Collect and use multi-column dependency stats

Follow on patch in the multi-variate statistics patch series.

CREATE STATISTICS s1 WITH (dependencies) ON (a, b) FROM t;
ANALYZE;
will collect dependency stats on (a, b) and then use the measured
dependency in subsequent query planning.

Commit 7b504eb282ca2f5104b5c00b4f05a3ef6bb1385b added
CREATE STATISTICS with n-distinct coefficients. These are now
specified using the mutually exclusive option WITH (ndistinct).

Author: Tomas Vondra, David Rowley
Reviewed-by: Kyotaro HORIGUCHI, Álvaro Herrera, Dean Rasheed, Robert Haas
and many other comments and contributions
Discussion: https://postgr.es/m/56f40b20-c464-fad2-ff39-06b668fac47c@2ndquadrant.com

1 files changed, 53 insertions, 1 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 0c1a201ecb5..342e52bcf76 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -1452,6 +1452,13 @@ pg_get_statisticsext_worker(Oid statextid, bool missing_ok)
 	StringInfoData buf;
 	int			colno;
 	char	   *nsp;
+	ArrayType  *arr;
+	char	   *enabled;
+	Datum		datum;
+	bool		isnull;
+	bool		ndistinct_enabled;
+	bool		dependencies_enabled;
+	int			i;
 
 	statexttup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(statextid));
 
@@ -1467,10 +1474,55 @@ pg_get_statisticsext_worker(Oid statextid, bool missing_ok)
 	initStringInfo(&buf);
 
 	nsp = get_namespace_name(statextrec->stanamespace);
-	appendStringInfo(&buf, "CREATE STATISTICS %s ON (",
+	appendStringInfo(&buf, "CREATE STATISTICS %s",
 					 quote_qualified_identifier(nsp,
 												NameStr(statextrec->staname)));
 
+	/*
+	 * Lookup the staenabled column so that we know how to handle the WITH
+	 * clause.
+	 */
+	datum = SysCacheGetAttr(STATEXTOID, statexttup,
+							Anum_pg_statistic_ext_staenabled, &isnull);
+	Assert(!isnull);
+	arr = DatumGetArrayTypeP(datum);
+	if (ARR_NDIM(arr) != 1 ||
+		ARR_HASNULL(arr) ||
+		ARR_ELEMTYPE(arr) != CHAROID)
+		elog(ERROR, "staenabled is not a 1-D char array");
+	enabled = (char *) ARR_DATA_PTR(arr);
+
+	ndistinct_enabled = false;
+	dependencies_enabled = false;
+
+	for (i = 0; i < ARR_DIMS(arr)[0]; i++)
+	{
+		if (enabled[i] == STATS_EXT_NDISTINCT)
+			ndistinct_enabled = true;
+		if (enabled[i] == STATS_EXT_DEPENDENCIES)
+			dependencies_enabled = true;
+	}
+
+	/*
+	 * If any option is disabled, then we'll need to append a WITH clause to
+	 * show which options are enabled.  We omit the WITH clause on purpose
+	 * when all options are enabled, so a pg_dump/pg_restore will create all
+	 * statistics types on a newer postgres version, if the statistics had all
+	 * options enabled on the original version.
+	 */
+	if (!ndistinct_enabled || !dependencies_enabled)
+	{
+		appendStringInfoString(&buf, " WITH (");
+		if (ndistinct_enabled)
+			appendStringInfoString(&buf, "ndistinct");
+		else if (dependencies_enabled)
+			appendStringInfoString(&buf, "dependencies");
+
+		appendStringInfoChar(&buf, ')');
+	}
+
+	appendStringInfoString(&buf, " ON (");
+
 	for (colno = 0; colno < statextrec->stakeys.dim1; colno++)
 	{
 		AttrNumber	attnum = statextrec->stakeys.values[colno];