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Improve eqjoinsel's ndistinct clamping to work for multiple levels of join.

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This patch fixes an oversight in my commit
7f3eba30c9 of 2008-10-23.  That patch
accounted for baserel restriction clauses that reduced the number of rows
coming out of a table (and hence the number of possibly-distinct values of
a join variable), but not for join restriction clauses that might have been
applied at a lower level of join.  To account for the latter, look up the
sizes of the min_lefthand and min_righthand inputs of the current join,
and clamp with those in the same way as for the base relations.

Noted while investigating a complaint from Ben Chobot, although this in
itself doesn't seem to explain his report.

Back-patch to 8.4; previous versions used different estimation methods
for which this heuristic isn't relevant.
This commit is contained in:
Tom Lane
2011-08-31 16:04:53 -04:00
parent edf4edae57
commit ca4f70ca77
1 changed files with 73 additions and 8 deletions
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81
src/backend/utils/adt/selfuncs.c
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@@ -141,9 +141,11 @@ static double ineq_histogram_selectivity(PlannerInfo *root,
FmgrInfo *opproc, bool isgt,
Datum constval, Oid consttype);
static double eqjoinsel_inner(Oid operator,
VariableStatData *vardata1, VariableStatData *vardata2);
VariableStatData *vardata1, VariableStatData *vardata2,
RelOptInfo *rel1, RelOptInfo *rel2);
static double eqjoinsel_semi(Oid operator,
VariableStatData *vardata1, VariableStatData *vardata2);
VariableStatData *vardata1, VariableStatData *vardata2,
RelOptInfo *rel1, RelOptInfo *rel2);
static bool convert_to_scalar(Datum value, Oid valuetypid, double *scaledvalue,
Datum lobound, Datum hibound, Oid boundstypid,
double *scaledlobound, double *scaledhibound);
@@ -172,6 +174,7 @@ static bool get_actual_variable_range(PlannerInfo *root,
VariableStatData *vardata,
Oid sortop,
Datum *min, Datum *max);
static RelOptInfo *find_join_input_rel(PlannerInfo *root, Relids relids);
static Selectivity prefix_selectivity(PlannerInfo *root,
VariableStatData *vardata,
Oid vartype, Oid opfamily, Const *prefixcon);
@@ -2007,24 +2010,47 @@ eqjoinsel(PG_FUNCTION_ARGS)
VariableStatData vardata1;
VariableStatData vardata2;
bool join_is_reversed;
RelOptInfo *rel1;
RelOptInfo *rel2;
get_join_variables(root, args, sjinfo,
&vardata1, &vardata2, &join_is_reversed);
/*
* Identify the join's direct input relations. We use the min lefthand
* and min righthand as the inputs, even though the join might actually
* get done with larger input relations. The min inputs are guaranteed to
* have been formed by now, though, and always using them ensures
* consistency of estimates.
*/
if (!join_is_reversed)
{
rel1 = find_join_input_rel(root, sjinfo->min_lefthand);
rel2 = find_join_input_rel(root, sjinfo->min_righthand);
}
else
{
rel1 = find_join_input_rel(root, sjinfo->min_righthand);
rel2 = find_join_input_rel(root, sjinfo->min_lefthand);
}
switch (sjinfo->jointype)
{
case JOIN_INNER:
case JOIN_LEFT:
case JOIN_FULL:
selec = eqjoinsel_inner(operator, &vardata1, &vardata2);
selec = eqjoinsel_inner(operator, &vardata1, &vardata2,
rel1, rel2);
break;
case JOIN_SEMI:
case JOIN_ANTI:
if (!join_is_reversed)
selec = eqjoinsel_semi(operator, &vardata1, &vardata2);
selec = eqjoinsel_semi(operator, &vardata1, &vardata2,
rel1, rel2);
else
selec = eqjoinsel_semi(get_commutator(operator),
&vardata2, &vardata1);
&vardata2, &vardata1,
rel2, rel1);
break;
default:
/* other values not expected here */
@@ -2050,7 +2076,8 @@ eqjoinsel(PG_FUNCTION_ARGS)
*/
static double
eqjoinsel_inner(Oid operator,
VariableStatData *vardata1, VariableStatData *vardata2)
VariableStatData *vardata1, VariableStatData *vardata2,
RelOptInfo *rel1, RelOptInfo *rel2)
{
double selec;
double nd1;
@@ -2251,15 +2278,19 @@ eqjoinsel_inner(Oid operator,
* be, providing a crude correction for the selectivity of restriction
* clauses on those relations. (We don't do that in the other path
* since there we are comparing the nd values to stats for the whole
* relations.)
* relations.) We can apply this clamp both with respect to the base
* relations from which the join variables come, and to the immediate
* input relations of the current join.
*/
double nullfrac1 = stats1 ? stats1->stanullfrac : 0.0;
double nullfrac2 = stats2 ? stats2->stanullfrac : 0.0;
if (vardata1->rel)
nd1 = Min(nd1, vardata1->rel->rows);
nd1 = Min(nd1, rel1->rows);
if (vardata2->rel)
nd2 = Min(nd2, vardata2->rel->rows);
nd2 = Min(nd2, rel2->rows);
selec = (1.0 - nullfrac1) * (1.0 - nullfrac2);
if (nd1 > nd2)
@@ -2286,7 +2317,8 @@ eqjoinsel_inner(Oid operator,
*/
static double
eqjoinsel_semi(Oid operator,
VariableStatData *vardata1, VariableStatData *vardata2)
VariableStatData *vardata1, VariableStatData *vardata2,
RelOptInfo *rel1, RelOptInfo *rel2)
{
double selec;
double nd1;
@@ -2434,8 +2466,10 @@ eqjoinsel_semi(Oid operator,
{
if (vardata1->rel)
nd1 = Min(nd1, vardata1->rel->rows);
nd1 = Min(nd1, rel1->rows);
if (vardata2->rel)
nd2 = Min(nd2, vardata2->rel->rows);
nd2 = Min(nd2, rel2->rows);
if (nd1 <= nd2 || nd2 <= 0)
selec = 1.0 - nullfrac1;
@@ -4758,6 +4792,37 @@ get_actual_variable_range(PlannerInfo *root, VariableStatData *vardata,
return have_data;
}
/*
* find_join_input_rel
* Look up the input relation for a join.
*
* We assume that the input relation's RelOptInfo must have been constructed
* already.
*/
static RelOptInfo *
find_join_input_rel(PlannerInfo *root, Relids relids)
{
RelOptInfo *rel = NULL;
switch (bms_membership(relids))
{
case BMS_EMPTY_SET:
/* should not happen */
break;
case BMS_SINGLETON:
rel = find_base_rel(root, bms_singleton_member(relids));
break;
case BMS_MULTIPLE:
rel = find_join_rel(root, relids);
break;
}
if (rel == NULL)
elog(ERROR, "could not find RelOptInfo for given relids");
return rel;
}
/*-------------------------------------------------------------------------
*