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Dept of better ideas: refrain from creating the planner's placeholder_list

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until vars are distributed to rels during query_planner() startup.  We don't
really need it before that, and not building it early has some advantages.
First, we don't need to put it through the various preprocessing steps, which
saves some cycles and eliminates the need for a number of routines to support
PlaceHolderInfo nodes at all.  Second, this means one less unused plan for any
sub-SELECT appearing in a placeholder's expression, since we don't build
placeholder_list until after sublink expansion is complete.
This commit is contained in:
Tom Lane
2008-10-22 20:17:52 +00:00
parent b9856b67a7
commit 31468d05d8
8 changed files with 95 additions and 168 deletions
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87
src/backend/optimizer/util/placeholder.c
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@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/placeholder.c,v 1.1 2008/10/21 20:42:53 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/placeholder.c,v 1.2 2008/10/22 20:17:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -25,8 +25,7 @@
/*
* make_placeholder_expr
* Make a PlaceHolderVar (and corresponding PlaceHolderInfo)
* for the given expression.
* Make a PlaceHolderVar for the given expression.
*
* phrels is the syntactic location (as a set of baserels) to attribute
* to the expression.
@@ -35,34 +34,25 @@ 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
* Fetch the PlaceHolderInfo for the given PHV; create it if not found
*
* Note: this should only be called after query_planner() has started.
*/
PlaceHolderInfo *
find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
{
PlaceHolderInfo *phinfo;
ListCell *lc;
/* if this ever isn't true, we'd need to be able to look in parent lists */
@@ -70,20 +60,33 @@ find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
foreach(lc, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
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 */
/* Not found, so create it */
phinfo = makeNode(PlaceHolderInfo);
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 *) phv->phexpr),
exprTypmod((Node *) phv->phexpr));
root->placeholder_list = lappend(root->placeholder_list, phinfo);
return phinfo;
}
/*
* 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
* The initial eval_at level set by find_placeholder_info 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
@@ -103,19 +106,9 @@ fix_placeholder_eval_levels(PlannerInfo *root)
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
@@ -160,11 +153,13 @@ fix_placeholder_eval_levels(PlannerInfo *root)
/*
* 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.)
* level. NOTE: this could cause more PlaceHolderInfos to be added
* to placeholder_list. That is okay because we'll process them
* before falling out of the foreach loop. Also, it could cause
* the ph_needed sets of existing list entries to expand, which
* is also okay because this loop doesn't examine those.
*/
eval_membership = bms_membership(eval_at);
if (eval_membership == BMS_MULTIPLE)
if (bms_membership(eval_at) == BMS_MULTIPLE)
{
List *vars = pull_var_clause((Node *) phinfo->ph_var->phexpr,
true);
@@ -172,14 +167,22 @@ fix_placeholder_eval_levels(PlannerInfo *root)
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)
/*
* Now, if any 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.) We have to do this as a separate step
* because the ph_needed values aren't stable until the previous loop
* finishes.
*/
foreach(lc1, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc1);
Relids eval_at = phinfo->ph_eval_at;
if (bms_membership(eval_at) == BMS_SINGLETON)
{
int varno = bms_singleton_member(eval_at);
RelOptInfo *rel = find_base_rel(root, varno);