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openGauss-server/src/gausskernel/optimizer/path/pathkeys.cpp

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/* -------------------------------------------------------------------------
*
* pathkeys.cpp
* Utilities for matching and building path keys
*
* Portions Copyright (c) 2020 Huawei Technologies Co.,Ltd.
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/gausskernel/optimizer/path/pathkeys.cpp
*
* -------------------------------------------------------------------------
*/
#include "postgres.h"
#include "knl/knl_variable.h"
#include "access/skey.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/clauses.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/streamplan.h"
#include "optimizer/tlist.h"
#include "pgxc/pgxc.h"
#include "utils/lsyscache.h"
static PathKey* make_canonical_pathkey(
PlannerInfo* root, EquivalenceClass* eclass, Oid opfamily, int strategy, bool nulls_first);
static bool pathkey_is_redundant(PathKey* new_pathkey, List* pathkeys);
static bool right_merge_direction(PlannerInfo* root, PathKey* pathkey);
/****************************************************************************
* PATHKEY CONSTRUCTION AND REDUNDANCY TESTING
****************************************************************************/
/*
* make_canonical_pathkey
* Given the parameters for a PathKey, find any pre-existing matching
* pathkey in the query's list of "canonical" pathkeys. Make a new
* entry if there's not one already.
*
* Note that this function must not be used until after we have completed
* merging EquivalenceClasses.
*/
static PathKey* make_canonical_pathkey(
PlannerInfo* root, EquivalenceClass* eclass, Oid opfamily, int strategy, bool nulls_first)
{
PathKey* pk = NULL;
ListCell* lc = NULL;
MemoryContext oldcontext;
/* The passed eclass might be non-canonical, so chase up to the top */
while (eclass->ec_merged)
eclass = eclass->ec_merged;
foreach (lc, root->canon_pathkeys) {
/* Here need ensure ec_group_set be also equal. */
pk = (PathKey*)lfirst(lc);
if (eclass == pk->pk_eclass && eclass->ec_group_set == pk->pk_eclass->ec_group_set &&
opfamily == pk->pk_opfamily && strategy == pk->pk_strategy && nulls_first == pk->pk_nulls_first)
return pk;
}
/*
* Be sure canonical pathkeys are allocated in the main planning context.
* Not an issue in normal planning, but it is for GEQO.
*/
oldcontext = MemoryContextSwitchTo(root->planner_cxt);
pk = makeNode(PathKey);
pk->pk_eclass = eclass;
pk->pk_opfamily = opfamily;
pk->pk_strategy = strategy;
pk->pk_nulls_first = nulls_first;
root->canon_pathkeys = lappend(root->canon_pathkeys, pk);
(void)MemoryContextSwitchTo(oldcontext);
return pk;
}
/*
* pathkey_is_redundant
* Is a pathkey redundant with one already in the given list?
*
* Both the given pathkey and the list members must be canonical for this
* to work properly. We detect two cases:
*
* 1. If the new pathkey's equivalence class contains a constant, and isn't
* below an outer join, then we can disregard it as a sort key. An example:
* SELECT ... WHERE x = 42 ORDER BY x, y;
* We may as well just sort by y. Note that because of opfamily matching,
* this is semantically correct: we know that the equality constraint is one
* that actually binds the variable to a single value in the terms of any
* ordering operator that might go with the eclass. This rule not only lets
* us simplify (or even skip) explicit sorts, but also allows matching index
* sort orders to a query when there are don't-care index columns.
*
* 2. If the new pathkey's equivalence class is the same as that of any
* existing member of the pathkey list, then it is redundant. Some examples:
* SELECT ... ORDER BY x, x;
* SELECT ... ORDER BY x, x DESC;
* SELECT ... WHERE x = y ORDER BY x, y;
* In all these cases the second sort key cannot distinguish values that are
* considered equal by the first, and so there's no point in using it.
* Note in particular that we need not compare opfamily (all the opfamilies
* of the EC have the same notion of equality) nor sort direction.
*
* Because the equivclass.c machinery forms only one copy of any EC per query,
* pointer comparison is enough to decide whether canonical ECs are the same.
*/
static bool pathkey_is_redundant(PathKey* new_pathkey, List* pathkeys)
{
EquivalenceClass* new_ec = new_pathkey->pk_eclass;
ListCell* lc = NULL;
/* Check for EC containing a constant --- unconditionally redundant */
if (EC_MUST_BE_REDUNDANT(new_ec) && !new_ec->ec_group_set)
return true;
/* If same EC already used in list, then redundant */
foreach (lc, pathkeys) {
PathKey* old_pathkey = (PathKey*)lfirst(lc);
if (new_ec == old_pathkey->pk_eclass)
return true;
}
return false;
}
/*
* canonicalize_pathkeys
* Convert a not-necessarily-canonical pathkeys list to canonical form.
*
* Note that this function must not be used until after we have completed
* merging EquivalenceClasses.
*
* aboveAgg marks whether this operation(sort or window funtion) is above agg.
* For example: select a, sum(b) from t1 group by a order by 1, 2;
* This order by operator is above agg.
*/
List* canonicalize_pathkeys(PlannerInfo* root, List* pathkeys)
{
return list_copy(pathkeys);
}
/*
* make_pathkey_from_sortinfo
* Given an expression and sort-order information, create a PathKey.
* If canonicalize = true, the result is a "canonical" PathKey,
* otherwise not. (But note it might be redundant anyway.)
*
* If the PathKey is being generated from a SortGroupClause, sortref should be
* the SortGroupClause's SortGroupRef; otherwise zero.
*
* If rel is not NULL, it identifies a specific relation we're considering
* a path for, and indicates that child EC members for that relation can be
* considered. Otherwise child members are ignored. (See the comments for
* get_eclass_for_sort_expr.)
*
* create_it is TRUE if we should create any missing EquivalenceClass
* needed to represent the sort key. If it's FALSE, we return NULL if the
* sort key isn't already present in any EquivalenceClass.
*
* canonicalize should always be TRUE after EquivalenceClass merging has
* been performed, but FALSE if we haven't done EquivalenceClass merging yet.
