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Fix nested PlaceHolderVar expressions that appear only in targetlists.

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A PlaceHolderVar's expression might contain another, lower-level
PlaceHolderVar.  If the outer PlaceHolderVar is used, the inner one
certainly will be also, and so we have to make sure that both of them get
into the placeholder_list with correct ph_may_need values during the
initial pre-scan of the query (before deconstruct_jointree starts).
We did this correctly for PlaceHolderVars appearing in the query quals,
but overlooked the issue for those appearing in the top-level targetlist;
with the result that nested placeholders referenced only in the targetlist
did not work correctly, as illustrated in bug #6154.

While at it, add some error checking to find_placeholder_info to ensure
that we don't try to create new placeholders after it's too late to do so;
they have to all be created before deconstruct_jointree starts.

Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
This commit is contained in:
Tom Lane
2011-08-09 00:48:51 -04:00
parent d82a9d2a60
commit 77ba232564
8 changed files with 163 additions and 40 deletions
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84
src/backend/optimizer/util/placeholder.c
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@@ -24,7 +24,7 @@
/* Local functions */
static Relids find_placeholders_recurse(PlannerInfo *root, Node *jtnode);
static void find_placeholders_in_qual(PlannerInfo *root, Node *qual,
static void mark_placeholders_in_expr(PlannerInfo *root, Node *expr,
Relids relids);
@@ -50,7 +50,10 @@ make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
/*
* find_placeholder_info
* Fetch the PlaceHolderInfo for the given PHV; create it if not found
* Fetch the PlaceHolderInfo for the given PHV
*
* If the PlaceHolderInfo doesn't exist yet, create it if create_new_ph is
* true, else throw an error.
*
* This is separate from make_placeholder_expr because subquery pullup has
* to make PlaceHolderVars for expressions that might not be used at all in
@@ -58,10 +61,13 @@ make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
* We build PlaceHolderInfos only for PHVs that are still present in the
* simplified query passed to query_planner().
*
* Note: this should only be called after query_planner() has started.
* Note: this should only be called after query_planner() has started. Also,
* create_new_ph must not be TRUE after deconstruct_jointree begins, because
* make_outerjoininfo assumes that we already know about all placeholders.
*/
PlaceHolderInfo *
find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv,
bool create_new_ph)
{
PlaceHolderInfo *phinfo;
ListCell *lc;
@@ -77,6 +83,9 @@ find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
}
/* Not found, so create it */
if (!create_new_ph)
elog(ERROR, "too late to create a new PlaceHolderInfo");
phinfo = makeNode(PlaceHolderInfo);
phinfo->phid = phv->phid;
@@ -157,7 +166,7 @@ find_placeholders_recurse(PlannerInfo *root, Node *jtnode)
/*
* Now process the top-level quals.
*/
find_placeholders_in_qual(root, f->quals, jtrelids);
mark_placeholders_in_expr(root, f->quals, jtrelids);
}
else if (IsA(jtnode, JoinExpr))
{
@@ -173,7 +182,7 @@ find_placeholders_recurse(PlannerInfo *root, Node *jtnode)
jtrelids = bms_join(leftids, rightids);
/* Process the qual clauses */
find_placeholders_in_qual(root, j->quals, jtrelids);
mark_placeholders_in_expr(root, j->quals, jtrelids);
}
else
{
@@ -185,14 +194,15 @@ find_placeholders_recurse(PlannerInfo *root, Node *jtnode)
}
/*
* find_placeholders_in_qual
* Process a qual clause for find_placeholders_in_jointree.
* mark_placeholders_in_expr
* Find all PlaceHolderVars in the given expression, and mark them
* as possibly needed at the specified join level.
*
* relids is the syntactic join level to mark as the "maybe needed" level
* for each PlaceHolderVar found in the qual clause.
* for each PlaceHolderVar found in the expression.
*/
static void
find_placeholders_in_qual(PlannerInfo *root, Node *qual, Relids relids)
mark_placeholders_in_expr(PlannerInfo *root, Node *expr, Relids relids)
{
List *vars;
ListCell *vl;
@@ -201,7 +211,7 @@ find_placeholders_in_qual(PlannerInfo *root, Node *qual, Relids relids)
* pull_var_clause does more than we need here, but it'll do and it's
* convenient to use.
*/
vars = pull_var_clause(qual,
vars = pull_var_clause(expr,
PVC_RECURSE_AGGREGATES,
PVC_INCLUDE_PLACEHOLDERS);
foreach(vl, vars)
@@ -214,25 +224,47 @@ find_placeholders_in_qual(PlannerInfo *root, Node *qual, Relids relids)
continue;
/* Create a PlaceHolderInfo entry if there's not one already */
phinfo = find_placeholder_info(root, phv);
phinfo = find_placeholder_info(root, phv, true);
/* Mark the PHV as possibly needed at the qual's syntactic level */
phinfo->ph_may_need = bms_add_members(phinfo->ph_may_need, relids);
/*
* This is a bit tricky: the PHV's contained expression may contain
* other, lower-level PHVs. We need to get those into the
* PlaceHolderInfo list, but they aren't going to be needed where the
* outer PHV is referenced. Rather, they'll be needed where the outer
* PHV is evaluated. We can estimate that (conservatively) as the
* syntactic location of the PHV's expression. Recurse to take care
* of any such PHVs.
*/
find_placeholders_in_qual(root, (Node *) phv->phexpr, phv->phrels);
/* Mark it, and recursively process any contained placeholders */
mark_placeholder_maybe_needed(root, phinfo, relids);
}
list_free(vars);
}
/*
* mark_placeholder_maybe_needed
* Mark a placeholder as possibly needed at the specified join level.
*
* relids is the syntactic join level to mark as the "maybe needed" level
* for the placeholder.
*
* This is called during an initial scan of the query's targetlist and quals
* before we begin deconstruct_jointree. Once we begin deconstruct_jointree,
* all active placeholders must be present in root->placeholder_list with
* their correct ph_may_need values, because make_outerjoininfo and
* update_placeholder_eval_levels require this info to be available while
* we crawl up the join tree.
*/
void
mark_placeholder_maybe_needed(PlannerInfo *root, PlaceHolderInfo *phinfo,
Relids relids)
{
/* Mark the PHV as possibly needed at the given syntactic level */
phinfo->ph_may_need = bms_add_members(phinfo->ph_may_need, relids);
/*
* This is a bit tricky: the PHV's contained expression may contain other,
* lower-level PHVs. We need to get those into the PlaceHolderInfo list,
* but they aren't going to be needed where the outer PHV is referenced.
* Rather, they'll be needed where the outer PHV is evaluated. We can
* estimate that (conservatively) as the syntactic location of the PHV's
* expression. Recurse to take care of any such PHVs.
*/
mark_placeholders_in_expr(root, (Node *) phinfo->ph_var->phexpr,
phinfo->ph_var->phrels);
}
/*
* update_placeholder_eval_levels
* Adjust the target evaluation levels for placeholders
@@ -353,7 +385,7 @@ fix_placeholder_input_needed_levels(PlannerInfo *root)
PVC_RECURSE_AGGREGATES,
PVC_INCLUDE_PLACEHOLDERS);
add_vars_to_targetlist(root, vars, eval_at);
add_vars_to_targetlist(root, vars, eval_at, false);
list_free(vars);
}
}