/*------------------------------------------------------------------------- * * extended_stats.c * POSTGRES extended statistics * * Generic code supporting statistics objects created via CREATE STATISTICS. * * * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION * src/backend/statistics/extended_stats.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/detoast.h" #include "access/genam.h" #include "access/htup_details.h" #include "access/table.h" #include "catalog/indexing.h" #include "catalog/pg_collation.h" #include "catalog/pg_statistic_ext.h" #include "catalog/pg_statistic_ext_data.h" #include "commands/progress.h" #include "miscadmin.h" #include "nodes/nodeFuncs.h" #include "optimizer/clauses.h" #include "optimizer/optimizer.h" #include "pgstat.h" #include "postmaster/autovacuum.h" #include "statistics/extended_stats_internal.h" #include "statistics/statistics.h" #include "utils/acl.h" #include "utils/array.h" #include "utils/builtins.h" #include "utils/fmgroids.h" #include "utils/lsyscache.h" #include "utils/memutils.h" #include "utils/rel.h" #include "utils/selfuncs.h" #include "utils/syscache.h" /* * To avoid consuming too much memory during analysis and/or too much space * in the resulting pg_statistic rows, we ignore varlena datums that are wider * than WIDTH_THRESHOLD (after detoasting!). This is legitimate for MCV * and distinct-value calculations since a wide value is unlikely to be * duplicated at all, much less be a most-common value. For the same reason, * ignoring wide values will not affect our estimates of histogram bin * boundaries very much. */ #define WIDTH_THRESHOLD 1024 /* * Used internally to refer to an individual statistics object, i.e., * a pg_statistic_ext entry. */ typedef struct StatExtEntry { Oid statOid; /* OID of pg_statistic_ext entry */ char *schema; /* statistics object's schema */ char *name; /* statistics object's name */ Bitmapset *columns; /* attribute numbers covered by the object */ List *types; /* 'char' list of enabled statistics kinds */ int stattarget; /* statistics target (-1 for default) */ } StatExtEntry; static List *fetch_statentries_for_relation(Relation pg_statext, Oid relid); static VacAttrStats **lookup_var_attr_stats(Relation rel, Bitmapset *attrs, int nvacatts, VacAttrStats **vacatts); static void statext_store(Oid relid, MVNDistinct *ndistinct, MVDependencies *dependencies, MCVList *mcv, VacAttrStats **stats); static int statext_compute_stattarget(int stattarget, int natts, VacAttrStats **stats); /* * Compute requested extended stats, using the rows sampled for the plain * (single-column) stats. * * This fetches a list of stats types from pg_statistic_ext, computes the * requested stats, and serializes them back into the catalog. */ void BuildRelationExtStatistics(Relation onerel, double totalrows, int numrows, HeapTuple *rows, int natts, VacAttrStats **vacattrstats) { Relation pg_stext; ListCell *lc; List *stats; MemoryContext cxt; MemoryContext oldcxt; int64 ext_cnt; cxt = AllocSetContextCreate(CurrentMemoryContext, "BuildRelationExtStatistics", ALLOCSET_DEFAULT_SIZES); oldcxt = MemoryContextSwitchTo(cxt); pg_stext = table_open(StatisticExtRelationId, RowExclusiveLock); stats = fetch_statentries_for_relation(pg_stext, RelationGetRelid(onerel)); /* report this phase */ if (stats != NIL) { const int index[] = { PROGRESS_ANALYZE_PHASE, PROGRESS_ANALYZE_EXT_STATS_TOTAL }; const int64 val[] = { PROGRESS_ANALYZE_PHASE_COMPUTE_EXT_STATS, list_length(stats) }; pgstat_progress_update_multi_param(2, index, val); } ext_cnt = 0; foreach(lc, stats) { StatExtEntry *stat = (StatExtEntry *) lfirst(lc); MVNDistinct *ndistinct = NULL; MVDependencies *dependencies = NULL; MCVList *mcv = NULL; VacAttrStats **stats; ListCell *lc2; int stattarget; /* * Check if we can build these stats based on the column analyzed. If * not, report this fact (except in autovacuum) and move on. */ stats = lookup_var_attr_stats(onerel, stat->columns, natts, vacattrstats); if (!stats) { if (!IsAutoVacuumWorkerProcess()) ereport(WARNING, (errcode(ERRCODE_INVALID_OBJECT_DEFINITION), errmsg("statistics object \"%s.%s\" could not be computed for relation \"%s.%s\"", stat->schema, stat->name, get_namespace_name(onerel->rd_rel->relnamespace), RelationGetRelationName(onerel)), errtable(onerel))); continue; } /* check allowed number of dimensions */ Assert(bms_num_members(stat->columns) >= 2 && bms_num_members(stat->columns) <= STATS_MAX_DIMENSIONS); /* compute statistics target for this statistics */ stattarget = statext_compute_stattarget(stat->stattarget, bms_num_members(stat->columns), stats); /* * Don't rebuild statistics objects with statistics target set to 0 * (we just leave the existing values around, just like we do for * regular per-column statistics). */ if (stattarget == 0) continue; /* compute statistic of each requested type */ foreach(lc2, stat->types) { char t = (char) lfirst_int(lc2); if (t == STATS_EXT_NDISTINCT) ndistinct = statext_ndistinct_build(totalrows, numrows, rows, stat->columns, stats); else if (t == STATS_EXT_DEPENDENCIES) dependencies = statext_dependencies_build(numrows, rows, stat->columns, stats); else if (t == STATS_EXT_MCV) mcv = statext_mcv_build(numrows, rows, stat->columns, stats, totalrows, stattarget); } /* store the statistics in the catalog */ statext_store(stat->statOid, ndistinct, dependencies, mcv, stats); /* for reporting progress */ pgstat_progress_update_param(PROGRESS_ANALYZE_EXT_STATS_COMPUTED, ++ext_cnt); } table_close(pg_stext, RowExclusiveLock); MemoryContextSwitchTo(oldcxt); MemoryContextDelete(cxt); } /* * ComputeExtStatisticsRows * Compute number of rows required by extended statistics on a table. * * Computes number of rows we need to sample to build extended statistics on a * table. This only looks at statistics we can actually build - for example * when analyzing only some of the columns, this will skip statistics objects * that would require additional columns. * * See statext_compute_stattarget for details about how we compute statistics * target for a statistics objects (from the object target, attribute targets * and default statistics target). */ int ComputeExtStatisticsRows(Relation onerel, int natts, VacAttrStats **vacattrstats) { Relation pg_stext; ListCell *lc; List *lstats; MemoryContext cxt; MemoryContext oldcxt; int result = 0; cxt = AllocSetContextCreate(CurrentMemoryContext, "ComputeExtStatisticsRows", ALLOCSET_DEFAULT_SIZES); oldcxt = MemoryContextSwitchTo(cxt); pg_stext = table_open(StatisticExtRelationId, RowExclusiveLock); lstats = fetch_statentries_for_relation(pg_stext, RelationGetRelid(onerel)); foreach(lc, lstats) { StatExtEntry *stat = (StatExtEntry *) lfirst(lc); int stattarget; VacAttrStats **stats; int nattrs = bms_num_members(stat->columns); /* * Check if we can build this statistics object based on the columns * analyzed. If not, ignore it (don't report anything, we'll do that * during the actual build BuildRelationExtStatistics). */ stats = lookup_var_attr_stats(onerel, stat->columns, natts, vacattrstats); if (!stats) continue; /* * Compute statistics target, based on what's set for the statistic * object itself, and for its attributes. */ stattarget = statext_compute_stattarget(stat->stattarget, nattrs, stats); /* Use the largest value for all statistics objects. */ if (stattarget > result) result = stattarget; } table_close(pg_stext, RowExclusiveLock); MemoryContextSwitchTo(oldcxt); MemoryContextDelete(cxt); /* compute sample size based on the statistics target */ return (300 * result); } /* * statext_compute_stattarget * compute statistics target for an extended statistic * * When computing target for extended statistics objects, we consider three * places where the target may be set - the statistics object itself, * attributes the statistics is defined on, and then the default statistics * target. * * First we look at what's set for the statistics object itself, using the * ALTER STATISTICS ... SET STATISTICS command. If we find a valid value * there (i.e. not -1) we're done. Otherwise we look at targets set for any * of the attributes the statistic is defined on, and if there are columns * with defined target, we use the maximum value. We do this mostly for * backwards compatibility, because this is what we did before having * statistics target for extended statistics. * * And finally, if we still don't have a statistics target, we use the value * set in default_statistics_target. */ static int statext_compute_stattarget(int stattarget, int nattrs, VacAttrStats **stats) { int i; /* * If there's statistics target set for the statistics object, use it. It * may be set to 0 which disables building of that statistic. */ if (stattarget >= 0) return stattarget; /* * The target for the statistics object is set to -1, in which case we * look at the maximum target set for any of the attributes the object is * defined on. */ for (i = 0; i < nattrs; i++) { /* keep the maximmum statistics target */ if (stats[i]->attr->attstattarget > stattarget) stattarget = stats[i]->attr->attstattarget; } /* * If the value is still negative (so neither the statistics object nor * any of the columns have custom statistics target set), use the global * default target. */ if (stattarget < 0) stattarget = default_statistics_target; /* As this point we should have a valid statistics target. */ Assert((stattarget >= 0) && (stattarget <= 10000)); return stattarget; } /* * statext_is_kind_built * Is this stat kind built in the given pg_statistic_ext_data tuple? */ bool statext_is_kind_built(HeapTuple htup, char type) { AttrNumber attnum; switch (type) { case STATS_EXT_NDISTINCT: attnum = Anum_pg_statistic_ext_data_stxdndistinct; break; case STATS_EXT_DEPENDENCIES: attnum = Anum_pg_statistic_ext_data_stxddependencies; break; case STATS_EXT_MCV: attnum = Anum_pg_statistic_ext_data_stxdmcv; break; default: elog(ERROR, "unexpected statistics type requested: %d", type); } return !heap_attisnull(htup, attnum, NULL); } /* * Return a list (of StatExtEntry) of statistics objects for the given relation. */ static List * fetch_statentries_for_relation(Relation pg_statext, Oid relid) { SysScanDesc scan; ScanKeyData skey; HeapTuple htup; List *result = NIL; /* * Prepare to scan pg_statistic_ext for entries having stxrelid = this * rel. */ ScanKeyInit(&skey, Anum_pg_statistic_ext_stxrelid, BTEqualStrategyNumber, F_OIDEQ, ObjectIdGetDatum(relid)); scan = systable_beginscan(pg_statext, StatisticExtRelidIndexId, true, NULL, 1, &skey); while (HeapTupleIsValid(htup = systable_getnext(scan))) { StatExtEntry *entry; Datum datum; bool isnull; int i; ArrayType *arr; char *enabled; Form_pg_statistic_ext staForm; entry = palloc0(sizeof(StatExtEntry)); staForm = (Form_pg_statistic_ext) GETSTRUCT(htup); entry->statOid = staForm->oid; entry->schema = get_namespace_name(staForm->stxnamespace); entry->name = pstrdup(NameStr(staForm->stxname)); entry->stattarget = staForm->stxstattarget; for (i = 0; i < staForm->stxkeys.dim1; i++) { entry->columns = bms_add_member(entry->columns, staForm->stxkeys.values[i]); } /* decode the stxkind char array into a list of chars */ datum = SysCacheGetAttr(STATEXTOID, htup, Anum_pg_statistic_ext_stxkind, &isnull); Assert(!isnull); arr = DatumGetArrayTypeP(datum); if (ARR_NDIM(arr) != 1 || ARR_HASNULL(arr) || ARR_ELEMTYPE(arr) != CHAROID) elog(ERROR, "stxkind is not a 1-D char array"); enabled = (char *) ARR_DATA_PTR(arr); for (i = 0; i < ARR_DIMS(arr)[0]; i++) { Assert((enabled[i] == STATS_EXT_NDISTINCT) || (enabled[i] == STATS_EXT_DEPENDENCIES) || (enabled[i] == STATS_EXT_MCV)); entry->types = lappend_int(entry->types, (int) enabled[i]); } result = lappend(result, entry); } systable_endscan(scan); return result; } /* * Using 'vacatts' of size 'nvacatts' as input data, return a newly built * VacAttrStats array which includes only the items corresponding to * attributes indicated by 'stxkeys'. If we don't have all of the per column * stats available to compute the extended stats, then we return NULL to indicate * to the caller that the stats should not be built. */ static VacAttrStats ** lookup_var_attr_stats(Relation rel, Bitmapset *attrs, int nvacatts, VacAttrStats **vacatts) { int i = 0; int x = -1; VacAttrStats **stats; stats = (VacAttrStats **) palloc(bms_num_members(attrs) * sizeof(VacAttrStats *)); /* lookup VacAttrStats info for the requested columns (same attnum) */ while ((x = bms_next_member(attrs, x)) >= 0) { int j; stats[i] = NULL; for (j = 0; j < nvacatts; j++) { if (x == vacatts[j]->tupattnum) { stats[i] = vacatts[j]; break; } } if (!stats[i]) { /* * Looks like stats were not gathered for one of the columns * required. We'll be unable to build the extended stats without * this column. */ pfree(stats); return NULL; } /* * Sanity check that the column is not dropped - stats should have * been removed in this case. */ Assert(!stats[i]->attr->attisdropped); i++; } return stats; } /* * statext_store * Serializes the statistics and stores them into the pg_statistic_ext_data * tuple. */ static void statext_store(Oid statOid, MVNDistinct *ndistinct, MVDependencies *dependencies, MCVList *mcv, VacAttrStats **stats) { Relation pg_stextdata; HeapTuple stup, oldtup; Datum values[Natts_pg_statistic_ext_data]; bool nulls[Natts_pg_statistic_ext_data]; bool replaces[Natts_pg_statistic_ext_data]; pg_stextdata = table_open(StatisticExtDataRelationId, RowExclusiveLock); memset(nulls, true, sizeof(nulls)); memset(replaces, false, sizeof(replaces)); memset(values, 0, sizeof(values)); /* * Construct a new pg_statistic_ext_data tuple, replacing the calculated * stats. */ if (ndistinct != NULL) { bytea *data = statext_ndistinct_serialize(ndistinct); nulls[Anum_pg_statistic_ext_data_stxdndistinct - 1] = (data == NULL); values[Anum_pg_statistic_ext_data_stxdndistinct - 1] = PointerGetDatum(data); } if (dependencies != NULL) { bytea *data = statext_dependencies_serialize(dependencies); nulls[Anum_pg_statistic_ext_data_stxddependencies - 1] = (data == NULL); values[Anum_pg_statistic_ext_data_stxddependencies - 1] = PointerGetDatum(data); } if (mcv != NULL) { bytea *data = statext_mcv_serialize(mcv, stats); nulls[Anum_pg_statistic_ext_data_stxdmcv - 1] = (data == NULL); values[Anum_pg_statistic_ext_data_stxdmcv - 1] = PointerGetDatum(data); } /* always replace the value (either by bytea or NULL) */ replaces[Anum_pg_statistic_ext_data_stxdndistinct - 1] = true; replaces[Anum_pg_statistic_ext_data_stxddependencies - 1] = true; replaces[Anum_pg_statistic_ext_data_stxdmcv - 1] = true; /* there should already be a pg_statistic_ext_data tuple */ oldtup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statOid)); if (!HeapTupleIsValid(oldtup)) elog(ERROR, "cache lookup failed for statistics object %u", statOid); /* replace it */ stup = heap_modify_tuple(oldtup, RelationGetDescr(pg_stextdata), values, nulls, replaces); ReleaseSysCache(oldtup); CatalogTupleUpdate(pg_stextdata, &stup->t_self, stup); heap_freetuple(stup); table_close(pg_stextdata, RowExclusiveLock); } /* initialize multi-dimensional sort */ MultiSortSupport multi_sort_init(int ndims) { MultiSortSupport mss; Assert(ndims >= 2); mss = (MultiSortSupport) palloc0(offsetof(MultiSortSupportData, ssup) + sizeof(SortSupportData) * ndims); mss->ndims = ndims; return mss; } /* * Prepare sort support info using the given sort operator and collation * at the position 'sortdim' */ void multi_sort_add_dimension(MultiSortSupport mss, int sortdim, Oid oper, Oid collation) { SortSupport ssup = &mss->ssup[sortdim]; ssup->ssup_cxt = CurrentMemoryContext; ssup->ssup_collation = collation; ssup->ssup_nulls_first = false; PrepareSortSupportFromOrderingOp(oper, ssup); } /* compare all the dimensions in the selected order */ int multi_sort_compare(const void *a, const void *b, void *arg) { MultiSortSupport mss = (MultiSortSupport) arg; SortItem *ia = (SortItem *) a; SortItem *ib = (SortItem *) b; int i; for (i = 0; i < mss->ndims; i++) { int compare; compare = ApplySortComparator(ia->values[i], ia->isnull[i], ib->values[i], ib->isnull[i], &mss->ssup[i]); if (compare != 0) return compare; } /* equal by default */ return 0; } /* compare selected dimension */ int multi_sort_compare_dim(int dim, const SortItem *a, const SortItem *b, MultiSortSupport mss) { return ApplySortComparator(a->values[dim], a->isnull[dim], b->values[dim], b->isnull[dim], &mss->ssup[dim]); } int multi_sort_compare_dims(int start, int end, const SortItem *a, const SortItem *b, MultiSortSupport mss) { int dim; for (dim = start; dim <= end; dim++) { int r = ApplySortComparator(a->values[dim], a->isnull[dim], b->values[dim], b->isnull[dim], &mss->ssup[dim]); if (r != 0) return r; } return 0; } int compare_scalars_simple(const void *a, const void *b, void *arg) { return compare_datums_simple(*(Datum *) a, *(Datum *) b, (SortSupport) arg); } int compare_datums_simple(Datum a, Datum b, SortSupport ssup) { return ApplySortComparator(a, false, b, false, ssup); } /* * build_attnums_array * Transforms a bitmap into an array of AttrNumber values. * * This is used for extended statistics only, so all the attribute must be * user-defined. That means offsetting by FirstLowInvalidHeapAttributeNumber * is not necessary here (and when querying the bitmap). */ AttrNumber * build_attnums_array(Bitmapset *attrs, int *numattrs) { int i, j; AttrNumber *attnums; int num = bms_num_members(attrs); if (numattrs) *numattrs = num; /* build attnums from the bitmapset */ attnums = (AttrNumber *) palloc(sizeof(AttrNumber) * num); i = 0; j = -1; while ((j = bms_next_member(attrs, j)) >= 0) { /* * Make sure the bitmap contains only user-defined attributes. As * bitmaps can't contain negative values, this can be violated in two * ways. Firstly, the bitmap might contain 0 as a member, and secondly * the integer value might be larger than MaxAttrNumber. */ Assert(AttrNumberIsForUserDefinedAttr(j)); Assert(j <= MaxAttrNumber); attnums[i++] = (AttrNumber) j; /* protect against overflows */ Assert(i <= num); } return attnums; } /* * build_sorted_items * build a sorted array of SortItem with values from rows * * Note: All the memory is allocated in a single chunk, so that the caller * can simply pfree the return value to release all of it. */ SortItem * build_sorted_items(int numrows, int *nitems, HeapTuple *rows, TupleDesc tdesc, MultiSortSupport mss, int numattrs, AttrNumber *attnums) { int i, j, len, idx; int nvalues = numrows * numattrs; SortItem *items; Datum *values; bool *isnull; char *ptr; /* Compute the total amount of memory we need (both items and values). */ len = numrows * sizeof(SortItem) + nvalues * (sizeof(Datum) + sizeof(bool)); /* Allocate the memory and split it into the pieces. */ ptr = palloc0(len); /* items to sort */ items = (SortItem *) ptr; ptr += numrows * sizeof(SortItem); /* values and null flags */ values = (Datum *) ptr; ptr += nvalues * sizeof(Datum); isnull = (bool *) ptr; ptr += nvalues * sizeof(bool); /* make sure we consumed the whole buffer exactly */ Assert((ptr - (char *) items) == len); /* fix the pointers to Datum and bool arrays */ idx = 0; for (i = 0; i < numrows; i++) { bool toowide = false; items[idx].values = &values[idx * numattrs]; items[idx].isnull = &isnull[idx * numattrs]; /* load the values/null flags from sample rows */ for (j = 0; j < numattrs; j++) { Datum value; bool isnull; value = heap_getattr(rows[i], attnums[j], tdesc, &isnull); /* * If this is a varlena value, check if it's too wide and if yes * then skip the whole item. Otherwise detoast the value. * * XXX It may happen that we've already detoasted some preceding * values for the current item. We don't bother to cleanup those * on the assumption that those are small (below WIDTH_THRESHOLD) * and will be discarded at the end of analyze. */ if ((!isnull) && (TupleDescAttr(tdesc, attnums[j] - 1)->attlen == -1)) { if (toast_raw_datum_size(value) > WIDTH_THRESHOLD) { toowide = true; break; } value = PointerGetDatum(PG_DETOAST_DATUM(value)); } items[idx].values[j] = value; items[idx].isnull[j] = isnull; } if (toowide) continue; idx++; } /* store the actual number of items (ignoring the too-wide ones) */ *nitems = idx; /* all items were too wide */ if (idx == 0) { /* everything is allocated as a single chunk */ pfree(items); return NULL; } /* do the sort, using the multi-sort */ qsort_arg((void *) items, idx, sizeof(SortItem), multi_sort_compare, mss); return items; } /* * has_stats_of_kind * Check whether the list contains statistic of a given kind */ bool has_stats_of_kind(List *stats, char requiredkind) { ListCell *l; foreach(l, stats) { StatisticExtInfo *stat = (StatisticExtInfo *) lfirst(l); if (stat->kind == requiredkind) return true; } return false; } /* * choose_best_statistics * Look for and return statistics with the specified 'requiredkind' which * have keys that match at least two of the given attnums. Return NULL if * there's no match. * * The current selection criteria is very simple - we choose the statistics * object referencing the most attributes in covered (and still unestimated * clauses), breaking ties in favor of objects with fewer keys overall. * * The clause_attnums is an array of bitmaps, storing attnums for individual * clauses. A NULL element means the clause is either incompatible or already * estimated. * * XXX If multiple statistics objects tie on both criteria, then which object * is chosen depends on the order that they appear in the stats list. Perhaps * further tiebreakers are needed. */ StatisticExtInfo * choose_best_statistics(List *stats, char requiredkind, Bitmapset **clause_attnums, int nclauses) { ListCell *lc; StatisticExtInfo *best_match = NULL; int best_num_matched = 2; /* goal #1: maximize */ int best_match_keys = (STATS_MAX_DIMENSIONS + 1); /* goal #2: minimize */ foreach(lc, stats) { int i; StatisticExtInfo *info = (StatisticExtInfo *) lfirst(lc); Bitmapset *matched = NULL; int num_matched; int numkeys; /* skip statistics that are not of the correct type */ if (info->kind != requiredkind) continue; /* * Collect attributes in remaining (unestimated) clauses fully covered * by this statistic object. */ for (i = 0; i < nclauses; i++) { /* ignore incompatible/estimated clauses */ if (!clause_attnums[i]) continue; /* ignore clauses that are not covered by this object */ if (!bms_is_subset(clause_attnums[i], info->keys)) continue; matched = bms_add_members(matched, clause_attnums[i]); } num_matched = bms_num_members(matched); bms_free(matched); /* * save the actual number of keys in the stats so that we can choose * the narrowest stats with the most matching keys. */ numkeys = bms_num_members(info->keys); /* * Use this object when it increases the number of matched clauses or * when it matches the same number of attributes but these stats have * fewer keys than any previous match. */ if (num_matched > best_num_matched || (num_matched == best_num_matched && numkeys < best_match_keys)) { best_match = info; best_num_matched = num_matched; best_match_keys = numkeys; } } return best_match; } /* * statext_is_compatible_clause_internal * Determines if the clause is compatible with MCV lists. * * Does the heavy lifting of actually inspecting the clauses for * statext_is_compatible_clause. It needs to be split like this because * of recursion. The attnums bitmap is an input/output parameter collecting * attribute numbers from all compatible clauses (recursively). */ static bool statext_is_compatible_clause_internal(PlannerInfo *root, Node *clause, Index relid, Bitmapset **attnums) { /* Look inside any binary-compatible relabeling (as in examine_variable) */ if (IsA(clause, RelabelType)) clause = (Node *) ((RelabelType *) clause)->arg; /* plain Var references (boolean Vars or recursive checks) */ if (IsA(clause, Var)) { Var *var = (Var *) clause; /* Ensure var is from the correct relation */ if (var->varno != relid) return false; /* we also better ensure the Var is from the current level */ if (var->varlevelsup > 0) return false; /* Also skip system attributes (we don't allow stats on those). */ if (!AttrNumberIsForUserDefinedAttr(var->varattno)) return false; *attnums = bms_add_member(*attnums, var->varattno); return true; } /* (Var op Const) or (Const op Var) */ if (is_opclause(clause)) { RangeTblEntry *rte = root->simple_rte_array[relid]; OpExpr *expr = (OpExpr *) clause; Var *var; /* Only expressions with two arguments are considered compatible. */ if (list_length(expr->args) != 2) return false; /* Check if the expression has the right shape (one Var, one Const) */ if (!examine_clause_args(expr->args, &var, NULL, NULL)) return false; /* * If it's not one of the supported operators ("=", "<", ">", etc.), * just ignore the clause, as it's not compatible with MCV lists. * * This uses the function for estimating selectivity, not the operator * directly (a bit awkward, but well ...). */ switch (get_oprrest(expr->opno)) { case F_EQSEL: case F_NEQSEL: case F_SCALARLTSEL: case F_SCALARLESEL: case F_SCALARGTSEL: case F_SCALARGESEL: /* supported, will continue with inspection of the Var */ break; default: /* other estimators are considered unknown/unsupported */ return false; } /* * If there are any securityQuals on the RTE from security barrier * views or RLS policies, then the user may not have access to all the * table's data, and we must check that the operator is leak-proof. * * If the operator is leaky, then we must ignore this clause for the * purposes of estimating with MCV lists, otherwise the operator might * reveal values from the MCV list that the user doesn't have * permission to see. */ if (rte->securityQuals != NIL && !get_func_leakproof(get_opcode(expr->opno))) return false; return statext_is_compatible_clause_internal(root, (Node *) var, relid, attnums); } /* Var IN Array */ if (IsA(clause, ScalarArrayOpExpr)) { RangeTblEntry *rte = root->simple_rte_array[relid]; ScalarArrayOpExpr *expr = (ScalarArrayOpExpr *) clause; Var *var; /* Only expressions with two arguments are considered compatible. */ if (list_length(expr->args) != 2) return false; /* Check if the expression has the right shape (one Var, one Const) */ if (!examine_clause_args(expr->args, &var, NULL, NULL)) return false; /* * If it's not one of the supported operators ("=", "<", ">", etc.), * just ignore the clause, as it's not compatible with MCV lists. * * This uses the function for estimating selectivity, not the operator * directly (a bit awkward, but well ...). */ switch (get_oprrest(expr->opno)) { case F_EQSEL: case F_NEQSEL: case F_SCALARLTSEL: case F_SCALARLESEL: case F_SCALARGTSEL: case F_SCALARGESEL: /* supported, will continue with inspection of the Var */ break; default: /* other estimators are considered unknown/unsupported */ return false; } /* * If there are any securityQuals on the RTE from security barrier * views or RLS policies, then the user may not have access to all the * table's data, and we must check that the operator is leak-proof. * * If the operator is leaky, then we must ignore this clause for the * purposes of estimating with MCV lists, otherwise the operator might * reveal values from the MCV list that the user doesn't have * permission to see. */ if (rte->securityQuals != NIL && !get_func_leakproof(get_opcode(expr->opno))) return false; return statext_is_compatible_clause_internal(root, (Node *) var, relid, attnums); } /* AND/OR/NOT clause */ if (is_andclause(clause) || is_orclause(clause) || is_notclause(clause)) { /* * AND/OR/NOT-clauses are supported if all sub-clauses are supported * * Perhaps we could improve this by handling mixed cases, when some of * the clauses are supported and some are not. Selectivity for the * supported subclauses would be computed using extended statistics, * and the remaining clauses would be estimated using the traditional * algorithm (product of selectivities). * * It however seems overly complex, and in a way we already do that * because if we reject the whole clause as unsupported here, it will * be eventually passed to clauselist_selectivity() which does exactly * this (split into supported/unsupported clauses etc). */ BoolExpr *expr = (BoolExpr *) clause; ListCell *lc; foreach(lc, expr->args) { /* * Had we found incompatible clause in the arguments, treat the * whole clause as incompatible. */ if (!statext_is_compatible_clause_internal(root, (Node *) lfirst(lc), relid, attnums)) return false; } return true; } /* Var IS NULL */ if (IsA(clause, NullTest)) { NullTest *nt = (NullTest *) clause; /* * Only simple (Var IS NULL) expressions supported for now. Maybe we * could use examine_variable to fix this? */ if (!IsA(nt->arg, Var)) return false; return statext_is_compatible_clause_internal(root, (Node *) (nt->arg), relid, attnums); } return false; } /* * statext_is_compatible_clause * Determines if the clause is compatible with MCV lists. * * Currently, we only support three types of clauses: * * (a) OpExprs of the form (Var op Const), or (Const op Var), where the op * is one of ("=", "<", ">", ">=", "<=") * * (b) (Var IS [NOT] NULL) * * (c) combinations using AND/OR/NOT * * In the future, the range of supported clauses may be expanded to more * complex cases, for example (Var op Var). */ static bool statext_is_compatible_clause(PlannerInfo *root, Node *clause, Index relid, Bitmapset **attnums) { RangeTblEntry *rte = root->simple_rte_array[relid]; RestrictInfo *rinfo = (RestrictInfo *) clause; Oid userid; /* * Special-case handling for bare BoolExpr AND clauses, because the * restrictinfo machinery doesn't build RestrictInfos on top of AND * clauses. */ if (is_andclause(clause)) { BoolExpr *expr = (BoolExpr *) clause; ListCell *lc; /* * Check that each sub-clause is compatible. We expect these to be * RestrictInfos. */ foreach(lc, expr->args) { if (!statext_is_compatible_clause(root, (Node *) lfirst(lc), relid, attnums)) return false; } return true; } /* Otherwise it must be a RestrictInfo. */ if (!IsA(rinfo, RestrictInfo)) return false; /* Pseudoconstants are not really interesting here. */ if (rinfo->pseudoconstant) return false; /* clauses referencing multiple varnos are incompatible */ if (bms_membership(rinfo->clause_relids) != BMS_SINGLETON) return false; /* Check the clause and determine what attributes it references. */ if (!statext_is_compatible_clause_internal(root, (Node *) rinfo->clause, relid, attnums)) return false; /* * Check that the user has permission to read all these attributes. Use * checkAsUser if it's set, in case we're accessing the table via a view. */ userid = rte->checkAsUser ? rte->checkAsUser : GetUserId(); if (pg_class_aclcheck(rte->relid, userid, ACL_SELECT) != ACLCHECK_OK) { /* Don't have table privilege, must check individual columns */ if (bms_is_member(InvalidAttrNumber, *attnums)) { /* Have a whole-row reference, must have access to all columns */ if (pg_attribute_aclcheck_all(rte->relid, userid, ACL_SELECT, ACLMASK_ALL) != ACLCHECK_OK) return false; } else { /* Check the columns referenced by the clause */ int attnum = -1; while ((attnum = bms_next_member(*attnums, attnum)) >= 0) { if (pg_attribute_aclcheck(rte->relid, attnum, userid, ACL_SELECT) != ACLCHECK_OK) return false; } } } /* If we reach here, the clause is OK */ return