*/
static PathKey* make_pathkey_from_sortinfo(PlannerInfo* root, Expr* expr, Oid opfamily, Oid opcintype, Oid collation,
bool reverse_sort, bool nulls_first, Index sortref, bool groupSet, Relids rel, bool create_it, bool canonicalize)
{
int16 strategy;
Oid equality_op;
List* opfamilies = NIL;
EquivalenceClass* eclass = NULL;
Assert(canonicalize);
strategy = reverse_sort ? BTGreaterStrategyNumber : BTLessStrategyNumber;
/*
* EquivalenceClasses need to contain opfamily lists based on the family
* membership of mergejoinable equality operators, which could belong to
* more than one opfamily. So we have to look up the opfamily's equality
* operator and get its membership.
*/
equality_op = get_opfamily_member(opfamily, opcintype, opcintype, BTEqualStrategyNumber);
if (!OidIsValid(equality_op)) /* shouldn't happen */
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg(
"could not find equality operator for opfamily %u when make pathkey from sortinfo", opfamily))));
opfamilies = get_mergejoin_opfamilies(equality_op);
if (opfamilies == NIL) /* certainly should find some */
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg("could not find opfamilies for equality operator %u when make pathkey from sortinfo",
equality_op))));
/* Now find or (optionally) create a matching EquivalenceClass */
eclass = get_eclass_for_sort_expr(root, expr, opfamilies, opcintype, collation, sortref, groupSet, rel, create_it);
/* Fail if no EC and !create_it */
if (eclass == NULL)
return NULL;
/* And finally we can find or create a PathKey node */
return make_canonical_pathkey(root, eclass, opfamily, strategy, nulls_first);
}
/*
* make_pathkey_from_sortop
* Like make_pathkey_from_sortinfo, but work from a sort operator.
*
* This should eventually go away, but we need to restructure SortGroupClause
* first.
*/
static PathKey* make_pathkey_from_sortop(PlannerInfo* root, Expr* expr, Oid ordering_op, bool nulls_first,
Index sortref, bool groupSet, bool create_it, bool canonicalize)
{
Oid opfamily, opcintype, collation;
int16 strategy;
/* Find the operator in pg_amop --- failure shouldn't happen */
if (!get_ordering_op_properties(ordering_op, &opfamily, &opcintype, &strategy))
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg("operator %u is not a valid ordering operator when make pathkey from sortinfo", ordering_op))));
/* Because SortGroupClause doesn't carry collation, consult the expr */
collation = exprCollation((Node*)expr);
return make_pathkey_from_sortinfo(root,
expr,
opfamily,
opcintype,
collation,
(strategy == BTGreaterStrategyNumber),
nulls_first,
sortref,
groupSet,
NULL,
create_it,
canonicalize);
}
/****************************************************************************
* PATHKEY COMPARISONS
****************************************************************************/
/*
* compare_pathkeys
* Compare two pathkeys to see if they are equivalent, and if not whether
* one is "better" than the other.
*
* This function may only be applied to canonicalized pathkey lists.
* In the canonical representation, pathkeys can be checked for equality
* by simple pointer comparison.
*/
PathKeysComparison compare_pathkeys(List* keys1, List* keys2)
{
ListCell* key1 = NULL;
ListCell* key2 = NULL;
/*
* Fall out quickly if we are passed two identical lists. This mostly
* catches the case where both are NIL, but that's common enough to
* warrant the test.
*/
if (keys1 == keys2)
return PATHKEYS_EQUAL;
forboth(key1, keys1, key2, keys2)
{
PathKey* pathkey1 = (PathKey*)lfirst(key1);
PathKey* pathkey2 = (PathKey*)lfirst(key2);
if (pathkey1 != pathkey2)
return PATHKEYS_DIFFERENT; /* no need to keep looking */
}
/*
* If we reached the end of only one list, the other is longer and
* therefore not a subset.
*/
if (key1 != NULL)
return PATHKEYS_BETTER1; /* key1 is longer */
if (key2 != NULL)
return PATHKEYS_BETTER2; /* key2 is longer */
return PATHKEYS_EQUAL;
}
/*
* pathkeys_contained_in
* Common special case of compare_pathkeys: we just want to know
* if keys2 are at least as well sorted as keys1.
*/
bool pathkeys_contained_in(List* keys1, List* keys2)
{
switch (compare_pathkeys(keys1, keys2)) {
case PATHKEYS_EQUAL:
case PATHKEYS_BETTER2:
return true;
default:
break;
}
return false;
}
/*
* get_cheapest_path_for_pathkeys
* Find the cheapest path (according to the specified criterion) that
* satisfies the given pathkeys and parameterization.
* Return NULL if no such path.
*
* 'paths' is a list of possible paths that all generate the same relation
* 'pathkeys' represents a required ordering (already canonicalized!)
* 'required_outer' denotes allowable outer relations for parameterized paths
* 'cost_criterion' is STARTUP_COST or TOTAL_COST
*/
Path* get_cheapest_path_for_pathkeys(List* paths, List* pathkeys, Relids required_outer, CostSelector cost_criterion)
{
Path* matched_path = NULL;
ListCell* l = NULL;
foreach (l, paths) {
Path* path = (Path*)lfirst(l);
/*
* Since cost comparison is a lot cheaper than pathkey comparison, do
* that first. (XXX is that still true?)
*/
if (matched_path != NULL && compare_path_costs(matched_path, path, cost_criterion) <= 0)
continue;
if (pathkeys_contained_in(pathkeys, path->pathkeys) && bms_is_subset(PATH_REQ_OUTER(path), required_outer))
matched_path = path;
}
return matched_path;
}
/*
* get_cheapest_fractional_path_for_pathkeys
* Find the cheapest path (for retrieving a specified fraction of all
* the tuples) that satisfies the given pathkeys and parameterization.
* Return NULL if no such path.
*
* See compare_fractional_path_costs() for the interpretation of the fraction
* parameter.
*
* 'paths' is a list of possible paths that all generate the same relation
* 'pathkeys' represents a required ordering (already canonicalized!)
* 'required_outer' denotes allowable outer relations for parameterized paths
* 'fraction' is the fraction of the total tuples expected to be retrieved
*/
Path* get_cheapest_fractional_path_for_pathkeys(List* paths, List* pathkeys, Relids required_outer, double fraction)
{
Path* matched_path = NULL;
ListCell* l = NULL;
foreach (l, paths) {
Path* path = (Path*)lfirst(l);
/*
* Since cost comparison is a lot cheaper than pathkey comparison, do
* that first. (XXX is that still true?)
