greenplumn planagg 源码
greenplumn planagg 代码
文件路径：/src/backend/optimizer/plan/planagg.c
/*-------------------------------------------------------------------------
*
* planagg.c
* Special planning for aggregate queries.
*
* This module tries to replace MIN/MAX aggregate functions by subqueries
* of the form
* (SELECT col FROM tab
* WHERE col IS NOT NULL AND existing-quals
* ORDER BY col ASC/DESC
* LIMIT 1)
* Given a suitable index on tab.col, this can be much faster than the
* generic scan-all-the-rows aggregation plan. We can handle multiple
* MIN/MAX aggregates by generating multiple subqueries, and their
* orderings can be different. However, if the query contains any
* non-optimizable aggregates, there's no point since we'll have to
* scan all the rows anyway.
*
*
* Portions Copyright (c) 2006-2008, Greenplum inc
* Portions Copyright (c) 2012-Present VMware, Inc. or its affiliates.
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/optimizer/plan/planagg.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_type.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/planmain.h"
#include "optimizer/subselect.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "parser/parse_clause.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "cdb/cdbpath.h"
#include "cdb/cdbsetop.h"
#include "cdb/cdbutil.h"
#include "cdb/cdbvars.h"
static bool find_minmax_aggs_walker(Node *node, List **context);
static bool build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
Oid eqop, Oid sortop, bool nulls_first);
static void minmax_qp_callback(PlannerInfo *root, void *extra);
static Oid fetch_agg_sort_op(Oid aggfnoid);
/*
* preprocess_minmax_aggregates - preprocess MIN/MAX aggregates
*
* Check to see whether the query contains MIN/MAX aggregate functions that
* might be optimizable via indexscans. If it does, and all the aggregates
* are potentially optimizable, then create a MinMaxAggPath and add it to
* the (UPPERREL_GROUP_AGG, NULL) upperrel.
*
* This should be called by grouping_planner() just before it's ready to call
* query_planner(), because we generate indexscan paths by cloning the
* planner's state and invoking query_planner() on a modified version of
* the query parsetree. Thus, all preprocessing needed before query_planner()
* must already be done.
*/
void
preprocess_minmax_aggregates(PlannerInfo *root)
{
Query *parse = root->parse;
FromExpr *jtnode;
RangeTblRef *rtr;
RangeTblEntry *rte;
List *aggs_list;
RelOptInfo *grouped_rel;
ListCell *lc;
/* minmax_aggs list should be empty at this point */
Assert(root->minmax_aggs == NIL);
/* Nothing to do if query has no aggregates */
if (!parse->hasAggs)
return;
Assert(!parse->setOperations); /* shouldn't get here if a setop */
Assert(parse->rowMarks == NIL); /* nor if FOR UPDATE */
/*
* Reject unoptimizable cases.
*
* We don't handle GROUP BY or windowing, because our current
* implementations of grouping require looking at all the rows anyway, and
* so there's not much point in optimizing MIN/MAX.
*/
if (parse->groupClause || list_length(parse->groupingSets) > 1 ||
parse->hasWindowFuncs)
return;
/*
* Reject if disabled by caller.
*/
if (!root->config->gp_enable_minmax_optimization)
return;
/*
* Reject if query contains any CTEs; there's no way to build an indexscan
* on one so we couldn't succeed here. (If the CTEs are unreferenced,
* that's not true, but it doesn't seem worth expending cycles to check.)
*/
if (parse->cteList)
return;
/*
* We also restrict the query to reference exactly one table, since join
* conditions can't be handled reasonably. (We could perhaps handle a
* query containing cartesian-product joins, but it hardly seems worth the
* trouble.) However, the single table could be buried in several levels
* of FromExpr due to subqueries. Note the "single" table could be an
* inheritance parent, too, including the case of a UNION ALL subquery
* that's been flattened to an appendrel.
*/
jtnode = parse->jointree;
while (IsA(jtnode, FromExpr))
{
if (list_length(jtnode->fromlist) != 1)
return;
jtnode = linitial(jtnode->fromlist);
}
if (!IsA(jtnode, RangeTblRef))
return;
rtr = (RangeTblRef *) jtnode;
rte = planner_rt_fetch(rtr->rtindex, root);
if (rte->rtekind == RTE_RELATION)
/* ordinary relation, ok */ ;
else if (rte->rtekind == RTE_SUBQUERY && rte->inh)
/* flattened UNION ALL subquery, ok */ ;
else
return;
/*
* Scan the tlist and HAVING qual to find all the aggregates and verify
* all are MIN/MAX aggregates. Stop as soon as we find one that isn't.
