On Wed, Mar 02, 2022 at 11:38:21AM -0600, Justin Pryzby wrote:
> Rebased over 269b532ae and muted compiler warnings.
And attached.
>From 587a5e9fe87c26cdcd9602fc349f092da95cc580 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas.von...@postgresql.org>
Date: Mon, 13 Dec 2021 14:05:17 +0100
Subject: [PATCH] Estimate joins using extended statistics
Use extended statistics (MCV) to improve join estimates. In general this
is similar to how we use regular statistics - we search for extended
statistics (with MCV) covering all join clauses, and if we find such MCV
on both sides of the join, we combine those two MCVs.
Extended statistics allow a couple additional improvements - e.g. if
there are baserel conditions, we can use them to restrict the part of
the MCVs combined. This means we're building conditional probability
distribution and calculating conditional probability
P(join clauses | baserel conditions)
instead of just P(join clauses).
The patch also allows combining regular and extended MCV - we don't need
extended MCVs on both sides. This helps when one of the tables does not
have extended statistics (e.g. because there are no correlations).
---
src/backend/optimizer/path/clausesel.c | 63 +-
src/backend/statistics/extended_stats.c | 805 ++++++++++++++++++
src/backend/statistics/mcv.c | 757 ++++++++++++++++
.../statistics/extended_stats_internal.h | 20 +
src/include/statistics/statistics.h | 12 +
src/test/regress/expected/stats_ext.out | 167 ++++
src/test/regress/sql/stats_ext.sql | 66 ++
7 files changed, 1889 insertions(+), 1 deletion(-)
diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 06f836308d0..1b2227321a2 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -50,6 +50,9 @@ static Selectivity clauselist_selectivity_or(PlannerInfo *root,
JoinType jointype,
SpecialJoinInfo *sjinfo,
bool use_extended_stats);
+static inline bool treat_as_join_clause(PlannerInfo *root,
+ Node *clause, RestrictInfo *rinfo,
+ int varRelid, SpecialJoinInfo *sjinfo);
/****************************************************************************
* ROUTINES TO COMPUTE SELECTIVITIES
@@ -129,12 +132,53 @@ clauselist_selectivity_ext(PlannerInfo *root,
RangeQueryClause *rqlist = NULL;
ListCell *l;
int listidx;
+ bool single_clause_optimization = true;
+
+ /*
+ * The optimization of skipping to clause_selectivity_ext for single
+ * clauses means we can't improve join estimates with a single join
+ * clause but additional baserel restrictions. So we disable it when
+ * estimating joins.
+ *
+ * XXX Not sure if this is the right way to do it, but more elaborate
+ * checks would mostly negate the whole point of the optimization.
+ * The (Var op Var) patch has the same issue.
+ *
+ * XXX An alternative might be making clause_selectivity_ext smarter
+ * and make it use the join extended stats there. But that seems kinda
+ * against the whole point of the optimization (skipping expensive
+ * stuff) and it's making other parts more complex.
+ *
+ * XXX Maybe this should check if there are at least some restrictions
+ * on some base relations, which seems important. But then again, that
+ * seems to go against the idea of this check to be cheap. Moreover, it
+ * won't work for OR clauses, which may have multiple parts but we still
+ * see them as a single BoolExpr clause (it doesn't work later, though).
+ */
+ if (list_length(clauses) == 1)
+ {
+ Node *clause = linitial(clauses);
+ RestrictInfo *rinfo = NULL;
+
+ if (IsA(clause, RestrictInfo))
+ {
+ rinfo = (RestrictInfo *) clause;
+ clause = (Node *) rinfo->clause;
+ }
+
+ single_clause_optimization
+ = !treat_as_join_clause(root, clause, rinfo, varRelid, sjinfo);
+ }
/*
* If there's exactly one clause, just go directly to
* clause_selectivity_ext(). None of what we might do below is relevant.
+ *
+ * XXX This means we won't try using extended stats on OR-clauses (which
+ * are a single BoolExpr clause at this point), although we'll do that
+ * later (once we look at the arguments).
*/
- if (list_length(clauses) == 1)
+ if ((list_length(clauses) == 1) && single_clause_optimization)
return clause_selectivity_ext(root, (Node *) linitial(clauses),
varRelid, jointype, sjinfo,
use_extended_stats);
@@ -157,6 +201,23 @@ clauselist_selectivity_ext(PlannerInfo *root,
&estimatedclauses, false);
}
+ /*
+ * Try applying extended statistics to joins. There's not much we can
+ * do to detect when this makes sense, but we can check that there are
+ * join clauses, and that at least some of the rels have stats.
+ *
+ * XXX Isn't this mutually exclusive with the preceding block which
+ * calculates estimates for a single relation?
+ */
+ if (use_extended_stats &&
+ statext_try_join_estimates(root, clauses, varRelid, jointype, sjinfo,
+ estimatedclauses))
+ {
+ s1 *= statext_clauselist_join_selectivity(root, clauses, varRelid,
+ jointype, sjinfo,
+ &estimatedclauses);
+ }
+
/*
* Apply normal selectivity estimates for remaining clauses. We'll be
* careful to skip any clauses which were already estimated above.
diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index ca48395d5c5..427ba015b73 100644
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -31,6 +31,7 @@
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/optimizer.h"
+#include "optimizer/pathnode.h"
#include "parser/parsetree.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
@@ -103,6 +104,8 @@ static StatsBuildData *make_build_data(Relation onerel, StatExtEntry *stat,
int numrows, HeapTuple *rows,
VacAttrStats **stats, int stattarget);
+static bool stat_covers_expressions(StatisticExtInfo *stat, List *exprs,
+ Bitmapset **expr_idxs);
/*
* Compute requested extended stats, using the rows sampled for the plain
@@ -2611,3 +2614,805 @@ make_build_data(Relation rel, StatExtEntry *stat, int numrows, HeapTuple *rows,
return result;
}
+
+/*
+ * statext_find_matching_mcv
+ * Search for a MCV covering all the attributes and expressions.
+ *
+ * We pick the statistics to use for join estimation. The statistics object has
+ * to have MCV, and we require it to match all the join conditions, because it
+ * makes the estimation simpler.
+ *
+ * If there are multiple candidate statistics objects (matching all join clauses),
+ * we pick the smallest one, and we also consider additional conditions on
+ * the base relations to restrict the MCV items used for estimation (using
+ * conditional probability).
+ *
+ * XXX The requirement that all the attributes need to be covered might be
+ * too strong. We could relax this and and require fewer matches (at least two,
+ * if counting the additional conditions), and we might even apply multiple
+ * statistics etc. But that would require matching statistics on both sides of
+ * the join, while now we simply know the statistics match. We don't really
+ * expect many candidate MCVs, so this simple approach seems sufficient. And
+ * the joins usually use only one or two columns, so there's not much room
+ * for applying multiple statistics anyway.
+ */
+StatisticExtInfo *
+statext_find_matching_mcv(PlannerInfo *root, RelOptInfo *rel,
+ Bitmapset *attnums, List *exprs)
+{
+ ListCell *l;
+ StatisticExtInfo *mcv = NULL;
+ List *stats = rel->statlist;
+
+ foreach(l, stats)
+ {
+ StatisticExtInfo *stat = (StatisticExtInfo *) lfirst(l);
+ List *conditions1 = NIL,
+ *conditions2 = NIL;
+
+ /* We only care about MCV statistics here. */
+ if (stat->kind != STATS_EXT_MCV)
+ continue;
+
+ /*
+ * Ignore MCVs not covering all the attributes/expressions.
+ *
+ * XXX Maybe we shouldn't be so strict and consider only partial
+ * matches for join clauses too?
+ */
+ if (!bms_is_subset(attnums, stat->keys) ||
+ !stat_covers_expressions(stat, exprs, NULL))
+ continue;
+
+ /* If there's no matching MCV yet, keep this one. */
+ if (!mcv)
+ {
+ mcv = stat;
+ continue;
+ }
+
+ /*
+ * OK, we have two candidate statistics objects and we need to decide
+ * which one to keep. We'll use two simple heuristics:
+ *
+ * (a) We prefer smaller statistics (fewer columns), on the assumption
+ * that it represents a larger fraction of the data (due to having fewer
+ * combinations with higher counts).
+ *
+ * (b) If the statistics object covers some additional conditions for the rels,
+ * that may help with considering additional dependencies between the
+ * tables.
+ *
+ * Of course, those two heuristict are somewhat contradictory - smaller
+ * stats are less likely to cover as many conditions as a larger one. We
+ * consider the additional conditions first - if someone created such
+ * statistics, there probably is a dependency worth considering.
