*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.263 2010/01/02 16:57:47 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.264 2010/02/10 03:38:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
static void preprocess_groupclause(PlannerInfo *root);
static bool choose_hashed_grouping(PlannerInfo *root,
double tuple_fraction, double limit_tuples,
+ double path_rows, int path_width,
Path *cheapest_path, Path *sorted_path,
double dNumGroups, AggClauseCounts *agg_counts);
static bool choose_hashed_distinct(PlannerInfo *root,
- Plan *input_plan, List *input_pathkeys,
double tuple_fraction, double limit_tuples,
+ double path_rows, int path_width,
+ Cost cheapest_startup_cost, Cost cheapest_total_cost,
+ Cost sorted_startup_cost, Cost sorted_total_cost,
+ List *sorted_pathkeys,
double dNumDistinctRows);
static List *make_subplanTargetList(PlannerInfo *root, List *tlist,
AttrNumber **groupColIdx, bool *need_tlist_eval);
Plan *result_plan;
List *current_pathkeys;
double dNumGroups = 0;
+ bool use_hashed_distinct = false;
+ bool tested_hashed_distinct = false;
/* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
if (parse->limitCount || parse->limitOffset)
long numGroups = 0;
AggClauseCounts agg_counts;
int numGroupCols;
+ double path_rows;
+ int path_width;
bool use_hashed_grouping = false;
WindowFuncLists *wflists = NULL;
List *activeWindows = NIL;
&cheapest_path, &sorted_path, &dNumGroups);
/*
- * If grouping, decide whether to use sorted or hashed grouping.
+ * Extract rowcount and width estimates for possible use in grouping
+ * decisions. Beware here of the possibility that
+ * cheapest_path->parent is NULL (ie, there is no FROM clause).
*/
- if (parse->groupClause)
+ if (cheapest_path->parent)
+ {
+ path_rows = cheapest_path->parent->rows;
+ path_width = cheapest_path->parent->width;
+ }
+ else
{
- bool can_hash;
- bool can_sort;
+ path_rows = 1; /* assume non-set result */
+ path_width = 100; /* arbitrary */
+ }
+ if (parse->groupClause)
+ {
/*
- * Executor doesn't support hashed aggregation with DISTINCT or
- * ORDER BY aggregates. (Doing so would imply storing *all* the
- * input values in the hash table, and/or running many sorts in
- * parallel, either of which seems like a certain loser.)
+ * If grouping, decide whether to use sorted or hashed grouping.
*/
- can_hash = (agg_counts.numOrderedAggs == 0 &&
- grouping_is_hashable(parse->groupClause));
- can_sort = grouping_is_sortable(parse->groupClause);
- if (can_hash && can_sort)
- {
- /* we have a meaningful choice to make ... */
- use_hashed_grouping =
- choose_hashed_grouping(root,
- tuple_fraction, limit_tuples,
- cheapest_path, sorted_path,
- dNumGroups, &agg_counts);
- }
- else if (can_hash)
- use_hashed_grouping = true;
- else if (can_sort)
- use_hashed_grouping = false;
- else
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("could not implement GROUP BY"),
- errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
-
+ use_hashed_grouping =
+ choose_hashed_grouping(root,
+ tuple_fraction, limit_tuples,
+ path_rows, path_width,
+ cheapest_path, sorted_path,
+ dNumGroups, &agg_counts);
/* Also convert # groups to long int --- but 'ware overflow! */
numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
}
+ else if (parse->distinctClause && sorted_path &&
+ !root->hasHavingQual && !parse->hasAggs && !activeWindows)
+ {
+ /*
+ * We'll reach the DISTINCT stage without any intermediate
+ * processing, so figure out whether we will want to hash or not
+ * so we can choose whether to use cheapest or sorted path.