*/
aggs_list = NIL;
if (find_minmax_aggs_walker((Node *) root->processed_tlist, &aggs_list))
return;
if (find_minmax_aggs_walker(parse->havingQual, &aggs_list))
return;
/*
* OK, there is at least the possibility of performing the optimization.
* Build an access path for each aggregate. If any of the aggregates
* prove to be non-indexable, give up; there is no point in optimizing
* just some of them.
*/
foreach(lc, aggs_list)
{
MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
Oid eqop;
bool reverse;
/*
* We'll need the equality operator that goes with the aggregate's
* ordering operator.
*/
eqop = get_equality_op_for_ordering_op(mminfo->aggsortop, &reverse);
if (!OidIsValid(eqop)) /* shouldn't happen */
elog(ERROR, "could not find equality operator for ordering operator %u",
mminfo->aggsortop);
/*
* We can use either an ordering that gives NULLS FIRST or one that
* gives NULLS LAST; furthermore there's unlikely to be much
* performance difference between them, so it doesn't seem worth
* costing out both ways if we get a hit on the first one. NULLS
* FIRST is more likely to be available if the operator is a
* reverse-sort operator, so try that first if reverse.
*/
if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse))
continue;
if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, !reverse))
continue;
/* No indexable path for this aggregate, so fail */
return;
}
/*
* OK, we can do the query this way. Prepare to create a MinMaxAggPath
* node.
*
* First, create an output Param node for each agg. (If we end up not
* using the MinMaxAggPath, we'll waste a PARAM_EXEC slot for each agg,
* which is not worth worrying about. We can't wait till create_plan time
* to decide whether to make the Param, unfortunately.)
*/
foreach(lc, aggs_list)
{
MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
mminfo->param =
SS_make_initplan_output_param(root,
exprType((Node *) mminfo->target),
-1,
exprCollation((Node *) mminfo->target));
}
/*
* Create a MinMaxAggPath node with the appropriate estimated costs and
* other needed data, and add it to the UPPERREL_GROUP_AGG upperrel, where
* it will compete against the standard aggregate implementation. (It
* will likely always win, but we need not assume that here.)
*
* Note: grouping_planner won't have created this upperrel yet, but it's
* fine for us to create it first. We will not have inserted the correct
* consider_parallel value in it, but MinMaxAggPath paths are currently
* never parallel-safe anyway, so that doesn't matter. Likewise, it
* doesn't matter that we haven't filled FDW-related fields in the rel.
* Also, because there are no rowmarks, we know that the processed_tlist
* doesn't need to change anymore, so making the pathtarget now is safe.
*/
grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);
add_path(grouped_rel, (Path *)
create_minmaxagg_path(root, grouped_rel,
create_pathtarget(root,
root->processed_tlist),
aggs_list,
(List *) parse->havingQual));
}
/*
* find_minmax_aggs_walker
* Recursively scan the Aggref nodes in an expression tree, and check
* that each one is a MIN/MAX aggregate. If so, build a list of the
* distinct aggregate calls in the tree.
*
* Returns true if a non-MIN/MAX aggregate is found, false otherwise.
* (This seemingly-backward definition is used because expression_tree_walker
* aborts the scan on true return, which is what we want.)
*
* Found aggregates are added to the list at *context; it's up to the caller
* to initialize the list to NIL.
*
* This does not descend into subqueries, and so should be used only after
* reduction of sublinks to subplans. There mustn't be outer-aggregate
* references either.
*/
static bool
find_minmax_aggs_walker(Node *node, List **context)
{
if (node == NULL)
return false;
if (IsA(node, Aggref))
{
Aggref *aggref = (Aggref *) node;
Oid aggsortop;
TargetEntry *curTarget;
MinMaxAggInfo *mminfo;
ListCell *l;
Assert(aggref->agglevelsup == 0);
if (list_length(aggref->args) != 1)
return true; /* it couldn't be MIN/MAX */
/*
* ORDER BY is usually irrelevant for MIN/MAX, but it can change the
* outcome if the aggsortop's operator class recognizes non-identical
* values as equal. For example, 4.0 and 4.00 are equal according to
* numeric_ops, yet distinguishable. If MIN() receives more than one
* value equal to 4.0 and no value less than 4.0, it is unspecified
* which of those equal values MIN() returns. An ORDER BY expression
* that differs for each of those equal values of the argument
* expression makes the result predictable once again. This is a
* niche requirement, and we do not implement it with subquery paths.
