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/*-------------------------------------------------------------------------
*
* tidpath.c
* 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 1.25 2005/10/15 02:49:20 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "optimizer/clauses.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "parser/parse_expr.h"
static Node *IsTidEqualClause(int varno, OpExpr *node);
static List *TidQualFromExpr(int varno, Node *expr);
static List *TidQualFromRestrictinfo(int varno, List *restrictinfo);
/*
* 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 *
IsTidEqualClause(int varno, OpExpr *node)
{
Node *arg1,
*arg2,
*other;
Var *var;
/* Operator must be tideq */
if (node->opno != TIDEqualOperator)
return NULL;
if (list_length(node->args) != 2)
return NULL;
arg1 = linitial(node->args);
arg2 = lsecond(node->args);
/* Look for CTID as either argument */
other = NULL;
if (arg1 && IsA(arg1, Var))
{
var = (Var *) arg1;
if (var->varattno == SelfItemPointerAttributeNumber &&
var->vartype == TIDOID &&
var->varno == varno &&
var->varlevelsup == 0)
other = arg2;
}
if (!other && arg2 && IsA(arg2, Var))
{
var = (Var *) arg2;
if (var->varattno == SelfItemPointerAttributeNumber &&
var->vartype == TIDOID &&
var->varno == varno &&
var->varlevelsup == 0)
other = arg1;
}
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 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, Node *expr)
{
List *rlst = NIL,
*frtn;
ListCell *l;
Node *rnode;
if (is_opclause(expr))
{
/* base case: check for tideq opclause */
rnode = IsTidEqualClause(varno, (OpExpr *) expr);
if (rnode)
rlst = list_make1(rnode);
}
else if (and_clause(expr))
{
foreach(l, ((BoolExpr *) expr)->args)
{
rlst = TidQualFromExpr(varno, (Node *) lfirst(l));
if (rlst)
break;
}
}
else if (or_clause(expr))
{
foreach(l, ((BoolExpr *) expr)->args)
{
frtn = TidQualFromExpr(varno, (Node *) lfirst(l));
if (frtn)
rlst = list_concat(rlst, frtn);
else
{
if (rlst)
list_free(rlst);
rlst = NIL;
break;
}
}
}
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(int varno, List *restrictinfo)
{
List *rlst = NIL;
ListCell *l;
foreach(l, restrictinfo)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
if (!IsA(rinfo, RestrictInfo))
continue; /* probably should never happen */
rlst = TidQualFromExpr(varno, (Node *) rinfo->clause);
if (rlst)
break;
}
return rlst;
}
/*
* create_tidscan_paths
* 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;
tideval = TidQualFromRestrictinfo(rel->relid, rel->baserestrictinfo);
if (tideval)
add_path(rel, (Path *) create_tidscan_path(root, rel, tideval));
}
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