+ *
+ * When inspecting the restrictions, we need to be careful - we don't
+ * know which of them are compatible with extended stats, so we have to
+ * run them through statext_is_compatible_clause first and then match
+ * them to the statistics.
+ *
+ * XXX Maybe we shouldn't pick statistics that covers just a single join
+ * clause, without any additional conditions. In such case we could just
+ * as well pick regular statistics for the column/expression, but it's
+ * not clear if that actually exists (so we might reject the stats here
+ * and then fail to find something simpler/better).
+ */
+ conditions1 = statext_determine_join_restrictions(root, rel, stat);
+ conditions2 = statext_determine_join_restrictions(root, rel, mcv);
+
+ /* if the new statistics object covers more conditions, use it */
+ if (list_length(conditions1) > list_length(conditions2))
+ {
+ mcv = stat;
+ continue;
+ }
+
+ /* The statistics seem about equal, so just use the smaller one. */
+ if (bms_num_members(mcv->keys) + list_length(mcv->exprs) >
+ bms_num_members(stat->keys) + list_length(stat->exprs))
+ {
+ mcv = stat;
+ }
+ }
+
+ return mcv;
+}
+
+/*
+ * statext_determine_join_restrictions
+ * Get restrictions on base relation, covered by the statistics object.
+ *
+ * Returns a list of baserel restrictinfos, compatible with extended statistics
+ * and covered by the extended statistics object.
+ *
+ * When using extended statistics to estimate joins, we can use conditions
+ * from base relations to calculate conditional probability
+ *
+ * P(join clauses | baserel restrictions)
+ *
+ * which should be a better estimate than just P(join clauses). We want to pick
+ * the statistics object covering the most such conditions.
+ */
+List *
+statext_determine_join_restrictions(PlannerInfo *root, RelOptInfo *rel,
+ StatisticExtInfo *info)
+{
+ ListCell *lc;
+ List *conditions = NIL;
+
+ /* extract conditions that may be applied to the MCV list */
+ foreach (lc, rel->baserestrictinfo)
+ {
+ RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+ Bitmapset *indexes = NULL;
+ Bitmapset *attnums = NULL;
+ List *exprs = NIL;
+
+ /* clause has to be supported by MCV in general */
+ if (!statext_is_compatible_clause(root, (Node *) rinfo, rel->relid,
+ &attnums, &exprs))
+ continue;
+
+ /*
+ * clause is compatible in general, but is it actually covered
+ * by this particular statistics object?
+ */
+ if (!bms_is_subset(attnums, info->keys) ||
+ !stat_covers_expressions(info, exprs, &indexes))
+ continue;
+
+ conditions = lappend(conditions, rinfo->clause);
+ }
+
+ return conditions;
+}
+
+/*
+ * statext_is_supported_join_clause
+ * Check if a join clause may be estimated using extended stats.
+ *
+ * Determines if this is a join clause of the form (Expr op Expr) which may be
+ * estimated using extended statistics. Each side must reference just a single
+ * relation for now.
+ *
+ * Similar to treat_as_join_clause, but we place additional restrictions
+ * on the conditions.
+ */
+static bool
+statext_is_supported_join_clause(PlannerInfo *root, Node *clause,
+ int varRelid, SpecialJoinInfo *sjinfo)
+{
+ Oid oprsel;
+ RestrictInfo *rinfo;
+ OpExpr *opclause;
+ ListCell *lc;
+
+ /*
+ * evaluation as a restriction clause, either at scan node or forced
+ *
+ * XXX See treat_as_join_clause.
+ */
+ if ((varRelid != 0) || (sjinfo == NULL))
+ return false;
+
+ /* XXX Can we rely on always getting RestrictInfo here? */
+ if (!IsA(clause, RestrictInfo))
+ return false;
+
+ /* strip the RestrictInfo */
+ rinfo = (RestrictInfo *) clause;
+ clause = (Node *) rinfo->clause;
+
+ /* is it referencing multiple relations? */
+ if (bms_membership(rinfo->clause_relids) != BMS_MULTIPLE)
+ return false;
+
+ /* we only support simple operator clauses for now */
+ if (!is_opclause(clause))
+ return false;
+
+ opclause = (OpExpr *) clause;
+
+ /* for now we only support estimating equijoins */
+ oprsel = get_oprjoin(opclause->opno);
+
+ /* has to be an equality condition */
+ if (oprsel != F_EQJOINSEL)
+ return false;
+
+ /*
+ * Make sure we're not mixing vars from multiple relations on the same
+ * side, like
+ *
+ * (t1.a + t2.a) = (t1.b + t2.b)
+ *
+ * which is still technically an opclause, but we can't match it to
+ * extended statistics in a simple way.
+ *
+ * XXX This also means we require rinfo->clause_relids to have 2 rels.
+ *
+ * XXX Also check it's not expression on system attributes, which we
+ * don't allow in extended statistics.
+ *
+ * XXX Although maybe we could allow cases that combine expressions
+ * from both relations on either side? Like (t1.a + t2.b = t1.c - t2.d)
+ * or something like that. We could do "cartesian product" of the MCV
+ * stats and restrict it using this condition.
+ */
+ foreach (lc, opclause->args)
+ {
+ Bitmapset *varnos = NULL;
+ Node *expr = (Node *) lfirst(lc);
+
+ varnos = pull_varnos(root, expr);
+
+ /*
+ * No argument should reference more than just one relation.
+ *
+ * This effectively means each side references just two relations.
+ * If there's no relation on one side, it's a Const, and the other
+ * side has to be either Const or Expr with a single rel. In which
+ * case it can't be a join clause.
+ */
+ if (bms_num_members(varnos) > 1)
+ return false;
+
+ /*
+ * XXX Maybe check that both relations have extended statistics
+ * (no point in considering the clause as useful without it). But
+ * we'll do that check later anyway, so keep this cheap.
+ */
+ }
+
+ return true;
+}
+
+/*
+ * statext_try_join_estimates
+ * Checks if it's worth considering extended stats on join estimates.
+ *
+ * This is supposed to be a quick/cheap check to decide whether to expend
+ * more effort on applying extended statistics to join clauses.
+ */
+bool
+statext_try_join_estimates(PlannerInfo *root, List *clauses, int varRelid,
+ JoinType jointype, SpecialJoinInfo *sjinfo,
+ Bitmapset *estimatedclauses)
+{
+ int listidx;
+ int k;
+ ListCell *lc;
+ Bitmapset *relids = NULL;
+
+ /*
+ * XXX Not having these values means treat_as_join_clause returns false,
+ * so we're not supposed to handle join clauses here. So just bail out.
+ */
+ if ((varRelid != 0) || (sjinfo == NULL))
+ return false;
+
+ /*
+ * Check if there are any unestimated join clauses, collect relids.
+ *
+ * XXX Currently this only allows simple OpExpr equality clauses with each
+ * argument referring to single relation, AND-ed together. Maybe we could
+ * relax this in the future, e.g. to allow more complex (deeper) expressions
+ * and to allow OR-ed join clauses too. And maybe supporting inequalities.
+ *
+ * Handling more complex expressions seems simple - we already do that for
+ * baserel estimates by building the match bitmap recursively, and we could
+ * do something similar for combinations of MCV items (a bit like building
+ * a single bit in the match bitmap). The challenge is what to do about the
+ * part not represented by MCV, which is now based on ndistinct estimates.
+ */
+ listidx = -1;
+ foreach (lc, clauses)
+ {
+ Node *clause = (Node *) lfirst(lc);
+ RestrictInfo *rinfo;
+
+ /* needs to happen before skipping any clauses */
+ listidx++;
+
+ /* Skip clauses that were already estimated. */
+ if (bms_is_member(listidx, estimatedclauses))
+ continue;
+
+ /*
+ * Skip clauses that are not join clauses or that we don't know
+ * how to handle estimate using extended statistics.
+ */
+ if (!statext_is_supported_join_clause(root, clause, varRelid, sjinfo))
+ continue;
+
+ /*
+ * XXX We're guaranteed to have RestrictInfo thanks to the checks
+ * in statext_is_supported_join_clause.
+ */
+ rinfo = (RestrictInfo *) clause;
+
+ /* Collect relids from all usable clauses. */
+ relids = bms_union(relids, rinfo->clause_relids);
+ }
+
+ /* no join clauses found, don't try applying extended stats */
+ if (bms_num_members(relids) == 0)
+ return false;
+
+ /*
+ * We expect either 0 or >= 2 relids, a case with 1 relid in join clauses
+ * should be impossible. And we just ruled out 0, so there are at least 2.
