diff options
Diffstat (limited to 'src/backend/utils/adt/selfuncs.c')
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 4bbb4a850eb..edff6da4109 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3361,6 +3361,7 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows, List **pgset) { List *varinfos = NIL; + double srf_multiplier = 1.0; double numdistinct; ListCell *l; int i; @@ -3394,6 +3395,7 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows, foreach(l, groupExprs) { Node *groupexpr = (Node *) lfirst(l); + double this_srf_multiplier; VariableStatData vardata; List *varshere; ListCell *l2; @@ -3402,6 +3404,21 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows, if (pgset && !list_member_int(*pgset, i++)) continue; + /* + * Set-returning functions in grouping columns are a bit problematic. + * The code below will effectively ignore their SRF nature and come up + * with a numdistinct estimate as though they were scalar functions. + * We compensate by scaling up the end result by the largest SRF + * rowcount estimate. (This will be an overestimate if the SRF + * produces multiple copies of any output value, but it seems best to + * assume the SRF's outputs are distinct. In any case, it's probably + * pointless to worry too much about this without much better + * estimates for SRF output rowcounts than we have today.) + */ + this_srf_multiplier = expression_returns_set_rows(groupexpr); + if (srf_multiplier < this_srf_multiplier) + srf_multiplier = this_srf_multiplier; + /* Short-circuit for expressions returning boolean */ if (exprType(groupexpr) == BOOLOID) { @@ -3467,9 +3484,15 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows, */ if (varinfos == NIL) { + /* Apply SRF multiplier as we would do in the long path */ + numdistinct *= srf_multiplier; + /* Round off */ + numdistinct = ceil(numdistinct); /* Guard against out-of-range answers */ if (numdistinct > input_rows) numdistinct = input_rows; + if (numdistinct < 1.0) + numdistinct = 1.0; return numdistinct; } @@ -3638,6 +3661,10 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows, varinfos = newvarinfos; } while (varinfos != NIL); + /* Now we can account for the effects of any SRFs */ + numdistinct *= srf_multiplier; + + /* Round off */ numdistinct = ceil(numdistinct); /* Guard against out-of-range answers */ |