true; } /* * statext_mcv_clauselist_selectivity * Estimate clauses using the best multi-column statistics. * * Applies available extended (multi-column) statistics on a table. There may * be multiple applicable statistics (with respect to the clauses), in which * case we use greedy approach. In each round we select the best statistic on * a table (measured by the number of attributes extracted from the clauses * and covered by it), and compute the selectivity for the supplied clauses. * We repeat this process with the remaining clauses (if any), until none of * the available statistics can be used. * * One of the main challenges with using MCV lists is how to extrapolate the * estimate to the data not covered by the MCV list. To do that, we compute * not only the "MCV selectivity" (selectivities for MCV items matching the * supplied clauses), but also the following related selectivities: * * - simple selectivity: Computed without extended statistics, i.e. as if the * columns/clauses were independent. * * - base selectivity: Similar to simple selectivity, but is computed using * the extended statistic by adding up the base frequencies (that we compute * and store for each MCV item) of matching MCV items. * * - total selectivity: Selectivity covered by the whole MCV list. * * These are passed to mcv_combine_selectivities() which combines them to * produce a selectivity estimate that makes use of both per-column statistics * and the multi-column MCV statistics. * * 'estimatedclauses' is an input/output parameter. We set bits for the * 0-based 'clauses' indexes we estimate for and also skip clause items that * already have a bit set. */ static Selectivity statext_mcv_clauselist_selectivity(PlannerInfo *root, List *clauses, int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo, RelOptInfo *rel, Bitmapset **estimatedclauses, bool is_or) { ListCell *l; Bitmapset **list_attnums; int listidx; Selectivity sel = (is_or) ? 0.0 : 1.0; /* check if there's any stats that might be useful for us. */ if (!has_stats_of_kind(rel->statlist, STATS_EXT_MCV)) return sel; list_attnums = (Bitmapset **) palloc(sizeof(Bitmapset *) * list_length(clauses)); /* * Pre-process the clauses list to extract the attnums seen in each item. * We need to determine if there's any clauses which will be useful for * selectivity estimations with extended stats. Along the way we'll record * all of the attnums for each clause in a list which we'll reference * later so we don't need to repeat the same work again. We'll also keep * track of all attnums seen. * * We also skip clauses that we already estimated using different types of * statistics (we treat them as incompatible). */ listidx = 0; foreach(l, clauses) { Node *clause = (Node *) lfirst(l); Bitmapset *attnums = NULL; if (!bms_is_member(listidx, *estimatedclauses) && statext_is_compatible_clause(root, clause, rel->relid, &attnums)) list_attnums[listidx] = attnums; else list_attnums[listidx] = NULL; listidx++; } /* apply as many extended statistics as possible */ while (true) { StatisticExtInfo *stat; List *stat_clauses; Bitmapset *simple_clauses; /* find the best suited statistics object for these attnums */ stat = choose_best_statistics(rel->statlist, STATS_EXT_MCV, list_attnums, list_length(clauses)); /* * if no (additional) matching stats could be found then we've nothing * to do */ if (!stat) break; /* Ensure choose_best_statistics produced an expected stats type. */ Assert(stat->kind == STATS_EXT_MCV); /* now filter the clauses to be estimated using the selected MCV */ stat_clauses = NIL; /* record which clauses are simple (single column) */ simple_clauses = NULL; listidx = 0; foreach(l, clauses) { /* * If the clause is compatible with the selected statistics, mark * it as estimated and add it to the list to estimate. */ if (list_attnums[listidx] != NULL && bms_is_subset(list_attnums[listidx], stat->keys)) { if (bms_membership(list_attnums[listidx]) == BMS_SINGLETON) simple_clauses = bms_add_member(simple_clauses, list_length(stat_clauses)); stat_clauses = lappend(stat_clauses, (Node *) lfirst(l)); *estimatedclauses = bms_add_member(*estimatedclauses, listidx); bms_free(list_attnums[listidx]); list_attnums[listidx] = NULL; } listidx++; } if (is_or) { bool *or_matches = NULL; Selectivity simple_or_sel = 0.0, stat_sel = 0.0; MCVList *mcv_list; /* Load the MCV list stored in the statistics object */ mcv_list = statext_mcv_load(stat->statOid); /* * Compute the selectivity of the ORed list of clauses covered by * this statistics object by estimating each in turn and combining * them using the formula P(A OR B) = P(A) + P(B) - P(A AND B). * This allows us to use the multivariate MCV stats to better * estimate the individual terms and their overlap. * * Each time we iterate this formula, the clause "A" above is * equal to all the clauses processed so far, combined with "OR". */ listidx = 0; foreach(l, stat_clauses) { Node *clause = (Node *) lfirst(l); Selectivity simple_sel, overlap_simple_sel, mcv_sel, mcv_basesel, overlap_mcvsel, overlap_basesel, mcv_totalsel, clause_sel, overlap_sel; /* * "Simple" selectivity of the next clause and its overlap * with any of the previous clauses. These are our initial * estimates of P(B) and P(A AND B), assuming independence of * columns/clauses. */ simple_sel = clause_selectivity_ext(root, clause, varRelid, jointype, sjinfo, false); overlap_simple_sel = simple_or_sel * simple_sel; /* * New "simple" selectivity of all clauses seen so far, * assuming independence. */ simple_or_sel += simple_sel - overlap_simple_sel; CLAMP_PROBABILITY(simple_or_sel); /* * Multi-column estimate of this clause using MCV statistics, * along with base and total selectivities, and corresponding * selectivities for the overlap term P(A AND B). */ mcv_sel = mcv_clause_selectivity_or(root, stat, mcv_list, clause, &or_matches, &mcv_basesel, &overlap_mcvsel, &overlap_basesel, &mcv_totalsel); /* * Combine the simple and multi-column estimates. * * If this clause is a simple single-column clause, then we * just use the simple selectivity estimate for it, since the * multi-column statistics are unlikely to improve on that * (and in fact could make it worse). For the overlap, we * always make use of the multi-column statistics. */ if (bms_is_member(listidx, simple_clauses)) clause_sel = simple_sel; else clause_sel = mcv_combine_selectivities(simple_sel, mcv_sel, mcv_basesel, mcv_totalsel); overlap_sel = mcv_combine_selectivities(overlap_simple_sel, overlap_mcvsel, overlap_basesel, mcv_totalsel); /* Factor these into the result for this statistics object */ stat_sel += clause_sel - overlap_sel; CLAMP_PROBABILITY(stat_sel); listidx++; } /* * Factor the result for this statistics object into the overall * result. We treat the results from each separate statistics * object as independent of one another. */ sel = sel + stat_sel - sel * stat_sel; } else /* Implicitly-ANDed list of clauses */ { Selectivity simple_sel, mcv_sel, mcv_basesel, mcv_totalsel, stat_sel; /* * "Simple" selectivity, i.e. without any extended statistics, * essentially assuming independence of the columns/clauses. */ simple_sel = clauselist_selectivity_ext(root, stat_clauses, varRelid, jointype, sjinfo, false); /* * Multi-column estimate using MCV statistics, along with base and * total selectivities. */ mcv_sel = mcv_clauselist_selectivity(root, stat, stat_clauses, varRelid, jointype, sjinfo, rel, &mcv_basesel, &mcv_totalsel); /* Combine the simple and multi-column estimates. */ stat_sel = mcv_combine_selectivities(simple_sel, mcv_sel, mcv_basesel, mcv_totalsel); /* Factor this into the overall result */ sel *= stat_sel; } } return sel; } /* * statext_clauselist_selectivity * Estimate clauses using the best multi-column statistics. */ Selectivity statext_clauselist_selectivity(PlannerInfo *root, List *clauses, int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo, RelOptInfo *rel, Bitmapset **estimatedclauses, bool is_or) { Selectivity sel; /* First, try estimating clauses using a multivariate MCV list. */ sel = statext_mcv_clauselist_selectivity(root, clauses, varRelid, jointype, sjinfo, rel, estimatedclauses, is_or); /* * Functional dependencies only work for clauses connected by AND, so for * OR clauses we're done. */ if (is_or) return sel; /* * Then, apply functional dependencies on the remaining clauses by calling * dependencies_clauselist_selectivity. Pass 'estimatedclauses' so the * function can properly skip clauses already estimated above. * * The reasoning for applying dependencies last is that the more complex * stats can track more complex correlations between the attributes, and * so may be considered more reliable. * * For example, MCV list can give us an exact selectivity for values in * two columns, while functional dependencies can only provide information * about the overall strength of the dependency. */ sel *= dependencies_clauselist_selectivity(root, clauses, varRelid, jointype, sjinfo, rel, estimatedclauses); return sel; } /* * examine_opclause_expression * Split expression into Var and Const parts. * * Attempts to match the arguments to either (Var op Const) or (Const op Var), * possibly with a RelabelType on top. When the expression matches this form, * returns true, otherwise returns false. * * Optionally returns pointers to the extracted Var/Const nodes, when passed * non-null pointers (varp, cstp and varonleftp). The varonleftp flag specifies * on which side of the operator we found the Var node. */ bool examine_clause_args(List *args, Var **varp, Const **cstp, bool *varonleftp) { Var *var; Const *cst; bool varonleft; Node *leftop, *rightop; /* enforced by statext_is_compatible_clause_internal */ Assert(list_length(args) == 2); leftop = linitial(args); rightop = lsecond(args); /* strip RelabelType from either side of the expression */ if (IsA(leftop, RelabelType)) leftop = (Node *) ((RelabelType *) leftop)->arg; if (IsA(rightop, RelabelType)) rightop = (Node *) ((RelabelType *) rightop)->arg; if (IsA(leftop, Var) && IsA(rightop, Const)) { var = (Var *) leftop; cst = (Const *) rightop; varonleft = true; } else if (IsA(leftop, Const) && IsA(rightop, Var)) { var = (Var *) rightop; cst = (Const *) leftop; varonleft = false; } else return false; /* return pointers to the extracted parts if requested */ if (varp) *varp = var; if (cstp) *cstp = cst; if (varonleftp) *varonleftp = varonleft; return true; }