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Explore alternative orderings of group-by pathkeys during optimization.

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When evaluating a query with a multi-column GROUP BY clause, we can minimize
sort operations or avoid them if we synchronize the order of GROUP BY clauses
with the ORDER BY sort clause or sort order, which comes from the underlying
query tree. Grouping does not imply any ordering, so we can compare
the keys in arbitrary order, and a Hash Agg leverages this. But for Group Agg,
we simply compared keys in the order specified in the query. This commit
explores alternative ordering of the keys, trying to find a cheaper one.

The ordering of group keys may interact with other parts of the query, some of
which may not be known while planning the grouping. For example, there may be
an explicit ORDER BY clause or some other ordering-dependent operation higher up
in the query, and using the same ordering may allow using either incremental
sort or even eliminating the sort entirely.

The patch always keeps the ordering specified in the query, assuming the user
might have additional insights.

This introduces a new GUC enable_group_by_reordering so that the optimization
may be disabled if needed.

Discussion: https://postgr.es/m/7c79e6a5-8597-74e8-0671-1c39d124c9d6%40sigaev.ru
Author: Andrei Lepikhov, Teodor Sigaev
Reviewed-by: Tomas Vondra, Claudio Freire, Gavin Flower, Dmitry Dolgov
Reviewed-by: Robert Haas, Pavel Borisov, David Rowley, Zhihong Yu
Reviewed-by: Tom Lane, Alexander Korotkov, Richard Guo, Alena Rybakina
This commit is contained in:
Alexander Korotkov
2024-01-21 22:21:36 +02:00
parent 7ab80ac1ca
commit 0452b461bc
11 changed files with 773 additions and 226 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
src/backend/optimizer/path/equivclass.c
View File

@@ -652,7 +652,18 @@ get_eclass_for_sort_expr(PlannerInfo *root,
if (opcintype == cur_em->em_datatype &&
equal(expr, cur_em->em_expr))
return cur_ec; /* Match! */
{
/*
* Match!
*
* Copy the sortref if it wasn't set yet. That may happen if
* the ec was constructed from a WHERE clause, i.e. it doesn't
* have a target reference at all.
*/
if (cur_ec->ec_sortref == 0 && sortref > 0)
cur_ec->ec_sortref = sortref;
return cur_ec;
}
}
}

252
src/backend/optimizer/path/pathkeys.c
View File

@@ -22,12 +22,15 @@
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/cost.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "partitioning/partbounds.h"
#include "utils/lsyscache.h"
/* Consider reordering of GROUP BY keys? */
bool enable_group_by_reordering = true;
static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys);
static bool matches_boolean_partition_clause(RestrictInfo *rinfo,
@@ -350,6 +353,202 @@ pathkeys_contained_in(List *keys1, List *keys2)
return false;
}
/*
* group_keys_reorder_by_pathkeys
* Reorder GROUP BY keys to match the input pathkeys.
*
* Function returns new lists (pathkeys and clauses), original GROUP BY lists
* stay untouched.
*
* Returns the number of GROUP BY keys with a matching pathkey.
*/
static int
group_keys_reorder_by_pathkeys(List *pathkeys, List **group_pathkeys,
List **group_clauses,
int num_groupby_pathkeys)
{
List *new_group_pathkeys = NIL,
*new_group_clauses = NIL;
ListCell *lc;
int n;
if (pathkeys == NIL || *group_pathkeys == NIL)
return 0;
/*
* Walk the pathkeys (determining ordering of the input path) and see if
* there's a matching GROUP BY key. If we find one, we append it to the
* list, and do the same for the clauses.
*
* Once we find the first pathkey without a matching GROUP BY key, the
* rest of the pathkeys are useless and can't be used to evaluate the
* grouping, so we abort the loop and ignore the remaining pathkeys.
*/
foreach(lc, pathkeys)
{
PathKey *pathkey = (PathKey *) lfirst(lc);
SortGroupClause *sgc;
/*
* Pathkeys are built in a way that allows simply comparing pointers.
* Give up if we can't find the matching pointer. Also give up if
* there is no sortclause reference for some reason.
*/
if (foreach_current_index(lc) >= num_groupby_pathkeys ||
!list_member_ptr(*group_pathkeys, pathkey) ||
pathkey->pk_eclass->ec_sortref == 0)
break;
/*
* Since 1349d27 pathkey coming from underlying node can be in the
* root->group_pathkeys but not in the processed_groupClause. So, we
* should be careful here.
