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postgres/src/backend/optimizer/plan/planner.c
Tom Lane 147fbf9c6e Repair bug reported by Laurent Perez: bad plan generated when UPDATE or 
DELETE of an inheritance tree references another inherited relation.
This bug has been latent since 7.1; I'm still not quite sure why 7.1 and
7.2 don't manifest it (at least, they don't crash on a simple test case).
2003-03-05 18:38:14 +00:00

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/*-------------------------------------------------------------------------
*
* planner.c
* The query optimizer external interface.
*
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.149 2003/03/05 18:38:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <limits.h>
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/subselect.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parsetree.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"
/* Expression kind codes for preprocess_expression */
#define EXPRKIND_QUAL 0
#define EXPRKIND_TARGET 1
#define EXPRKIND_RTFUNC 2
#define EXPRKIND_ININFO 3
static Node *preprocess_expression(Query *parse, Node *expr, int kind);
static void preprocess_qual_conditions(Query *parse, Node *jtnode);
static Plan *inheritance_planner(Query *parse, List *inheritlist);
static Plan *grouping_planner(Query *parse, double tuple_fraction);
static bool hash_safe_grouping(Query *parse);
static List *make_subplanTargetList(Query *parse, List *tlist,
AttrNumber **groupColIdx, bool *need_tlist_eval);
static void locate_grouping_columns(Query *parse,
List *tlist,
List *sub_tlist,
AttrNumber *groupColIdx);
static Plan *make_groupsortplan(Query *parse,
List *groupClause,
AttrNumber *grpColIdx,
Plan *subplan);
static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
/*****************************************************************************
*
* Query optimizer entry point
*
*****************************************************************************/
Plan *
planner(Query *parse)
{
Plan *result_plan;
Index save_PlannerQueryLevel;
List *save_PlannerParamVar;
/*
* The planner can be called recursively (an example is when
* eval_const_expressions tries to pre-evaluate an SQL function). So,
* these global state variables must be saved and restored.
*
* These vars cannot be moved into the Query structure since their whole
* purpose is communication across multiple sub-Queries.
*
* Note we do NOT save and restore PlannerPlanId: it exists to assign
* unique IDs to SubPlan nodes, and we want those IDs to be unique for
* the life of a backend. Also, PlannerInitPlan is saved/restored in
* subquery_planner, not here.
*/
save_PlannerQueryLevel = PlannerQueryLevel;
save_PlannerParamVar = PlannerParamVar;
/* Initialize state for handling outer-level references and params */
PlannerQueryLevel = 0; /* will be 1 in top-level subquery_planner */
PlannerParamVar = NIL;
/* primary planning entry point (may recurse for subqueries) */
result_plan = subquery_planner(parse, -1.0 /* default case */ );
Assert(PlannerQueryLevel == 0);
/* executor wants to know total number of Params used overall */
result_plan->nParamExec = length(PlannerParamVar);
/* final cleanup of the plan */
set_plan_references(result_plan, parse->rtable);
/* restore state for outer planner, if any */
PlannerQueryLevel = save_PlannerQueryLevel;
PlannerParamVar = save_PlannerParamVar;
return result_plan;
}
/*--------------------
* subquery_planner
* Invokes the planner on a subquery. We recurse to here for each
* sub-SELECT found in the query tree.
*
* parse is the querytree produced by the parser & rewriter.
* tuple_fraction is the fraction of tuples we expect will be retrieved.
* tuple_fraction is interpreted as explained for grouping_planner, below.
*
* Basically, this routine does the stuff that should only be done once
* per Query object. It then calls grouping_planner. At one time,
* grouping_planner could be invoked recursively on the same Query object;
* that's not currently true, but we keep the separation between the two
* routines anyway, in case we need it again someday.
*
* subquery_planner will be called recursively to handle sub-Query nodes
* found within the query's expressions and rangetable.
*
* Returns a query plan.
*--------------------
*/
Plan *
subquery_planner(Query *parse, double tuple_fraction)
{
List *saved_initplan = PlannerInitPlan;
int saved_planid = PlannerPlanId;
bool hasOuterJoins;
Plan *plan;
List *newHaving;
List *lst;
/* Set up for a new level of subquery */
PlannerQueryLevel++;
PlannerInitPlan = NIL;
/*
* Look for IN clauses at the top level of WHERE, and transform them
* into joins. Note that this step only handles IN clauses originally
* at top level of WHERE; if we pull up any subqueries in the next step,
* their INs are processed just before pulling them up.
*/
parse->in_info_list = NIL;
if (parse->hasSubLinks)
parse->jointree->quals = pull_up_IN_clauses(parse,
parse->jointree->quals);
/*
* Check to see if any subqueries in the rangetable can be merged into
* this query.
*/
parse->jointree = (FromExpr *)
pull_up_subqueries(parse, (Node *) parse->jointree, false);
/*
* Detect whether any rangetable entries are RTE_JOIN kind; if not,
* we can avoid the expense of doing flatten_join_alias_vars(). Also
* check for outer joins --- if none, we can skip reduce_outer_joins().
* This must be done after we have done pull_up_subqueries, of course.
*/
parse->hasJoinRTEs = false;
hasOuterJoins = false;
foreach(lst, parse->rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(lst);
if (rte->rtekind == RTE_JOIN)
{
parse->hasJoinRTEs = true;
if (IS_OUTER_JOIN(rte->jointype))
{
hasOuterJoins = true;
/* Can quit scanning once we find an outer join */
break;
}
}
}
/*
* Do expression preprocessing on targetlist and quals.