*/
if (matched_path != NULL && compare_fractional_path_costs(matched_path, path, fraction) <= 0)
continue;
if (pathkeys_contained_in(pathkeys, path->pathkeys) && bms_is_subset(PATH_REQ_OUTER(path), required_outer))
matched_path = path;
}
return matched_path;
}
/****************************************************************************
* NEW PATHKEY FORMATION
****************************************************************************/
/*
* build_index_pathkeys
* Build a pathkeys list that describes the ordering induced by an index
* scan using the given index. (Note that an unordered index doesn't
* induce any ordering, so we return NIL.)
*
* If 'scandir' is BackwardScanDirection, build pathkeys representing a
* backwards scan of the index.
*
* We iterate only key columns of covering indexes, since non-key columns
* don't influence index ordering. The result is canonical, meaning that
* redundant pathkeys are removed; it may therefore have fewer entries than
* there are key columns in the index.
*
* Another reason for stopping early is that we may be able to tell that
* an index column's sort order is uninteresting for this query. However,
* that test is just based on the existence of an EquivalenceClass and not
* on position in pathkey lists, so it's not complete. Caller should call
* truncate_useless_pathkeys() to possibly remove more pathkeys.
*/
List* build_index_pathkeys(PlannerInfo* root, IndexOptInfo* index, ScanDirection scandir)
{
List* retval = NIL;
ListCell* lc = NULL;
int i;
if (index->sortopfamily == NULL)
return NIL; /* non-orderable index */
i = 0;
foreach (lc, index->indextlist) {
TargetEntry* indextle = (TargetEntry*)lfirst(lc);
Expr* indexkey = NULL;
bool reverse_sort = false;
bool nulls_first = false;
PathKey* cpathkey = NULL;
/*
* INCLUDE columns are stored in index unordered, so they don't
* support ordered index scan.
*/
if (i >= index->nkeycolumns) {
break;
}
/* We assume we don't need to make a copy of the tlist item */
indexkey = indextle->expr;
if (ScanDirectionIsBackward(scandir)) {
reverse_sort = !index->reverse_sort[i];
nulls_first = !index->nulls_first[i];
} else {
reverse_sort = index->reverse_sort[i];
nulls_first = index->nulls_first[i];
}
/* OK, try to make a canonical pathkey for this sort key */
cpathkey = make_pathkey_from_sortinfo(root,
indexkey,
index->sortopfamily[i],
index->opcintype[i],
index->indexcollations[i],
reverse_sort,
nulls_first,
0,
false,
index->rel->relids,
false,
true);
/*
* If the sort key isn't already present in any EquivalenceClass, then
* it's not an interesting sort order for this query. So we can stop
* now --- lower-order sort keys aren't useful either.
*/
if (cpathkey == NULL)
break;
/* Add to list unless redundant */
if (!pathkey_is_redundant(cpathkey, retval))
retval = lappend(retval, cpathkey);
i++;
}
return retval;
}
/*
* convert_subquery_pathkeys
* Build a pathkeys list that describes the ordering of a subquery's
* result, in the terms of the outer query. This is essentially a
* task of conversion.
*
* 'rel': outer query's RelOptInfo for the subquery relation.
* 'subquery_pathkeys': the subquery's output pathkeys, in its terms.
*
* It is not necessary for caller to do truncate_useless_pathkeys(),
* because we select keys in a way that takes usefulness of the keys into
* account.
*/
List* convert_subquery_pathkeys(PlannerInfo* root, RelOptInfo* rel, List* subquery_pathkeys)
{
List* retval = NIL;
int retvallen = 0;
int outer_query_keys = list_length(root->query_pathkeys);
List* sub_tlist = rel->subplan->targetlist;
ListCell* i = NULL;
foreach (i, subquery_pathkeys) {
PathKey* sub_pathkey = (PathKey*)lfirst(i);
EquivalenceClass* sub_eclass = sub_pathkey->pk_eclass;
PathKey* best_pathkey = NULL;
if (sub_eclass->ec_has_volatile) {
/*
* If the sub_pathkey's EquivalenceClass is volatile, then it must
* have come from an ORDER BY clause, and we have to match it to
* that same targetlist entry.
*/
TargetEntry* tle = NULL;
if (sub_eclass->ec_sortref == 0) /* can't happen */
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg("volatile EquivalenceClass has no sortref when convert subquery pathkeys"))));
tle = get_sortgroupref_tle(sub_eclass->ec_sortref, sub_tlist);
AssertEreport(tle != NULL, MOD_OPT, "tle is NULL");
/* resjunk items aren't visible to outer query */
if (!tle->resjunk) {
/* We can represent this sub_pathkey */
EquivalenceMember* sub_member = NULL;
Expr* outer_expr = NULL;
EquivalenceClass* outer_ec = NULL;
AssertEreport(list_length(sub_eclass->ec_members) == 1, MOD_OPT, "ec member number is not 1");
sub_member = (EquivalenceMember*)linitial(sub_eclass->ec_members);
outer_expr = (Expr*)makeVarFromTargetEntry(rel->relid, tle);
/*
* Note: it might look funny to be setting sortref = 0 for a
* reference to a volatile sub_eclass. However, the
* expression is *not* volatile in the outer query: it's just
* a Var referencing whatever the subquery emitted. (IOW, the
* outer query isn't going to re-execute the volatile
* expression itself.) So this is okay.
*/
outer_ec = get_eclass_for_sort_expr(root,
outer_expr,
sub_eclass->ec_opfamilies,
sub_member->em_datatype,
sub_eclass->ec_collation,
0,
false,
rel->relids,
false);
/*
* If we don't find a matching EC, sub-pathkey isn't
* interesting to the outer query
*/
if (outer_ec != NULL)
best_pathkey = make_canonical_pathkey(root,
outer_ec,
sub_pathkey->pk_opfamily,
sub_pathkey->pk_strategy,
sub_pathkey->pk_nulls_first);
}
} else {
/*
* Otherwise, the sub_pathkey's EquivalenceClass could contain
* multiple elements (representing knowledge that multiple items
* are effectively equal). Each element might match none, one, or
* more of the output columns that are visible to the outer query.