*/
sgc = get_sortgroupref_clause_noerr(pathkey->pk_eclass->ec_sortref,
*group_clauses);
if (!sgc)
/* The grouping clause does not cover this pathkey */
break;
/*
* Sort group clause should have an ordering operator as long as there
* is an associated pathkey.
*/
Assert(OidIsValid(sgc->sortop));
new_group_pathkeys = lappend(new_group_pathkeys, pathkey);
new_group_clauses = lappend(new_group_clauses, sgc);
}
/* remember the number of pathkeys with a matching GROUP BY key */
n = list_length(new_group_pathkeys);
/* append the remaining group pathkeys (will be treated as not sorted) */
*group_pathkeys = list_concat_unique_ptr(new_group_pathkeys,
*group_pathkeys);
*group_clauses = list_concat_unique_ptr(new_group_clauses,
*group_clauses);
return n;
}
/*
* pathkeys_are_duplicate
* Check if give pathkeys are already contained the list of
* PathKeyInfo's.
*/
static bool
pathkeys_are_duplicate(List *infos, List *pathkeys)
{
ListCell *lc;
foreach(lc, infos)
{
PathKeyInfo *info = lfirst_node(PathKeyInfo, lc);
if (compare_pathkeys(pathkeys, info->pathkeys) == PATHKEYS_EQUAL)
return true;
}
return false;
}
/*
* get_useful_group_keys_orderings
* Determine which orderings of GROUP BY keys are potentially interesting.
*
* Returns a list of PathKeyInfo items, each representing an interesting
* ordering of GROUP BY keys. Each item stores pathkeys and clauses in the
* matching order.
*
* The function considers (and keeps) multiple GROUP BY orderings:
*
* - the original ordering, as specified by the GROUP BY clause,
* - GROUP BY keys reordered to match 'path' ordering (as much as possible),
* - GROUP BY keys to match target ORDER BY clause (as much as possible).
*/
List *
get_useful_group_keys_orderings(PlannerInfo *root, Path *path)
{
Query *parse = root->parse;
List *infos = NIL;
PathKeyInfo *info;
List *pathkeys = root->group_pathkeys;
List *clauses = root->processed_groupClause;
/* always return at least the original pathkeys/clauses */
info = makeNode(PathKeyInfo);
info->pathkeys = pathkeys;
info->clauses = clauses;
infos = lappend(infos, info);
/*
* Should we try generating alternative orderings of the group keys? If
* not, we produce only the order specified in the query, i.e. the
* optimization is effectively disabled.
*/
if (!enable_group_by_reordering)
return infos;
/*
* Grouping sets have own and more complex logic to decide the ordering.
*/
if (parse->groupingSets)
return infos;
/*
* If the path is sorted in some way, try reordering the group keys to
* match the path as much of the ordering as possible. Then thanks to
* incremental sort we would get this sort as cheap as possible.
*/
if (path->pathkeys &&
!pathkeys_contained_in(path->pathkeys, root->group_pathkeys))
{
int n;
n = group_keys_reorder_by_pathkeys(path->pathkeys, &pathkeys, &clauses,
root->num_groupby_pathkeys);
if (n > 0 &&
(enable_incremental_sort || n == root->num_groupby_pathkeys) &&
!pathkeys_are_duplicate(infos, pathkeys))
{
info = makeNode(PathKeyInfo);
info->pathkeys = pathkeys;
info->clauses = clauses;
infos = lappend(infos, info);
}
}
/*
* Try reordering pathkeys to minimize the sort cost (this time consider
* the ORDER BY clause).
*/
if (root->sort_pathkeys &&
!pathkeys_contained_in(root->sort_pathkeys, root->group_pathkeys))
{
int n;
n = group_keys_reorder_by_pathkeys(root->sort_pathkeys, &pathkeys,
&clauses,
root->num_groupby_pathkeys);
if (n > 0 &&
(enable_incremental_sort || n == list_length(root->sort_pathkeys)) &&
!pathkeys_are_duplicate(infos, pathkeys))
{
info = makeNode(PathKeyInfo);
info->pathkeys = pathkeys;
info->clauses = clauses;
infos = lappend(infos, info);
}
}
return infos;
}
/*
* pathkeys_count_contained_in
* Same as pathkeys_contained_in, but also sets length of longest
@@ -1939,6 +2138,54 @@ pathkeys_useful_for_ordering(PlannerInfo *root, List *pathkeys)
return n_common_pathkeys;
}
/*
* pathkeys_useful_for_grouping
* Count the number of pathkeys that are useful for grouping (instead of
* explicit sort)
*
* Group pathkeys could be reordered to benefit from the ordering. The
* ordering may not be "complete" and may require incremental sort, but that's
* fine. So we simply count prefix pathkeys with a matching group key, and
* stop once we find the first pathkey without a match.