+ */
+ Assert(bms_num_members(relids) >= 2);
+
+ /*
+ * Check that at least some of the rels referenced by the clauses have
+ * extended stats.
+ *
+ * XXX Maybe we should check how many rels have stats, and cross-check how
+ * compatible they are (e.g. that both have MCVs, etc.). We might also
+ * cross-check the exact joined pairs of rels, but it's supposed to be a
+ * cheap check, so maybe better leave that for later.
+ *
+ * XXX We could also check the number of parameters in each rel to consider
+ * extended stats. If there's just a single attribute, it's pointless to use
+ * extended statistics. OTOH we can also consider restriction clauses from
+ * baserestrictinfo and use them to calculate conditional probabilities.
+ */
+ k = -1;
+ while ((k = bms_next_member(relids, k)) >= 0)
+ {
+ RelOptInfo *rel = find_base_rel(root, k);
+ if (rel->statlist)
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * Information about two joined relations, along with the join clauses between.
+ */
+typedef struct JoinPairInfo
+{
+ Bitmapset *rels;
+ List *clauses;
+} JoinPairInfo;
+
+/*
+ * statext_build_join_pairs
+ * Extract pairs of joined rels with join clauses for each pair.
+ *
+ * Walks the remaining (not yet estimated) clauses, and splits them into
+ * lists for each pair of joined relations. Returns NULL if there are no
+ * suitable join pairs that might be estimated using extended stats.
+ *
+ * XXX It's possible there are join clauses, but the clauses are not
+ * supported by the extended stats machinery (we only support opclauses
+ * with F_EQJOINSEL selectivity function at the moment).
+ */
+static JoinPairInfo *
+statext_build_join_pairs(PlannerInfo *root, List *clauses, int varRelid,
+ JoinType jointype, SpecialJoinInfo *sjinfo,
+ Bitmapset *estimatedclauses, int *npairs)
+{
+ int cnt;
+ int listidx;
+ JoinPairInfo *info;
+ ListCell *lc;
+
+ /*
+ * Assume each clause is for a different pair of relations (some of them
+ * might be already estimated, but meh - there shouldn't be too many of
+ * them and it's cheaper than repalloc).
+ */
+ info = (JoinPairInfo *) palloc0(sizeof(JoinPairInfo) * list_length(clauses));
+ cnt = 0;
+
+ listidx = -1;
+ foreach(lc, clauses)
+ {
+ int i;
+ bool found;
+ Node *clause = (Node *) lfirst(lc);
+ RestrictInfo *rinfo;
+
+ listidx++;
+
+ /* skip already estimated clauses */
+ if (bms_is_member(listidx, estimatedclauses))
+ continue;
+
+ /*
+ * Make sure the clause is a join clause of a supported shape (at
+ * the moment we support just (Expr op Expr) clauses with each
+ * side referencing just a single relation).
+ */
+ if (!statext_is_supported_join_clause(root, clause, varRelid, sjinfo))
+ continue;
+
+ /* statext_is_supported_join_clause guarantees RestrictInfo */
+ rinfo = (RestrictInfo *) clause;
+ clause = (Node *) rinfo->clause;
+
+ /* search for a matching join pair */
+ found = false;
+ for (i = 0; i < cnt; i++)
+ {
+ if (bms_is_subset(rinfo->clause_relids, info[i].rels))
+ {
+ info[i].clauses = lappend(info[i].clauses, clause);
+ found = true;
+ break;
+ }
+ }
+
+ if (!found)
+ {
+ info[cnt].rels = rinfo->clause_relids;
+ info[cnt].clauses = lappend(info[cnt].clauses, clause);
+ cnt++;
+ }
+ }
+
+ if (cnt == 0)
+ return NULL;
+
+ *npairs = cnt;
+ return info;
+}
+
+/*
+ * extract_relation_info
+ * Extract information about a relation in a join pair.
+ *
+ * The relation is identified by index (generally 0 or 1), and picks extended
+ * statistics object covering the join clauses and baserel restrictions.
+ *
+ * XXX Can we have cases with indexes above 1? Probably for clauses mixing
+ * vars from 3 relations, but statext_is_supported_join_clause rejects those.
+ */
+static RelOptInfo *
+extract_relation_info(PlannerInfo *root, JoinPairInfo *info, int index,
+ StatisticExtInfo **stat)
+{
+ int k;
+ int relid;
+ RelOptInfo *rel;
+ ListCell *lc;
+ List *exprs = NIL;
+
+ Bitmapset *attnums = NULL;
+
+ Assert((index >= 0) && (index <= 1));
+
+ k = -1;
+ while (index >= 0)
+ {
+ k = bms_next_member(info->rels, k);
+ if (k < 0)
+ elog(ERROR, "failed to extract relid");
+
+ relid = k;
+ index--;
+ }
+
+ rel = find_base_rel(root, relid);
+
+ /*
+ * Walk the clauses for this join pair, and extract expressions about
+ * the relation identified by index / relid. For simple Vars we extract
+ * the attnum. Otherwise we keep the whole expression.
+ */
+ foreach (lc, info->clauses)
+ {
+ ListCell *lc2;
+ Node *clause = (Node *) lfirst(lc);
+ OpExpr *opclause = (OpExpr *) clause;
+
+ /* only opclauses supported for now */
+ Assert(is_opclause(clause));
+
+ foreach (lc2, opclause->args)
+ {
+ Node *arg = (Node *) lfirst(lc2);
+ Bitmapset *varnos = NULL;
+
+ /* plain Var references (boolean Vars or recursive checks) */
+ if (IsA(arg, Var))
+ {
+ Var *var = (Var *) arg;
+
+ /* Ignore vars from other relations. */
+ if (var->varno != relid)
+ continue;
+
+ /* we also better ensure the Var is from the current level */
+ if (var->varlevelsup > 0)
+ continue;
+
+ /* Also skip system attributes (we don't allow stats on those). */
+ if (!AttrNumberIsForUserDefinedAttr(var->varattno))
+ elog(ERROR, "unexpected system attribute");
+
+ attnums = bms_add_member(attnums, var->varattno);
+
+ /* Done, process the next argument. */
+ continue;
+ }
+
+ /*
+ * OK, it's a more complex expression, so check if it matches
+ * the relid and maybe keep it as a whole. It should be
+ * compatible because we already checked it when building the
+ * join pairs.
+ */
+ varnos = pull_varnos(root, arg);
+
+ if (relid == bms_singleton_member(varnos))
+ exprs = lappend(exprs, arg);
+ }
+ }
+
+ *stat = statext_find_matching_mcv(root, rel, attnums, exprs);
+
+ return rel;
+}
+
+/*
+ * get_expression_for_rel
+ * Extract expression for a given relation from the join clause.
+ *
+ * Given a join clause supported by the extended statistics object (currently
+ * that means just OpExpr clauses with each argument referencing single rel),
+ * return either the left or right argument expression for the rel.
+ *
+ * XXX This should probably return a flag identifying whether it's the
+ * left or right argument.
+ */
+static Node *
+get_expression_for_rel(PlannerInfo *root, RelOptInfo *rel, Node *clause)
+{
+ OpExpr *opexpr;
+ Node *expr;
+
+ /*
+ * Strip the RestrictInfo node, get the actual clause.
+ *
+ * XXX Not sure if we need to care about removing other node types
+ * too (e.g. RelabelType etc.). statext_is_supported_join_clause
+ * matches this, but maybe we need to relax it?
+ */
+ if (IsA(clause, RestrictInfo))
+ clause = (Node *) ((RestrictInfo *) clause)->clause;
+
+ opexpr = (OpExpr *) clause;
+
+ /* Make sure we have the expected node type. */
+ Assert(is_opclause(clause));
+ Assert(list_length(opexpr->args) == 2);
+
+ /* FIXME strip relabel etc. the way examine_opclause_args does */
+ expr = linitial(opexpr->args);
+ if (bms_singleton_member(pull_varnos(root, expr)) == rel->relid)
+ return expr;
+
+ expr = lsecond(opexpr->args);
+ if (bms_singleton_member(pull_varnos(root, expr)) == rel->relid)
+ return expr;
+
+ return NULL;
+}
+
+/*
+ * statext_clauselist_join_selectivity
+ * Use extended stats to estimate join clauses.
+ *
+ * XXX In principle, we should not restrict this to cases with multiple
+ * join clauses - we should consider dependencies with conditions at the
+ * base relations, i.e. calculate P(join clause | base restrictions).
+ * But currently that does not happen, because clauselist_selectivity_ext
+ * treats a single clause as a special case (and we don't apply extended
+ * statistics in that case yet).