* This means we may have multiple possible representations of the
* sub_pathkey in the context of the outer query. Ideally we
* would generate them all and put them all into an EC of the
* outer query, thereby propagating equality knowledge up to the
* outer query. Right now we cannot do so, because the outer
* query's EquivalenceClasses are already frozen when this is
* called. Instead we prefer the one that has the highest "score"
* (number of EC peers, plus one if it matches the outer
* query_pathkeys). This is the most likely to be useful in the
* outer query.
*/
int best_score = -1;
ListCell* j = NULL;
foreach (j, sub_eclass->ec_members) {
EquivalenceMember* sub_member = (EquivalenceMember*)lfirst(j);
Expr* sub_expr = sub_member->em_expr;
Oid sub_expr_type = sub_member->em_datatype;
Oid sub_expr_coll = sub_eclass->ec_collation;
ListCell* k = NULL;
int seq = 0;
if (sub_member->em_is_child)
continue; /* ignore children here */
foreach (k, sub_tlist) {
TargetEntry* tle = (TargetEntry*)lfirst(k);
Expr* tle_expr = NULL;
Expr* outer_expr = NULL;
EquivalenceClass* outer_ec = NULL;
PathKey* outer_pk = NULL;
int score;
ListCell* lc = NULL;
seq++;
/* resjunk items aren't visible to outer query */
if (tle->resjunk)
continue;
/* check if targetentry exists in final subquery targetlist */
foreach (lc, rel->reltargetlist) {
Node* n = (Node*)lfirst(lc);
if (IsA(n, Var) && ((Var*)n)->varattno == seq)
break;
}
if (lc == NULL)
continue;
/*
* The targetlist entry is considered to match if it
* matches after sort-key canonicalization. That is
* needed since the sub_expr has been through the same
* process.
*/
tle_expr = canonicalize_ec_expression(tle->expr, sub_expr_type, sub_expr_coll);
if (!equal(tle_expr, sub_expr))
continue;
/*
* Build a representation of this targetlist entry as an
* outer Var.
*/
outer_expr = (Expr*)makeVarFromTargetEntry(rel->relid, tle);
/* See if we have a matching EC for that */
outer_ec = get_eclass_for_sort_expr(root,
outer_expr,
sub_eclass->ec_opfamilies,
sub_expr_type,
sub_expr_coll,
0,
false,
rel->relids,
false);
/*
* If we don't find a matching EC, this sub-pathkey isn't
* interesting to the outer query
*/
if (outer_ec == NULL)
continue;
outer_pk = make_canonical_pathkey(root,
outer_ec,
sub_pathkey->pk_opfamily,
sub_pathkey->pk_strategy,
sub_pathkey->pk_nulls_first);
/* score = # of equivalence peers */
score = list_length(outer_ec->ec_members) - 1;
/* +1 if it matches the proper query_pathkeys item */
if (retvallen < outer_query_keys && list_nth(root->query_pathkeys, retvallen) == outer_pk)
score++;
if (score > best_score) {
best_pathkey = outer_pk;
best_score = score;
}
}
}
}
/*
* If we couldn't find a representation of this sub_pathkey, we're
* done (we can't use the ones to its right, either).
*/
if (best_pathkey == NULL)
break;
/*
* Eliminate redundant ordering info; could happen if outer query
* equivalences subquery keys...
*/
if (!pathkey_is_redundant(best_pathkey, retval)) {
retval = lappend(retval, best_pathkey);
retvallen++;
}
}
return retval;
}
/*
* build_join_pathkeys
* Build the path keys for a join relation constructed by mergejoin or
* nestloop join. This is normally the same as the outer path's keys.
*
* EXCEPTION: in a FULL or RIGHT join, we cannot treat the result as
* having the outer path's path keys, because null lefthand rows may be
* inserted at random points. It must be treated as unsorted.
*
* We truncate away any pathkeys that are uninteresting for higher joins.
*
* 'joinrel' is the join relation that paths are being formed for
* 'jointype' is the join type (inner, left, full, etc)
* 'outer_pathkeys' is the list of the current outer path's path keys
*
* Returns the list of new path keys.
*/
List* build_join_pathkeys(PlannerInfo* root, RelOptInfo* joinrel, JoinType jointype, List* outer_pathkeys)
{
if (jointype == JOIN_FULL || jointype == JOIN_RIGHT || jointype == JOIN_RIGHT_ANTI_FULL)
return NIL;
/*
* This used to be quite a complex bit of code, but now that all pathkey
* sublists start out life canonicalized, we don't have to do a darn thing
* here!
*
* We do, however, need to truncate the pathkeys list, since it may
* contain pathkeys that were useful for forming this joinrel but are
* uninteresting to higher levels.
*/
return truncate_useless_pathkeys(root, joinrel, outer_pathkeys);
}
/****************************************************************************
* PATHKEYS AND SORT CLAUSES
****************************************************************************/
/*
* make_pathkeys_for_sortclauses
* Generate a pathkeys list that represents the sort order specified
* by a list of SortGroupClauses
*
* If canonicalize is TRUE, the resulting PathKeys are all in canonical form;
* otherwise not. canonicalize should always be TRUE after EquivalenceClass
* merging has been performed, but FALSE if we haven't done EquivalenceClass
* merging yet. (We provide this option because grouping_planner() needs to
* be able to represent requested pathkeys before the equivalence classes have
* been created for the query.)
*
* 'sortclauses' is a list of SortGroupClause nodes
* 'tlist' is the targetlist to find the referenced tlist entries in
*/
List* make_pathkeys_for_sortclauses(PlannerInfo* root, List* sortclauses, List* tlist, bool canonicalize)
{
List* pathkeys = NIL;
ListCell* l = NULL;
Assert(canonicalize);
foreach (l, sortclauses) {
SortGroupClause* sortcl = (SortGroupClause*)lfirst(l);
Expr* sortkey = NULL;
PathKey* pathkey = NULL;
sortkey = (Expr*)get_sortgroupclause_expr(sortcl, tlist);
AssertEreport(OidIsValid(sortcl->sortop), MOD_OPT, "ordering operator is invalid");
pathkey = make_pathkey_from_sortop(root,
sortkey,
sortcl->sortop,
sortcl->nulls_first,
sortcl->tleSortGroupRef,
sortcl->groupSet,
true,
true);
/* Canonical form eliminates redundant ordering keys */
if (!pathkey_is_redundant(pathkey, pathkeys))
pathkeys = lappend(pathkeys, pathkey);
}
return pathkeys;
}
/****************************************************************************
* PATHKEYS AND MERGECLAUSES
****************************************************************************/
/*
* initialize_mergeclause_eclasses
* Set the EquivalenceClass links in a mergeclause restrictinfo.
