/*-------------------------------------------------------------------------
*
* tidpath.c
- * Routines to determine which tids are usable for scanning a
- * given relation, and create TidPaths accordingly.
+ * Routines to determine which TID conditions are usable for scanning
+ * a given relation, and create TidPaths accordingly.
+ *
+ * What we are looking for here is WHERE conditions of the form
+ * "CTID = pseudoconstant", which can be implemented by just fetching
+ * the tuple directly via heap_fetch(). We can also handle OR conditions
+ * if each OR arm contains such a condition; in particular this allows
+ * WHERE ctid IN (tid1, tid2, ...)
+ *
+ * There is currently no special support for joins involving CTID; in
+ * particular nothing corresponding to best_inner_indexscan(). Since it's
+ * not very useful to store TIDs of one table in another table, there
+ * doesn't seem to be enough use-case to justify adding a lot of code
+ * for that.
+ *
*
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/tidpath.c,v 1.23 2005/06/05 22:32:55 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/tidpath.c,v 1.24 2005/08/23 20:49:47 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
-#include <math.h>
-
+#include "access/htup.h"
#include "catalog/pg_operator.h"
+#include "catalog/pg_type.h"
#include "optimizer/clauses.h"
-#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
-#include "parser/parse_coerce.h"
-#include "utils/lsyscache.h"
-
+#include "parser/parse_expr.h"
-static List *TidqualFromRestrictinfo(Relids relids, List *restrictinfo);
-static bool isEvaluable(int varno, Node *node);
-static Node *TidequalClause(int varno, OpExpr *node);
-static List *TidqualFromExpr(int varno, Expr *expr);
+static Node *IsTidEqualClause(int varno, OpExpr *node);
+static List *TidQualFromExpr(int varno, Node *expr);
+static List *TidQualFromRestrictinfo(int varno, List *restrictinfo);
-static bool
-isEvaluable(int varno, Node *node)
-{
- ListCell *l;
- FuncExpr *expr;
-
- if (IsA(node, Const))
- return true;
- if (IsA(node, Param))
- return true;
- if (IsA(node, Var))
- {
- Var *var = (Var *) node;
-
- if (var->varno == varno)
- return false;
- return true;
- }
- if (!is_funcclause(node))
- return false;
- expr = (FuncExpr *) node;
- foreach(l, expr->args)
- {
- if (!isEvaluable(varno, lfirst(l)))
- return false;
- }
-
- return true;
-}
/*
- * The 2nd parameter should be an opclause
- * Extract the right node if the opclause is CTID= ....
- * or the left node if the opclause is ....=CTID
+ * Check to see if an opclause is of the form
+ * CTID = pseudoconstant
+ * or
+ * pseudoconstant = CTID
+ *
+ * If it is, return the pseudoconstant subnode; if not, return NULL.
+ *
+ * We check that the CTID Var belongs to relation "varno". That is probably
+ * redundant considering this is only applied to restriction clauses, but
+ * let's be safe.
*/
static Node *
-TidequalClause(int varno, OpExpr *node)
+IsTidEqualClause(int varno, OpExpr *node)
{
- Node *rnode = NULL,
- *arg1,
+ Node *arg1,
*arg2,
- *arg;
+ *other;
Var *var;
- Const *aconst;
- Param *param;
- FuncExpr *expr;
+ /* Operator must be tideq */
if (node->opno != TIDEqualOperator)
- return rnode;
+ return NULL;
if (list_length(node->args) != 2)
- return rnode;
+ return NULL;
arg1 = linitial(node->args);
arg2 = lsecond(node->args);
- arg = NULL;
- if (IsA(arg1, Var))
+ /* Look for CTID as either argument */
+ other = NULL;
+ if (arg1 && IsA(arg1, Var))
{
var = (Var *) arg1;
- if (var->varno == varno &&
- var->varattno == SelfItemPointerAttributeNumber &&
- var->vartype == TIDOID)
- arg = arg2;
- else if (var->varnoold == varno &&
- var->varoattno == SelfItemPointerAttributeNumber &&
- var->vartype == TIDOID)
- arg = arg2;
+ if (var->varattno == SelfItemPointerAttributeNumber &&
+ var->vartype == TIDOID &&
+ var->varno == varno &&
+ var->varlevelsup == 0)
+ other = arg2;
}
- if ((!arg) && IsA(arg2, Var))
+ if (!other && arg2 && IsA(arg2, Var))
{
var = (Var *) arg2;
- if (var->varno == varno &&
- var->varattno == SelfItemPointerAttributeNumber &&
- var->vartype == TIDOID)
- arg = arg1;
+ if (var->varattno == SelfItemPointerAttributeNumber &&
+ var->vartype == TIDOID &&
+ var->varno == varno &&
+ var->varlevelsup == 0)
+ other = arg1;
}
- if (!arg)
- return rnode;
- switch (nodeTag(arg))
- {
- case T_Const:
- aconst = (Const *) arg;
- if (aconst->consttype != TIDOID)
- return rnode;
- if (aconst->constbyval)
- return rnode;
- rnode = arg;
- break;
- case T_Param:
- param = (Param *) arg;
- if (param->paramtype != TIDOID)
- return rnode;
- rnode = arg;
- break;
- case T_Var:
- var = (Var *) arg;
- if (var->varno == varno ||
- var->vartype != TIDOID)
- return rnode;
- rnode = arg;
- break;
- case T_FuncExpr:
- expr = (FuncExpr *) arg;
- if (expr->funcresulttype != TIDOID)
- return rnode;
- if (isEvaluable(varno, (Node *) expr))
- rnode = arg;
- break;
- default:
- break;
- }
- return rnode;
+ if (!other)
+ return NULL;
+ if (exprType(other) != TIDOID)
+ return NULL; /* probably can't happen */
+
+ /* The other argument must be a pseudoconstant */
+ if (!is_pseudo_constant_clause(other))
+ return NULL;
+
+ return other; /* success */
}
/*
- * Extract the list of CTID values from a specified expr node.