+ */
+Selectivity
+statext_clauselist_join_selectivity(PlannerInfo *root, List *clauses, int varRelid,
+ JoinType jointype, SpecialJoinInfo *sjinfo,
+ Bitmapset **estimatedclauses)
+{
+ int i;
+ int listidx;
+ Selectivity s = 1.0;
+
+ JoinPairInfo *info;
+ int ninfo;
+
+ if (!clauses)
+ return 1.0;
+
+ /* extract pairs of joined relations from the list of clauses */
+ info = statext_build_join_pairs(root, clauses, varRelid, jointype, sjinfo,
+ *estimatedclauses, &ninfo);
+
+ /* no useful join pairs */
+ if (!info)
+ return 1.0;
+
+ /*
+ * Process the join pairs, try to find a matching MCV on each side.
+ *
+ * XXX The basic principle is quite similar to eqjoinsel_inner, i.e.
+ * we try to find a MCV on both sides of the join, and use it to get
+ * a better join estimate. It's a bit more complicated, because there
+ * might be multiple MCV lists, we also need ndistinct estimate, and
+ * there may be interesting baserestrictions too.
+ *
+ * XXX At the moment we only handle the case with matching MCVs on
+ * both sides, but it'd be good to also handle case with just ndistinct
+ * statistics improving ndistinct estimates.
+ *
+ * XXX We might also handle cases with a regular MCV on one side and
+ * an extended MCV on the other side.
+ *
+ * XXX Perhaps it'd be good to also handle case with one side only
+ * having "regular" statistics (e.g. MCV), especially in cases with
+ * no conditions on that side of the join (where we can't use the
+ * extended MCV to calculate conditional probability).
+ */
+ for (i = 0; i < ninfo; i++)
+ {
+ ListCell *lc;
+
+ RelOptInfo *rel1;
+ RelOptInfo *rel2;
+
+ StatisticExtInfo *stat1;
+ StatisticExtInfo *stat2;
+
+ /* extract info about the first relation */
+ rel1 = extract_relation_info(root, &info[i], 0, &stat1);
+
+ /* extract info about the second relation */
+ rel2 = extract_relation_info(root, &info[i], 1, &stat2);
+
+ /*
+ * We can handle three basic cases:
+ *
+ * a) Extended stats (with MCV) on both sides is an ideal case, and we
+ * can simply combine the two MCVs, possibly with additional conditions
+ * from the relations.
+ *
+ * b) Extended stats on one side, regular MCV on the other side (this
+ * means there's just one join clause / expression). It also means the
+ * extended stats likely covers at least one extra condition, otherwise
+ * we could just use regular statistics. We can combine the stats just
+ * similarly to (a).
+ *
+ * c) No extended stats with MCV. If there are multiple join clauses,
+ * we can try using ndistinct coefficients and do what eqjoinsel does.
+ *
+ * If none of these applies, we fallback to the regular selectivity
+ * estimation in eqjoinsel.
+ */
+ if (stat1 && stat2)
+ {
+ s *= mcv_combine_extended(root, rel1, rel2, stat1, stat2, info[i].clauses);
+ }
+ else if (stat1 && (list_length(info[i].clauses) == 1))
+ {
+ /* try finding MCV on the other relation */
+ VariableStatData vardata;
+ AttStatsSlot sslot;
+ Form_pg_statistic stats = NULL;
+ bool have_mcvs = false;
+ Node *clause = linitial(info[i].clauses);
+ Node *expr = get_expression_for_rel(root, rel2, clause);
+ double nd;
+ bool isdefault;
+
+ examine_variable(root, expr, 0, &vardata);
+
+ nd = get_variable_numdistinct(&vardata, &isdefault);
+
+ memset(&sslot, 0, sizeof(sslot));
+
+ if (HeapTupleIsValid(vardata.statsTuple))
+ {
+ /* note we allow use of nullfrac regardless of security check */
+ stats = (Form_pg_statistic) GETSTRUCT(vardata.statsTuple);
+ /* FIXME should this call statistic_proc_security_check like eqjoinsel? */
+ have_mcvs = get_attstatsslot(&sslot, vardata.statsTuple,
+ STATISTIC_KIND_MCV, InvalidOid,
+ ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS);
+ }
+
+ if (have_mcvs)
+ s *= mcv_combine_simple(root, rel1, stat1, &sslot,
+ stats->stanullfrac, nd, isdefault, clause);
+
+ free_attstatsslot(&sslot);
+
+ ReleaseVariableStats(vardata);
+
+ /* no stats, don't mark the clauses as estimated */
+ if (!have_mcvs)
+ continue;
+ }
+ else if (stat2 && (list_length(info[i].clauses) == 1))
+ {
+ /* try finding MCV on the other relation */
+ VariableStatData vardata;
+ AttStatsSlot sslot;
+ Form_pg_statistic stats = NULL;
+ bool have_mcvs = false;
+ Node *clause = (Node *) linitial(info[i].clauses);
+ Node *expr = get_expression_for_rel(root, rel1, clause);
+ double nd;
+ bool isdefault;
+
+ examine_variable(root, expr, 0, &vardata);
+
+ nd = get_variable_numdistinct(&vardata, &isdefault);
+
+ memset(&sslot, 0, sizeof(sslot));
+
+ if (HeapTupleIsValid(vardata.statsTuple))
+ {
+ /* note we allow use of nullfrac regardless of security check */
+ stats = (Form_pg_statistic) GETSTRUCT(vardata.statsTuple);
+ /* FIXME should this call statistic_proc_security_check like eqjoinsel? */
+ have_mcvs = get_attstatsslot(&sslot, vardata.statsTuple,
+ STATISTIC_KIND_MCV, InvalidOid,
+ ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS);
+ }
+
+ if (have_mcvs)
+ s *= mcv_combine_simple(root, rel2, stat2, &sslot,
+ stats->stanullfrac, nd, isdefault, clause);
+
+ free_attstatsslot(&sslot);
+
+ ReleaseVariableStats(vardata);
+
+ /* no stats, don't mark the clauses as estimated */
+ if (!have_mcvs)
+ continue;
+ }
+ else
+ continue;
+
+ /*
+ * Now mark all the clauses for this join pair as estimated.
+ *
+ * XXX Maybe track the indexes in JoinPairInfo, so that we can
+ * simply union the two bitmaps, without the extra matching.
+ */
+ foreach (lc, info->clauses)
+ {
+ Node *clause = (Node *) lfirst(lc);
+ ListCell *lc2;
+
+ listidx = -1;
+ foreach (lc2, clauses)
+ {
+ Node *clause2 = (Node *) lfirst(lc2);
+ listidx++;
+
+ Assert(IsA(clause2, RestrictInfo));
+
+ clause2 = (Node *) ((RestrictInfo *) clause2)->clause;
+
+ if (equal(clause, clause2))
+ {
+ *estimatedclauses = bms_add_member(*estimatedclauses, listidx);
+ break;
+ }
+ }
+ }
+ }
+
+ return s;
+}
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c
index 1ef30344285..fbfebf88ac0 100644
--- a/src/backend/statistics/mcv.c
+++ b/src/backend/statistics/mcv.c
@@ -24,6 +24,7 @@
#include "funcapi.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
+#include "optimizer/optimizer.h"
#include "statistics/extended_stats_internal.h"
#include "statistics/statistics.h"
#include "utils/array.h"
@@ -2158,3 +2159,759 @@ mcv_clause_selectivity_or(PlannerInfo *root, StatisticExtInfo *stat,
return s;
}
+
+/*
+ * statext_compare_mcvs
+ * Calculate join selectivity using extended statistics, similar to
+ * eqjoinsel_inner.
+ *
+ * Considers restrictions on base relations too, essentially computing a
+ * conditional probability
+ *
+ * P(join clauses | baserestrictinfos on either side)
+ *
+ * Compared to eqjoinsel_inner there's a couple problems. With per-column MCV
+ * lists it's obvious that the number of distinct values not covered by the MCV
+ * is (ndistinct - size(MCV)). With multi-column MCVs it's not that simple,
+ * particularly when the conditions are on a subset of the MCV attributes and/or
+ * NULLs are involved. E.g. with MCV (a,b,c) and conditions on (a,b), it's not
+ * clear if the number of (a,b) combinations not covered by the MCV is
+ *
+ * (ndistinct(a,b) - ndistinct_mcv(a,b))
+ *
+ * where ndistinct_mcv(a,b) is the number of distinct (a,b) combinations
+ * included in the MCV list. These combinations may be present in the rest
+ * of the data (outside MCV), just with some extra values in "c". So in
+ * principle there may be between
+ *
+ * (ndistinct(a,b) - ndistinct_mcv(a,b)) and ndistinct(a,b)
+ *
+ * distinct values in the part of the data not covered by the MCV. So we need
+ * to pick something in between, there's no way to calculate this accurately.