* In any case, this test lets us reject ordered-set aggregates
* quickly.
*/
if (aggref->aggorder != NIL)
return true;
/* note: we do not care if DISTINCT is mentioned ... */
/*
* We might implement the optimization when a FILTER clause is present
* by adding the filter to the quals of the generated subquery. For
* now, just punt.
*/
if (aggref->aggfilter != NULL)
return true;
aggsortop = fetch_agg_sort_op(aggref->aggfnoid);
if (!OidIsValid(aggsortop))
return true; /* not a MIN/MAX aggregate */
curTarget = (TargetEntry *) linitial(aggref->args);
if (contain_mutable_functions((Node *) curTarget->expr))
return true; /* not potentially indexable */
if (type_is_rowtype(exprType((Node *) curTarget->expr)))
return true; /* IS NOT NULL would have weird semantics */
/*
* Check whether it's already in the list, and add it if not.
*/
foreach(l, *context)
{
mminfo = (MinMaxAggInfo *) lfirst(l);
if (mminfo->aggfnoid == aggref->aggfnoid &&
equal(mminfo->target, curTarget->expr))
return false;
}
mminfo = makeNode(MinMaxAggInfo);
mminfo->aggfnoid = aggref->aggfnoid;
mminfo->aggsortop = aggsortop;
mminfo->target = curTarget->expr;
mminfo->subroot = NULL; /* don't compute path yet */
mminfo->path = NULL;
mminfo->pathcost = 0;
mminfo->param = NULL;
*context = lappend(*context, mminfo);
/*
* We need not recurse into the argument, since it can't contain any
* aggregates.
*/
return false;
}
Assert(!IsA(node, SubLink));
return expression_tree_walker(node, find_minmax_aggs_walker,
(void *) context);
}
/*
* build_minmax_path
* Given a MIN/MAX aggregate, try to build an indexscan Path it can be
* optimized with.
*
* If successful, stash the best path in *mminfo and return true.
* Otherwise, return false.
*/
static bool
build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
Oid eqop, Oid sortop, bool nulls_first)
{
PlannerInfo *subroot;
Query *parse;
TargetEntry *tle;
List *tlist;
NullTest *ntest;
SortGroupClause *sortcl;
RelOptInfo *final_rel;
Path *sorted_path;
Cost path_cost;
double path_fraction;
/*
* We are going to construct what is effectively a sub-SELECT query, so
* clone the current query level's state and adjust it to make it look
* like a subquery. Any outer references will now be one level higher
* than before. (This means that when we are done, there will be no Vars
* of level 1, which is why the subquery can become an initplan.)
*/
subroot = (PlannerInfo *) palloc(sizeof(PlannerInfo));
memcpy(subroot, root, sizeof(PlannerInfo));
subroot->query_level++;
subroot->parent_root = root;
/* reset subplan-related stuff */
subroot->plan_params = NIL;
subroot->outer_params = NULL;
subroot->init_plans = NIL;
subroot->parse = parse = copyObject(root->parse);
IncrementVarSublevelsUp((Node *) parse, 1, 1);
/* append_rel_list might contain outer Vars? */
subroot->append_rel_list = copyObject(root->append_rel_list);
IncrementVarSublevelsUp((Node *) subroot->append_rel_list, 1, 1);
/* There shouldn't be any OJ info to translate, as yet */
Assert(subroot->join_info_list == NIL);
/* and we haven't made equivalence classes, either */
Assert(subroot->eq_classes == NIL);
/* and we haven't created PlaceHolderInfos, either */
Assert(subroot->placeholder_list == NIL);
/*----------
* Generate modified query of the form
* (SELECT col FROM tab
* WHERE col IS NOT NULL AND existing-quals
* ORDER BY col ASC/DESC
* LIMIT 1)
*----------
*/
/* single tlist entry that is the aggregate target */
tle = makeTargetEntry(copyObject(mminfo->target),
(AttrNumber) 1,
pstrdup("agg_target"),
false);
tlist = list_make1(tle);
subroot->processed_tlist = parse->targetList = tlist;
/* No HAVING, no DISTINCT, no aggregates anymore */
parse->havingQual = NULL;
subroot->hasHavingQual = false;
parse->distinctClause = NIL;
parse->hasDistinctOn = false;
parse->hasAggs = false;
/* Build "target IS NOT NULL" expression */
ntest = makeNode(NullTest);
ntest->nulltesttype = IS_NOT_NULL;
ntest->arg = copyObject(mminfo->target);
/* we checked it wasn't a rowtype in find_minmax_aggs_walker */
ntest->argisrow = false;
ntest->location = -1;
/* User might have had that in WHERE already */
if (!list_member((List *) parse->jointree->quals, ntest))
parse->jointree->quals = (Node *)
lcons(ntest, (List *) parse->jointree->quals);
/* Build suitable ORDER BY clause */
sortcl = makeNode(SortGroupClause);
sortcl->tleSortGroupRef = assignSortGroupRef(tle, subroot->processed_tlist);
sortcl->eqop = eqop;
sortcl->sortop = sortop;
sortcl->nulls_first = nulls_first;
sortcl->hashable = false; /* no need to make this accurate */
parse->sortClause = list_make1(sortcl);
/* set up expressions for LIMIT 1 */
parse->limitOffset = NULL;
parse->limitCount = (Node *) makeConst(INT8OID, -1, InvalidOid,
sizeof(int64),
Int64GetDatum(1), false,
FLOAT8PASSBYVAL);
/*
* Generate the best paths for this query, telling query_planner that we
* have LIMIT 1.