*
* So e.g. with pathkeys (a,b,c) and group keys (a,b,e) this determines (a,b)
* pathkeys are useful for grouping, and we might do incremental sort to get
* path ordered by (a,b,e).
*
* This logic is necessary to retain paths with ordering not matching grouping
* keys directly, without the reordering.
*
* Returns the length of pathkey prefix with matching group keys.
*/
static int
pathkeys_useful_for_grouping(PlannerInfo *root, List *pathkeys)
{
ListCell *key;
int n = 0;
/* no special ordering requested for grouping */
if (root->group_pathkeys == NIL)
return 0;
/* unordered path */
if (pathkeys == NIL)
return 0;
/* walk the pathkeys and search for matching group key */
foreach(key, pathkeys)
{
PathKey *pathkey = (PathKey *) lfirst(key);
/* no matching group key, we're done */
if (!list_member_ptr(root->group_pathkeys, pathkey))
break;
n++;
}
return n;
}
/*
* truncate_useless_pathkeys
* Shorten the given pathkey list to just the useful pathkeys.
@@ -1953,6 +2200,9 @@ truncate_useless_pathkeys(PlannerInfo *root,
nuseful = pathkeys_useful_for_merging(root, rel, pathkeys);
nuseful2 = pathkeys_useful_for_ordering(root, pathkeys);
if (nuseful2 > nuseful)
nuseful = nuseful2;
nuseful2 = pathkeys_useful_for_grouping(root, pathkeys);
if (nuseful2 > nuseful)
nuseful = nuseful2;
@@ -1988,6 +2238,8 @@ 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->group_pathkeys != NIL)
return true; /* might be able to use pathkeys for grouping */
if (root->query_pathkeys != NIL)
return true; /* might be able to use them for ordering */
return false; /* definitely useless */

430
src/backend/optimizer/plan/planner.c
View File

@@ -140,7 +140,7 @@ static double preprocess_limit(PlannerInfo *root,
double tuple_fraction,
int64 *offset_est, int64 *count_est);
static void remove_useless_groupby_columns(PlannerInfo *root);
static List *preprocess_groupclause(PlannerInfo *root, List *force);
static List *groupclause_apply_groupingset(PlannerInfo *root, List *force);
static List *extract_rollup_sets(List *groupingSets);
static List *reorder_grouping_sets(List *groupingSets, List *sortclause);
static void standard_qp_callback(PlannerInfo *root, void *extra);
@@ -1423,7 +1423,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
else if (parse->groupClause)
{
/* Preprocess regular GROUP BY clause, if any */
root->processed_groupClause = preprocess_groupclause(root, NIL);
root->processed_groupClause = list_copy(parse->groupClause);;
/* Remove any redundant GROUP BY columns */
remove_useless_groupby_columns(root);
}
@@ -2144,7 +2144,7 @@ preprocess_grouping_sets(PlannerInfo *root)
* The groupClauses for hashed grouping sets are built later on.)
*/
if (gs->set)
rollup->groupClause = preprocess_groupclause(root, gs->set);
rollup->groupClause = groupclause_apply_groupingset(root, gs->set);
else
rollup->groupClause = NIL;
@@ -2796,111 +2796,24 @@ remove_useless_groupby_columns(PlannerInfo *root)
}
/*
* preprocess_groupclause - do preparatory work on GROUP BY clause
*
* The idea here is to adjust the ordering of the GROUP BY elements
* (which in itself is semantically insignificant) to match ORDER BY,
* thereby allowing a single sort operation to both implement the ORDER BY
* requirement and set up for a Unique step that implements GROUP BY.