+ */
+Selectivity
+mcv_combine_extended(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
+ StatisticExtInfo *stat1, StatisticExtInfo *stat2,
+ List *clauses)
+{
+ ListCell *lc;
+
+ MCVList *mcv1,
+ *mcv2;
+ int idx,
+ i,
+ j;
+ Selectivity s = 0;
+
+ /* match bitmaps and selectivity for baserel conditions (if any) */
+ List *exprs1 = NIL,
+ *exprs2 = NIL;
+ List *conditions1 = NIL,
+ *conditions2 = NIL;
+ bool *cmatches1 = NULL,
+ *cmatches2 = NULL;
+
+ double csel1 = 1.0,
+ csel2 = 1.0;
+
+ bool *matches1 = NULL,
+ *matches2 = NULL;
+
+ /* estimates for the two relations */
+ double matchfreq1,
+ unmatchfreq1,
+ otherfreq1,
+ mcvfreq1,
+ nd1,
+ totalsel1;
+
+ double matchfreq2,
+ unmatchfreq2,
+ otherfreq2,
+ mcvfreq2,
+ nd2,
+ totalsel2;
+
+ /* info about clauses and how they match to MCV stats */
+ FmgrInfo *opprocs;
+ int *indexes1,
+ *indexes2;
+ bool *reverse;
+ RangeTblEntry *rte1 = root->simple_rte_array[rel1->relid];
+ RangeTblEntry *rte2 = root->simple_rte_array[rel2->relid];
+
+ /* we picked the stats so that they have MCV enabled */
+ Assert((stat1->kind = STATS_EXT_MCV) && (stat2->kind = STATS_EXT_MCV));
+
+ mcv1 = statext_mcv_load(stat1->statOid, rte1->inh);
+ mcv2 = statext_mcv_load(stat2->statOid, rte2->inh);
+
+ /* should only get here with MCV on both sides */
+ Assert(mcv1 && mcv2);
+
+ /* Determine which baserel clauses to use for conditional probability. */
+ conditions1 = statext_determine_join_restrictions(root, rel1, stat1);
+ conditions2 = statext_determine_join_restrictions(root, rel2, stat2);
+
+ /*
+ * Calculate match bitmaps for restrictions on either side of the join
+ * (there may be none, in which case this will be NULL).
+ */
+ if (conditions1)
+ {
+ cmatches1 = mcv_get_match_bitmap(root, conditions1,
+ stat1->keys, stat1->exprs,
+ mcv1, false);
+ csel1 = clauselist_selectivity(root, conditions1, rel1->relid, 0, NULL);
+ }
+
+ if (conditions2)
+ {
+ cmatches2 = mcv_get_match_bitmap(root, conditions2,
+ stat2->keys, stat2->exprs,
+ mcv2, false);
+ csel2 = clauselist_selectivity(root, conditions2, rel2->relid, 0, NULL);
+ }
+
+ /*
+ * Match bitmaps for matches between MCV elements. By default there
+ * are no matches, so we set all items to 0.
+ */
+ matches1 = (bool *) palloc0(sizeof(bool) * mcv1->nitems);
+ matches2 = (bool *) palloc0(sizeof(bool) * mcv2->nitems);
+
+ /*
+ * Initialize information about clauses and how they match to the MCV
+ * stats we picked. We do this only once before processing the lists,
+ * so that we don't have to do that for each MCV item or so.
+ */
+ opprocs = (FmgrInfo *) palloc(sizeof(FmgrInfo) * list_length(clauses));
+ indexes1 = (int *) palloc(sizeof(int) * list_length(clauses));
+ indexes2 = (int *) palloc(sizeof(int) * list_length(clauses));
+ reverse = (bool *) palloc(sizeof(bool) * list_length(clauses));
+
+ idx = 0;
+ foreach (lc, clauses)
+ {
+ Node *clause = (Node *) lfirst(lc);
+ OpExpr *opexpr;
+ Node *expr1,
+ *expr2;
+ Bitmapset *relids1,
+ *relids2;
+
+ /*
+ * Strip the RestrictInfo node, get the actual clause.
+ *
+ * XXX Not sure if we need to care about removing other node types
+ * too (e.g. RelabelType etc.). statext_is_supported_join_clause
+ * matches this, but maybe we need to relax it?
+ */
+ if (IsA(clause, RestrictInfo))
+ clause = (Node *) ((RestrictInfo *) clause)->clause;
+
+ opexpr = (OpExpr *) clause;
+
+ /* Make sure we have the expected node type. */
+ Assert(is_opclause(clause));
+ Assert(list_length(opexpr->args) == 2);
+
+ fmgr_info(get_opcode(opexpr->opno), &opprocs[idx]);
+
+ /* FIXME strip relabel etc. the way examine_opclause_args does */
+ expr1 = linitial(opexpr->args);
+ expr2 = lsecond(opexpr->args);
+
+ /* determine order of clauses (rel1 op rel2) or (rel2 op rel1) */
+ relids1 = pull_varnos(root, expr1);
+ relids2 = pull_varnos(root, expr2);
+
+ if ((bms_singleton_member(relids1) == rel1->relid) &&
+ (bms_singleton_member(relids2) == rel2->relid))
+ {
+ Oid collid;
+
+ indexes1[idx] = mcv_match_expression(expr1,
+ stat1->keys, stat1->exprs,
+ &collid);
+ indexes2[idx] = mcv_match_expression(expr2,
+ stat2->keys, stat2->exprs,
+ &collid);
+ reverse[idx] = false;
+
+ exprs1 = lappend(exprs1, expr1);
+ exprs2 = lappend(exprs2, expr2);
+ }
+ else if ((bms_singleton_member(relids2) == rel1->relid) &&
+ (bms_singleton_member(relids1) == rel2->relid))
+ {
+ Oid collid;
+
+ indexes1[idx] = mcv_match_expression(expr2,
+ stat2->keys, stat2->exprs,
+ &collid);
+ indexes2[idx] = mcv_match_expression(expr1,
+ stat1->keys, stat1->exprs,
+ &collid);
+ reverse[idx] = true;
+
+ exprs1 = lappend(exprs1, expr2);
+ exprs2 = lappend(exprs2, expr1);
+ }
+ else
+ /* should never happen */
+ Assert(false);
+
+ Assert((indexes1[idx] >= 0) &&
+ (indexes1[idx] < bms_num_members(stat1->keys) + list_length(stat1->exprs)));
+
+ Assert((indexes2[idx] >= 0) &&
+ (indexes2[idx] < bms_num_members(stat2->keys) + list_length(stat2->exprs)));
+
+ idx++;
+ }
+
+ /*
+ * Match items between the two MCV lists.
+ *
+ * We don't know if the join conditions match all attributes in the MCV, the
+ * overlap may be just on a subset of attributes, e.g. (a,b,c) vs. (b,c,d).
+ * So there may be multiple matches on either side. So we can't optimize by
+ * aborting the inner loop after the first match, etc.
+ *
+ * XXX We can skip the items eliminated by the base restrictions, of course.
+ *
+ * XXX We might optimize this in two ways. We might sort the MCV items on
+ * both sides using the "join" attributes, and then perform something like
+ * merge join. Or we might calculate a hash from the join columns, and then
+ * compare this (to eliminate the most expensive equality functions).
+ */
+ for (i = 0; i < mcv1->nitems; i++)
+ {
+ bool has_nulls;
+
+ /* skip items eliminated by restrictions on rel1 */
+ if (cmatches1 && !cmatches1[i])
+ continue;
+
+ /*
+ * Check if any value in the first MCV item is NULL, because it'll be
+ * mismatch anyway.
+ *
+ * XXX This might not work for some join clauses, e.g. IS NOT DISTINCT
+ * FROM, but those are currently not considered compatible (we only
+ * allow OpExpr at the moment).
+ */
+ has_nulls = false;
+ for (j = 0; j < list_length(clauses); j++)
+ has_nulls |= mcv1->items[i].isnull[indexes1[j]];
+
+ if (has_nulls)
+ continue;
+
+ /* find matches in the second MCV list */
+ for (j = 0; j < mcv2->nitems; j++)
+ {
+ int idx;
+ bool items_match = true;
+
+ /* skip items eliminated by restrictions on rel2 */
+ if (cmatches2 && !cmatches2[j])
+ continue;
+
+ /*
+ * XXX We can't skip based on existing matches2 value, because there
+ * may be duplicates in the first MCV.