*
* RestrictInfo contains fields in which we may cache pointers to
* EquivalenceClasses for the left and right inputs of the mergeclause.
* (If the mergeclause is a true equivalence clause these will be the
* same EquivalenceClass, otherwise not.) If the mergeclause is either
* used to generate an EquivalenceClass, or derived from an EquivalenceClass,
* then it's easy to set up the left_ec and right_ec members --- otherwise,
* this function should be called to set them up. We will generate new
* EquivalenceClauses if necessary to represent the mergeclause's left and
* right sides.
*
* Note this is called before EC merging is complete, so the links won't
* necessarily point to canonical ECs. Before they are actually used for
* anything, update_mergeclause_eclasses must be called to ensure that
* they've been updated to point to canonical ECs.
*/
void initialize_mergeclause_eclasses(PlannerInfo* root, RestrictInfo* restrictinfo)
{
Expr* clause = restrictinfo->clause;
Oid lefttype, righttype;
/* Should be a mergeclause ... */
AssertEreport(restrictinfo->mergeopfamilies != NIL, MOD_OPT, "clause is not mergejoinable");
/* ... with links not yet set */
AssertEreport(restrictinfo->left_ec == NULL, MOD_OPT, "lefthand mergeclause processing is set");
AssertEreport(restrictinfo->right_ec == NULL, MOD_OPT, "righthand mergeclause processing is set");
/* Need the declared input types of the operator */
op_input_types(((OpExpr*)clause)->opno, &lefttype, &righttype);
/* Find or create a matching EquivalenceClass for each side */
restrictinfo->left_ec = get_eclass_for_sort_expr(root,
(Expr*)get_leftop(clause),
restrictinfo->mergeopfamilies,
lefttype,
((OpExpr*)clause)->inputcollid,
0,
false,
NULL,
true);
restrictinfo->right_ec = get_eclass_for_sort_expr(root,
(Expr*)get_rightop(clause),
restrictinfo->mergeopfamilies,
righttype,
((OpExpr*)clause)->inputcollid,
0,
false,
NULL,
true);
}
/*
* update_mergeclause_eclasses
* Make the cached EquivalenceClass links valid in a mergeclause
* restrictinfo.
*
* These pointers should have been set by process_equivalence or
* initialize_mergeclause_eclasses, but they might have been set to
* non-canonical ECs that got merged later. Chase up to the canonical
* merged parent if so.
*/
void update_mergeclause_eclasses(PlannerInfo* root, RestrictInfo* restrictinfo)
{
/* Should be a merge clause ... */
AssertEreport(restrictinfo->mergeopfamilies != NIL, MOD_OPT, "clause is not mergejoinable");
/* ... with pointers already set */
AssertEreport(restrictinfo->left_ec != NULL, MOD_OPT, "lefthand mergeclause processing is not set");
AssertEreport(restrictinfo->right_ec != NULL, MOD_OPT, "righthand mergeclause processing is not set");
/* Chase up to the top as needed */
while (restrictinfo->left_ec->ec_merged)
restrictinfo->left_ec = restrictinfo->left_ec->ec_merged;
while (restrictinfo->right_ec->ec_merged)
restrictinfo->right_ec = restrictinfo->right_ec->ec_merged;
}
/*
* find_mergeclauses_for_outer_pathkeys
* This routine attempts to find a list of mergeclauses that can be
* used with a specified ordering for the join's outer relation.
* If successful, it returns a list of mergeclauses.
*
* 'pathkeys' is a pathkeys list showing the ordering of an outer-rel path.
* 'restrictinfos' is a list of mergejoinable restriction clauses for the
* join relation being formed, in no particular order.
*
* The restrictinfos must be marked (via outer_is_left) to show which side
* of each clause is associated with the current outer path. (See
* select_mergejoin_clauses())
*
* The result is NIL if no merge can be done, else a maximal list of
* usable mergeclauses (represented as a list of their restrictinfo nodes).
* The list is ordered to match the pathkeys, as required for execution.
*/
List* find_mergeclauses_for_outer_pathkeys(PlannerInfo* root, List* pathkeys, List* restrictinfos)
{
List* mergeclauses = NIL;
ListCell* i = NULL;
/* make sure we have eclasses cached in the clauses */
foreach (i, restrictinfos) {
RestrictInfo* rinfo = (RestrictInfo*)lfirst(i);
update_mergeclause_eclasses(root, rinfo);
}
foreach (i, pathkeys) {
PathKey* pathkey = (PathKey*)lfirst(i);
EquivalenceClass* pathkey_ec = pathkey->pk_eclass;
List* matched_restrictinfos = NIL;
ListCell* j = NULL;
/* ----------
* A mergejoin clause matches a pathkey if it has the same EC.
* If there are multiple matching clauses, take them all. In plain
* inner-join scenarios we expect only one match, because
* equivalence-class processing will have removed any redundant
* mergeclauses. However, in outer-join scenarios there might be
* multiple matches. An example is
*
* select * from a full join b
* on a.v1 = b.v1 and a.v2 = b.v2 and a.v1 = b.v2;
*
* Given the pathkeys ({a.v1}, {a.v2}) it is okay to return all three
* clauses (in the order a.v1=b.v1, a.v1=b.v2, a.v2=b.v2) and indeed
* we *must* do so or we will be unable to form a valid plan.
*
* We expect that the given pathkeys list is canonical, which means
* no two members have the same EC, so it's not possible for this
* code to enter the same mergeclause into the result list twice.
*
* It's possible that multiple matching clauses might have different
* ECs on the other side, in which case the order we put them into our
* result makes a difference in the pathkeys required for the inner
* input rel. However this routine hasn't got any info about which
* order would be best, so we don't worry about that.