*
* In principle it might be interesting to consider other orderings of the
* GROUP BY elements, which could match the sort ordering of other
* possible plans (eg an indexscan) and thereby reduce cost. We don't
* bother with that, though. Hashed grouping will frequently win anyway.
*
* Note: we need no comparable processing of the distinctClause because
* the parser already enforced that that matches ORDER BY.
*
* Note: we return a fresh List, but its elements are the same
* SortGroupClauses appearing in parse->groupClause. This is important
* because later processing may modify the processed_groupClause list.
*
* For grouping sets, the order of items is instead forced to agree with that
* of the grouping set (and items not in the grouping set are skipped). The
* work of sorting the order of grouping set elements to match the ORDER BY if
* possible is done elsewhere.
* groupclause_apply_groupingset
* Apply the order of GROUP BY clauses defined by grouping sets. Items
* not in the grouping set are skipped.
*/
static List *
preprocess_groupclause(PlannerInfo *root, List *force)
groupclause_apply_groupingset(PlannerInfo *root, List *gset)
{
Query *parse = root->parse;
List *new_groupclause = NIL;
bool partial_match;
ListCell *sl;
ListCell *gl;
/* For grouping sets, we need to force the ordering */
if (force)
foreach(sl, gset)
{
foreach(sl, force)
{
Index ref = lfirst_int(sl);
SortGroupClause *cl = get_sortgroupref_clause(ref, parse->groupClause);
Index ref = lfirst_int(sl);
SortGroupClause *cl = get_sortgroupref_clause(ref, parse->groupClause);
new_groupclause = lappend(new_groupclause, cl);
}
return new_groupclause;
new_groupclause = lappend(new_groupclause, cl);
}
/* If no ORDER BY, nothing useful to do here */
if (parse->sortClause == NIL)
return list_copy(parse->groupClause);
/*
* Scan the ORDER BY clause and construct a list of matching GROUP BY
* items, but only as far as we can make a matching prefix.
*
* This code assumes that the sortClause contains no duplicate items.
*/
foreach(sl, parse->sortClause)
{
SortGroupClause *sc = lfirst_node(SortGroupClause, sl);
foreach(gl, parse->groupClause)
{
SortGroupClause *gc = lfirst_node(SortGroupClause, gl);
if (equal(gc, sc))
{
new_groupclause = lappend(new_groupclause, gc);
break;
}
}
if (gl == NULL)
break; /* no match, so stop scanning */
}
/* Did we match all of the ORDER BY list, or just some of it? */
partial_match = (sl != NULL);
/* If no match at all, no point in reordering GROUP BY */
if (new_groupclause == NIL)
return list_copy(parse->groupClause);
/*
* Add any remaining GROUP BY items to the new list, but only if we were
* able to make a complete match. In other words, we only rearrange the
* GROUP BY list if the result is that one list is a prefix of the other
* --- otherwise there's no possibility of a common sort. Also, give up
* if there are any non-sortable GROUP BY items, since then there's no
* hope anyway.
*/
foreach(gl, parse->groupClause)
{
SortGroupClause *gc = lfirst_node(SortGroupClause, gl);
if (list_member_ptr(new_groupclause, gc))
continue; /* it matched an ORDER BY item */
if (partial_match) /* give up, no common sort possible */
return list_copy(parse->groupClause);
if (!OidIsValid(gc->sortop)) /* give up, GROUP BY can't be sorted */
return list_copy(parse->groupClause);
new_groupclause = lappend(new_groupclause, gc);
}
/* Success --- install the rearranged GROUP BY list */
Assert(list_length(parse->groupClause) == list_length(new_groupclause));
return new_groupclause;
}
@@ -4200,7 +4113,7 @@ consider_groupingsets_paths(PlannerInfo *root,
{
rollup = makeNode(RollupData);
rollup->groupClause = preprocess_groupclause(root, gset);
rollup->groupClause = groupclause_apply_groupingset(root, gset);
rollup->gsets_data = list_make1(gs);
rollup->gsets = remap_to_groupclause_idx(rollup->groupClause,
rollup->gsets_data,
@@ -4389,7 +4302,7 @@ consider_groupingsets_paths(PlannerInfo *root,
Assert(gs->set != NIL);
rollup->groupClause = preprocess_groupclause(root, gs->set);
rollup->groupClause = groupclause_apply_groupingset(root, gs->set);
rollup->gsets_data = list_make1(gs);
rollup->gsets = remap_to_groupclause_idx(rollup->groupClause,
rollup->gsets_data,
@@ -6891,60 +6804,75 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
*/
foreach(lc, input_rel->pathlist)
{
ListCell *lc2;
Path *path = (Path *) lfirst(lc);
Path *path_save = path;
List *pathkey_orderings = NIL;
path = make_ordered_path(root,
grouped_rel,
path,
cheapest_path,
root->group_pathkeys);
/* generate alternative group orderings that might be useful */
pathkey_orderings = get_useful_group_keys_orderings(root, path);
if (path == NULL)
continue;
Assert(list_length(pathkey_orderings) > 0);
/* Now decide what to stick atop it */
if (parse->groupingSets)
foreach(lc2, pathkey_orderings)
{
consider_groupingsets_paths(root, grouped_rel,
path, true, can_hash,
gd, agg_costs, dNumGroups);
}
else if (parse->hasAggs)
{
/*
* We have aggregation, possibly with plain GROUP BY. Make an
* AggPath.