*/
subroot->tuple_fraction = 1.0;
subroot->limit_tuples = 1.0;
final_rel = query_planner(subroot, minmax_qp_callback, NULL);
/*
* Since we didn't go through subquery_planner() to handle the subquery,
* we have to do some of the same cleanup it would do, in particular cope
* with params and initplans used within this subquery. (This won't
* matter if we end up not using the subplan.)
*/
SS_identify_outer_params(subroot);
SS_charge_for_initplans(subroot, final_rel);
/*
* Get the best presorted path, that being the one that's cheapest for
* fetching just one row. If there's no such path, fail.
*/
if (final_rel->rows > 1.0)
path_fraction = 1.0 / final_rel->rows;
else
path_fraction = 1.0;
sorted_path =
get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
subroot->query_pathkeys,
NULL,
path_fraction);
if (!sorted_path)
return false;
/*
* The path might not return exactly what we want, so fix that. (We
* assume that this won't change any conclusions about which was the
* cheapest path.)
*/
sorted_path = apply_projection_to_path(subroot, final_rel, sorted_path,
create_pathtarget(subroot,
subroot->processed_tlist));
/*
* Need to gather the results to a single node, if it's not already
* like that. Otherwise, we won't get the single min/max row, but
* one min/max row from every segment.
*/
if (Gp_role == GP_ROLE_DISPATCH && CdbPathLocus_IsPartitioned(sorted_path->locus))
{
CdbPathLocus singleQE;
List *pathkeys;
CdbPathLocus_MakeSingleQE(&singleQE, getgpsegmentCount());
pathkeys = sorted_path->pathkeys;
sorted_path = cdbpath_create_motion_path(root, sorted_path, sorted_path->pathkeys,
false, singleQE);
/*
* Sanity check that order was preserved. (Given how cdbpath_create_motion_path() is
* implemented, pointer equality is enough here, but in principle we should be
* using something more sophisticated for the comparison.)
*/
if (sorted_path->pathkeys != pathkeys)
elog(ERROR, "could not create an order-preserving gather motion for min/max path");
}
/*
* Determine cost to get just the first row of the presorted path.
*
* Note: cost calculation here should match
* compare_fractional_path_costs().
*/
path_cost = sorted_path->startup_cost +
path_fraction * (sorted_path->total_cost - sorted_path->startup_cost);
/* Save state for further processing */
mminfo->subroot = subroot;
mminfo->path = sorted_path;
mminfo->pathcost = path_cost;
return true;
}
/*
* Compute query_pathkeys and other pathkeys during query_planner()
*/
static void
minmax_qp_callback(PlannerInfo *root, void *extra)
{
root->group_pathkeys = NIL;
root->window_pathkeys = NIL;
root->distinct_pathkeys = NIL;
root->sort_pathkeys =
make_pathkeys_for_sortclauses(root,
root->parse->sortClause,
root->parse->targetList);
root->query_pathkeys = root->sort_pathkeys;
}
/*
* Get the OID of the sort operator, if any, associated with an aggregate.
* Returns InvalidOid if there is no such operator.
*/
static Oid
fetch_agg_sort_op(Oid aggfnoid)
{
HeapTuple aggTuple;
Form_pg_aggregate aggform;
Oid aggsortop;
/* fetch aggregate entry from pg_aggregate */
aggTuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(aggfnoid));
if (!HeapTupleIsValid(aggTuple))
return InvalidOid;
aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
aggsortop = aggform->aggsortop;
ReleaseSysCache(aggTuple);
return aggsortop;
}
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