diff options
Diffstat (limited to 'src/backend/access/table/tableam.c')
| -rw-r--r-- | src/backend/access/table/tableam.c | 22 |
1 files changed, 9 insertions, 13 deletions
diff --git a/src/backend/access/table/tableam.c b/src/backend/access/table/tableam.c index c6383197657..6438c457161 100644 --- a/src/backend/access/table/tableam.c +++ b/src/backend/access/table/tableam.c @@ -701,18 +701,14 @@ table_block_relation_estimate_size(Relation rel, int32 *attr_widths, * doesn't happen instantaneously, and it won't happen at all for cases * such as temporary tables.) * - * We approximate "never vacuumed" by "has relpages = 0", which means this - * will also fire on genuinely empty relations. Not great, but - * fortunately that's a seldom-seen case in the real world, and it - * shouldn't degrade the quality of the plan too much anyway to err in - * this direction. + * We test "never vacuumed" by seeing whether reltuples < 0. * * If the table has inheritance children, we don't apply this heuristic. * Totally empty parent tables are quite common, so we should be willing * to believe that they are empty. */ if (curpages < 10 && - relpages == 0 && + reltuples < 0 && !rel->rd_rel->relhassubclass) curpages = 10; @@ -727,17 +723,17 @@ table_block_relation_estimate_size(Relation rel, int32 *attr_widths, } /* estimate number of tuples from previous tuple density */ - if (relpages > 0) + if (reltuples >= 0 && relpages > 0) density = reltuples / (double) relpages; else { /* - * When we have no data because the relation was truncated, estimate - * tuple width from attribute datatypes. We assume here that the - * pages are completely full, which is OK for tables (since they've - * presumably not been VACUUMed yet) but is probably an overestimate - * for indexes. Fortunately get_relation_info() can clamp the - * overestimate to the parent table's size. + * When we have no data because the relation was never yet vacuumed, + * estimate tuple width from attribute datatypes. We assume here that + * the pages are completely full, which is OK for tables but is + * probably an overestimate for indexes. Fortunately + * get_relation_info() can clamp the overestimate to the parent + * table's size. * * Note: this code intentionally disregards alignment considerations, * because (a) that would be gilding the lily considering how crude |