+ */
+
+ /*
+ * Evaluate if all the join clauses match between the two MCV items.
+ *
+ * XXX We might optimize the order of evaluation, using the costs of
+ * operator functions for individual columns. It does depend on the
+ * number of distinct values, etc.
+ */
+ idx = 0;
+ foreach (lc, clauses)
+ {
+ bool match;
+ int index1 = indexes1[idx],
+ index2 = indexes2[idx];
+ Datum value1,
+ value2;
+ bool reverse_args = reverse[idx];
+
+ /* If either value is null, it's a mismatch */
+ if (mcv2->items[j].isnull[index2])
+ match = false;
+ else
+ {
+ value1 = mcv1->items[i].values[index1];
+ value2 = mcv2->items[j].values[index2];
+
+ /*
+ * Careful about order of parameters. For same-type equality
+ * that should not matter, but easy enough.
+ *
+ * FIXME Use appropriate collation.
+ */
+ if (reverse_args)
+ match = DatumGetBool(FunctionCall2Coll(&opprocs[idx],
+ InvalidOid,
+ value2, value1));
+ else
+ match = DatumGetBool(FunctionCall2Coll(&opprocs[idx],
+ InvalidOid,
+ value1, value2));
+ }
+
+ items_match &= match;
+
+ if (!items_match)
+ break;
+
+ idx++;
+ }
+
+ if (items_match)
+ {
+ /* XXX Do we need to do something about base frequency? */
+ matches1[i] = matches2[j] = true;
+ s += mcv1->items[i].frequency * mcv2->items[j].frequency;
+ }
+ }
+ }
+
+ matchfreq1 = unmatchfreq1 = mcvfreq1 = 0.0;
+ for (i = 0; i < mcv1->nitems; i++)
+ {
+ mcvfreq1 += mcv1->items[i].frequency;
+
+ /* ignore MCV items eliminated by baserel conditions */
+ if (cmatches1 && !cmatches1[i])
+ continue;
+
+ if (matches1[i])
+ matchfreq1 += mcv1->items[i].frequency;
+ else
+ unmatchfreq1 += mcv1->items[i].frequency;
+ }
+
+ /* not represented by the MCV */
+ otherfreq1 = 1.0 - mcvfreq1;
+
+ matchfreq2 = unmatchfreq2 = mcvfreq2 = 0.0;
+ for (i = 0; i < mcv2->nitems; i++)
+ {
+ mcvfreq2 += mcv2->items[i].frequency;
+
+ /* ignore MCV items eliminated by baserel conditions */
+ if (cmatches2 && !cmatches2[i])
+ continue;
+
+ if (matches2[i])
+ matchfreq2 += mcv2->items[i].frequency;
+ else
+ unmatchfreq2 += mcv2->items[i].frequency;
+ }
+
+ /* not represented by the MCV */
+ otherfreq2 = 1.0 - mcvfreq2;
+
+ /*
+ * Correction for MCV parts eliminated by the conditions.
+ *
+ * We need to be careful about cases where conditions eliminated all
+ * the MCV items. We must not divide by 0.0, because that would either
+ * produce bogus value or trigger division by zero. Instead we simply
+ * set the selectivity to 0.0, because there can't be any matches.
+ */
+ if ((matchfreq1 + unmatchfreq1) > 0)
+ s = s * mcvfreq1 / (matchfreq1 + unmatchfreq1);
+ else
+ s = 0.0;
+
+ if ((matchfreq2 + unmatchfreq2) > 0)
+ s = s * mcvfreq2 / (matchfreq2 + unmatchfreq2);
+ else
+ s = 0.0;
+
+ /* calculate ndistinct for the expression in join clauses for each rel */
+ nd1 = estimate_num_groups(root, exprs1, rel1->rows, NULL, NULL);
+ nd2 = estimate_num_groups(root, exprs2, rel2->rows, NULL, NULL);
+
+ /*
+ * Consider the part of the data not represented by the MCV lists.
+ *
+ * XXX this is a bit bogus, because we don't know what fraction of
+ * distinct combinations is covered by the MCV list (we're only
+ * dealing with some of the columns), so we can't use the same
+ * formular as eqjoinsel_inner exactly. We just use the estimates
+ * for the whole table - this is likely an overestimate, because
+ * (a) items may repeat in the MCV list, if it has more columns,
+ * and (b) some of the combinations may be present in non-MCV data.
+ *
+ * Moreover, we need to look at the conditions. For now we simply
+ * assume the conditions affect the distinct groups, and use that.
+ *
+ * XXX We might calculate the number of distinct groups in the MCV,
+ * and then use something between (nd1 - distinct(MCV)) and (nd1),
+ * which are the possible extreme values, assuming the estimates
+ * are accurate. Maybe mean or geometric mean would work?
+ *
+ * XXX Not sure multiplying ndistinct with probabilities is good.
+ * Maybe we should do something more like estimate_num_groups?
+ */
+ nd1 *= csel1;
+ nd2 *= csel2;
+
+ totalsel1 = s;
+ totalsel1 += unmatchfreq1 * otherfreq2 / nd2;
+ totalsel1 += otherfreq1 * (otherfreq2 + unmatchfreq2) / nd2;
+
+// if (nd2 > mcvb->nitems)
+// totalsel1 += unmatchfreq1 * otherfreq2 / (nd2 - mcvb->nitems);
+// if (nd2 > nmatches)
+// totalsel1 += otherfreq1 * (otherfreq2 + unmatchfreq2) /
+// (nd2 - nmatches);
+
+ totalsel2 = s;
+ totalsel2 += unmatchfreq2 * otherfreq1 / nd1;
+ totalsel2 += otherfreq2 * (otherfreq1 + unmatchfreq1) / nd1;
+
+// if (nd1 > mcva->nitems)
+// totalsel2 += unmatchfreq2 * otherfreq1 / (nd1 - mcva->nitems);
+// if (nd1 > nmatches)
+// totalsel2 += otherfreq2 * (otherfreq1 + unmatchfreq1) /
+// (nd1 - nmatches);
+
+ s = Min(totalsel1, totalsel2);
+
+ return s;
+}
+
+
+/*
+ * statext_compare_simple
+ * Calculate join selectivity using a combination of extended
+ * statistics MCV on one side, and simple per-column MCV on the other.
+ *
+ * Most of the mcv_combine_extended comment applies here too, but we can make
+ * some simplifications because we know the second (per-column) MCV is simpler,
+ * contains no NULL or duplicate values, etc.
+ */
+Selectivity
+mcv_combine_simple(PlannerInfo *root, RelOptInfo *rel, StatisticExtInfo *stat,
+ AttStatsSlot *sslot, double stanullfrac, double nd,
+ bool isdefault, Node *clause)
+{
+ MCVList *mcv;
+ int i,
+ j;
+ Selectivity s = 0;
+
+ /* match bitmaps and selectivity for baserel conditions (if any) */
+ List *conditions = NIL;
+ bool *cmatches = NULL;
+
+ double csel = 1.0;
+
+ bool *matches1 = NULL,
+ *matches2 = NULL;
+
+ /* estimates for the two sides */
+ double matchfreq1,
+ unmatchfreq1,
+ otherfreq1,
+ mcvfreq1,
+ nd1,
+ totalsel1;
+
+ double matchfreq2,
+ unmatchfreq2,
+ otherfreq2,
+ mcvfreq2,
+ nd2,
+ totalsel2;
+
+ List *exprs1 = NIL,
+ *exprs2 = NIL;
+
+ /* info about clauses and how they match to MCV stats */
+ FmgrInfo opproc;
+ int index = 0;
+ bool reverse = false;
+ RangeTblEntry *rte = root->simple_rte_array[rel->relid];
+
+ /* we picked the stats so that they have MCV enabled */
+ Assert(stat->kind = STATS_EXT_MCV);
+
+ mcv = statext_mcv_load(stat->statOid, rte->inh);
+
+ /* should only get here with MCV on both sides */
+ Assert(mcv);
+
+ /* Determine which baserel clauses to use for conditional probability. */
+ conditions = statext_determine_join_restrictions(root, rel, stat);
+
+ /*
+ * Calculate match bitmaps for restrictions on either side of the join
+ * (there may be none, in which case this will be NULL).
+ */
+ if (conditions)
+ {
+ cmatches = mcv_get_match_bitmap(root, conditions,
+ stat->keys, stat->exprs,
+ mcv, false);
+ csel = clauselist_selectivity(root, conditions, rel->relid, 0, NULL);
+ }
+
+ /*
+ * Match bitmaps for matches between MCV elements. By default there
+ * are no matches, so we set all items to 0.