*/
add_path(grouped_rel, (Path *)
create_agg_path(root,
PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
/* restore the path (we replace it in the loop) */
path = path_save;
path = make_ordered_path(root,
grouped_rel,
path,
grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_SIMPLE,
root->processed_groupClause,
havingQual,
agg_costs,
dNumGroups));
}
else if (parse->groupClause)
{
/*
* We have GROUP BY without aggregation or grouping sets. Make
* a GroupPath.
*/
add_path(grouped_rel, (Path *)
create_group_path(root,
grouped_rel,
path,
root->processed_groupClause,
havingQual,
dNumGroups));
}
else
{
/* Other cases should have been handled above */
Assert(false);
cheapest_path,
info->pathkeys);
if (path == NULL)
continue;
/* Now decide what to stick atop it */
if (parse->groupingSets)
{
consider_groupingsets_paths(root, grouped_rel,
path, true, can_hash,
gd, agg_costs, dNumGroups);
}
else if (parse->hasAggs)
{
/*
* We have aggregation, possibly with plain GROUP BY. Make
* an AggPath.
*/
add_path(grouped_rel, (Path *)
create_agg_path(root,
grouped_rel,
path,
grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_SIMPLE,
info->clauses,
havingQual,
agg_costs,
dNumGroups));
}
else if (parse->groupClause)
{
/*
* We have GROUP BY without aggregation or grouping sets.
* Make a GroupPath.
*/
add_path(grouped_rel, (Path *)
create_group_path(root,
grouped_rel,
path,
info->clauses,
havingQual,
dNumGroups));
}
else
{
/* Other cases should have been handled above */
Assert(false);
}
}
}
@@ -6956,38 +6884,55 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
{
foreach(lc, partially_grouped_rel->pathlist)
{
ListCell *lc2;
Path *path = (Path *) lfirst(lc);
Path *path_save = path;
List *pathkey_orderings = NIL;
path = make_ordered_path(root,
grouped_rel,
path,
partially_grouped_rel->cheapest_total_path,
root->group_pathkeys);
/* generate alternative group orderings that might be useful */
pathkey_orderings = get_useful_group_keys_orderings(root, path);
if (path == NULL)
continue;
Assert(list_length(pathkey_orderings) > 0);
if (parse->hasAggs)
add_path(grouped_rel, (Path *)
create_agg_path(root,
/* process all potentially interesting grouping reorderings */
foreach(lc2, pathkey_orderings)
{
PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
/* restore the path (we replace it in the loop) */
path = path_save;
path = make_ordered_path(root,
grouped_rel,
path,
grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_FINAL_DESERIAL,
root->processed_groupClause,
havingQual,
agg_final_costs,
dNumGroups));
else
add_path(grouped_rel, (Path *)
create_group_path(root,
grouped_rel,
path,
root->processed_groupClause,
havingQual,
dNumGroups));
partially_grouped_rel->cheapest_total_path,
info->pathkeys);
if (path == NULL)
continue;
if (parse->hasAggs)
add_path(grouped_rel, (Path *)
create_agg_path(root,
grouped_rel,
path,
grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_FINAL_DESERIAL,
info->clauses,
havingQual,
agg_final_costs,
dNumGroups));
else
add_path(grouped_rel, (Path *)
create_group_path(root,
grouped_rel,
path,
info->clauses,
havingQual,
dNumGroups));
}
}
}
}
@@ -7190,37 +7135,54 @@ create_partial_grouping_paths(PlannerInfo *root,
*/
foreach(lc, input_rel->pathlist)
{
ListCell *lc2;
Path *path = (Path *) lfirst(lc);
Path *path_save = path;
List *pathkey_orderings = NIL;
path = make_ordered_path(root,
partially_grouped_rel,
path,
cheapest_total_path,
root->group_pathkeys);
/* generate alternative group orderings that might be useful */