*/
parse->targetList = (List *)
preprocess_expression(parse, (Node *) parse->targetList,
EXPRKIND_TARGET);
preprocess_qual_conditions(parse, (Node *) parse->jointree);
parse->havingQual = preprocess_expression(parse, parse->havingQual,
EXPRKIND_QUAL);
parse->in_info_list = (List *)
preprocess_expression(parse, (Node *) parse->in_info_list,
EXPRKIND_ININFO);
/* Also need to preprocess expressions for function RTEs */
foreach(lst, parse->rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(lst);
if (rte->rtekind == RTE_FUNCTION)
rte->funcexpr = preprocess_expression(parse, rte->funcexpr,
EXPRKIND_RTFUNC);
}
/*
* A HAVING clause without aggregates is equivalent to a WHERE clause
* (except it can only refer to grouped fields). Transfer any
* agg-free clauses of the HAVING qual into WHERE. This may seem like
* wasting cycles to cater to stupidly-written queries, but there are
* other reasons for doing it. Firstly, if the query contains no aggs
* at all, then we aren't going to generate an Agg plan node, and so
* there'll be no place to execute HAVING conditions; without this
* transfer, we'd lose the HAVING condition entirely, which is wrong.
* Secondly, when we push down a qual condition into a sub-query, it's
* easiest to push the qual into HAVING always, in case it contains
* aggs, and then let this code sort it out.
*
* Note that both havingQual and parse->jointree->quals are in
* implicitly-ANDed-list form at this point, even though they are
* declared as Node *. Also note that contain_agg_clause does not
* recurse into sub-selects, which is exactly what we need here.
*/
newHaving = NIL;
foreach(lst, (List *) parse->havingQual)
{
Node *havingclause = (Node *) lfirst(lst);
if (contain_agg_clause(havingclause))
newHaving = lappend(newHaving, havingclause);
else
parse->jointree->quals = (Node *)
lappend((List *) parse->jointree->quals, havingclause);
}
parse->havingQual = (Node *) newHaving;
/*
* If we have any outer joins, try to reduce them to plain inner joins.
* This step is most easily done after we've done expression preprocessing.
*/
if (hasOuterJoins)
reduce_outer_joins(parse);
/*
* See if we can simplify the jointree; opportunities for this may come
* from having pulled up subqueries, or from flattening explicit JOIN
* syntax. We must do this after flattening JOIN alias variables, since
* eliminating explicit JOIN nodes from the jointree will cause
* get_relids_for_join() to fail. But it should happen after
* reduce_outer_joins, anyway.
*/
parse->jointree = (FromExpr *)
simplify_jointree(parse, (Node *) parse->jointree);
/*
* Do the main planning. If we have an inherited target relation,
* that needs special processing, else go straight to
* grouping_planner.
*/
if (parse->resultRelation &&
(lst = expand_inherted_rtentry(parse, parse->resultRelation, false))
!= NIL)
plan = inheritance_planner(parse, lst);
else
plan = grouping_planner(parse, tuple_fraction);
/*
* If any subplans were generated, or if we're inside a subplan, build
* initPlan list and extParam/allParam sets for plan nodes.
*/
if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
{
Cost initplan_cost = 0;
/* Prepare extParam/allParam sets for all nodes in tree */
SS_finalize_plan(plan, parse->rtable);
/*
* SS_finalize_plan doesn't handle initPlans, so we have to manually
* attach them to the topmost plan node, and add their extParams to
* the topmost node's, too.
*
* We also add the total_cost of each initPlan to the startup cost
* of the top node. This is a conservative overestimate, since in
* fact each initPlan might be executed later than plan startup, or
* even not at all.
*/
plan->initPlan = PlannerInitPlan;
foreach(lst, plan->initPlan)
{
SubPlan *initplan = (SubPlan *) lfirst(lst);
plan->extParam = bms_add_members(plan->extParam,
initplan->plan->extParam);
initplan_cost += initplan->plan->total_cost;
}
plan->startup_cost += initplan_cost;
plan->total_cost += initplan_cost;
}
/* Return to outer subquery context */
PlannerQueryLevel--;
PlannerInitPlan = saved_initplan;
/* we do NOT restore PlannerPlanId; that's not an oversight! */
return plan;
}
/*
* preprocess_expression
* Do subquery_planner's preprocessing work for an expression,
* which can be a targetlist, a WHERE clause (including JOIN/ON
* conditions), or a HAVING clause.
*/
static Node *
preprocess_expression(Query *parse, Node *expr, int kind)
{
/*
* If the query has any join RTEs, replace join alias variables with
* base-relation variables. We must do this before sublink processing,
* else sublinks expanded out from join aliases wouldn't get processed.
*/
if (parse->hasJoinRTEs)
expr = flatten_join_alias_vars(parse, expr);
/*
* Simplify constant expressions.
*
* Note that at this point quals have not yet been converted to
* implicit-AND form, so we can apply eval_const_expressions directly.
*/
expr = eval_const_expressions(expr);
/*
* If it's a qual or havingQual, canonicalize it, and convert it to
* implicit-AND format.
*
* XXX Is there any value in re-applying eval_const_expressions after
* canonicalize_qual?
*/
if (kind == EXPRKIND_QUAL)
{
expr = (Node *) canonicalize_qual((Expr *) expr, true);
#ifdef OPTIMIZER_DEBUG
printf("After canonicalize_qual()\n");
pprint(expr);
#endif
}
/* Expand SubLinks to SubPlans */
if (parse->hasSubLinks)
expr = SS_process_sublinks(expr, (kind == EXPRKIND_QUAL));
/* Replace uplevel vars with Param nodes */
if (PlannerQueryLevel > 1)
expr = SS_replace_correlation_vars(expr);
return expr;
}
/*
* preprocess_qual_conditions
* Recursively scan the query's jointree and do subquery_planner's
* preprocessing work on each qual condition found therein.
