/*
* query_planner
* Generate a path (that is, a simplified plan) for a basic query,
* which may involve joins but not any fancier features.
*
* Since query_planner does not handle the toplevel processing (grouping,
* sorting, etc) it cannot select the best path by itself. Instead, it
* returns the RelOptInfo for the top level of joining, and the caller
* (grouping_planner) can choose one of the surviving paths for the rel.
* Normally it would choose either the rel's cheapest path, or the cheapest
* path for the desired sort order.
*
* root describes the query to plan
* tlist is the target list the query should produce
* (this is NOT necessarily root->parse->targetList!)
* qp_callback is a function to compute query_pathkeys once it's safe to do so
* qp_extra is optional extra data to pass to qp_callback
*
* Note: the PlannerInfo node also includes a query_pathkeys field, which
* tells query_planner the sort order that is desired in the final output
* plan. This value is *not* available at call time, but is computed by
* qp_callback once we have completed merging the query's equivalence classes.
* (We cannot construct canonical pathkeys until that's done.)
*/
RelOptInfo *
query_planner(PlannerInfo *root, List *tlist,
query_pathkeys_callback qp_callback, void *qp_extra)
{
Query *parse = root->parse;
List *joinlist;
RelOptInfo *final_rel;
Index rti;
double total_pages;
/*
* If the query has an empty join tree, then it's something easy like
* "SELECT 2+2;" or "INSERT ... VALUES()". Fall through quickly.
*/
if (parse->jointree->fromlist == NIL)
{
/* We need a dummy joinrel to describe the empty set of baserels */
final_rel = build_empty_join_rel(root);
/* The only path for it is a trivial Result path */
add_path(final_rel, (Path *)
create_result_path((List *) parse->jointree->quals));
/* Select cheapest path (pretty easy in this case...) */
set_cheapest(final_rel);
/*
* We still are required to call qp_callback, in case it's something
* like "SELECT 2+2 ORDER BY 1".
*/
root->canon_pathkeys = NIL;
(*qp_callback) (root, qp_extra);
return final_rel;
}
/*
* Init planner lists to empty.
*
* NOTE: append_rel_list was set up by subquery_planner, so do not touch
* here; eq_classes and minmax_aggs may contain data already, too.
*/
root->join_rel_list = NIL;
root->join_rel_hash = NULL;
root->join_rel_level = NULL;
root->join_cur_level = 0;
root->canon_pathkeys = NIL;
root->left_join_clauses = NIL;
root->right_join_clauses = NIL;
root->full_join_clauses = NIL;
root->join_info_list = NIL;
root->lateral_info_list = NIL;
root->placeholder_list = NIL;
root->initial_rels = NIL;
/*
* Make a flattened version of the rangetable for faster access (this is
* OK because the rangetable won't change any more), and set up an empty
* array for indexing base relations.
*/
setup_simple_rel_arrays(root);
/*
* Construct RelOptInfo nodes for all base relations in query, and
* indirectly for all appendrel member relations ("other rels"). This
* will give us a RelOptInfo for every "simple" (non-join) rel involved in
* the query.
*
* Note: the reason we find the rels by searching the jointree and
* appendrel list, rather than just scanning the rangetable, is that the
* rangetable may contain RTEs for rels not actively part of the query,
* for example views. We don't want to make RelOptInfos for them.
*/
add_base_rels_to_query(root, (Node *) parse->jointree);
/*
* Examine the targetlist and join tree, adding entries to baserel
* targetlists for all referenced Vars, and generating PlaceHolderInfo
* entries for all referenced PlaceHolderVars. Restrict and join clauses
* are added to appropriate lists belonging to the mentioned relations. We
* also build EquivalenceClasses for provably equivalent expressions. The
* SpecialJoinInfo list is also built to hold information about join order
* restrictions. Finally, we form a target joinlist for make_one_rel() to
* work from.
