diff options
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 18 | ||||
| -rw-r--r-- | src/test/regress/expected/subselect.out | 4 |
2 files changed, 18 insertions, 4 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 2f2f2c4e5e6..1621b6ee294 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -15,7 +15,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.169.4.1 2005/01/28 20:35:10 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.169.4.2 2005/02/01 23:08:56 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -2043,6 +2043,7 @@ estimate_num_groups(Query *root, List *groupExprs, double input_rows) GroupVarInfo *varinfo1 = (GroupVarInfo *) linitial(varinfos); RelOptInfo *rel = varinfo1->rel; double reldistinct = varinfo1->ndistinct; + double relmaxndistinct = reldistinct; int relvarcount = 1; List *newvarinfos = NIL; @@ -2057,6 +2058,8 @@ estimate_num_groups(Query *root, List *groupExprs, double input_rows) if (varinfo2->rel == varinfo1->rel) { reldistinct *= varinfo2->ndistinct; + if (relmaxndistinct < varinfo2->ndistinct) + relmaxndistinct = varinfo2->ndistinct; relvarcount++; } else @@ -2075,12 +2078,23 @@ estimate_num_groups(Query *root, List *groupExprs, double input_rows) /* * Clamp to size of rel, or size of rel / 10 if multiple Vars. * The fudge factor is because the Vars are probably correlated - * but we don't know by how much. + * but we don't know by how much. We should never clamp to less + * than the largest ndistinct value for any of the Vars, though, + * since there will surely be at least that many groups. */ double clamp = rel->tuples; if (relvarcount > 1) + { clamp *= 0.1; + if (clamp < relmaxndistinct) + { + clamp = relmaxndistinct; + /* for sanity in case some ndistinct is too large: */ + if (clamp > rel->tuples) + clamp = rel->tuples; + } + } if (reldistinct > clamp) reldistinct = clamp; diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out index 56bea035981..07e727de482 100644 --- a/src/test/regress/expected/subselect.out +++ b/src/test/regress/expected/subselect.out @@ -134,11 +134,11 @@ SELECT '' AS five, f1 AS "Correlated Field" WHERE f3 IS NOT NULL); five | Correlated Field ------+------------------ + | 2 | 3 | 1 - | 3 - | 2 | 2 + | 3 (5 rows) -- |