diff options
Diffstat (limited to 'src/backend/optimizer/path/allpaths.c')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 1115ebeee29..b5bc9b602e2 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -958,6 +958,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, { int parentRTindex = rti; bool has_live_children; + double parent_tuples; double parent_rows; double parent_size; double *parent_attrsizes; @@ -983,6 +984,15 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, /* * Initialize to compute size estimates for whole append relation. * + * We handle tuples estimates by setting "tuples" to the total number of + * tuples accumulated from each live child, rather than using "rows". + * Although an appendrel itself doesn't directly enforce any quals, its + * child relations may. Therefore, setting "tuples" equal to "rows" for + * an appendrel isn't always appropriate, and can lead to inaccurate cost + * estimates. For example, when estimating the number of distinct values + * from an appendrel, we would be unable to adjust the estimate based on + * the restriction selectivity (see estimate_num_groups). + * * We handle width estimates by weighting the widths of different child * rels proportionally to their number of rows. This is sensible because * the use of width estimates is mainly to compute the total relation @@ -995,6 +1005,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, * have zero rows and/or width, if they were excluded by constraints. */ has_live_children = false; + parent_tuples = 0; parent_rows = 0; parent_size = 0; nattrs = rel->max_attr - rel->min_attr + 1; @@ -1161,6 +1172,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, */ Assert(childrel->rows > 0); + parent_tuples += childrel->tuples; parent_rows += childrel->rows; parent_size += childrel->reltarget->width * childrel->rows; @@ -1207,18 +1219,13 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel, int i; Assert(parent_rows > 0); + rel->tuples = parent_tuples; rel->rows = parent_rows; rel->reltarget->width = rint(parent_size / parent_rows); for (i = 0; i < nattrs; i++) rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows); /* - * Set "raw tuples" count equal to "rows" for the appendrel; needed - * because some places assume rel->tuples is valid for any baserel. - */ - rel->tuples = parent_rows; - - /* * Note that we leave rel->pages as zero; this is important to avoid * double-counting the appendrel tree in total_table_pages. */ |