diff options
Diffstat (limited to 'src/backend/statistics/extended_stats.c')
| -rw-r--r-- | src/backend/statistics/extended_stats.c | 1508 |
1 files changed, 1508 insertions, 0 deletions
diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c new file mode 100644 index 0000000..0c80e55 --- /dev/null +++ b/src/backend/statistics/extended_stats.c @@ -0,0 +1,1508 @@ +/*------------------------------------------------------------------------- + * + * extended_stats.c + * POSTGRES extended statistics + * + * Generic code supporting statistics objects created via CREATE STATISTICS. + * + * + * Portions Copyright (c) 1996-2020, 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 = stat->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); +} + +/* simple counterpart to qsort_arg */ +void * +bsearch_arg(const void *key, const void *base, size_t nmemb, size_t size, + int (*compar) (const void *, const void *, void *), + void *arg) +{ + size_t l, + u, + idx; + const void *p; + int comparison; + + l = 0; + u = nmemb; + while (l < u) + { + idx = (l + u) / 2; + p = (void *) (((const char *) base) + (idx * size)); + comparison = (*compar) (key, p, arg); + + if (comparison < 0) + u = idx; + else if (comparison > 0) + l = idx + 1; + else + return (void *) p; + } + + return NULL; +} + +/* + * 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; + + 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 a couple of derived selectivities: + * + * - simple selectivity: Computed without extended statistic, 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. + * + * - other selectivity: A selectivity estimate for data not covered by the MCV + * list (i.e. satisfying the clauses, but not common enough to make it into + * the MCV list) + * + * Note: While simple and base selectivities are defined in a quite similar + * way, the values are computed differently and are not therefore equal. The + * simple selectivity is computed as a product of per-clause estimates, while + * the base selectivity is computed by adding up base frequencies of matching + * items of the multi-column MCV list. So the values may differ for two main + * reasons - (a) the MCV list may not cover 100% of the data and (b) some of + * the MCV items did not match the estimated clauses. + * + * As both (a) and (b) reduce the base selectivity value, it generally holds + * that (simple_selectivity >= base_selectivity). If the MCV list covers all + * the data, the values may be equal. + * + * So, (simple_selectivity - base_selectivity) is an estimate for the part + * not covered by the MCV list, and (mcv_selectivity - base_selectivity) may + * be seen as a correction for the part covered by the MCV list. Those two + * statements are actually equivalent. + * + * Note: Due to rounding errors and minor differences in how the estimates + * are computed, the inequality may not always hold. Which is why we clamp + * the selectivities to prevent strange estimate (negative etc.). + * + * '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) +{ + ListCell *l; + Bitmapset **list_attnums; + int listidx; + Selectivity sel = 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 1.0; + + 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; + Selectivity simple_sel, + mcv_sel, + mcv_basesel, + mcv_totalsel, + other_sel, + stat_sel; + + /* 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; + + 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)) + { + stat_clauses = lappend(stat_clauses, (Node *) lfirst(l)); + *estimatedclauses = bms_add_member(*estimatedclauses, listidx); + + bms_free(list_attnums[listidx]); + list_attnums[listidx] = NULL; + } + + listidx++; + } + + /* + * First compute "simple" selectivity, i.e. without the extended + * statistics, and essentially assuming independence of the + * columns/clauses. We'll then use the various selectivities computed + * from MCV list to improve it. + */ + simple_sel = clauselist_selectivity_simple(root, stat_clauses, varRelid, + jointype, sjinfo, NULL); + + /* + * Now compute the multi-column estimate from the MCV list, along with + * the other selectivities (base & total selectivity). + */ + mcv_sel = mcv_clauselist_selectivity(root, stat, stat_clauses, varRelid, + jointype, sjinfo, rel, + &mcv_basesel, &mcv_totalsel); + + /* Estimated selectivity of values not covered by MCV matches */ + other_sel = simple_sel - mcv_basesel; + CLAMP_PROBABILITY(other_sel); + + /* The non-MCV selectivity can't exceed the 1 - mcv_totalsel. */ + if (other_sel > 1.0 - mcv_totalsel) + other_sel = 1.0 - mcv_totalsel; + + /* + * Overall selectivity is the combination of MCV and non-MCV + * estimates. + */ + stat_sel = mcv_sel + other_sel; + CLAMP_PROBABILITY(stat_sel); + + /* Factor the estimate from this MCV to the oveall estimate. */ + 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) +{ + Selectivity sel; + + /* First, try estimating clauses using a multivariate MCV list. */ + sel = statext_mcv_clauselist_selectivity(root, clauses, varRelid, jointype, + sjinfo, rel, estimatedclauses); + + /* + * 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; +} |