*/
build_base_rel_tlists(root, tlist);
find_placeholders_in_jointree(root);
find_lateral_references(root);
joinlist = deconstruct_jointree(root);
/*
* Reconsider any postponed outer-join quals now that we have built up
* equivalence classes. (This could result in further additions or
* mergings of classes.)
*/
reconsider_outer_join_clauses(root);
/*
* If we formed any equivalence classes, generate additional restriction
* clauses as appropriate. (Implied join clauses are formed on-the-fly
* later.)
*/
generate_base_implied_equalities(root);
/*
* We have completed merging equivalence sets, so it's now possible to
* generate pathkeys in canonical form; so compute query_pathkeys and
* other pathkeys fields in PlannerInfo.
*/
(*qp_callback) (root, qp_extra);
/*
* Examine any "placeholder" expressions generated during subquery pullup.
* Make sure that the Vars they need are marked as needed at the relevant
* join level. This must be done before join removal because it might
* cause Vars or placeholders to be needed above a join when they weren't
* so marked before.
*/
fix_placeholder_input_needed_levels(root);
/*
* Remove any useless outer joins. Ideally this would be done during
* jointree preprocessing, but the necessary information isn't available
* until we've built baserel data structures and classified qual clauses.
*/
joinlist = remove_useless_joins(root, joinlist);
/*
* Now distribute "placeholders" to base rels as needed. This has to be
* done after join removal because removal could change whether a
* placeholder is evaluatable at a base rel.
*/
add_placeholders_to_base_rels(root);
/*
* Create the LateralJoinInfo list now that we have finalized
* PlaceHolderVar eval levels and made any necessary additions to the
* lateral_vars lists for lateral references within PlaceHolderVars.
*/
create_lateral_join_info(root);
/*
* Look for join OR clauses that we can extract single-relation
* restriction OR clauses from.
*/
extract_restriction_or_clauses(root);
/*
* We should now have size estimates for every actual table involved in
* the query, and we also know which if any have been deleted from the
* query by join removal; so we can compute total_table_pages.
*
* Note that appendrels are not double-counted here, even though we don't
* bother to distinguish RelOptInfos for appendrel parents, because the
* parents will still have size zero.
*
* XXX if a table is self-joined, we will count it once per appearance,
* which perhaps is the wrong thing ... but that's not completely clear,
* and detecting self-joins here is difficult, so ignore it for now.
*/
total_pages = 0;
for (rti = 1; rti < root->simple_rel_array_size; rti++)
{
RelOptInfo *brel = root->simple_rel_array[rti];
if (brel == NULL)
continue;
Assert(brel->relid == rti); /* sanity check on array */
if (brel->reloptkind == RELOPT_BASEREL ||
brel->reloptkind == RELOPT_OTHER_MEMBER_REL)
total_pages += (double) brel->pages;
}
root->total_table_pages = total_pages;
/*
* Ready to do the primary planning.
*/
final_rel = make_one_rel(root, joinlist);
/* Check that we got at least one usable path */
if (!final_rel || !final_rel->cheapest_total_path ||
final_rel->cheapest_total_path->param_info != NULL)
elog(ERROR, "failed to construct the join relation");
return final_rel;
}
/*
* query_planner
* Generate a path (that is, a simplified plan) for a basic query,
* which may involve joins but not any fancier features.
*
* Since query_planner does not handle the toplevel processing (grouping,
* sorting, etc) it cannot select the best path by itself. It selects
* two paths: the cheapest path that produces all the required tuples,
* independent of any ordering considerations, and the cheapest path that
* produces the expected fraction of the required tuples in the required
* ordering, if there is a path that is cheaper for this than just sorting
* the output of the cheapest overall path. The caller (grouping_planner)
* will make the final decision about which to use.
*
* Input parameters:
* root describes the query to plan
* tlist is the target list the query should produce
* (this is NOT necessarily root->parse->targetList!)
