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Merge restrictlist_selectivity into clauselist_selectivity by

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teaching the latter to accept either RestrictInfo nodes or bare
clause expressions; and cache the selectivity result in the RestrictInfo
node when possible.  This extends the caching behavior of approx_selectivity
to many more contexts, and should reduce duplicate selectivity
calculations.
This commit is contained in:
Tom Lane
2004-01-04 03:51:52 +00:00
parent 21a1202281
commit 82b4dd394f
12 changed files with 196 additions and 200 deletions
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205
src/backend/optimizer/path/clausesel.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.62 2003/12/29 21:44:49 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.63 2004/01/04 03:51:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -54,33 +54,13 @@ static void addRangeClause(RangeQueryClause **rqlist, Node *clause,
* ROUTINES TO COMPUTE SELECTIVITIES
****************************************************************************/
/*
* restrictlist_selectivity -
* Compute the selectivity of an implicitly-ANDed list of RestrictInfo
* clauses.
*
* This is the same as clauselist_selectivity except for the representation
* of the clause list.
*/
Selectivity
restrictlist_selectivity(Query *root,
List *restrictinfo_list,
int varRelid,
JoinType jointype)
{
List *clauselist = get_actual_clauses(restrictinfo_list);
Selectivity result;
result = clauselist_selectivity(root, clauselist, varRelid, jointype);
freeList(clauselist);
return result;
}
/*
* clauselist_selectivity -
* Compute the selectivity of an implicitly-ANDed list of boolean
* expression clauses. The list can be empty, in which case 1.0
* must be returned.
* must be returned. List elements may be either RestrictInfos
* or bare expression clauses --- the former is preferred since
* it allows caching of results.
*
* See clause_selectivity() for the meaning of the additional parameters.
*
@@ -133,64 +113,80 @@ clauselist_selectivity(Query *root,
foreach(clist, clauses)
{
Node *clause = (Node *) lfirst(clist);
RestrictInfo *rinfo;
Selectivity s2;
/* Always compute the selectivity using clause_selectivity */
s2 = clause_selectivity(root, clause, varRelid, jointype);
/*
* Check for being passed a RestrictInfo.
*/
if (IsA(clause, RestrictInfo))
{
rinfo = (RestrictInfo *) clause;
clause = (Node *) rinfo->clause;
}
else
rinfo = NULL;
/*
* See if it looks like a restriction clause with a pseudoconstant
* on one side. (Anything more complicated than that might not
* behave in the simple way we are expecting.)
*
* NB: for consistency of results, this fragment of code had better
* match what clause_selectivity() would do in the cases it
* handles.
* behave in the simple way we are expecting.) Most of the tests
* here can be done more efficiently with rinfo than without.
*/
if (is_opclause(clause) &&
(varRelid != 0 || NumRelids(clause) == 1))
if (is_opclause(clause) && length(((OpExpr *) clause)->args) == 2)
{
OpExpr *expr = (OpExpr *) clause;
bool varonleft = true;
bool ok;
if (length(expr->args) == 2)
if (rinfo)
{
bool varonleft = true;
ok = (bms_membership(rinfo->clause_relids) == BMS_SINGLETON) &&
(is_pseudo_constant_clause_relids(lsecond(expr->args),
rinfo->right_relids) ||
(varonleft = false,
is_pseudo_constant_clause_relids(lfirst(expr->args),
rinfo->left_relids)));
}
else
{
ok = (NumRelids(clause) == 1) &&
(is_pseudo_constant_clause(lsecond(expr->args)) ||
(varonleft = false,
is_pseudo_constant_clause(lfirst(expr->args))));
}
if (is_pseudo_constant_clause(lsecond(expr->args)) ||
(varonleft = false,
is_pseudo_constant_clause(lfirst(expr->args))))
if (ok)
{
/*
* If it's not a "<" or ">" operator, just merge the
* selectivity in generically. But if it's the
* right oprrest, add the clause to rqlist for later
* processing.
*/
switch (get_oprrest(expr->opno))
{
Oid opno = expr->opno;
RegProcedure oprrest = get_oprrest(opno);
s2 = restriction_selectivity(root, opno,
expr->args, varRelid);
/*
* If we reach here, we have computed the same result
* that clause_selectivity would, so we can just use
* s2 if it's the wrong oprrest. But if it's the
* right oprrest, add the clause to rqlist for later
* processing.