+ */
+ use_hashed_distinct =
+ choose_hashed_distinct(root,
+ tuple_fraction, limit_tuples,
+ path_rows, path_width,
+ cheapest_path->startup_cost,
+ cheapest_path->total_cost,
+ sorted_path->startup_cost,
+ sorted_path->total_cost,
+ sorted_path->pathkeys,
+ dNumGroups);
+ tested_hashed_distinct = true;
+ }
/*
* Select the best path. 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 (use_hashed_grouping || !sorted_path)
+ if (use_hashed_grouping || use_hashed_distinct || !sorted_path)
best_path = cheapest_path;
else
best_path = sorted_path;
{
double dNumDistinctRows;
long numDistinctRows;
- bool use_hashed_distinct;
- bool can_sort;
- bool can_hash;
/*
* If there was grouping or aggregation, use the current number of
/* Also convert to long int --- but 'ware overflow! */
numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);
- /*
- * If we have a sortable DISTINCT ON clause, we always use sorting.
- * This enforces the expected behavior of DISTINCT ON.
- */
- can_sort = grouping_is_sortable(parse->distinctClause);
- if (can_sort && parse->hasDistinctOn)
- use_hashed_distinct = false;
- else
+ /* Choose implementation method if we didn't already */
+ if (!tested_hashed_distinct)
{
- can_hash = grouping_is_hashable(parse->distinctClause);
- if (can_hash && can_sort)
- {
- /* we have a meaningful choice to make ... */
- use_hashed_distinct =
- choose_hashed_distinct(root,
- result_plan, current_pathkeys,
- tuple_fraction, limit_tuples,
- dNumDistinctRows);
- }
- else if (can_hash)
- use_hashed_distinct = true;
- else if (can_sort)
- use_hashed_distinct = false;
- else
- {
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("could not implement DISTINCT"),
- errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
- use_hashed_distinct = false; /* keep compiler quiet */
- }
+ /*
+ * At this point, either hashed or sorted grouping will have to
+ * work from result_plan, so we pass that as both "cheapest" and
+ * "sorted".
+ */
+ use_hashed_distinct =
+ choose_hashed_distinct(root,
+ tuple_fraction, limit_tuples,
+ result_plan->plan_rows,
+ result_plan->plan_width,
+ result_plan->startup_cost,
+ result_plan->total_cost,
+ result_plan->startup_cost,
+ result_plan->total_cost,
+ current_pathkeys,
+ dNumDistinctRows);
}
if (use_hashed_distinct)
/*
* choose_hashed_grouping - should we use hashed grouping?
*
- * Note: this is only applied when both alternatives are actually feasible.
+ * Returns TRUE to select hashing, FALSE to select sorting.
*/
static bool
choose_hashed_grouping(PlannerInfo *root,
double tuple_fraction, double limit_tuples,
+ double path_rows, int path_width,
Path *cheapest_path, Path *sorted_path,
double dNumGroups, AggClauseCounts *agg_counts)
{
- int numGroupCols = list_length(root->parse->groupClause);
- double cheapest_path_rows;
- int cheapest_path_width;
+ Query *parse = root->parse;
+ int numGroupCols = list_length(parse->groupClause);
+ bool can_hash;
+ bool can_sort;
Size hashentrysize;
List *target_pathkeys;
List *current_pathkeys;
Path hashed_p;
Path sorted_p;
+ /*
+ * Executor doesn't support hashed aggregation with DISTINCT or ORDER BY
+ * aggregates. (Doing so would imply storing *all* the input values in
+ * the hash table, and/or running many sorts in parallel, either of which
+ * seems like a certain loser.)
+ */
+ can_hash = (agg_counts->numOrderedAggs == 0 &&
+ grouping_is_hashable(parse->groupClause));
+ can_sort = grouping_is_sortable(parse->groupClause);
+
+ /* Quick out if only one choice is workable */
+ if (!(can_hash && can_sort))
+ {
+ if (can_hash)
+ return true;
+ else if (can_sort)
+ return false;
+ else
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("could not implement GROUP BY"),
+ errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
+ }
+
/* Prefer sorting when enable_hashagg is off */
if (!enable_hashagg)
return false;
/*
* Don't do it if it doesn't look like the hashtable will fit into
* work_mem.