* tuple_fraction is the fraction of tuples we expect will be retrieved
* limit_tuples is a hard limit on number of tuples to retrieve,
* or -1 if no limit
*
* Output parameters:
* *cheapest_path receives the overall-cheapest path for the query
* *sorted_path receives the cheapest presorted path for the query,
* if any (NULL if there is no useful presorted path)
* *num_groups receives the estimated number of groups, or 1 if query
* does not use grouping
*
* Note: the PlannerInfo node also includes a query_pathkeys field, which is
* both an input and an output of query_planner(). The input value signals
* query_planner that the indicated sort order is wanted in the final output
* plan. But this value has not yet been "canonicalized", since the needed
* info does not get computed until we scan the qual clauses. We canonicalize
* it as soon as that task is done. (The main reason query_pathkeys is a
* PlannerInfo field and not a passed parameter is that the low-level routines
* in indxpath.c need to see it.)
*
* Note: the PlannerInfo node includes other pathkeys fields besides
* query_pathkeys, all of which need to be canonicalized once the info is
* available. See canonicalize_all_pathkeys.
*
* tuple_fraction is interpreted as follows:
* 0: expect all tuples to be retrieved (normal case)
* 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)
* Note that a nonzero tuple_fraction could come from outer context; it is
* therefore not redundant with limit_tuples. We use limit_tuples to determine
* whether a bounded sort can be used at runtime.
*/
void
query_planner(PlannerInfo *root, List *tlist,
double tuple_fraction, double limit_tuples,
Path **cheapest_path, Path **sorted_path,
double *num_groups)
{
Query *parse = root->parse;
List *joinlist;
RelOptInfo *final_rel;
Path *cheapestpath;
Path *sortedpath;
Index rti;
double total_pages;
/* Make tuple_fraction, limit_tuples accessible to lower-level routines */
root->tuple_fraction = tuple_fraction;
root->limit_tuples = limit_tuples;
*num_groups = 1; /* default result */
/*
* If the query has an empty join tree, then it's something easy like
* "SELECT 2+2;" or "INSERT ... VALUES()". Fall through quickly.
*/
if (parse->jointree->fromlist == NIL)
{
/* We need a trivial path result */
*cheapest_path = (Path *)
create_result_path((List *) parse->jointree->quals);
*sorted_path = NULL;
/*
* We still are required to canonicalize any pathkeys, in case it's
* something like "SELECT 2+2 ORDER BY 1".
*/
root->canon_pathkeys = NIL;
canonicalize_all_pathkeys(root);
return;
}
/*
* Init planner lists to empty.
*
* NOTE: append_rel_list was set up by subquery_planner, so do not touch
* here; eq_classes and minmax_aggs may contain data already, too.
*/
root->join_rel_list = NIL;
root->join_rel_hash = NULL;
root->join_rel_level = NULL;
root->join_cur_level = 0;
root->canon_pathkeys = NIL;
root->left_join_clauses = NIL;
root->right_join_clauses = NIL;
root->full_join_clauses = NIL;
root->join_info_list = NIL;
root->placeholder_list = NIL;
root->initial_rels = NIL;
/*
* Make a flattened version of the rangetable for faster access (this is
* OK because the rangetable won't change any more), and set up an empty
* array for indexing base relations.
*/
setup_simple_rel_arrays(root);
/*
* Construct RelOptInfo nodes for all base relations in query, and
* indirectly for all appendrel member relations ("other rels"). This
* will give us a RelOptInfo for every "simple" (non-join) rel involved in
* the query.
*
* Note: the reason we find the rels by searching the jointree and
* appendrel list, rather than just scanning the rangetable, is that the
* rangetable may contain RTEs for rels not actively part of the query,
* for example views. We don't want to make RelOptInfos for them.
*/
add_base_rels_to_query(root, (Node *) parse->jointree);
/*
* Examine the targetlist and join tree, adding entries to baserel
* targetlists for all referenced Vars, and generating PlaceHolderInfo
* entries for all referenced PlaceHolderVars. Restrict and join clauses
* are added to appropriate lists belonging to the mentioned relations. We
* also build EquivalenceClasses for provably equivalent expressions. The
* SpecialJoinInfo list is also built to hold information about join order
* restrictions. Finally, we form a target joinlist for make_one_rel() to
* work from.