*
* It's also possible that the selected mergejoin clauses produce
* a noncanonical ordering of pathkeys for the inner side, ie, we
* might select clauses that reference b.v1, b.v2, b.v1 in that
* order. This is not harmful in itself, though it suggests that
* the clauses are partially redundant. Since the alternative is
* to omit mergejoin clauses and thereby possibly fail to generate a
* plan altogether, we live with it. make_inner_pathkeys_for_merge()
* has to delete duplicates when it constructs the inner pathkeys
* list, and we also have to deal with such cases specially
* in create_mergejoin_plan().
* ----------
*/
foreach (j, restrictinfos) {
RestrictInfo* rinfo = (RestrictInfo*)lfirst(j);
EquivalenceClass* clause_ec = NULL;
clause_ec = rinfo->outer_is_left ? rinfo->left_ec : rinfo->right_ec;
if (clause_ec == pathkey_ec)
matched_restrictinfos = lappend(matched_restrictinfos, rinfo);
}
/*
* If we didn't find a mergeclause, we're done --- any additional
* sort-key positions in the pathkeys are useless. (But we can still
* mergejoin if we found at least one mergeclause.)
*/
if (matched_restrictinfos == NIL)
break;
/*
* If we did find usable mergeclause(s) for this sort-key position,
* add them to result list.
*/
mergeclauses = list_concat(mergeclauses, matched_restrictinfos);
}
return mergeclauses;
}
/*
* select_outer_pathkeys_for_merge
* Builds a pathkey list representing a possible sort ordering
* that can be used with the given mergeclauses.
*
* 'mergeclauses' is a list of RestrictInfos for mergejoin clauses
* that will be used in a merge join.
* 'joinrel' is the join relation we are trying to construct.
*
* The restrictinfos must be marked (via outer_is_left) to show which side
* of each clause is associated with the current outer path. (See
* select_mergejoin_clauses())
*
* Returns a pathkeys list that can be applied to the outer relation.
*
* Since we assume here that a sort is required, there is no particular use
* in matching any available ordering of the outerrel. (joinpath.c has an
* entirely separate code path for considering sort-free mergejoins.) Rather,
* it's interesting to try to match the requested query_pathkeys so that a
* second output sort may be avoided; and failing that, we try to list "more
* popular" keys (those with the most unmatched EquivalenceClass peers)
* earlier, in hopes of making the resulting ordering useful for as many
* higher-level mergejoins as possible.
*/
List* select_outer_pathkeys_for_merge(PlannerInfo* root, List* mergeclauses, RelOptInfo* joinrel)
{
List* pathkeys = NIL;
int nClauses = list_length(mergeclauses);
EquivalenceClass** ecs;
int* scores = NULL;
int necs;
ListCell* lc = NULL;
int j;
/* Might have no mergeclauses */
if (nClauses == 0)
return NIL;
/*
* Make arrays of the ECs used by the mergeclauses (dropping any
* duplicates) and their "popularity" scores.
*/
ecs = (EquivalenceClass**)palloc(nClauses * sizeof(EquivalenceClass*));
scores = (int*)palloc(nClauses * sizeof(int));
necs = 0;
foreach (lc, mergeclauses) {
RestrictInfo* rinfo = (RestrictInfo*)lfirst(lc);
EquivalenceClass* oeclass = NULL;
int score;
ListCell* lc2 = NULL;
/* get the outer eclass */
update_mergeclause_eclasses(root, rinfo);
if (rinfo->outer_is_left)
oeclass = rinfo->left_ec;
else
oeclass = rinfo->right_ec;
/* reject duplicates */
for (j = 0; j < necs; j++) {
if (ecs[j] == oeclass)
break;
}
if (j < necs)
continue;
/* compute score */
score = 0;
foreach (lc2, oeclass->ec_members) {
EquivalenceMember* em = (EquivalenceMember*)lfirst(lc2);
/* Potential future join partner? */
if (!em->em_is_const && !em->em_is_child && !bms_overlap(em->em_relids, joinrel->relids))
score++;
}
ecs[necs] = oeclass;
scores[necs] = score;
necs++;
}
/*
* Find out if we have all the ECs mentioned in query_pathkeys; if so we
* can generate a sort order that's also useful for final output. There is
* no percentage in a partial match, though, so we have to have 'em all.
*/
if (root->query_pathkeys) {
foreach (lc, root->query_pathkeys) {
PathKey* query_pathkey = (PathKey*)lfirst(lc);
EquivalenceClass* query_ec = query_pathkey->pk_eclass;
for (j = 0; j < necs; j++) {
if (ecs[j] == query_ec)
break; /* found match */
}
if (j >= necs)
break; /* didn't find match */
}
/* if we got to the end of the list, we have them all */
if (lc == NULL) {
/* copy query_pathkeys as starting point for our output */
pathkeys = list_copy(root->query_pathkeys);
/* mark their ECs as already-emitted */
foreach (lc, root->query_pathkeys) {
PathKey* query_pathkey = (PathKey*)lfirst(lc);
EquivalenceClass* query_ec = query_pathkey->pk_eclass;
for (j = 0; j < necs; j++) {
if (ecs[j] == query_ec) {
scores[j] = -1;
break;
}
}
}
}
}
/*
* Add remaining ECs to the list in popularity order, using a default sort
* ordering. (We could use qsort() here, but the list length is usually
* so small it's not worth it.)
*/
for (;;) {
int best_j;
int best_score;
EquivalenceClass* ec = NULL;
PathKey* pathkey = NULL;
best_j = 0;
best_score = scores[0];
for (j = 1; j < necs; j++) {
if (scores[j] > best_score) {
best_j = j;
best_score = scores[j];
}
}
if (best_score < 0)
break; /* all done */
ec = ecs[best_j];
scores[best_j] = -1;
pathkey = make_canonical_pathkey(root, ec, linitial_oid(ec->ec_opfamilies), BTLessStrategyNumber, false);
/* can't be redundant because no duplicate ECs */
AssertEreport(!pathkey_is_redundant(pathkey, pathkeys), MOD_OPT, "pathkey is redundant");
pathkeys = lappend(pathkeys, pathkey);
}
pfree_ext(ecs);
pfree_ext(scores);
return pathkeys;
}
/*
* make_inner_pathkeys_for_merge
* Builds a pathkey list representing the explicit sort order that
* must be applied to an inner path to make it usable with the
* given mergeclauses.