*/
switch (oprrest)
{
case F_SCALARLTSEL:
addRangeClause(&rqlist, clause,
varonleft, true, s2);
break;
case F_SCALARGTSEL:
addRangeClause(&rqlist, clause,
varonleft, false, s2);
break;
default:
/* Just merge the selectivity in generically */
s1 = s1 * s2;
break;
}
continue; /* drop to loop bottom */
case F_SCALARLTSEL:
addRangeClause(&rqlist, clause,
varonleft, true, s2);
break;
case F_SCALARGTSEL:
addRangeClause(&rqlist, clause,
varonleft, false, s2);
break;
default:
/* Just merge the selectivity in generically */
s1 = s1 * s2;
break;
}
continue; /* drop to loop bottom */
}
}
/* Not the right form, so treat it generically. */
s2 = clause_selectivity(root, clause, varRelid, jointype);
s1 = s1 * s2;
}
@@ -352,11 +348,39 @@ addRangeClause(RangeQueryClause **rqlist, Node *clause,
*rqlist = rqelem;
}
/*
* bms_is_subset_singleton
*
* Same result as bms_is_subset(s, bms_make_singleton(x)),
* but a little faster and doesn't leak memory.
*
* Is this of use anywhere else? If so move to bitmapset.c ...
*/
static bool
bms_is_subset_singleton(const Bitmapset *s, int x)
{
switch (bms_membership(s))
{
case BMS_EMPTY_SET:
return true;
case BMS_SINGLETON:
return bms_is_member(x, s);
case BMS_MULTIPLE:
return false;
}
/* can't get here... */
return false;
}
/*
* clause_selectivity -
* Compute the selectivity of a general boolean expression clause.
*
* The clause can be either a RestrictInfo or a plain expression. If it's
* a RestrictInfo, we try to cache the selectivity for possible re-use,
* so passing RestrictInfos is preferred.
*
* varRelid is either 0 or a rangetable index.
*
* When varRelid is not 0, only variables belonging to that relation are
@@ -379,9 +403,37 @@ clause_selectivity(Query *root,
JoinType jointype)
{
Selectivity s1 = 1.0; /* default for any unhandled clause type */
RestrictInfo *rinfo = NULL;
bool cacheable = false;
if (clause == NULL)
if (clause == NULL) /* can this still happen? */
return s1;
if (IsA(clause, RestrictInfo))
{
rinfo = (RestrictInfo *) clause;
/*
* If possible, cache the result of the selectivity calculation for
* the clause. We can cache if varRelid is zero or the clause
* contains only vars of that relid --- otherwise varRelid will affect
* the result, so mustn't cache. We ignore the possibility that
* jointype will affect the result, which should be okay because outer
* join clauses will always be examined with the same jointype value.
*/
if (varRelid == 0 ||
bms_is_subset_singleton(rinfo->clause_relids, varRelid))
{
/* Cacheable --- do we already have the result? */
if (rinfo->this_selec >= 0)
return rinfo->this_selec;
cacheable = true;
}
/* Proceed with examination of contained clause */
clause = (Node *) rinfo->clause;
}
if (IsA(clause, Var))
{
Var *var = (Var *) clause;
@@ -448,9 +500,10 @@ clause_selectivity(Query *root,
else if (or_clause(clause))
{
/*
* Selectivities for an 'or' clause are computed as s1+s2 - s1*s2
* to account for the probable overlap of selected tuple sets. XXX
* is this too conservative?
* Selectivities for an OR clause are computed as s1+s2 - s1*s2
* to account for the probable overlap of selected tuple sets.
*
* XXX is this too conservative?
*/
List *arg;
@@ -483,9 +536,13 @@ clause_selectivity(Query *root,
{
/*
* Otherwise, it's a join if there's more than one relation
* used.
* used. We can optimize this calculation if an rinfo was passed.
*/
is_join_clause = (NumRelids(clause) > 1);
if (rinfo)
is_join_clause = (bms_membership(rinfo->clause_relids) ==
BMS_MULTIPLE);
else
is_join_clause = (NumRelids(clause) > 1);
}
if (is_join_clause)
@@ -559,6 +616,10 @@ clause_selectivity(Query *root,
jointype);
}
/* Cache the result if possible */
if (cacheable)
rinfo->this_selec = s1;
#ifdef SELECTIVITY_DEBUG
elog(DEBUG4, "clause_selectivity: s1 %f", s1);
#endif /* SELECTIVITY_DEBUG */