*/
build_base_rel_tlists(root, tlist);
find_placeholders_in_jointree(root);
joinlist = deconstruct_jointree(root);
/*
* Reconsider any postponed outer-join quals now that we have built up
* equivalence classes. (This could result in further additions or
* mergings of classes.)
*/
reconsider_outer_join_clauses(root);
/*
* If we formed any equivalence classes, generate additional restriction
* clauses as appropriate. (Implied join clauses are formed on-the-fly
* later.)
*/
generate_base_implied_equalities(root);
/*
* We have completed merging equivalence sets, so it's now possible to
* convert previously generated pathkeys (in particular, the requested
* query_pathkeys) to canonical form.
*/
canonicalize_all_pathkeys(root);
/*
* Examine any "placeholder" expressions generated during subquery pullup.
* Make sure that the Vars they need are marked as needed at the relevant
* join level. This must be done before join removal because it might
* cause Vars or placeholders to be needed above a join when they weren't
* so marked before.
*/
fix_placeholder_input_needed_levels(root);
/*
* Remove any useless outer joins. Ideally this would be done during
* jointree preprocessing, but the necessary information isn't available
* until we've built baserel data structures and classified qual clauses.
*/
joinlist = remove_useless_joins(root, joinlist);
/*
* Now distribute "placeholders" to base rels as needed. This has to be
* done after join removal because removal could change whether a
* placeholder is evaluatable at a base rel.
*/
add_placeholders_to_base_rels(root);
/*
* We should now have size estimates for every actual table involved in
* the query, and we also know which if any have been deleted from the
* query by join removal; so we can compute total_table_pages.
*
* Note that appendrels are not double-counted here, even though we don't
* bother to distinguish RelOptInfos for appendrel parents, because the
* parents will still have size zero.
*
* XXX if a table is self-joined, we will count it once per appearance,
* which perhaps is the wrong thing ... but that's not completely clear,
* and detecting self-joins here is difficult, so ignore it for now.
*/
total_pages = 0;
for (rti = 1; rti < root->simple_rel_array_size; rti++)
{
RelOptInfo *brel = root->simple_rel_array[rti];
if (brel == NULL)
continue;
Assert(brel->relid == rti); /* sanity check on array */
if (brel->reloptkind == RELOPT_BASEREL ||
brel->reloptkind == RELOPT_OTHER_MEMBER_REL)
total_pages += (double) brel->pages;
}
root->total_table_pages = total_pages;
/*
* Ready to do the primary planning.
*/
final_rel = make_one_rel(root, joinlist);
if (!final_rel || !final_rel->cheapest_total_path)
elog(ERROR, "failed to construct the join relation");
/*
* If there's grouping going on, estimate the number of result groups. We
* couldn't do this any earlier because it depends on relation size
* estimates that were set up above.
*
* Then convert tuple_fraction to fractional form if it is absolute, and
* adjust it based on the knowledge that grouping_planner will be doing
* grouping or aggregation work with our result.
*
* This introduces some undesirable coupling between this code and
* grouping_planner, but the alternatives seem even uglier; we couldn't
* pass back completed paths without making these decisions here.
*/
if (parse->groupClause)
{
List *groupExprs;
groupExprs = get_sortgrouplist_exprs(parse->groupClause,
parse->targetList);
*num_groups = estimate_num_groups(root,
groupExprs,
final_rel->rows);
/*
* In GROUP BY mode, an absolute LIMIT is relative to the number of
* groups not the number of tuples. If the caller gave us a fraction,
* keep it as-is. (In both cases, we are effectively assuming that
* all the groups are about the same size.)
