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Diffstat (limited to 'src/backend/optimizer/prep/prepagg.c')
| -rw-r--r-- | src/backend/optimizer/prep/prepagg.c | 674 |
1 files changed, 674 insertions, 0 deletions
diff --git a/src/backend/optimizer/prep/prepagg.c b/src/backend/optimizer/prep/prepagg.c new file mode 100644 index 0000000..e1c5257 --- /dev/null +++ b/src/backend/optimizer/prep/prepagg.c @@ -0,0 +1,674 @@ +/*------------------------------------------------------------------------- + * + * prepagg.c + * Routines to preprocess aggregate function calls + * + * If there are identical aggregate calls in the query, they only need to + * be computed once. Also, some aggregate functions can share the same + * transition state, so that we only need to call the final function for + * them separately. These optimizations are independent of how the + * aggregates are executed. + * + * preprocess_aggrefs() detects those cases, creates AggInfo and + * AggTransInfo structs for each aggregate and transition state that needs + * to be computed, and sets the 'aggno' and 'transno' fields in the Aggrefs + * accordingly. It also resolves polymorphic transition types, and sets + * the 'aggtranstype' fields accordingly. + * + * XXX: The AggInfo and AggTransInfo structs are thrown away after + * planning, so executor startup has to perform some of the same lookups + * of transition functions and initial values that we do here. One day, we + * might want to carry that information to the Agg nodes to save the effort + * at executor startup. The Agg nodes are constructed much later in the + * planning, however, so it's not trivial. + * + * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/optimizer/prep/prepagg.c + * + *------------------------------------------------------------------------- + */ + +#include "postgres.h" + +#include "access/htup_details.h" +#include "catalog/pg_aggregate.h" +#include "catalog/pg_type.h" +#include "nodes/nodeFuncs.h" +#include "nodes/pathnodes.h" +#include "optimizer/clauses.h" +#include "optimizer/cost.h" +#include "optimizer/optimizer.h" +#include "optimizer/plancat.h" +#include "optimizer/prep.h" +#include "parser/parse_agg.h" +#include "utils/builtins.h" +#include "utils/datum.h" +#include "utils/fmgroids.h" +#include "utils/lsyscache.h" +#include "utils/memutils.h" +#include "utils/syscache.h" + +static bool preprocess_aggrefs_walker(Node *node, PlannerInfo *root); +static int find_compatible_agg(PlannerInfo *root, Aggref *newagg, + List **same_input_transnos); +static int find_compatible_trans(PlannerInfo *root, Aggref *newagg, + bool shareable, + Oid aggtransfn, Oid aggtranstype, + int transtypeLen, bool transtypeByVal, + Oid aggcombinefn, + Oid aggserialfn, Oid aggdeserialfn, + Datum initValue, bool initValueIsNull, + List *transnos); +static Datum GetAggInitVal(Datum textInitVal, Oid transtype); + +/* ----------------- + * Resolve the transition type of all Aggrefs, and determine which Aggrefs + * can share aggregate or transition state. + * + * Information about the aggregates and transition functions are collected + * in the root->agginfos and root->aggtransinfos lists. The 'aggtranstype', + * 'aggno', and 'aggtransno' fields of each Aggref are filled in. + * + * NOTE: This modifies the Aggrefs in the input expression in-place! + * + * We try to optimize by detecting duplicate aggregate functions so that + * their state and final values are re-used, rather than needlessly being + * re-calculated independently. We also detect aggregates that are not + * the same, but which can share the same transition state. + * + * Scenarios: + * + * 1. Identical aggregate function calls appear in the query: + * + * SELECT SUM(x) FROM ... HAVING SUM(x) > 0 + * + * Since these aggregates are identical, we only need to calculate + * the value once. Both aggregates will share the same 'aggno' value. + * + * 2. Two different aggregate functions appear in the query, but the + * aggregates have the same arguments, transition functions and + * initial values (and, presumably, different final functions): + * + * SELECT AVG(x), STDDEV(x) FROM ... + * + * In this case we must create a new AggInfo for the varying aggregate, + * and we need to call the final functions separately, but we need + * only run the transition function once. (This requires that the + * final functions