*/
static void
preprocess_qual_conditions(Query *parse, Node *jtnode)
{
if (jtnode == NULL)
return;
if (IsA(jtnode, RangeTblRef))
{
/* nothing to do here */
}
else if (IsA(jtnode, FromExpr))
{
FromExpr *f = (FromExpr *) jtnode;
List *l;
foreach(l, f->fromlist)
preprocess_qual_conditions(parse, lfirst(l));
f->quals = preprocess_expression(parse, f->quals, EXPRKIND_QUAL);
}
else if (IsA(jtnode, JoinExpr))
{
JoinExpr *j = (JoinExpr *) jtnode;
preprocess_qual_conditions(parse, j->larg);
preprocess_qual_conditions(parse, j->rarg);
j->quals = preprocess_expression(parse, j->quals, EXPRKIND_QUAL);
}
else
elog(ERROR, "preprocess_qual_conditions: unexpected node type %d",
nodeTag(jtnode));
}
/*--------------------
* inheritance_planner
* Generate a plan in the case where the result relation is an
* inheritance set.
*
* We have to handle this case differently from cases where a source
* relation is an inheritance set. Source inheritance is expanded at
* the bottom of the plan tree (see allpaths.c), but target inheritance
* has to be expanded at the top. The reason is that for UPDATE, each
* target relation needs a different targetlist matching its own column
* set. (This is not so critical for DELETE, but for simplicity we treat
* inherited DELETE the same way.) Fortunately, the UPDATE/DELETE target
* can never be the nullable side of an outer join, so it's OK to generate
* the plan this way.
*
* parse is the querytree produced by the parser & rewriter.
* inheritlist is an integer list of RT indexes for the result relation set.
*
* Returns a query plan.
*--------------------
*/
static Plan *
inheritance_planner(Query *parse, List *inheritlist)
{
int parentRTindex = parse->resultRelation;
Oid parentOID = getrelid(parentRTindex, parse->rtable);
int mainrtlength = length(parse->rtable);
List *subplans = NIL;
List *tlist = NIL;
List *l;
foreach(l, inheritlist)
{
int childRTindex = lfirsti(l);
Oid childOID = getrelid(childRTindex, parse->rtable);
int subrtlength;
Query *subquery;
Plan *subplan;
/* Generate modified query with this rel as target */
subquery = (Query *) adjust_inherited_attrs((Node *) parse,
parentRTindex, parentOID,
childRTindex, childOID);
/* Generate plan */
subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */ );
subplans = lappend(subplans, subplan);
/*
* It's possible that additional RTEs got added to the rangetable
* due to expansion of inherited source tables (see allpaths.c).
* If so, we must copy 'em back to the main parse tree's rtable.
*
* XXX my goodness this is ugly. Really need to think about ways
* to rein in planner's habit of scribbling on its input.
*/
subrtlength = length(subquery->rtable);
if (subrtlength > mainrtlength)
{
List *subrt = subquery->rtable;
while (mainrtlength-- > 0) /* wish we had nthcdr() */
subrt = lnext(subrt);
parse->rtable = nconc(parse->rtable, subrt);
mainrtlength = subrtlength;
}
/* Save preprocessed tlist from first rel for use in Append */
if (tlist == NIL)
tlist = subplan->targetlist;
}
/* Save the target-relations list for the executor, too */
parse->resultRelations = inheritlist;
/* Mark result as unordered (probably unnecessary) */
parse->query_pathkeys = NIL;
return (Plan *) make_append(subplans, true, tlist);
}
/*--------------------
* grouping_planner
* Perform planning steps related to grouping, aggregation, etc.
* This primarily means adding top-level processing to the basic
* query plan produced by query_planner.
*
* parse is the querytree produced by the parser & rewriter.
* tuple_fraction is the fraction of tuples we expect will be retrieved
*
* tuple_fraction is interpreted as follows:
* < 0: determine fraction by inspection of query (normal case)
* 0: expect all tuples to be retrieved
* 0 < tuple_fraction < 1: expect the given fraction of tuples available
* from the plan to be retrieved
* tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
* expected to be retrieved (ie, a LIMIT specification)
* The normal case is to pass -1, but some callers pass values >= 0 to
* override this routine's determination of the appropriate fraction.
*
* Returns a query plan. Also, parse->query_pathkeys is returned as the
* actual output ordering of the plan (in pathkey format).
*--------------------
*/
static Plan *
grouping_planner(Query *parse, double tuple_fraction)
{
List *tlist = parse->targetList;
Plan *result_plan;
List *current_pathkeys;
List *sort_pathkeys;
if (parse->setOperations)
{
/*
* Construct the plan for set operations. The result will not
* need any work except perhaps a top-level sort and/or LIMIT.
*/
result_plan = plan_set_operations(parse);
/*
* We should not need to call preprocess_targetlist, since we must
* be in a SELECT query node. Instead, use the targetlist
* returned by plan_set_operations (since this tells whether it
* returned any resjunk columns!), and transfer any sort key
* information from the original tlist.
*/
Assert(parse->commandType == CMD_SELECT);
tlist = postprocess_setop_tlist(result_plan->targetlist, tlist);
/*
* Can't handle FOR UPDATE here (parser should have checked
* already, but let's make sure).
