Add jsonb statistics

Author: Nikita Glukhov

src/backend/catalog/system_functions.sql

@@ -594,6 +594,42 @@ LANGUAGE internal
 STRICT IMMUTABLE PARALLEL SAFE
 AS 'unicode_is_normalized';
 
+-- XXX is this function immutable / parallel safe?
+-- XXX do we actually need to cast to text and then to jsonb?
+CREATE FUNCTION pg_json_path_stats(tab regclass, path_index integer) RETURNS text
+AS $$
+	SELECT jsonb_pretty((
+		CASE
+			WHEN stakind1 = 8 THEN stavalues1
+			WHEN stakind2 = 8 THEN stavalues2
+			WHEN stakind3 = 8 THEN stavalues3
+			WHEN stakind4 = 8 THEN stavalues4
+			WHEN stakind5 = 8 THEN stavalues5
+		END::text::jsonb[])[$2])
+	FROM pg_statistic
+	WHERE starelid = $1
+$$ LANGUAGE 'sql';
+
+-- XXX is this function immutable / parallel safe?
+-- XXX do we actually need to cast to text and then to jsonb?
+CREATE FUNCTION pg_json_path_stats(tab regclass, path text) RETURNS text
+AS $$
+	SELECT jsonb_pretty(pathstats)
+	FROM (
+		SELECT unnest(
+			CASE
+				WHEN stakind1 = 8 THEN stavalues1
+				WHEN stakind2 = 8 THEN stavalues2
+				WHEN stakind3 = 8 THEN stavalues3
+				WHEN stakind4 = 8 THEN stavalues4
+				WHEN stakind5 = 8 THEN stavalues5
+			END::text::jsonb[]) pathstats
+		FROM pg_statistic
+		WHERE starelid = $1
+	) paths
+	WHERE pathstats->>'path' = $2
+$$ LANGUAGE 'sql';
+
 --
 -- The default permissions for functions mean that anyone can execute them.
 -- A number of functions shouldn't be executable by just anyone, but rather

src/backend/catalog/system_views.sql

@@ -364,6 +364,62 @@ CREATE VIEW pg_stats_ext_exprs WITH (security_barrier) AS
 -- unprivileged users may read pg_statistic_ext but not pg_statistic_ext_data
 REVOKE ALL ON pg_statistic_ext_data FROM public;
 
+-- XXX This probably needs to do the same checks as pg_stats, i.e.
+--    WHERE NOT attisdropped
+--    AND has_column_privilege(c.oid, a.attnum, 'select')
+--    AND (c.relrowsecurity = false OR NOT row_security_active(c.oid));
+CREATE VIEW pg_stats_json AS
+	SELECT
+		nspname AS schemaname,
+		relname AS tablename,
+		attname AS attname,
+
+		path->>'path' AS json_path,
+
+		stainherit AS inherited,
+
+		(path->'json'->>'nullfrac')::float4 AS null_frac,
+		(path->'json'->>'width')::float4 AS avg_width,
+		(path->'json'->>'distinct')::float4 AS n_distinct,
+
+		ARRAY(SELECT val FROM jsonb_array_elements(
+				path->'json'->'mcv'->'values') val)::anyarray
+			AS most_common_vals,
+
+		ARRAY(SELECT num::text::float4 FROM jsonb_array_elements(
+				path->'json'->'mcv'->'numbers') num)
+			AS most_common_freqs,
+
+		ARRAY(SELECT val FROM jsonb_array_elements(
+				path->'json'->'histogram'->'values') val)
+			AS histogram_bounds,
+
+		ARRAY(SELECT val::text::int FROM jsonb_array_elements(
+				path->'array_length'->'mcv'->'values') val)
+			AS most_common_array_lengths,
+
+		ARRAY(SELECT num::text::float4 FROM jsonb_array_elements(
+				path->'array_length'->'mcv'->'numbers') num)
+			AS most_common_array_length_freqs,
+
+		(path->'json'->>'correlation')::float4 AS correlation
+
+	FROM
+		pg_statistic s JOIN pg_class c ON (c.oid = s.starelid)
+		JOIN pg_attribute a ON (c.oid = attrelid AND attnum = s.staattnum)
+		LEFT JOIN pg_namespace n ON (n.oid = c.relnamespace),
+		LATERAL (
+			SELECT unnest((CASE
+					WHEN stakind1 = 8 THEN stavalues1
+					WHEN stakind2 = 8 THEN stavalues2
+					WHEN stakind3 = 8 THEN stavalues3
+					WHEN stakind4 = 8 THEN stavalues4
+					WHEN stakind5 = 8 THEN stavalues5
+				END ::text::jsonb[])[2:]) AS path
+		) paths;
+
+-- no need to revoke any privileges, we've already revoked accss to pg_statistic
+
 CREATE VIEW pg_publication_tables AS
     SELECT
         P.pubname AS pubname,

src/backend/utils/adt/Makefile

@@ -50,6 +50,8 @@ OBJS = \
 	jsonb.o \
 	jsonb_gin.o \
 	jsonb_op.o \
+	jsonb_selfuncs.o \
+	jsonb_typanalyze.o \
 	jsonb_util.o \
 	jsonfuncs.o \
 	jsonbsubs.o \