*
* 'mergeclauses' is a list of RestrictInfos for the mergejoin clauses
* that will be used in a merge join, in order.
* 'outer_pathkeys' are the already-known canonical pathkeys for the outer
* side of the join.
*
* The restrictinfos must be marked (via outer_is_left) to show which side
* of each clause is associated with the current outer path. (See
* select_mergejoin_clauses())
*
* Returns a pathkeys list that can be applied to the inner relation.
*
* Note that it is not this routine's job to decide whether sorting is
* actually needed for a particular input path. Assume a sort is necessary;
* just make the keys, eh?
*/
List* make_inner_pathkeys_for_merge(PlannerInfo* root, List* mergeclauses, List* outer_pathkeys)
{
List* pathkeys = NIL;
EquivalenceClass* lastoeclass = NULL;
PathKey* opathkey = NULL;
ListCell* lc = NULL;
ListCell* lop = NULL;
lastoeclass = NULL;
opathkey = NULL;
lop = list_head(outer_pathkeys);
foreach (lc, mergeclauses) {
RestrictInfo* rinfo = (RestrictInfo*)lfirst(lc);
EquivalenceClass* oeclass = NULL;
EquivalenceClass* ieclass = NULL;
PathKey* pathkey = NULL;
update_mergeclause_eclasses(root, rinfo);
if (rinfo->outer_is_left) {
oeclass = rinfo->left_ec;
ieclass = rinfo->right_ec;
} else {
oeclass = rinfo->right_ec;
ieclass = rinfo->left_ec;
}
/* outer eclass should match current or next pathkeys */
/* we check this carefully for debugging reasons */
if (oeclass != lastoeclass) {
if (lop == NULL)
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg("too few pathkeys for mergeclauses when make inner pathkeys for merge"))));
opathkey = (PathKey*)lfirst(lop);
lop = lnext(lop);
lastoeclass = opathkey->pk_eclass;
if (oeclass != lastoeclass)
ereport(ERROR,
(errmodule(MOD_OPT),
errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
(errmsg("outer pathkeys do not match mergeclause when make inner pathkeys for merge"))));
}
/*
* Often, we'll have same EC on both sides, in which case the outer
* pathkey is also canonical for the inner side, and we can skip a
* useless search.
*/
if (ieclass == oeclass)
pathkey = opathkey;
else
pathkey = make_canonical_pathkey(
root, ieclass, opathkey->pk_opfamily, opathkey->pk_strategy, opathkey->pk_nulls_first);
/*
* Don't generate redundant pathkeys (which can happen if multiple
* mergeclauses refer to the same EC). Because we do this, the output
* pathkey list isn't necessarily ordered like the mergeclauses, which
* complicates life for create_mergejoin_plan(). But if we didn't,
* we'd have a noncanonical sort key list, which would be bad; for one
* reason, it certainly wouldn't match any available sort order for
* the input relation.
*/
if (!pathkey_is_redundant(pathkey, pathkeys))
pathkeys = lappend(pathkeys, pathkey);
}
return pathkeys;
}
/*
* trim_mergeclauses_for_inner_pathkeys
* This routine trims a list of mergeclauses to include just those that
* work with a specified ordering for the join's inner relation.
*
* 'mergeclauses' is a list of RestrictInfos for mergejoin clauses for the
* join relation being formed, in an order known to work for the
* currently-considered sort ordering of the join's outer rel.
* 'pathkeys' is a pathkeys list showing the ordering of an inner-rel path;
* it should be equal to, or a truncation of, the result of
* make_inner_pathkeys_for_merge for these mergeclauses.
*
* What we return will be a prefix of the given mergeclauses list.
*
* We need this logic because make_inner_pathkeys_for_merge's result isn't
* necessarily in the same order as the mergeclauses. That means that if we
* consider an inner-rel pathkey list that is a truncation of that result,
* we might need to drop mergeclauses even though they match a surviving inner
* pathkey. This happens when they are to the right of a mergeclause that
* matches a removed inner pathkey.
*
* The mergeclauses must be marked (via outer_is_left) to show which side
* of each clause is associated with the current outer path. (See
* select_mergejoin_clauses())
*/
List* trim_mergeclauses_for_inner_pathkeys(PlannerInfo* root, List* mergeclauses, List* pathkeys)
{
List* new_mergeclauses = NIL;
PathKey* pathkey = NULL;
EquivalenceClass* pathkey_ec = NULL;
bool matched_pathkey = false;
ListCell* lip = NULL;
ListCell* i = NULL;
/* No pathkeys => no mergeclauses (though we don't expect this case) */
if (pathkeys == NIL)
return NIL;
/* Initialize to consider first pathkey */
lip = list_head(pathkeys);
pathkey = (PathKey*)lfirst(lip);
pathkey_ec = pathkey->pk_eclass;
lip = lnext(lip);
/* Scan mergeclauses to see how many we can use */
foreach (i, mergeclauses) {
RestrictInfo* rinfo = (RestrictInfo*)lfirst(i);
EquivalenceClass* clause_ec;
/* Assume we needn't do update_mergeclause_eclasses again here */
/* Check clause's inner-rel EC against current pathkey */
clause_ec = rinfo->outer_is_left ? rinfo->right_ec : rinfo->left_ec;
/* If we don't have a match, attempt to advance to next pathkey */
if (clause_ec != pathkey_ec) {
/* If we had no clauses matching this inner pathkey, must stop */
if (!matched_pathkey)
break;
/* Advance to next inner pathkey, if any */
if (lip == NULL)
break;
pathkey = (PathKey*)lfirst(lip);
pathkey_ec = pathkey->pk_eclass;
lip = lnext(lip);
matched_pathkey = false;
}
/* If mergeclause matches current inner pathkey, we can use it */
if (clause_ec == pathkey_ec) {
new_mergeclauses = lappend(new_mergeclauses, rinfo);
matched_pathkey = true;
} else {
/* Else, no hope of adding any more mergeclauses */
break;
}
}
return new_mergeclauses;
}
/****************************************************************************
* PATHKEY USEFULNESS CHECKS
*
* We only want to remember as many of the pathkeys of a path as have some
* potential use, either for subsequent mergejoins or for meeting the query's
* requested output ordering. This ensures that add_path() won't consider
* a path to have a usefully different ordering unless it really is useful.
