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/*-------------------------------------------------------------------------
*
* placeholder.c
* PlaceHolderVar and PlaceHolderInfo manipulation routines
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/placeholder.c,v 1.1 2008/10/21 20:42:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/pathnode.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "optimizer/var.h"
#include "utils/lsyscache.h"
/*
* make_placeholder_expr
* Make a PlaceHolderVar (and corresponding PlaceHolderInfo)
* for the given expression.
*
* phrels is the syntactic location (as a set of baserels) to attribute
* to the expression.
*/
PlaceHolderVar *
make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
{
PlaceHolderVar *phv = makeNode(PlaceHolderVar);
PlaceHolderInfo *phinfo = makeNode(PlaceHolderInfo);
phv->phexpr = expr;
phv->phrels = phrels;
phv->phid = ++(root->glob->lastPHId);
phv->phlevelsup = 0;
phinfo->phid = phv->phid;
phinfo->ph_var = copyObject(phv);
phinfo->ph_eval_at = pull_varnos((Node *) phv);
/* ph_eval_at may change later, see fix_placeholder_eval_levels */
phinfo->ph_needed = NULL; /* initially it's unused */
/* for the moment, estimate width using just the datatype info */
phinfo->ph_width = get_typavgwidth(exprType((Node *) expr),
exprTypmod((Node *) expr));
root->placeholder_list = lappend(root->placeholder_list, phinfo);
return phv;
}
/*
* find_placeholder_info
* Fetch the PlaceHolderInfo for the given PHV; error if not found
*/
PlaceHolderInfo *
find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
{
ListCell *lc;
/* if this ever isn't true, we'd need to be able to look in parent lists */
Assert(phv->phlevelsup == 0);
foreach(lc, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
if (phinfo->phid == phv->phid)
return phinfo;
}
elog(ERROR, "could not find PlaceHolderInfo with id %u", phv->phid);
return NULL; /* keep compiler quiet */
}
/*
* fix_placeholder_eval_levels
* Adjust the target evaluation levels for placeholders
*
* The initial eval_at level set by make_placeholder_expr was the set of
* rels used in the placeholder's expression (or the whole subselect if
* the expr is variable-free). If the subselect contains any outer joins
* that can null any of those rels, we must delay evaluation to above those
* joins.
*
* In future we might want to put additional policy/heuristics here to
* try to determine an optimal evaluation level. The current rules will
* result in evaluation at the lowest possible level.
*/
void
fix_placeholder_eval_levels(PlannerInfo *root)
{
ListCell *lc1;
foreach(lc1, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc1);
Relids syn_level = phinfo->ph_var->phrels;
Relids eval_at = phinfo->ph_eval_at;
BMS_Membership eval_membership;
bool found_some;
ListCell *lc2;
/*
* Ignore unreferenced placeholders. Note: if a placeholder is
* referenced only by some other placeholder's expr, we will do
* the right things because the referencing placeholder must appear
* earlier in the list.
*/
if (bms_is_empty(phinfo->ph_needed))
continue;
/*
* Check for delays due to lower outer joins. This is the same logic
* as in check_outerjoin_delay in initsplan.c, except that we don't
* want to modify the delay_upper_joins flags; that was all handled
* already during distribute_qual_to_rels.
*/
do
{
found_some = false;
foreach(lc2, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc2);
/* disregard joins not within the expr's sub-select */
if (!bms_is_subset(sjinfo->syn_lefthand, syn_level) ||
!bms_is_subset(sjinfo->syn_righthand, syn_level))
continue;
/* do we reference any nullable rels of this OJ? */
if (bms_overlap(eval_at, sjinfo->min_righthand) ||
(sjinfo->jointype == JOIN_FULL &&
bms_overlap(eval_at, sjinfo->min_lefthand)))
{
/* yes; have we included all its rels in eval_at? */
if (!bms_is_subset(sjinfo->min_lefthand, eval_at) ||
!bms_is_subset(sjinfo->min_righthand, eval_at))
{
/* no, so add them in */
eval_at = bms_add_members(eval_at,
sjinfo->min_lefthand);
eval_at = bms_add_members(eval_at,
sjinfo->min_righthand);
/* we'll need another iteration */
found_some = true;
}
}
}
} while (found_some);
phinfo->ph_eval_at = eval_at;
/*
* Now that we know where to evaluate the placeholder, make sure that
* any vars or placeholders it uses will be available at that join
* level. (Note that this has to be done within this loop to make
* sure we don't skip over such placeholders when we get to them.)
*/
eval_membership = bms_membership(eval_at);
if (eval_membership == BMS_MULTIPLE)
{
List *vars = pull_var_clause((Node *) phinfo->ph_var->phexpr,
true);
add_vars_to_targetlist(root, vars, eval_at);
list_free(vars);
}
/*
* Also, if the placeholder can be computed at a base rel and is
* needed above it, add it to that rel's targetlist. (This is
* essentially the same logic as in add_placeholders_to_joinrel, but
* we can't do that part until joinrels are formed.)
*/
if (eval_membership == BMS_SINGLETON)
{
int varno = bms_singleton_member(eval_at);
RelOptInfo *rel = find_base_rel(root, varno);
if (bms_nonempty_difference(phinfo->ph_needed, rel->relids))
rel->reltargetlist = lappend(rel->reltargetlist,
copyObject(phinfo->ph_var));
}
}
}
/*
* add_placeholders_to_joinrel
* Add any required PlaceHolderVars to a join rel's targetlist.
*
* A join rel should emit a PlaceHolderVar if (a) the PHV is needed above
* this join level and (b) the PHV can be computed at or below this level.
* At this time we do not need to distinguish whether the PHV will be
* computed here or copied up from below.
*/
void
add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel)
{
Relids relids = joinrel->relids;
ListCell *lc;
foreach(lc, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
/* Is it still needed above this joinrel? */
if (bms_nonempty_difference(phinfo->ph_needed, relids))
{
/* Is it computable here? */
if (bms_is_subset(phinfo->ph_eval_at, relids))
{
/* Yup, add it to the output */
joinrel->reltargetlist = lappend(joinrel->reltargetlist,
phinfo->ph_var);
joinrel->width += phinfo->ph_width;
}
}
}
}
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