- * When the expr node is an or_clause,we try to extract CTID
- * values from all member nodes. However we would discard them
- * all if we couldn't extract CTID values from a member node.
- * When the expr node is an and_clause,we return the list of
- * CTID values if we could extract the CTID values from a member
- * node.
+ * Extract a set of CTID conditions from the given qual expression
+ *
+ * If the expression is an AND clause, we can use a CTID condition
+ * from any sub-clause. If it is an OR clause, we must be able to
+ * extract a CTID condition from every sub-clause, or we can't use it.
+ *
+ * In theory, in the AND case we could get CTID conditions from different
+ * sub-clauses, in which case we could try to pick the most efficient one.
+ * In practice, such usage seems very unlikely, so we don't bother; we
+ * just exit as soon as we find the first candidate.
+ *
+ * Returns a List of pseudoconstant TID expressions, or NIL if no match.
+ * (Has to be a list for the OR case.)
*/
static List *
-TidqualFromExpr(int varno, Expr *expr)
+TidQualFromExpr(int varno, Node *expr)
{
List *rlst = NIL,
*frtn;
ListCell *l;
- Node *node = (Node *) expr,
- *rnode;
+ Node *rnode;
- if (is_opclause(node))
+ if (is_opclause(expr))
{
- rnode = TidequalClause(varno, (OpExpr *) expr);
+ /* base case: check for tideq opclause */
+ rnode = IsTidEqualClause(varno, (OpExpr *) expr);
if (rnode)
- rlst = lcons(rnode, rlst);
+ rlst = list_make1(rnode);
}
- else if (and_clause(node))
+ else if (and_clause(expr))
{
foreach(l, ((BoolExpr *) expr)->args)
{
- node = (Node *) lfirst(l);
- rlst = TidqualFromExpr(varno, (Expr *) node);
+ rlst = TidQualFromExpr(varno, (Node *) lfirst(l));
if (rlst)
break;
}
}
- else if (or_clause(node))
+ else if (or_clause(expr))
{
foreach(l, ((BoolExpr *) expr)->args)
{
- node = (Node *) lfirst(l);
- frtn = TidqualFromExpr(varno, (Expr *) node);
+ frtn = TidQualFromExpr(varno, (Node *) lfirst(l));
if (frtn)
rlst = list_concat(rlst, frtn);
else
return rlst;
}
+/*
+ * Extract a set of CTID conditions from the given restrictinfo list
+ *
+ * This is essentially identical to the AND case of TidQualFromExpr,
+ * except for the format of the input.
+ */
static List *
-TidqualFromRestrictinfo(Relids relids, List *restrictinfo)
+TidQualFromRestrictinfo(int varno, List *restrictinfo)
{
- ListCell *l;
List *rlst = NIL;
- int varno;
- Node *node;
- Expr *expr;
+ ListCell *l;
- if (bms_membership(relids) != BMS_SINGLETON)
- return NIL;
- varno = bms_singleton_member(relids);
foreach(l, restrictinfo)
{
- node = (Node *) lfirst(l);
- if (!IsA(node, RestrictInfo))
- continue;
- expr = ((RestrictInfo *) node)->clause;
- rlst = TidqualFromExpr(varno, expr);
+ RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
+
+ if (!IsA(rinfo, RestrictInfo))
+ continue; /* probably should never happen */
+ rlst = TidQualFromExpr(varno, (Node *) rinfo->clause);
if (rlst)
break;
}
/*
* create_tidscan_paths
- * Creates paths corresponding to tid direct scans of the given rel.
+ * Create paths corresponding to direct TID scans of the given rel.
+ *
* Candidate paths are added to the rel's pathlist (using add_path).
*/
void
create_tidscan_paths(PlannerInfo *root, RelOptInfo *rel)
{
- List *tideval = TidqualFromRestrictinfo(rel->relids,
- rel->baserestrictinfo);
+ List *tideval;
+
+ tideval = TidQualFromRestrictinfo(rel->relid, rel->baserestrictinfo);
if (tideval)
add_path(rel, (Path *) create_tidscan_path(root, rel, tideval));
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