be nondestructive of the transition state, but + * that's required anyway for other reasons.) + * + * For either of these optimizations to be valid, all aggregate properties + * used in the transition phase must be the same, including any modifiers + * such as ORDER BY, DISTINCT and FILTER, and the arguments mustn't + * contain any volatile functions. + * ----------------- + */ +void +preprocess_aggrefs(PlannerInfo *root, Node *clause) +{ + (void) preprocess_aggrefs_walker(clause, root); +} + +static void +preprocess_aggref(Aggref *aggref, PlannerInfo *root) +{ + HeapTuple aggTuple; + Form_pg_aggregate aggform; + Oid aggtransfn; + Oid aggfinalfn; + Oid aggcombinefn; + Oid aggserialfn; + Oid aggdeserialfn; + Oid aggtranstype; + int32 aggtranstypmod; + int32 aggtransspace; + bool shareable; + int aggno; + int transno; + List *same_input_transnos; + int16 resulttypeLen; + bool resulttypeByVal; + Datum textInitVal; + Datum initValue; + bool initValueIsNull; + bool transtypeByVal; + int16 transtypeLen; + Oid inputTypes[FUNC_MAX_ARGS]; + int numArguments; + + Assert(aggref->agglevelsup == 0); + + /* + * Fetch info about the aggregate from pg_aggregate. Note it's correct to + * ignore the moving-aggregate variant, since what we're concerned with + * here is aggregates not window functions. + */ + aggTuple = SearchSysCache1(AGGFNOID, + ObjectIdGetDatum(aggref->aggfnoid)); + if (!HeapTupleIsValid(aggTuple)) + elog(ERROR, "cache lookup failed for aggregate %u", + aggref->aggfnoid); + aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple); + aggtransfn = aggform->aggtransfn; + aggfinalfn = aggform->aggfinalfn; + aggcombinefn = aggform->aggcombinefn; + aggserialfn = aggform->aggserialfn; + aggdeserialfn = aggform->aggdeserialfn; + aggtranstype = aggform->aggtranstype; + aggtransspace = aggform->aggtransspace; + + /* + * Resolve the possibly-polymorphic aggregate transition type. + */ + + /* extract argument types (ignoring any ORDER BY expressions) */ + numArguments = get_aggregate_argtypes(aggref, inputTypes); + + /* resolve actual type of transition state, if polymorphic */ + aggtranstype = resolve_aggregate_transtype(aggref->aggfnoid, + aggtranstype, + inputTypes, + numArguments); + aggref->aggtranstype = aggtranstype; + + /* + * If transition state is of same type as first aggregated input, assume + * it's the same typmod (same width) as well. This works for cases like + * MAX/MIN and is probably somewhat reasonable otherwise. + */ + aggtranstypmod = -1; + if (aggref->args) + { + TargetEntry *tle = (TargetEntry *) linitial(aggref->args); + + if (aggtranstype == exprType((Node *) tle->expr)) + aggtranstypmod = exprTypmod((Node *) tle->expr); + } + + /* + * If finalfn is marked read-write, we can't share transition states; but + * it is okay to share states for AGGMODIFY_SHAREABLE aggs. + * + * In principle, in a partial aggregate, we could share the transition + * state even if the final function is marked as read-write, because the + * partial aggregate doesn't execute the final function. But it's too + * early to know whether we're going perform a partial aggregate. + */ + shareable = (aggform->aggfinalmodify != AGGMODIFY_READ_WRITE); + + /* get info about the output value's datatype */ + get_typlenbyval(aggref->aggtype, + &resulttypeLen, + &resulttypeByVal); + + /* get initial value */ + textInitVal = SysCacheGetAttr(AGGFNOID, aggTuple, + Anum_pg_aggregate_agginitval, + &initValueIsNull); + if (initValueIsNull) + initValue = (Datum) 0; + else + initValue = GetAggInitVal(textInitVal, aggtranstype); + + ReleaseSysCache(aggTuple); + + /* + * 1. See if this is identical to another aggregate function call that + * we've seen already. + */ + aggno = find_compatible_agg(root, aggref, &same_input_transnos); + if (aggno != -1) + { + AggInfo *agginfo = list_nth(root->agginfos, aggno); + + transno = agginfo->transno; + } + else + { + AggInfo *agginfo = palloc(sizeof(AggInfo)); + + agginfo->finalfn_oid = aggfinalfn; + agginfo->representative_aggref = aggref; + agginfo->shareable = shareable; + + aggno = list_length(root->agginfos); + root->agginfos = lappend(root->agginfos, agginfo); + + /* + * Count it, and check for cases requiring ordered input. Note that + * ordered-set aggs always have nonempty aggorder. Any ordered-input + * case also defeats partial aggregation. + */ + if (aggref->aggorder != NIL || aggref->aggdistinct != NIL) + { + root->numOrderedAggs++; + root->hasNonPartialAggs = true; + } + + get_typlenbyval(aggtranstype, + &transtypeLen, + &transtypeByVal); + + /* + * 2. See if this aggregate can share transition state with another + * aggregate that we've initialized already. + */ + transno = find_compatible_trans(root, aggref, shareable, + aggtransfn, aggtranstype, + transtypeLen, transtypeByVal, + aggcombinefn, + aggserialfn, aggdeserialfn, + initValue, initValueIsNull, + same_input_transnos); + if (transno == -1) + { + AggTransInfo *transinfo = palloc(sizeof(AggTransInfo)); + + transinfo->args = aggref->args; + transinfo->aggfilter = aggref->aggfilter; + transinfo->transfn_oid = aggtransfn; + transinfo->combinefn_oid = aggcombinefn; + transinfo->serialfn_oid = aggserialfn; + transinfo->deserialfn_oid = aggdeserialfn; + transinfo->aggtranstype = aggtranstype; + transinfo->aggtranstypmod = aggtranstypmod; + transinfo->transtypeLen = transtypeLen; + transinfo->transtypeByVal = transtypeByVal; + transinfo->aggtransspace = aggtransspace; + transinfo->initValue = initValue; + transinfo->initValueIsNull = initValueIsNull; + + transno = list_length(root->aggtransinfos); + root->aggtransinfos = lappend(root->aggtransinfos, transinfo); + + /* + * Check whether partial aggregation is feasible, unless we + * already found out that we can't do it. + */ + if (!root->hasNonPartialAggs) + { + /* + * If there is no combine function, then partial aggregation + * is not possible. + */ + if (!OidIsValid(transinfo->combinefn_oid)) + root->hasNonPartialAggs = true; + + /* + * If we have any aggs with transtype INTERNAL then we must + * check whether they have serialization/deserialization + * functions; if not, we can't serialize partial-aggregation + * results. + */ + else if (transinfo->aggtranstype == INTERNALOID && + (!OidIsValid(transinfo->serialfn_oid) || + !OidIsValid(transinfo->deserialfn_oid))) + root->hasNonSerialAggs = true; + } + } + agginfo->transno = transno; + } + + /* + * Fill in the fields in the Aggref (aggtranstype was set above already) + */ + aggref->aggno = aggno; + aggref->aggtransno = transno; +} + +static bool +preprocess_aggrefs_walker(Node *node, PlannerInfo *root) +{ + if (node == NULL) + return false; + if (IsA(node, Aggref)) + { + Aggref *aggref = (Aggref *) node; + + preprocess_aggref(aggref, root); + + /* + * We assume that the parser checked that there are no aggregates (of + * this level anyway) in the aggregated arguments, direct arguments, + * or filter clause. Hence, we need not recurse into any of them. + */ + return false; + } + Assert(!IsA(node, SubLink)); + return expression_tree_walker(node, preprocess_aggrefs_walker, + (void *) root); +} + + +/* + * find_compatible_agg - search for a previously initialized per-Agg struct + * + * Searches the previously looked at aggregates to find one which is compatible + * with this one, with the same input parameters. If no compatible aggregate + * can be found, returns -1. + * + * As a side-effect, this also collects a list of existing, shareable per-Trans + * structs with matching inputs. If no identical Aggref is found, the list is + * passed later to find_compatible_trans, to see if we can at least reuse + * the state value of another aggregate. + */ +static int +find_compatible_agg(PlannerInfo *root, Aggref *newagg, + List **same_input_transnos) +{ + ListCell *lc; + int aggno; + + *same_input_transnos = NIL; + + /* we mustn't reuse the aggref if it contains volatile function calls */ + if (contain_volatile_functions((Node *) newagg)) + return -1; + + /* + * Search through the list of already seen aggregates. If we find an + * existing identical aggregate call, then we can re-use that one. While + * searching, we'll also collect a list of Aggrefs with the same input + * parameters. If no matching Aggref is found, the caller can potentially + * still re-use the transition state of one of them. (At this stage we + * just compare the parsetrees; whether different aggregates share the + * same transition function will be checked later.) + */ + aggno = -1; + foreach(lc, root->agginfos) + { + AggInfo *agginfo = (AggInfo *) lfirst(lc); + Aggref *existingRef; + + aggno++; + + existingRef = agginfo->representative_aggref; + + /* all of the following must be the same or it's no match */ + if (newagg->inputcollid != existingRef->inputcollid || + newagg->aggtranstype != existingRef->aggtranstype || + newagg->aggstar != existingRef->aggstar || + newagg->aggvariadic != existingRef->aggvariadic || + newagg->aggkind != existingRef->aggkind || + !equal(newagg->args, existingRef->args) || + !equal(newagg->aggorder, existingRef->aggorder) || + !equal(newagg->aggdistinct, existingRef->aggdistinct) || + !equal(newagg->aggfilter, existingRef->aggfilter)) + continue; + + /* if it's the same aggregate function then report exact match */ + if (newagg->aggfnoid == existingRef->aggfnoid && + newagg->aggtype == existingRef->aggtype && + newagg->aggcollid == existingRef->aggcollid && + equal(newagg->aggdirectargs, existingRef->aggdirectargs)) + { + list_free(*same_input_transnos); + *same_input_transnos = NIL; + return aggno; + } + + /* + * Not identical, but it had the same inputs. If the final function + * permits sharing, return its transno to the caller, in case we can + * re-use its per-trans state. (If there's already sharing going on, + * we might report a transno more than once. find_compatible_trans is + * cheap enough that it's not worth spending cycles to avoid that.) + */ + if (agginfo->shareable) + *same_input_transnos = lappend_int(*same_input_transnos, + agginfo->transno); + } + + return -1; +} + +/* + * find_compatible_trans - search for a previously initialized per-Trans + * struct + * + * Searches the list of transnos for a per-Trans struct with the same + * transition function and initial condition. (The inputs have already been + * verified to match.) + */ +static int +find_compatible_trans(PlannerInfo *root, Aggref *newagg, bool shareable, + Oid aggtransfn, Oid aggtranstype, + int transtypeLen, bool transtypeByVal, + Oid aggcombinefn, + Oid aggserialfn, Oid aggdeserialfn, + Datum initValue, bool initValueIsNull, + List *transnos) +{ + ListCell *lc; + + /* If this aggregate can't share transition states, give up */ + if (!shareable) + return -1; + + foreach(lc, transnos) + { + int transno = lfirst_int(lc); + AggTransInfo *pertrans = (AggTransInfo *) list_nth(root->aggtransinfos, transno); + + /* + * if the transfns or transition state types are not the same then the + * state can't be shared. + */ + if (aggtransfn != pertrans->transfn_oid || + aggtranstype != pertrans->aggtranstype) + continue; + + /* + * The serialization and deserialization functions must match, if + * present, as we're unable to share the trans state for aggregates + * which will serialize or deserialize into different formats. + * Remember that these will be InvalidOid if they're not required for + * this agg node. + */ + if (aggserialfn != pertrans->serialfn_oid || + aggdeserialfn != pertrans->deserialfn_oid) + continue; + + /* + * Combine function must also match. We only care about the combine + * function with partial aggregates, but it's too early in the + * planning to know if we will do partial aggregation, so be + * conservative. + */ + if (aggcombinefn != pertrans->combinefn_oid) + continue; + + /* + * Check that the initial condition matches, too. + */ + if (initValueIsNull && pertrans->initValueIsNull) + return transno; + + if (!initValueIsNull && !pertrans->initValueIsNull && + datumIsEqual(initValue, pertrans->initValue, + transtypeByVal, transtypeLen)) + return transno; + } + return -1; +} + +static Datum +GetAggInitVal(Datum textInitVal, Oid transtype) +{ + Oid typinput, + typioparam; + char *strInitVal; + Datum initVal; + + getTypeInputInfo(transtype, &typinput, &typioparam); + strInitVal = TextDatumGetCString(textInitVal); + initVal = OidInputFunctionCall(typinput, strInitVal, + typioparam, -1); + pfree(strInitVal); + return initVal; +} + + +/* + * get_agg_clause_costs + * Process the PlannerInfo's 'aggtransinfos' and 'agginfos' lists + * accumulating the cost information about them. + * + * 'aggsplit' tells us the expected partial-aggregation mode, which affects + * the cost estimates. + * + * NOTE that the costs are ADDED to those already in *costs ... so the caller + * is responsible for zeroing the struct initially. + * + * For each AggTransInfo, we add the cost of an aggregate transition using + * either the transfn or combinefn depending on the 'aggsplit' value. We also + * account for the costs of any aggfilters and any serializations and + * deserializations of the transition state and also estimate the total