*/
if (parse->rowMarks)
elog(ERROR, "SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT");
/*
* We set current_pathkeys NIL indicating we do not know sort
* order. This is correct when the top set operation is UNION
* ALL, since the appended-together results are unsorted even if
* the subplans were sorted. For other set operations we could be
* smarter --- room for future improvement!
*/
current_pathkeys = NIL;
/*
* Calculate pathkeys that represent ordering requirements
*/
sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
tlist);
sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
}
else
{
/* No set operations, do regular planning */
List *sub_tlist;
List *group_pathkeys;
AttrNumber *groupColIdx = NULL;
bool need_tlist_eval = true;
QualCost tlist_cost;
double sub_tuple_fraction;
Path *cheapest_path;
Path *sorted_path;
double dNumGroups = 0;
long numGroups = 0;
int numAggs = 0;
int numGroupCols = length(parse->groupClause);
bool use_hashed_grouping = false;
/* Preprocess targetlist in case we are inside an INSERT/UPDATE. */
tlist = preprocess_targetlist(tlist,
parse->commandType,
parse->resultRelation,
parse->rtable);
/*
* Add TID targets for rels selected FOR UPDATE (should this be
* done in preprocess_targetlist?). The executor uses the TID to
* know which rows to lock, much as for UPDATE or DELETE.
*/
if (parse->rowMarks)
{
List *l;
/*
* We've got trouble if the FOR UPDATE appears inside
* grouping, since grouping renders a reference to individual
* tuple CTIDs invalid. This is also checked at parse time,
* but that's insufficient because of rule substitution, query
* pullup, etc.
*/
CheckSelectForUpdate(parse);
/*
* Currently the executor only supports FOR UPDATE at top
* level
*/
if (PlannerQueryLevel > 1)
elog(ERROR, "SELECT FOR UPDATE is not allowed in subselects");
foreach(l, parse->rowMarks)
{
Index rti = lfirsti(l);
char *resname;
Resdom *resdom;
Var *var;
TargetEntry *ctid;
resname = (char *) palloc(32);
snprintf(resname, 32, "ctid%u", rti);
resdom = makeResdom(length(tlist) + 1,
TIDOID,
-1,
resname,
true);
var = makeVar(rti,
SelfItemPointerAttributeNumber,
TIDOID,
-1,
0);
ctid = makeTargetEntry(resdom, (Expr *) var);
tlist = lappend(tlist, ctid);
}
}
/*
* Generate appropriate target list for subplan; may be different
* from tlist if grouping or aggregation is needed.
*/
sub_tlist = make_subplanTargetList(parse, tlist,
&groupColIdx, &need_tlist_eval);
/*
* Calculate pathkeys that represent grouping/ordering
* requirements
*/
group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause,
tlist);
sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
tlist);
/*
* Will need actual number of aggregates for estimating costs.
* Also, it's possible that optimization has eliminated all
* aggregates, and we may as well check for that here.
*
* Note: we do not attempt to detect duplicate aggregates here;
* a somewhat-overestimated count is okay for our present purposes.
*/
if (parse->hasAggs)
{
numAggs = count_agg_clause((Node *) tlist) +
count_agg_clause(parse->havingQual);
if (numAggs == 0)
parse->hasAggs = false;
}
/*
* Figure out whether we need a sorted result from query_planner.
*
* If we have a GROUP BY clause, then we want a result sorted
* properly for grouping. Otherwise, if there is an ORDER BY
* clause, we want to sort by the ORDER BY clause. (Note: if we
* have both, and ORDER BY is a superset of GROUP BY, it would be
* tempting to request sort by ORDER BY --- but that might just
* leave us failing to exploit an available sort order at all.
* Needs more thought...)
*/
if (parse->groupClause)
parse->query_pathkeys = group_pathkeys;
else if (parse->sortClause)
parse->query_pathkeys = sort_pathkeys;
else
parse->query_pathkeys = NIL;
/*
* Figure out whether we expect to retrieve all the tuples that
* the plan can generate, or to stop early due to outside factors
* such as a cursor. If the caller passed a value >= 0, believe
* that value, else do our own examination of the query context.
*/
if (tuple_fraction < 0.0)
{
/* Initial assumption is we need all the tuples */
tuple_fraction = 0.0;
/*
* Check for retrieve-into-portal, ie DECLARE CURSOR.
*
* We have no real idea how many tuples the user will ultimately
* FETCH from a cursor, but it seems a good bet that he
* doesn't want 'em all. Optimize for 10% retrieval (you
* gotta better number? Should this be a SETtable parameter?)
*/
if (parse->isPortal)
tuple_fraction = 0.10;
}
/*
* Adjust tuple_fraction if we see that we are going to apply
* limiting/grouping/aggregation/etc. This is not overridable by
* the caller, since it reflects plan actions that this routine
* will certainly take, not assumptions about context.
*/
if (parse->limitCount != NULL)
{
/*
* A LIMIT clause limits the absolute number of tuples
* returned. However, if it's not a constant LIMIT then we
* have to punt; for lack of a better idea, assume 10% of the
* plan's result is wanted.
*/
double limit_fraction = 0.0;
if (IsA(parse->limitCount, Const))
{
Const *limitc = (Const *) parse->limitCount;
int32 count = DatumGetInt32(limitc->constvalue);
/*
* A NULL-constant LIMIT represents "LIMIT ALL", which we
* treat the same as no limit (ie, expect to retrieve all
* the tuples).