*/
if (tuple_fraction >= 1.0)
tuple_fraction /= *num_groups;
/*
* If both GROUP BY and ORDER BY are specified, we will need two
* levels of sort --- and, therefore, certainly need to read all the
* tuples --- unless ORDER BY is a subset of GROUP BY. Likewise if we
* have both DISTINCT and GROUP BY, or if we have a window
* specification not compatible with the GROUP BY.
*/
if (!pathkeys_contained_in(root->sort_pathkeys, root->group_pathkeys) ||
!pathkeys_contained_in(root->distinct_pathkeys, root->group_pathkeys) ||
!pathkeys_contained_in(root->window_pathkeys, root->group_pathkeys))
tuple_fraction = 0.0;
/* In any case, limit_tuples shouldn't be specified here */
Assert(limit_tuples < 0);
}
else if (parse->hasAggs || root->hasHavingQual)
{
/*
* Ungrouped aggregate will certainly want to read all the tuples, and
* it will deliver a single result row (so leave *num_groups 1).
*/
tuple_fraction = 0.0;
/* limit_tuples shouldn't be specified here */
Assert(limit_tuples < 0);
}
else if (parse->distinctClause)
{
/*
* Since there was no grouping or aggregation, it's reasonable to
* assume the UNIQUE filter has effects comparable to GROUP BY. Return
* the estimated number of output rows for use by caller. (If DISTINCT
* is used with grouping, we ignore its effects for rowcount
* estimation purposes; this amounts to assuming the grouped rows are
* distinct already.)
*/
List *distinctExprs;
distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
parse->targetList);
*num_groups = estimate_num_groups(root,
distinctExprs,
final_rel->rows);
/*
* Adjust tuple_fraction the same way as for GROUP BY, too.
*/
if (tuple_fraction >= 1.0)
tuple_fraction /= *num_groups;
/* limit_tuples shouldn't be specified here */
Assert(limit_tuples < 0);
}
else
{
/*
* Plain non-grouped, non-aggregated query: an absolute tuple fraction
* can be divided by the number of tuples.
*/
if (tuple_fraction >= 1.0)
tuple_fraction /= final_rel->rows;
}
/*
* Pick out the cheapest-total path and the cheapest presorted path for
* the requested pathkeys (if there is one). We should take the tuple
* fraction into account when selecting the cheapest presorted path, but
* not when selecting the cheapest-total path, since if we have to sort
* then we'll have to fetch all the tuples. (But there's a special case:
* if query_pathkeys is NIL, meaning order doesn't matter, then the
* "cheapest presorted" path will be the cheapest overall for the tuple
* fraction.)
*
* The cheapest-total path is also the one to use if grouping_planner
* decides to use hashed aggregation, so we return it separately even if
* this routine thinks the presorted path is the winner.
*/
cheapestpath = final_rel->cheapest_total_path;
sortedpath =
get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
root->query_pathkeys,
NULL,
tuple_fraction);
/* Don't return same path in both guises; just wastes effort */
if (sortedpath == cheapestpath)
sortedpath = NULL;
/*
* Forget about the presorted path if it would be cheaper to sort the
* cheapest-total path. Here we need consider only the behavior at the
* tuple fraction point.
*/
if (sortedpath)
{
Path sort_path; /* dummy for result of cost_sort */
if (root->query_pathkeys == NIL ||
pathkeys_contained_in(root->query_pathkeys,
cheapestpath->pathkeys))
{
/* No sort needed for cheapest path */
sort_path.startup_cost = cheapestpath->startup_cost;
sort_path.total_cost = cheapestpath->total_cost;
}
else
{
/* Figure cost for sorting */
cost_sort(&sort_path, root, root->query_pathkeys,
cheapestpath->total_cost,
final_rel->rows, final_rel->width,
0.0, work_mem, limit_tuples);
}
if (compare_fractional_path_costs(sortedpath, &sort_path,
tuple_fraction) > 0)
{
/* Presorted path is a loser */
sortedpath = NULL;
}
}
*cheapest_path = cheapestpath;
*sorted_path = sortedpath;
}