- *
- * Beware here of the possibility that cheapest_path->parent is NULL. This
- * could happen if user does something silly like SELECT 'foo' GROUP BY 1;
*/
- if (cheapest_path->parent)
- {
- cheapest_path_rows = cheapest_path->parent->rows;
- cheapest_path_width = cheapest_path->parent->width;
- }
- else
- {
- cheapest_path_rows = 1; /* assume non-set result */
- cheapest_path_width = 100; /* arbitrary */
- }
/* Estimate per-hash-entry space at tuple width... */
- hashentrysize = MAXALIGN(cheapest_path_width) + MAXALIGN(sizeof(MinimalTupleData));
+ hashentrysize = MAXALIGN(path_width) + MAXALIGN(sizeof(MinimalTupleData));
/* plus space for pass-by-ref transition values... */
hashentrysize += agg_counts->transitionSpace;
/* plus the per-hash-entry overhead */
cost_agg(&hashed_p, root, AGG_HASHED, agg_counts->numAggs,
numGroupCols, dNumGroups,
cheapest_path->startup_cost, cheapest_path->total_cost,
- cheapest_path_rows);
+ path_rows);
/* Result of hashed agg is always unsorted */
if (target_pathkeys)
cost_sort(&hashed_p, root, target_pathkeys, hashed_p.total_cost,
- dNumGroups, cheapest_path_width, limit_tuples);
+ dNumGroups, path_width, limit_tuples);
if (sorted_path)
{
if (!pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
{
cost_sort(&sorted_p, root, root->group_pathkeys, sorted_p.total_cost,
- cheapest_path_rows, cheapest_path_width, -1.0);
+ path_rows, path_width, -1.0);
current_pathkeys = root->group_pathkeys;
}
- if (root->parse->hasAggs)
+ if (parse->hasAggs)
cost_agg(&sorted_p, root, AGG_SORTED, agg_counts->numAggs,
numGroupCols, dNumGroups,
sorted_p.startup_cost, sorted_p.total_cost,
- cheapest_path_rows);
+ path_rows);
else
cost_group(&sorted_p, root, numGroupCols, dNumGroups,
sorted_p.startup_cost, sorted_p.total_cost,
- cheapest_path_rows);
+ path_rows);
/* The Agg or Group node will preserve ordering */
if (target_pathkeys &&
!pathkeys_contained_in(target_pathkeys, current_pathkeys))
cost_sort(&sorted_p, root, target_pathkeys, sorted_p.total_cost,
- dNumGroups, cheapest_path_width, limit_tuples);
+ dNumGroups, path_width, limit_tuples);
/*
* Now make the decision using the top-level tuple fraction. First we
*
* This is fairly similar to choose_hashed_grouping, but there are enough
* differences that it doesn't seem worth trying to unify the two functions.
+ * (One difference is that we sometimes apply this after forming a Plan,
+ * so the input alternatives can't be represented as Paths --- instead we
+ * pass in the costs as individual variables.)
*
* But note that making the two choices independently is a bit bogus in
* itself. If the two could be combined into a single choice operation
* extra preference to using a sorting implementation when a common sort key
* is available ... and that's not necessarily wrong anyway.
*
- * Note: this is only applied when both alternatives are actually feasible.
+ * Returns TRUE to select hashing, FALSE to select sorting.
*/
static bool
choose_hashed_distinct(PlannerInfo *root,
- Plan *input_plan, List *input_pathkeys,
double tuple_fraction, double limit_tuples,
+ double path_rows, int path_width,
+ Cost cheapest_startup_cost, Cost cheapest_total_cost,
+ Cost sorted_startup_cost, Cost sorted_total_cost,
+ List *sorted_pathkeys,
double dNumDistinctRows)
{
- int numDistinctCols = list_length(root->parse->distinctClause);
+ Query *parse = root->parse;
+ int numDistinctCols = list_length(parse->distinctClause);
+ bool can_sort;
+ bool can_hash;
Size hashentrysize;
List *current_pathkeys;
List *needed_pathkeys;
Path hashed_p;
Path sorted_p;
+ /*
+ * If we have a sortable DISTINCT ON clause, we always use sorting.