*/
if (!limitc->constisnull && count > 0)
{
limit_fraction = (double) count;
/* We must also consider the OFFSET, if present */
if (parse->limitOffset != NULL)
{
if (IsA(parse->limitOffset, Const))
{
int32 offset;
limitc = (Const *) parse->limitOffset;
offset = DatumGetInt32(limitc->constvalue);
if (!limitc->constisnull && offset > 0)
limit_fraction += (double) offset;
}
else
{
/* OFFSET is an expression ... punt ... */
limit_fraction = 0.10;
}
}
}
}
else
{
/* LIMIT is an expression ... punt ... */
limit_fraction = 0.10;
}
if (limit_fraction > 0.0)
{
/*
* If we have absolute limits from both caller and LIMIT,
* use the smaller value; if one is fractional and the
* other absolute, treat the fraction as a fraction of the
* absolute value; else we can multiply the two fractions
* together.
*/
if (tuple_fraction >= 1.0)
{
if (limit_fraction >= 1.0)
{
/* both absolute */
tuple_fraction = Min(tuple_fraction, limit_fraction);
}
else
{
/* caller absolute, limit fractional */
tuple_fraction *= limit_fraction;
if (tuple_fraction < 1.0)
tuple_fraction = 1.0;
}
}
else if (tuple_fraction > 0.0)
{
if (limit_fraction >= 1.0)
{
/* caller fractional, limit absolute */
tuple_fraction *= limit_fraction;
if (tuple_fraction < 1.0)
tuple_fraction = 1.0;
}
else
{
/* both fractional */
tuple_fraction *= limit_fraction;
}
}
else
{
/* no info from caller, just use limit */
tuple_fraction = limit_fraction;
}
}
}
/*
* With grouping or aggregation, the tuple fraction to pass to
* query_planner() may be different from what it is at top level.
*/
sub_tuple_fraction = tuple_fraction;
if (parse->groupClause)
{
/*
* In GROUP BY mode, we have the little problem that we don't
* really know how many input tuples will be needed to make a
* group, so we can't translate an output LIMIT count into an
* input count. For lack of a better idea, assume 25% of the
* input data will be processed if there is any output limit.
* However, if the caller gave us a fraction rather than an
* absolute count, we can keep using that fraction (which
* amounts to assuming that all the groups are about the same
* size).
*/
if (sub_tuple_fraction >= 1.0)
sub_tuple_fraction = 0.25;
/*
* If both GROUP BY and ORDER BY are specified, we will need
* two levels of sort --- and, therefore, certainly need to
* read all the input tuples --- unless ORDER BY is a subset
* of GROUP BY. (We have not yet canonicalized the pathkeys,
* so must use the slower noncanonical comparison method.)
*/
if (parse->groupClause && parse->sortClause &&
!noncanonical_pathkeys_contained_in(sort_pathkeys,
group_pathkeys))
sub_tuple_fraction = 0.0;
}
else if (parse->hasAggs)
{
/*
* Ungrouped aggregate will certainly want all the input
* tuples.
*/
sub_tuple_fraction = 0.0;
}
else if (parse->distinctClause)
{
/*
* SELECT DISTINCT, like GROUP, will absorb an unpredictable
* number of input tuples per output tuple. Handle the same
* way.
*/
if (sub_tuple_fraction >= 1.0)
sub_tuple_fraction = 0.25;
}
/*
* Generate the best unsorted and presorted paths for this Query
* (but note there may not be any presorted path).
*/
query_planner(parse, sub_tlist, sub_tuple_fraction,
&cheapest_path, &sorted_path);
/*
* We couldn't canonicalize group_pathkeys and sort_pathkeys before
* running query_planner(), so do it now.
*/
group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys);
sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
/*
* Consider whether we might want to use hashed grouping.
*/
if (parse->groupClause)
{
List *groupExprs;
/*
* Always estimate the number of groups. We can't do this until
* after running query_planner(), either.
*/
groupExprs = get_sortgrouplist_exprs(parse->groupClause,
parse->targetList);
dNumGroups = estimate_num_groups(parse,
groupExprs,
cheapest_path->parent->rows);
/* Also want it as a long int --- but 'ware overflow! */
numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
/*
* Check can't-do-it conditions, including whether the grouping
* operators are hashjoinable.
*
* Executor doesn't support hashed aggregation with DISTINCT
* aggregates. (Doing so would imply storing *all* the input
* values in the hash table, which seems like a certain loser.)
*/
if (!enable_hashagg || !hash_safe_grouping(parse))
use_hashed_grouping = false;
else if (parse->hasAggs &&
(contain_distinct_agg_clause((Node *) tlist) ||
contain_distinct_agg_clause(parse->havingQual)))
use_hashed_grouping = false;
else
{
/*
* Use hashed grouping if (a) we think we can fit the
* hashtable into SortMem, *and* (b) the estimated cost
* is no more than doing it the other way. While avoiding
* the need for sorted input is usually a win, the fact
* that the output won't be sorted may be a loss; so we
* need to do an actual cost comparison.
*
* In most cases we have no good way to estimate the size of
* the transition value needed by an aggregate; arbitrarily
* assume it is 100 bytes. Also set the overhead per hashtable
* entry at 64 bytes.
*/
int hashentrysize = cheapest_path->parent->width + 64 +
numAggs * 100;
if (hashentrysize * dNumGroups <= SortMem * 1024L)
{
/*
* Okay, do the cost comparison. We need to consider
* cheapest_path + hashagg [+ final sort]
* versus either
* cheapest_path [+ sort] + group or agg [+ final sort]
* or
* presorted_path + group or agg [+ final sort]
* where brackets indicate a step that may not be needed.
* We assume query_planner() will have returned a
* presorted path only if it's a winner compared to
* cheapest_path for this purpose.