+ */
+ matches1 = (bool *) palloc0(sizeof(bool) * mcv->nitems);
+
+ /* Matches for the side with just regular single-column MCV. */
+ matches2 = (bool *) palloc0(sizeof(bool) * sslot->nvalues);
+
+ /*
+ * Initialize information about the clause and how it matches to the
+ * extended stats we picked. We do this only once before processing
+ * the lists, so that we don't have to do that for each item or so.
+ */
+ {
+ OpExpr *opexpr;
+ Node *expr1,
+ *expr2;
+ Bitmapset *relids1,
+ *relids2;
+
+ /*
+ * Strip the RestrictInfo node, get the actual clause.
+ *
+ * XXX Not sure if we need to care about removing other node types
+ * too (e.g. RelabelType etc.). statext_is_supported_join_clause
+ * matches this, but maybe we need to relax it?
+ */
+ if (IsA(clause, RestrictInfo))
+ clause = (Node *) ((RestrictInfo *) clause)->clause;
+
+ opexpr = (OpExpr *) clause;
+
+ /* Make sure we have the expected node type. */
+ Assert(is_opclause(clause));
+ Assert(list_length(opexpr->args) == 2);
+
+ fmgr_info(get_opcode(opexpr->opno), &opproc);
+
+ /* FIXME strip relabel etc. the way examine_opclause_args does */
+ expr1 = linitial(opexpr->args);
+ expr2 = lsecond(opexpr->args);
+
+ /* determine order of clauses (rel1 op rel2) or (rel2 op rel1) */
+ relids1 = pull_varnos(root, expr1);
+ relids2 = pull_varnos(root, expr2);
+
+ if (bms_singleton_member(relids1) == rel->relid)
+ {
+ Oid collid;
+
+ index = mcv_match_expression(expr1, stat->keys, stat->exprs,
+ &collid);
+ reverse = false;
+
+ exprs1 = lappend(exprs1, expr1);
+ exprs2 = lappend(exprs2, expr2);
+ }
+ else if (bms_singleton_member(relids2) == rel->relid)
+ {
+ Oid collid;
+
+ index = mcv_match_expression(expr2, stat->keys, stat->exprs,
+ &collid);
+ reverse = true;
+
+ exprs1 = lappend(exprs1, expr2);
+ exprs2 = lappend(exprs2, expr1);
+ }
+ else
+ /* should never happen */
+ Assert(false);
+
+ Assert((index >= 0) &&
+ (index < bms_num_members(stat->keys) + list_length(stat->exprs)));
+ }
+
+ /*
+ * Match items between the two MCV lists.
+ *
+ * We don't know if the join conditions match all attributes in the MCV, the
+ * overlap may be just on a subset of attributes, e.g. (a,b,c) vs. (b,c,d).
+ * So there may be multiple matches on either side. So we can't optimize by
+ * aborting the inner loop after the first match, etc.
+ *
+ * XXX We can skip the items eliminated by the base restrictions, of course.
+ *
+ * XXX We might optimize this in two ways. We might sort the MCV items on
+ * both sides using the "join" attributes, and then perform something like
+ * merge join. Or we might calculate a hash from the join columns, and then
+ * compare this (to eliminate the most expensive equality functions).
+ */
+ for (i = 0; i < mcv->nitems; i++)
+ {
+ /* skip items eliminated by restrictions on rel1 */
+ if (cmatches && !cmatches[i])
+ continue;
+
+ /*
+ * We can check mcv1->items[i].isnull[index1] here, because it'll be a
+ * mismatch anyway (the simple MCV does not contain NULLs).
+ */
+ if (mcv->items[i].isnull[index])
+ continue;
+
+ /* find matches in the second MCV list */
+ for (j = 0; j < sslot->nvalues; j++)
+ {
+ bool match;
+ Datum value1 = mcv->items[i].values[index];
+ Datum value2 = sslot->values[j];
+
+ /*
+ * Evaluate the join clause between the two MCV lists. We don't
+ * need to deal with NULL values here - we've already checked for
+ * NULL in the extended statistics earlier, and the simple MCV
+ * does not contain NULL values.
+ *
+ * Careful about order of parameters. For same-type equality
+ * that should not matter, but easy enough.
+ *
+ * FIXME Use appropriate collation.
+ */
+ if (reverse)
+ match = DatumGetBool(FunctionCall2Coll(&opproc,
+ InvalidOid,
+ value2, value1));
+ else
+ match = DatumGetBool(FunctionCall2Coll(&opproc,
+ InvalidOid,
+ value1, value2));
+
+ if (match)
+ {
+ /* XXX Do we need to do something about base frequency? */
+ matches1[i] = matches2[j] = true;
+ s += mcv->items[i].frequency * sslot->numbers[j];
+
+ /*
+ * We know there can be just a single match in the regular
+ * MCV list, so we can abort the inner loop.
+ */
+ break;
+ }
+ }
+ }
+
+ matchfreq1 = unmatchfreq1 = mcvfreq1 = 0.0;
+ for (i = 0; i < mcv->nitems; i++)
+ {
+ mcvfreq1 += mcv->items[i].frequency;
+
+ /* ignore MCV items eliminated by baserel conditions */
+ if (cmatches && !cmatches[i])
+ continue;
+
+ if (matches1[i])
+ matchfreq1 += mcv->items[i].frequency;
+ else
+ unmatchfreq1 += mcv->items[i].frequency;
+ }
+
+ /* not represented by the MCV */
+ otherfreq1 = 1.0 - mcvfreq1;
+
+ matchfreq2 = unmatchfreq2 = mcvfreq2 = 0.0;
+ for (i = 0; i < sslot->nvalues; i++)
+ {
+ mcvfreq2 += sslot->numbers[i];
+
+ if (matches2[i])
+ matchfreq2 += sslot->numbers[i];
+ else
+ unmatchfreq2 += sslot->numbers[i];
+ }
+
+ /* not represented by the MCV */
+ otherfreq2 = 1.0 - mcvfreq2;
+
+ /*
+ * Correction for MCV parts eliminated by the conditions.
+ *
+ * We need to be careful about cases where conditions eliminated all
+ * the MCV items. We must not divide by 0.0, because that would either
+ * produce bogus value or trigger division by zero. Instead we simply
+ * set the selectivity to 0.0, because there can't be any matches.
+ */
+ if ((matchfreq1 + unmatchfreq1) > 0)
+ s = s * mcvfreq1 / (matchfreq1 + unmatchfreq1);
+ else
+ s = 0.0;
+
+ if ((matchfreq2 + unmatchfreq2) > 0)
+ s = s * mcvfreq2 / (matchfreq2 + unmatchfreq2);
+ else
+ s = 0.0;
+
+ /* calculate ndistinct for the expression in join clauses for each rel */
+ nd1 = estimate_num_groups(root, exprs1, rel->rows, NULL, NULL);
+ nd2 = nd;
+
+ /*
+ * Consider the part of the data not represented by the MCV lists.
+ *
+ * XXX this is a bit bogus, because we don't know what fraction of
+ * distinct combinations is covered by the MCV list (we're only
+ * dealing with some of the columns), so we can't use the same
+ * formular as eqjoinsel_inner exactly. We just use the estimates
+ * for the whole table - this is likely an overestimate, because
+ * (a) items may repeat in the MCV list, if it has more columns,
+ * and (b) some of the combinations may be present in non-MCV data.
+ *
+ * Moreover, we need to look at the conditions. For now we simply
+ * assume the conditions affect the distinct groups, and use that.
+ *
+ * XXX We might calculate the number of distinct groups in the MCV,
+ * and then use something between (nd1 - distinct(MCV)) and (nd1),
+ * which are the possible extreme values, assuming the estimates
+ * are accurate. Maybe mean or geometric mean would work?
+ *
+ * XXX Not sure multiplying ndistinct with probabilities is good.
+ * Maybe we should do something more like estimate_num_groups?
