RelOptInfo *rel, - JoinPath *joinpath) +set_joinrel_size_estimates(Query *root, RelOptInfo *rel, + RelOptInfo *outer_rel, + RelOptInfo *inner_rel, + List *restrictlist) { double temp; /* cartesian product */ - temp = joinpath->outerjoinpath->parent->rows * - joinpath->innerjoinpath->parent->rows; + temp = outer_rel->rows * inner_rel->rows; - /* apply join restrictivity */ + /* + * Apply join restrictivity. Note that we are only considering clauses + * that become restriction clauses at this join level; we are not + * double-counting them because they were not considered in estimating + * the sizes of the component rels. + */ temp *= restrictlist_selectivity(root, - joinpath->path.parent->restrictinfo, + restrictlist, 0); Assert(temp >= 0); rel->rows = temp; - set_rel_width(root, rel); + /* + * We could apply set_rel_width() to compute the output tuple width + * from scratch, but at present it's always just the sum of the input + * widths, so why work harder than necessary? If relnode.c is ever + * taught to remove unneeded columns from join targetlists, go back + * to using set_rel_width here. + */ + rel->width = outer_rel->width + inner_rel->width; } /* @@ -516,6 +548,7 @@ set_rel_width(Query *root, RelOptInfo *rel) * * If a field is variable-length, we make a default assumption. Would be * better if VACUUM recorded some stats about the average field width... + * also, we have access to the atttypmod, but fail to use it... */ static int compute_attribute_width(TargetEntry *tlistentry) |