+ * This enforces the expected behavior of DISTINCT ON.
+ */
+ can_sort = grouping_is_sortable(parse->distinctClause);
+ if (can_sort && parse->hasDistinctOn)
+ return false;
+
+ can_hash = grouping_is_hashable(parse->distinctClause);
+
+ /* Quick out if only one choice is workable */
+ if (!(can_hash && can_sort))
+ {
+ if (can_hash)
+ return true;
+ else if (can_sort)
+ return false;
+ else
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("could not implement DISTINCT"),
+ errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
+ }
+
/* Prefer sorting when enable_hashagg is off */
if (!enable_hashagg)
return false;
* Don't do it if it doesn't look like the hashtable will fit into
* work_mem.
*/
- hashentrysize = MAXALIGN(input_plan->plan_width) + MAXALIGN(sizeof(MinimalTupleData));
+ hashentrysize = MAXALIGN(path_width) + MAXALIGN(sizeof(MinimalTupleData));
if (hashentrysize * dNumDistinctRows > work_mem * 1024L)
return false;
* output won't be sorted may be a loss; so we need to do an actual cost
* comparison.
*
- * We need to consider input_plan + hashagg [+ final sort] versus
- * input_plan [+ sort] + group [+ final sort] where brackets indicate a
+ * We need to consider cheapest_path + hashagg [+ final sort] versus
+ * sorted_path [+ sort] + group [+ final sort] where brackets indicate a
* step that may not be needed.
*
* These path variables are dummies that just hold cost fields; we don't
*/
cost_agg(&hashed_p, root, AGG_HASHED, 0,
numDistinctCols, dNumDistinctRows,
- input_plan->startup_cost, input_plan->total_cost,
- input_plan->plan_rows);
+ cheapest_startup_cost, cheapest_total_cost,
+ path_rows);
/*
* Result of hashed agg is always unsorted, so if ORDER BY is present we
* need to charge for the final sort.
*/
- if (root->parse->sortClause)
+ if (parse->sortClause)
cost_sort(&hashed_p, root, root->sort_pathkeys, hashed_p.total_cost,
- dNumDistinctRows, input_plan->plan_width, limit_tuples);
+ dNumDistinctRows, path_width, limit_tuples);
/*
* Now for the GROUP case. See comments in grouping_planner about the
* sorting choices here --- this code should match that code.
*/
- sorted_p.startup_cost = input_plan->startup_cost;
- sorted_p.total_cost = input_plan->total_cost;
- current_pathkeys = input_pathkeys;
- if (root->parse->hasDistinctOn &&
+ sorted_p.startup_cost = sorted_startup_cost;
+ sorted_p.total_cost = sorted_total_cost;
+ current_pathkeys = sorted_pathkeys;
+ if (parse->hasDistinctOn &&
list_length(root->distinct_pathkeys) <
list_length(root->sort_pathkeys))
needed_pathkeys = root->sort_pathkeys;
else
current_pathkeys = root->sort_pathkeys;
cost_sort(&sorted_p, root, current_pathkeys, sorted_p.total_cost,
- input_plan->plan_rows, input_plan->plan_width, -1.0);
+ path_rows, path_width, -1.0);
}
cost_group(&sorted_p, root, numDistinctCols, dNumDistinctRows,
sorted_p.startup_cost, sorted_p.total_cost,
- input_plan->plan_rows);
- if (root->parse->sortClause &&
+ path_rows);
+ if (parse->sortClause &&
!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
cost_sort(&sorted_p, root, root->sort_pathkeys, sorted_p.total_cost,
- dNumDistinctRows, input_plan->plan_width, limit_tuples);
+ dNumDistinctRows, path_width, limit_tuples);
/*
* Now make the decision using the top-level tuple fraction. First we
return false;
}
-/*---------------
+/*
* make_subplanTargetList
* Generate appropriate target list when grouping is required.
*
* result tlist.
*
* The result is the targetlist to be passed to the subplan.
- *---------------
*/
static List *
make_subplanTargetList(PlannerInfo *root,
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