* These routines check for usefulness of given pathkeys.
****************************************************************************/
/*
* pathkeys_useful_for_merging
* Count the number of pathkeys that may be useful for mergejoins
* above the given relation.
*
* We consider a pathkey potentially useful if it corresponds to the merge
* ordering of either side of any joinclause for the rel. This might be
* overoptimistic, since joinclauses that require different other relations
* might never be usable at the same time, but trying to be exact is likely
* to be more trouble than it's worth.
*
* To avoid doubling the number of mergejoin paths considered, we would like
* to consider only one of the two scan directions (ASC or DESC) as useful
* for merging for any given target column. The choice is arbitrary unless
* one of the directions happens to match an ORDER BY key, in which case
* that direction should be preferred, in hopes of avoiding a final sort step.
* right_merge_direction() implements this heuristic.
*/
static int pathkeys_useful_for_merging(PlannerInfo* root, RelOptInfo* rel, List* pathkeys)
{
int useful = 0;
ListCell* i = NULL;
foreach (i, pathkeys) {
PathKey* pathkey = (PathKey*)lfirst(i);
bool matched = false;
ListCell* j = NULL;
/* If "wrong" direction, not useful for merging */
if (!right_merge_direction(root, pathkey))
break;
/*
* First look into the EquivalenceClass of the pathkey, to see if
* there are any members not yet joined to the rel. If so, it's
* surely possible to generate a mergejoin clause using them.
*/
if (rel->has_eclass_joins && eclass_useful_for_merging(pathkey->pk_eclass, rel))
matched = true;
else {
/*
* Otherwise search the rel's joininfo list, which contains
* non-EquivalenceClass-derivable join clauses that might
* nonetheless be mergejoinable.
*/
foreach (j, rel->joininfo) {
RestrictInfo* restrictinfo = (RestrictInfo*)lfirst(j);
if (restrictinfo->mergeopfamilies == NIL)
continue;
update_mergeclause_eclasses(root, restrictinfo);
if (pathkey->pk_eclass == restrictinfo->left_ec || pathkey->pk_eclass == restrictinfo->right_ec) {
matched = true;
break;
}
}
}
/*
* If we didn't find a mergeclause, we're done --- any additional
* sort-key positions in the pathkeys are useless. (But we can still
* mergejoin if we found at least one mergeclause.)
*/
if (matched)
useful++;
else
break;
}
return useful;
}
/*
* right_merge_direction
* Check whether the pathkey embodies the preferred sort direction
* for merging its target column.
*/
static bool right_merge_direction(PlannerInfo* root, PathKey* pathkey)
{
ListCell* l = NULL;
foreach (l, root->query_pathkeys) {
PathKey* query_pathkey = (PathKey*)lfirst(l);
if (pathkey->pk_eclass == query_pathkey->pk_eclass && pathkey->pk_opfamily == query_pathkey->pk_opfamily) {
/*
* Found a matching query sort column. Prefer this pathkey's
* direction iff it matches. Note that we ignore pk_nulls_first,
* which means that a sort might be needed anyway ... but we still
* want to prefer only one of the two possible directions, and we
* might as well use this one.
*/
return (pathkey->pk_strategy == query_pathkey->pk_strategy);
}
}
/* If no matching ORDER BY request, prefer the ASC direction */
return (pathkey->pk_strategy == BTLessStrategyNumber);
}
/*
* pathkeys_useful_for_ordering
* Count the number of pathkeys that are useful for meeting the
* query's requested output ordering.
*
* Unlike merge pathkeys, this is an all-or-nothing affair: it does us
* no good to order by just the first key(s) of the requested ordering.
* So the result is always either 0 or list_length(root->query_pathkeys).
*/
static int pathkeys_useful_for_ordering(PlannerInfo* root, List* pathkeys)
{
if (root->query_pathkeys == NIL)
return 0; /* no special ordering requested */
if (pathkeys == NIL)
return 0; /* unordered path */
if (pathkeys_contained_in(root->query_pathkeys, pathkeys)) {
/* It's useful ... or at least the first N keys are */
return list_length(root->query_pathkeys);
}
return 0; /* path ordering not useful */
}
/*
* truncate_useless_pathkeys
* Shorten the given pathkey list to just the useful pathkeys.
*/
List* truncate_useless_pathkeys(PlannerInfo* root, RelOptInfo* rel, List* pathkeys)
{
int nuseful;
int nuseful2;
nuseful = pathkeys_useful_for_merging(root, rel, pathkeys);
nuseful2 = pathkeys_useful_for_ordering(root, pathkeys);
if (nuseful2 > nuseful) {
nuseful = nuseful2;
}
/*
* Note: not safe to modify input list destructively, but we can avoid
* copying the list if we're not actually going to change it
*/
if (nuseful == 0)
return NIL;
else if (nuseful == list_length(pathkeys))
return pathkeys;
else
return list_truncate(list_copy(pathkeys), nuseful);
}
/*
* has_useful_pathkeys
* Detect whether the specified rel could have any pathkeys that are
* useful according to truncate_useless_pathkeys().
*
* This is a cheap test that lets us skip building pathkeys at all in very
* simple queries. It's OK to err in the direction of returning "true" when
* there really aren't any usable pathkeys, but erring in the other direction
* is bad --- so keep this in sync with the routines above!
*
* We could make the test more complex, for example checking to see if any of
* the joinclauses are really mergejoinable, but that likely wouldn't win
* often enough to repay the extra cycles. Queries with neither a join nor
* a sort are reasonably common, though, so this much work seems worthwhile.
*/
bool has_useful_pathkeys(PlannerInfo* root, RelOptInfo* rel)
{
if (rel->joininfo != NIL || rel->has_eclass_joins)
return true; /* might be able to use pathkeys for merging */
if (root->query_pathkeys != NIL)
return true; /* might be able to use them for ordering */
return false; /* definitely useless */
}
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