space + * needed for the transition states as if each aggregate's state was stored in + * memory concurrently (as would be done in a HashAgg plan). + * + * For each AggInfo in the 'agginfos' list we add the cost of running the + * final function and the direct args, if any. + */ +void +get_agg_clause_costs(PlannerInfo *root, AggSplit aggsplit, AggClauseCosts *costs) +{ + ListCell *lc; + + foreach(lc, root->aggtransinfos) + { + AggTransInfo *transinfo = (AggTransInfo *) lfirst(lc); + + /* + * Add the appropriate component function execution costs to + * appropriate totals. + */ + if (DO_AGGSPLIT_COMBINE(aggsplit)) + { + /* charge for combining previously aggregated states */ + add_function_cost(root, transinfo->combinefn_oid, NULL, + &costs->transCost); + } + else + add_function_cost(root, transinfo->transfn_oid, NULL, + &costs->transCost); + if (DO_AGGSPLIT_DESERIALIZE(aggsplit) && + OidIsValid(transinfo->deserialfn_oid)) + add_function_cost(root, transinfo->deserialfn_oid, NULL, + &costs->transCost); + if (DO_AGGSPLIT_SERIALIZE(aggsplit) && + OidIsValid(transinfo->serialfn_oid)) + add_function_cost(root, transinfo->serialfn_oid, NULL, + &costs->finalCost); + + /* + * These costs are incurred only by the initial aggregate node, so we + * mustn't include them again at upper levels. + */ + if (!DO_AGGSPLIT_COMBINE(aggsplit)) + { + /* add the input expressions' cost to per-input-row costs */ + QualCost argcosts; + + cost_qual_eval_node(&argcosts, (Node *) transinfo->args, root); + costs->transCost.startup += argcosts.startup; + costs->transCost.per_tuple += argcosts.per_tuple; + + /* + * Add any filter's cost to per-input-row costs. + * + * XXX Ideally we should reduce input expression costs according + * to filter selectivity, but it's not clear it's worth the + * trouble. + */ + if (transinfo->aggfilter) + { + cost_qual_eval_node(&argcosts, (Node *) transinfo->aggfilter, + root); + costs->transCost.startup += argcosts.startup; + costs->transCost.per_tuple += argcosts.per_tuple; + } + } + + /* + * If the transition type is pass-by-value then it doesn't add + * anything to the required size of the hashtable. If it is + * pass-by-reference then we have to add the estimated size of the + * value itself, plus palloc overhead. + */ + if (!transinfo->transtypeByVal) + { + int32 avgwidth; + + /* Use average width if aggregate definition gave one */ + if (transinfo->aggtransspace > 0) + avgwidth = transinfo->aggtransspace; + else if (transinfo->transfn_oid == F_ARRAY_APPEND) + { + /* + * If the transition function is array_append(), it'll use an + * expanded array as transvalue, which will occupy at least + * ALLOCSET_SMALL_INITSIZE and possibly more. Use that as the + * estimate for lack of a better idea. + */ + avgwidth = ALLOCSET_SMALL_INITSIZE; + } + else + { + avgwidth = get_typavgwidth(transinfo->aggtranstype, transinfo->aggtranstypmod); + } + + avgwidth = MAXALIGN(avgwidth); + costs->transitionSpace += avgwidth + 2 * sizeof(void *); + } + else if (transinfo->aggtranstype == INTERNALOID) + { + /* + * INTERNAL transition type is a special case: although INTERNAL + * is pass-by-value, it's almost certainly being used as a pointer + * to some large data structure. The aggregate definition can + * provide an estimate of the size. If it doesn't, then we assume + * ALLOCSET_DEFAULT_INITSIZE, which is a good guess if the data is + * being kept in a private memory context, as is done by + * array_agg() for instance. + */ + if (transinfo->aggtransspace > 0) + costs->transitionSpace += transinfo->aggtransspace; + else + costs->transitionSpace += ALLOCSET_DEFAULT_INITSIZE; + } + } + + foreach(lc, root->agginfos) + { + AggInfo *agginfo = (AggInfo *) lfirst(lc); + Aggref *aggref = agginfo->representative_aggref; + + /* + * Add the appropriate component function execution costs to + * appropriate totals. + */ + if (!DO_AGGSPLIT_SKIPFINAL(aggsplit) && + OidIsValid(agginfo->finalfn_oid)) + add_function_cost(root, agginfo->finalfn_oid, NULL, + &costs->finalCost); + + /* + * If there are direct arguments, treat their evaluation cost like the + * cost of the finalfn. + */ + if (aggref->aggdirectargs) + { + QualCost argcosts; + + cost_qual_eval_node(&argcosts, (Node *) aggref->aggdirectargs, + root); + costs->finalCost.startup += argcosts.startup; + costs->finalCost.per_tuple += argcosts.per_tuple; + } + } +} |