*
* These path variables are dummies that just hold cost
* fields; we don't make actual Paths for these steps.
*/
Path hashed_p;
Path sorted_p;
cost_agg(&hashed_p, parse,
AGG_HASHED, numAggs,
numGroupCols, dNumGroups,
cheapest_path->startup_cost,
cheapest_path->total_cost,
cheapest_path->parent->rows);
/* Result of hashed agg is always unsorted */
if (sort_pathkeys)
cost_sort(&hashed_p, parse, sort_pathkeys,
hashed_p.total_cost,
dNumGroups,
cheapest_path->parent->width);
if (sorted_path)
{
sorted_p.startup_cost = sorted_path->startup_cost;
sorted_p.total_cost = sorted_path->total_cost;
current_pathkeys = sorted_path->pathkeys;
}
else
{
sorted_p.startup_cost = cheapest_path->startup_cost;
sorted_p.total_cost = cheapest_path->total_cost;
current_pathkeys = cheapest_path->pathkeys;
}
if (!pathkeys_contained_in(group_pathkeys,
current_pathkeys))
{
cost_sort(&sorted_p, parse, group_pathkeys,
sorted_p.total_cost,
cheapest_path->parent->rows,
cheapest_path->parent->width);
current_pathkeys = group_pathkeys;
}
if (parse->hasAggs)
cost_agg(&sorted_p, parse,
AGG_SORTED, numAggs,
numGroupCols, dNumGroups,
sorted_p.startup_cost,
sorted_p.total_cost,
cheapest_path->parent->rows);
else
cost_group(&sorted_p, parse,
numGroupCols, dNumGroups,
sorted_p.startup_cost,
sorted_p.total_cost,
cheapest_path->parent->rows);
/* The Agg or Group node will preserve ordering */
if (sort_pathkeys &&
!pathkeys_contained_in(sort_pathkeys,
current_pathkeys))
{
cost_sort(&sorted_p, parse, sort_pathkeys,
sorted_p.total_cost,
dNumGroups,
cheapest_path->parent->width);
}
/*
* Now make the decision using the top-level tuple
* fraction. First we have to convert an absolute
* count (LIMIT) into fractional form.
*/
if (tuple_fraction >= 1.0)
tuple_fraction /= dNumGroups;
if (compare_fractional_path_costs(&hashed_p, &sorted_p,
tuple_fraction) < 0)
{
/* Hashed is cheaper, so use it */
use_hashed_grouping = true;
}
}
}
}
/*
* Select the best path and create a plan to execute it.
*
* If we are doing hashed grouping, we will always read all the
* input tuples, so use the cheapest-total path. Otherwise,
* trust query_planner's decision about which to use.
*/
if (sorted_path && !use_hashed_grouping)
{
result_plan = create_plan(parse, sorted_path);
current_pathkeys = sorted_path->pathkeys;
}
else
{
result_plan = create_plan(parse, cheapest_path);
current_pathkeys = cheapest_path->pathkeys;
}
/*
* create_plan() returns a plan with just a "flat" tlist of required
* Vars. Usually we need to insert the sub_tlist as the tlist of the
* top plan node. However, we can skip that if we determined that
* whatever query_planner chose to return will be good enough.
*/
if (need_tlist_eval)
{
/*
* If the top-level plan node is one that cannot do expression
* evaluation, we must insert a Result node to project the desired
* tlist.
* Currently, the only plan node we might see here that falls into
* that category is Append.
*/
if (IsA(result_plan, Append))
{
result_plan = (Plan *) make_result(sub_tlist, NULL,
result_plan);
}
else
{
/*
* Otherwise, just replace the subplan's flat tlist with
* the desired tlist.
*/
result_plan->targetlist = sub_tlist;
}
/*
* Also, account for the cost of evaluation of the sub_tlist.
*
* Up to now, we have only been dealing with "flat" tlists,
* containing just Vars. So their evaluation cost is zero
* according to the model used by cost_qual_eval() (or if you
* prefer, the cost is factored into cpu_tuple_cost). Thus we can
* avoid accounting for tlist cost throughout query_planner() and
* subroutines. But now we've inserted a tlist that might contain
* actual operators, sub-selects, etc --- so we'd better account
* for its cost.
*
* Below this point, any tlist eval cost for added-on nodes should
* be accounted for as we create those nodes. Presently, of the
* node types we can add on, only Agg and Group project new tlists
* (the rest just copy their input tuples) --- so make_agg() and
* make_group() are responsible for computing the added cost.
*/
cost_qual_eval(&tlist_cost, sub_tlist);
result_plan->startup_cost += tlist_cost.startup;
result_plan->total_cost += tlist_cost.startup +
tlist_cost.per_tuple * result_plan->plan_rows;
}
else
{
/*
* Since we're using query_planner's tlist and not the one
* make_subplanTargetList calculated, we have to refigure
* any grouping-column indexes make_subplanTargetList computed.
*/
locate_grouping_columns(parse, tlist, result_plan->targetlist,
groupColIdx);
}
/*
* Insert AGG or GROUP node if needed, plus an explicit sort step
* if necessary.
*
* HAVING clause, if any, becomes qual of the Agg node
*/
if (use_hashed_grouping)
{
/* Hashed aggregate plan --- no sort needed */
result_plan = (Plan *) make_agg(parse,
tlist,
(List *) parse->havingQual,
AGG_HASHED,
numGroupCols,
groupColIdx,
numGroups,
numAggs,
result_plan);
/* Hashed aggregation produces randomly-ordered results */
current_pathkeys = NIL;
}
else if (parse->hasAggs)
{
/* Plain aggregate plan --- sort if needed */
AggStrategy aggstrategy;
if (parse->groupClause)
{
if (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
{
result_plan = make_groupsortplan(parse,
parse->groupClause,
groupColIdx,
result_plan);
current_pathkeys = group_pathkeys;
}
aggstrategy = AGG_SORTED;
/*
* The AGG node will not change the sort ordering of its
* groups, so current_pathkeys describes the result too.