pathkey_orderings = get_useful_group_keys_orderings(root, path);
if (path == NULL)
continue;
Assert(list_length(pathkey_orderings) > 0);
if (parse->hasAggs)
add_path(partially_grouped_rel, (Path *)
create_agg_path(root,
/* process all potentially interesting grouping reorderings */
foreach(lc2, pathkey_orderings)
{
PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
/* restore the path (we replace it in the loop) */
path = path_save;
path = make_ordered_path(root,
partially_grouped_rel,
path,
partially_grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_INITIAL_SERIAL,
root->processed_groupClause,
NIL,
agg_partial_costs,
dNumPartialGroups));
else
add_path(partially_grouped_rel, (Path *)
create_group_path(root,
partially_grouped_rel,
path,
root->processed_groupClause,
NIL,
dNumPartialGroups));
cheapest_total_path,
info->pathkeys);
if (path == NULL)
continue;
if (parse->hasAggs)
add_path(partially_grouped_rel, (Path *)
create_agg_path(root,
partially_grouped_rel,
path,
partially_grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_INITIAL_SERIAL,
info->clauses,
NIL,
agg_partial_costs,
dNumPartialGroups));
else
add_path(partially_grouped_rel, (Path *)
create_group_path(root,
partially_grouped_rel,
path,
info->clauses,
NIL,
dNumPartialGroups));
}
}
}
@@ -7229,37 +7191,55 @@ create_partial_grouping_paths(PlannerInfo *root,
/* Similar to above logic, but for partial paths. */
foreach(lc, input_rel->partial_pathlist)
{
ListCell *lc2;
Path *path = (Path *) lfirst(lc);
Path *path_save = path;
List *pathkey_orderings = NIL;
path = make_ordered_path(root,
partially_grouped_rel,
path,
cheapest_partial_path,
root->group_pathkeys);
/* generate alternative group orderings that might be useful */
pathkey_orderings = get_useful_group_keys_orderings(root, path);
if (path == NULL)
continue;
Assert(list_length(pathkey_orderings) > 0);
if (parse->hasAggs)
add_partial_path(partially_grouped_rel, (Path *)
create_agg_path(root,
partially_grouped_rel,
path,
partially_grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_INITIAL_SERIAL,
root->processed_groupClause,
NIL,
agg_partial_costs,
dNumPartialPartialGroups));
else
add_partial_path(partially_grouped_rel, (Path *)
create_group_path(root,
partially_grouped_rel,
path,
root->processed_groupClause,
NIL,
dNumPartialPartialGroups));
/* process all potentially interesting grouping reorderings */
foreach(lc2, pathkey_orderings)
{
PathKeyInfo *info = (PathKeyInfo *) lfirst(lc2);
/* restore the path (we replace it in the loop) */
path = path_save;
path = make_ordered_path(root,
partially_grouped_rel,
path,
cheapest_partial_path,
info->pathkeys);
if (path == NULL)
continue;
if (parse->hasAggs)
add_partial_path(partially_grouped_rel, (Path *)
create_agg_path(root,
partially_grouped_rel,
path,
partially_grouped_rel->reltarget,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
AGGSPLIT_INITIAL_SERIAL,
info->clauses,
NIL,
agg_partial_costs,
dNumPartialPartialGroups));
else
add_partial_path(partially_grouped_rel, (Path *)
create_group_path(root,
partially_grouped_rel,
path,
info->clauses,
NIL,
dNumPartialPartialGroups));
}
}
}
@@ -7373,6 +7353,8 @@ gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel)
* We can also skip the entire loop when we only have a single-item
* group_pathkeys because then we can't possibly have a presorted prefix
* of the list without having the list be fully sorted.
*
* XXX Shouldn't this also consider the group-key-reordering?
*/
if (!enable_incremental_sort || list_length(root->group_pathkeys) == 1)
return;