+ */
+ nd1 *= csel;
+
+ totalsel1 = s;
+ totalsel1 += unmatchfreq1 * otherfreq2 / nd2;
+ totalsel1 += otherfreq1 * (otherfreq2 + unmatchfreq2) / nd2;
+
+// if (nd2 > mcvb->nitems)
+// totalsel1 += unmatchfreq1 * otherfreq2 / (nd2 - mcvb->nitems);
+// if (nd2 > nmatches)
+// totalsel1 += otherfreq1 * (otherfreq2 + unmatchfreq2) /
+// (nd2 - nmatches);
+
+ totalsel2 = s;
+ totalsel2 += unmatchfreq2 * otherfreq1 / nd1;
+ totalsel2 += otherfreq2 * (otherfreq1 + unmatchfreq1) / nd1;
+
+// if (nd1 > mcva->nitems)
+// totalsel2 += unmatchfreq2 * otherfreq1 / (nd1 - mcva->nitems);
+// if (nd1 > nmatches)
+// totalsel2 += otherfreq2 * (otherfreq1 + unmatchfreq1) /
+// (nd1 - nmatches);
+
+ s = Min(totalsel1, totalsel2);
+
+ return s;
+}
diff --git a/src/include/statistics/extended_stats_internal.h b/src/include/statistics/extended_stats_internal.h
index 71f852c157b..d115c6c791c 100644
--- a/src/include/statistics/extended_stats_internal.h
+++ b/src/include/statistics/extended_stats_internal.h
@@ -15,6 +15,7 @@
#define EXTENDED_STATS_INTERNAL_H
#include "statistics/statistics.h"
+#include "utils/lsyscache.h"
#include "utils/sortsupport.h"
typedef struct
@@ -127,4 +128,23 @@ extern Selectivity mcv_clause_selectivity_or(PlannerInfo *root,
Selectivity *overlap_basesel,
Selectivity *totalsel);
+extern Selectivity mcv_combine_simple(PlannerInfo *root,
+ RelOptInfo *rel,
+ StatisticExtInfo *stat,
+ AttStatsSlot *sslot,
+ double stanullfrac,
+ double nd, bool isdefault,
+ Node *clause);
+
+extern Selectivity mcv_combine_extended(PlannerInfo *root,
+ RelOptInfo *rel1,
+ RelOptInfo *rel2,
+ StatisticExtInfo *stat1,
+ StatisticExtInfo *stat2,
+ List *clauses);
+
+extern List *statext_determine_join_restrictions(PlannerInfo *root,
+ RelOptInfo *rel,
+ StatisticExtInfo *info);
+
#endif /* EXTENDED_STATS_INTERNAL_H */
diff --git a/src/include/statistics/statistics.h b/src/include/statistics/statistics.h
index bb7ef1240e0..c69cadff3a8 100644
--- a/src/include/statistics/statistics.h
+++ b/src/include/statistics/statistics.h
@@ -127,4 +127,16 @@ extern StatisticExtInfo *choose_best_statistics(List *stats, char requiredkind,
int nclauses);
extern HeapTuple statext_expressions_load(Oid stxoid, bool inh, int idx);
+extern StatisticExtInfo *statext_find_matching_mcv(PlannerInfo *root, RelOptInfo *rel,
+ Bitmapset *attnums, List *exprs);
+
+extern bool statext_try_join_estimates(PlannerInfo *root, List *clauses, int varRelid,
+ JoinType jointype, SpecialJoinInfo *sjinfo,
+ Bitmapset *estimatedclauses);
+
+extern Selectivity statext_clauselist_join_selectivity(PlannerInfo *root, List *clauses,
+ int varRelid,
+ JoinType jointype, SpecialJoinInfo *sjinfo,
+ Bitmapset **estimatedclauses);
+
#endif /* STATISTICS_H */
diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out
index 042316aeed8..e5577e680f4 100644
--- a/src/test/regress/expected/stats_ext.out
+++ b/src/test/regress/expected/stats_ext.out
@@ -3045,6 +3045,173 @@ SELECT c0 FROM ONLY expr_stats_incompatible_test WHERE
(0 rows)
DROP TABLE expr_stats_incompatible_test;
+-- Test join estimates.
+CREATE TABLE join_test_1 (a int, b int, c int);
+CREATE TABLE join_test_2 (a int, b int, c int);
+INSERT INTO join_test_1 SELECT mod(i,10), mod(i,10), mod(i,10) FROM generate_series(1,1000) s(i);
+INSERT INTO join_test_2 SELECT mod(i,10), mod(i,10), mod(i,10) FROM generate_series(1,1000) s(i);
+ANALYZE join_test_1;
+ANALYZE join_test_2;
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b))');
+ estimated | actual
+-----------+--------
+ 500 | 100000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 250 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 0');
+ estimated | actual
+-----------+--------
+ 1 | 0
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c < 3');
+ estimated | actual
+-----------+--------
+ 75 | 30000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c > 5');
+ estimated | actual
+-----------+--------
+ 100 | 0
+(1 row)
+
+-- can't be improved due to the optimization in clauselist_selectivity_ext,
+-- which skips cases with a single (join) clause
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 2500 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c < 5');
+ estimated | actual
+-----------+--------
+ 1250 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c > 5');
+ estimated | actual
+-----------+--------
+ 1000 | 0
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 2500 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 2500 | 50000
+(1 row)
+
+-- create extended statistics on the join/where columns
+CREATE STATISTICS join_stats_1 ON a, b, c, (a+1), (b+1) FROM join_test_1;
+CREATE STATISTICS join_stats_2 ON a, b, c, (a+1), (b+1) FROM join_test_2;
+ANALYZE join_test_1;
+ANALYZE join_test_2;
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b))');
+ estimated | actual
+-----------+--------
+ 100000 | 100000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 0');
+ estimated | actual
+-----------+--------
+ 1 | 0
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c < 3');
+ estimated | actual
+-----------+--------
+ 30000 | 30000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c > 5');
+ estimated | actual
+-----------+--------
+ 1 | 0
+(1 row)
+
+-- can't be improved due to the optimization in clauselist_selectivity_ext,
+-- which skips cases with a single (join) clause
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c > 5');
+ estimated | actual
+-----------+--------
+ 1 | 0
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+-- try combining with single-column (and single-expression) statistics
+DROP STATISTICS join_stats_2;
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+-- no MCV on join_test_2 (on the (a+1) expression)
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 2500 | 50000
+(1 row)
+
+CREATE STATISTICS join_stats_2 ON (a+1) FROM join_test_2;
+ANALYZE join_test_2;
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+ estimated | actual
+-----------+--------
+ 50000 | 50000
+(1 row)
+
+DROP TABLE join_test_1;
+DROP TABLE join_test_2;
-- Permission tests. Users should not be able to see specific data values in
-- the extended statistics, if they lack permission to see those values in
-- the underlying table.
diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql
index 6b954c9e500..4fb2c518d2c 100644
--- a/src/test/regress/sql/stats_ext.sql
+++ b/src/test/regress/sql/stats_ext.sql
@@ -1533,6 +1533,72 @@ SELECT c0 FROM ONLY expr_stats_incompatible_test WHERE
DROP TABLE expr_stats_incompatible_test;
+
+-- Test join estimates.
+CREATE TABLE join_test_1 (a int, b int, c int);
+CREATE TABLE join_test_2 (a int, b int, c int);
+
+INSERT INTO join_test_1 SELECT mod(i,10), mod(i,10), mod(i,10) FROM generate_series(1,1000) s(i);
+INSERT INTO join_test_2 SELECT mod(i,10), mod(i,10), mod(i,10) FROM generate_series(1,1000) s(i);
+
+ANALYZE join_test_1;
+ANALYZE join_test_2;
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b))');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 0');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c < 3');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c > 5');
+
+-- can't be improved due to the optimization in clauselist_selectivity_ext,
+-- which skips cases with a single (join) clause
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c > 5');
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+
+-- create extended statistics on the join/where columns
+CREATE STATISTICS join_stats_1 ON a, b, c, (a+1), (b+1) FROM join_test_1;
+CREATE STATISTICS join_stats_2 ON a, b, c, (a+1), (b+1) FROM join_test_2;
+
+ANALYZE join_test_1;
+ANALYZE join_test_2;
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b))');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 0');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c < 3');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1) and (j1.b = j2.b)) where j1.c < 5 and j2.c > 5');
+
+-- can't be improved due to the optimization in clauselist_selectivity_ext,
+-- which skips cases with a single (join) clause
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on ((j1.a + 1 = j2.a + 1)) where j1.c < 5 and j2.c > 5');
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+
+-- try combining with single-column (and single-expression) statistics
+DROP STATISTICS join_stats_2;
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+
+-- no MCV on join_test_2 (on the (a+1) expression)
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+
+CREATE STATISTICS join_stats_2 ON (a+1) FROM join_test_2;
+ANALYZE join_test_2;
+
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a) where j1.c < 5');
+SELECT * FROM check_estimated_rows('select * from join_test_1 j1 join join_test_2 j2 on (j1.a + 1 = j2.a + 1) where j1.c < 5');
+
+
+DROP TABLE join_test_1;
+DROP TABLE join_test_2;
+
-- Permission tests. Users should not be able to see specific data values in
-- the extended statistics, if they lack permission to see those values in
-- the underlying table.
--
2.17.1
