Add support for multivariate MCV lists

Introduce a third extended statistic type, supported by the CREATE STATISTICS command - MCV lists, a generalization of the statistic already built and used for individual columns. Compared to the already supported types (n-distinct coefficients and functional dependencies), MCV lists are more complex, include column values and allow estimation of much wider range of common clauses (equality and inequality conditions, IS NULL, IS NOT NULL etc.). Similarly to the other types, a new pseudo-type (pg_mcv_list) is used. Author: Tomas Vondra Reviewed-by: Dean Rasheed, David Rowley, Mark Dilger, Alvaro Herrera Discussion: https://postgr.es/m/dfdac334-9cf2-2597-fb27-f0fb3753f435@2ndquadrant.com
2026-01-13 12:22:55 +03:00 · 2019-03-27 18:32:18 +01:00
parent 333ed246c6
commit 7300a69950
32 changed files with 3597 additions and 134 deletions
--- a/src/test/regress/sql/stats_ext.sql
+++ b/src/test/regress/sql/stats_ext.sql
@@ -280,3 +280,189 @@ EXPLAIN (COSTS OFF)
 SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;

 RESET random_page_cost;
+
+-- check the number of estimated/actual rows in the top node
+create function check_estimated_rows(text) returns table (estimated int, actual int)
+language plpgsql as
+$$
+declare
+    ln text;
+    tmp text[];
+    first_row bool := true;
+begin
+    for ln in
+        execute format('explain analyze %s', $1)
+    loop
+        if first_row then
+            first_row := false;
+            tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)');
+            return query select tmp[1]::int, tmp[2]::int;
+        end if;
+    end loop;
+end;
+$$;
+
+-- MCV lists
+CREATE TABLE mcv_lists (
+    filler1 TEXT,
+    filler2 NUMERIC,
+    a INT,
+    b VARCHAR,
+    filler3 DATE,
+    c INT,
+    d TEXT
+);
+
+-- random data (no MCV list)
+INSERT INTO mcv_lists (a, b, c, filler1)
+     SELECT mod(i,37), mod(i,41), mod(i,43), mod(i,47) FROM generate_series(1,5000) s(i);
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1'' AND c = 1');
+
+-- create statistics
+CREATE STATISTICS mcv_lists_stats (mcv) ON a, b, c FROM mcv_lists;
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1'' AND c = 1');
+
+-- 100 distinct combinations, all in the MCV list
+TRUNCATE mcv_lists;
+DROP STATISTICS mcv_lists_stats;
+
+INSERT INTO mcv_lists (a, b, c, filler1)
+     SELECT mod(i,100), mod(i,50), mod(i,25), i FROM generate_series(1,5000) s(i);
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a < 1 AND b < ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 0 AND b <= ''0''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1'' AND c = 1');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a < 5 AND b < ''1'' AND c < 5');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 4 AND b <= ''0'' AND c <= 4');
+
+-- create statistics
+CREATE STATISTICS mcv_lists_stats (mcv) ON a, b, c FROM mcv_lists;
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a < 1 AND b < ''1''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 0 AND b <= ''0''');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1'' AND c = 1');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a < 5 AND b < ''1'' AND c < 5');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 4 AND b <= ''0'' AND c <= 4');
+
+-- check change of unrelated column type does not reset the MCV statistics
+ALTER TABLE mcv_lists ALTER COLUMN d TYPE VARCHAR(64);
+
+SELECT stxmcv IS NOT NULL FROM pg_statistic_ext WHERE stxname = 'mcv_lists_stats';
+
+-- check change of column type resets the MCV statistics
+ALTER TABLE mcv_lists ALTER COLUMN c TYPE numeric;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a = 1 AND b = ''1''');
+
+-- 100 distinct combinations with NULL values, all in the MCV list
+TRUNCATE mcv_lists;
+DROP STATISTICS mcv_lists_stats;
+
+INSERT INTO mcv_lists (a, b, c, filler1)
+     SELECT
+         (CASE WHEN mod(i,100) = 1 THEN NULL ELSE mod(i,100) END),
+         (CASE WHEN mod(i,50) = 1  THEN NULL ELSE mod(i,50) END),
+         (CASE WHEN mod(i,25) = 1  THEN NULL ELSE mod(i,25) END),
+         i
+     FROM generate_series(1,5000) s(i);
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a IS NULL AND b IS NULL');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a IS NULL AND b IS NULL AND c IS NULL');
+
+-- create statistics
+CREATE STATISTICS mcv_lists_stats (mcv) ON a, b, c FROM mcv_lists;
+
+ANALYZE mcv_lists;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a IS NULL AND b IS NULL');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a IS NULL AND b IS NULL AND c IS NULL');
+
+RESET random_page_cost;
+
+-- mcv with arrays
+CREATE TABLE mcv_lists_arrays (
+    a TEXT[],
+    b NUMERIC[],
+    c INT[]
+);
+
+INSERT INTO mcv_lists_arrays (a, b, c)
+     SELECT
+         ARRAY[md5((i/100)::text), md5((i/100-1)::text), md5((i/100+1)::text)],
+         ARRAY[(i/100-1)::numeric/1000, (i/100)::numeric/1000, (i/100+1)::numeric/1000],
+         ARRAY[(i/100-1), i/100, (i/100+1)]
+     FROM generate_series(1,5000) s(i);
+
+CREATE STATISTICS mcv_lists_arrays_stats (mcv) ON a, b, c
+  FROM mcv_lists_arrays;
+
+ANALYZE mcv_lists_arrays;
+
+-- mcv with bool
+CREATE TABLE mcv_lists_bool (
+    a BOOL,
+    b BOOL,
+    c BOOL
+);
+
+INSERT INTO mcv_lists_bool (a, b, c)
+     SELECT
+         (mod(i,2) = 0), (mod(i,4) = 0), (mod(i,8) = 0)
+     FROM generate_series(1,10000) s(i);
+
+ANALYZE mcv_lists_bool;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE a AND b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND NOT b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND b AND NOT c');
+
+CREATE STATISTICS mcv_lists_bool_stats (mcv) ON a, b, c
+  FROM mcv_lists_bool;
+
+ANALYZE mcv_lists_bool;
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE a AND b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND NOT b AND c');
+
+SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists_bool WHERE NOT a AND b AND NOT c');