*/
}
else
{
aggstrategy = AGG_PLAIN;
/* Result will be only one row anyway; no sort order */
current_pathkeys = NIL;
}
result_plan = (Plan *) make_agg(parse,
tlist,
(List *) parse->havingQual,
aggstrategy,
numGroupCols,
groupColIdx,
numGroups,
numAggs,
result_plan);
}
else
{
/*
* If there are no Aggs, we shouldn't have any HAVING qual anymore
*/
Assert(parse->havingQual == NULL);
/*
* If we have a GROUP BY clause, insert a group node (plus the
* appropriate sort node, if necessary).
*/
if (parse->groupClause)
{
/*
* Add an explicit sort if we couldn't make the path come out
* the way the GROUP node needs it.
*/
if (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
{
result_plan = make_groupsortplan(parse,
parse->groupClause,
groupColIdx,
result_plan);
current_pathkeys = group_pathkeys;
}
result_plan = (Plan *) make_group(parse,
tlist,
numGroupCols,
groupColIdx,
dNumGroups,
result_plan);
/* The Group node won't change sort ordering */
}
}
} /* end of if (setOperations) */
/*
* If we were not able to make the plan come out in the right order,
* add an explicit sort step.
*/
if (parse->sortClause)
{
if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys))
{
result_plan = (Plan *) make_sort_from_sortclauses(parse,
tlist,
result_plan,
parse->sortClause);
current_pathkeys = sort_pathkeys;
}
}
/*
* If there is a DISTINCT clause, add the UNIQUE node.
*/
if (parse->distinctClause)
{
result_plan = (Plan *) make_unique(tlist, result_plan,
parse->distinctClause);
/*
* If there was grouping or aggregation, leave plan_rows as-is
* (ie, assume the result was already mostly unique). If not,
* it's reasonable to assume the UNIQUE filter has effects
* comparable to GROUP BY.
*/
if (!parse->groupClause && !parse->hasAggs)
{
List *distinctExprs;
distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
parse->targetList);
result_plan->plan_rows = estimate_num_groups(parse,
distinctExprs,
result_plan->plan_rows);
}
}
/*
* Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
*/
if (parse->limitOffset || parse->limitCount)
{
result_plan = (Plan *) make_limit(tlist, result_plan,
parse->limitOffset,
parse->limitCount);
}
/*
* Return the actual output ordering in query_pathkeys for possible
* use by an outer query level.
*/
parse->query_pathkeys = current_pathkeys;
return result_plan;
}
/*
* hash_safe_grouping - are grouping operators hashable?
*
* We assume hashed aggregation will work if the datatype's equality operator
* is marked hashjoinable.
*/
static bool
hash_safe_grouping(Query *parse)
{
List *gl;
foreach(gl, parse->groupClause)
{
GroupClause *grpcl = (GroupClause *) lfirst(gl);
TargetEntry *tle = get_sortgroupclause_tle(grpcl, parse->targetList);
Operator optup;
bool oprcanhash;
optup = equality_oper(tle->resdom->restype, false);
oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash;
ReleaseSysCache(optup);
if (!oprcanhash)
return false;
}
return true;
}
/*---------------
* make_subplanTargetList
* Generate appropriate target list when grouping is required.
*
* When grouping_planner inserts Aggregate or Group plan nodes above
* the result of query_planner, we typically want to pass a different
* target list to query_planner than the outer plan nodes should have.
* This routine generates the correct target list for the subplan.
*
* The initial target list passed from the parser already contains entries
* for all ORDER BY and GROUP BY expressions, but it will not have entries
* for variables used only in HAVING clauses; so we need to add those
* variables to the subplan target list. Also, if we are doing either
* grouping or aggregation, we flatten all expressions except GROUP BY items
* into their component variables; the other expressions will be computed by
* the inserted nodes rather than by the subplan. For example,
* given a query like
* SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
* we want to pass this targetlist to the subplan:
* a,b,c,d,a+b
* where the a+b target will be used by the Sort/Group steps, and the
* other targets will be used for computing the final results. (In the
* above example we could theoretically suppress the a and b targets and
* pass down only c,d,a+b, but it's not really worth the trouble to
* eliminate simple var references from the subplan. We will avoid doing
* the extra computation to recompute a+b at the outer level; see
* replace_vars_with_subplan_refs() in setrefs.c.)
*
* If we are grouping or aggregating, *and* there are no non-Var grouping
* expressions, then the returned tlist is effectively dummy; we do not
* need to force it to be evaluated, because all the Vars it contains
* should be present in the output of query_planner anyway.
*
* 'parse' is the query being processed.
* 'tlist' is the query's target list.
* 'groupColIdx' receives an array of column numbers for the GROUP BY
* expressions (if there are any) in the subplan's target list.
* 'need_tlist_eval' is set true if we really need to evaluate the
* result tlist.
*
* The result is the targetlist to be passed to the subplan.
*---------------
*/
static List *
make_subplanTargetList(Query *parse,
List *tlist,
AttrNumber **groupColIdx,
bool *need_tlist_eval)
{
List *sub_tlist;
List *extravars;
int numCols;
*groupColIdx = NULL;
/*
* If we're not grouping or aggregating, nothing to do here;
* query_planner should receive the unmodified target list.
*/
if (!parse->hasAggs && !parse->groupClause && !parse->havingQual)
{
*need_tlist_eval = true;
return tlist;
}
/*
* Otherwise, start with a "flattened" tlist (having just the vars
* mentioned in the targetlist and HAVING qual --- but not upper-
* level Vars; they will be replaced by Params later on).
*/
sub_tlist = flatten_tlist(tlist);
extravars = pull_var_clause(parse->havingQual, false);
sub_tlist = add_to_flat_tlist(sub_tlist, extravars);
freeList(extravars);
*need_tlist_eval = false; /* only eval if not flat tlist */
/*
* If grouping, create sub_tlist entries for all GROUP BY expressions
* (GROUP BY items that are simple Vars should be in the list
* already), and make an array showing where the group columns are in
* the sub_tlist.
*/
numCols = length(parse->groupClause);
if (numCols > 0)
{
int keyno = 0;
AttrNumber *grpColIdx;
List *gl;
grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
*groupColIdx = grpColIdx;
foreach(gl, parse->groupClause)
{
GroupClause *grpcl = (GroupClause *) lfirst(gl);
Node *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
TargetEntry *te = NULL;
List *sl;
/* Find or make a matching sub_tlist entry */
foreach(sl, sub_tlist)
{
te = (TargetEntry *) lfirst(sl);
if (equal(groupexpr, te->expr))
break;
}
if (!sl)
{
te = makeTargetEntry(makeResdom(length(sub_tlist) + 1,
exprType(groupexpr),
exprTypmod(groupexpr),
NULL,
false),
(Expr *) groupexpr);
sub_tlist = lappend(sub_tlist, te);
*need_tlist_eval = true; /* it's not flat anymore */
}
/* and save its resno */
grpColIdx[keyno++] = te->resdom->resno;
}
}
return sub_tlist;
}
/*
* locate_grouping_columns
* Locate grouping columns in the tlist chosen by query_planner.
*
* This is only needed if we don't use the sub_tlist chosen by
* make_subplanTargetList. We have to forget the column indexes found
* by that routine and re-locate the grouping vars in the real sub_tlist.
*/
static void
locate_grouping_columns(Query *parse,
List *tlist,
List *sub_tlist,
AttrNumber *groupColIdx)
{
int keyno = 0;
List *gl;
/*
* No work unless grouping.
*/
if (!parse->groupClause)
{
Assert(groupColIdx == NULL);
return;
}
Assert(groupColIdx != NULL);
foreach(gl, parse->groupClause)
{
GroupClause *grpcl = (GroupClause *) lfirst(gl);
Node *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
TargetEntry *te = NULL;
List *sl;
foreach(sl, sub_tlist)
{
te = (TargetEntry *) lfirst(sl);
if (equal(groupexpr, te->expr))
break;
}
if (!sl)
elog(ERROR, "locate_grouping_columns: failed");
groupColIdx[keyno++] = te->resdom->resno;
}
}
/*
* make_groupsortplan
* Add a Sort node to explicitly sort according to the GROUP BY clause.
*
* Note: the Sort node always just takes a copy of the subplan's tlist
* plus ordering information. (This might seem inefficient if the
* subplan contains complex GROUP BY expressions, but in fact Sort
* does not evaluate its targetlist --- it only outputs the same
* tuples in a new order. So the expressions we might be copying
* are just dummies with no extra execution cost.)
*/
static Plan *
make_groupsortplan(Query *parse,
List *groupClause,
AttrNumber *grpColIdx,
Plan *subplan)
{
List *sort_tlist = new_unsorted_tlist(subplan->targetlist);
int keyno = 0;
List *gl;
foreach(gl, groupClause)
{
GroupClause *grpcl = (GroupClause *) lfirst(gl);
TargetEntry *te = nth(grpColIdx[keyno] - 1, sort_tlist);
Resdom *resdom = te->resdom;
/*
* Check for the possibility of duplicate group-by clauses ---
* the parser should have removed 'em, but the Sort executor
* will get terribly confused if any get through!
*/
if (resdom->reskey == 0)
{
/* OK, insert the ordering info needed by the executor. */
resdom->reskey = ++keyno;
resdom->reskeyop = grpcl->sortop;
}
}
Assert(keyno > 0);
return (Plan *) make_sort(parse, sort_tlist, subplan, keyno);
}
/*
* postprocess_setop_tlist
* Fix up targetlist returned by plan_set_operations().
*
* We need to transpose sort key info from the orig_tlist into new_tlist.
* NOTE: this would not be good enough if we supported resjunk sort keys
* for results of set operations --- then, we'd need to project a whole
* new tlist to evaluate the resjunk columns. For now, just elog if we
* find any resjunk columns in orig_tlist.
*/
static List *
postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
{
List *l;
foreach(l, new_tlist)
{
TargetEntry *new_tle = (TargetEntry *) lfirst(l);
TargetEntry *orig_tle;
/* ignore resjunk columns in setop result */
if (new_tle->resdom->resjunk)
continue;
Assert(orig_tlist != NIL);
orig_tle = (TargetEntry *) lfirst(orig_tlist);
orig_tlist = lnext(orig_tlist);
if (orig_tle->resdom->resjunk)
elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented");
Assert(new_tle->resdom->resno == orig_tle->resdom->resno);
Assert(new_tle->resdom->restype == orig_tle->resdom->restype);
new_tle->resdom->ressortgroupref = orig_tle->resdom->ressortgroupref;
}
if (orig_tlist != NIL)
elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented");
return new_tlist;
}
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