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Convert pre-existing stats_ext tests to new style

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The regression tests added in commit 7300a69950 test cardinality
estimates using a function that extracts the interesting pieces
from the EXPLAIN output, instead of testing the whole plan. That
seems both easier to understand and less fragile, so this applies
the same approach to pre-existing tests of ndistinct coefficients
and functional dependencies.

Discussion: https://postgr.es/m/dfdac334-9cf2-2597-fb27-f0fb3753f435@2ndquadrant.com
pull/41/head
Tomas Vondra 6 years ago
parent 3824ca30d1
commit dbb984128e
2 changed files with 257 additions and 419 deletions
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  1. 526
      src/test/regress/expected/stats_ext.out
  2. 150
      src/test/regress/sql/stats_ext.sql

526
src/test/regress/expected/stats_ext.out
Unescape View File

@ -2,9 +2,26 @@
-- We will be checking execution plans without/with statistics, so
-- let's make sure we get simple non-parallel plans. Also set the
-- work_mem low so that we can use small amounts of data.
SET max_parallel_workers = 0;
SET max_parallel_workers_per_gather = 0;
SET work_mem = '128kB';
-- 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
$$
declare
ln text;
tmp text[];
first_row bool := true;
begin
for ln in
execute format('explain analyze %s', $1)
loop
if first_row then
first_row := false;
tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)');
return query select tmp[1]::int, tmp[2]::int;
end if;
end loop;
end;
$$;
-- Verify failures
CREATE STATISTICS tst;
ERROR: syntax error at or near ";"
@ -146,191 +163,126 @@ CREATE TABLE ndistinct (
-- over-estimates when using only per-column statistics
INSERT INTO ndistinct (a, b, c, filler1)
SELECT i/100, i/100, i/100, cash_words((i/100)::money)
FROM generate_series(1,30000) s(i);
FROM generate_series(1,1000) s(i);
ANALYZE ndistinct;
-- Group Aggregate, due to over-estimate of the number of groups
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b
-> Sort
Sort Key: a, b
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: b, c
-> Sort
Sort Key: b, c
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b, c
-> Sort
Sort Key: a, b, c
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b, c, d
-> Sort
Sort Key: a, b, c, d
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: b, c, d
-> Sort
Sort Key: b, c, d
-> Seq Scan on ndistinct
(5 rows)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
estimated | actual
-----------+--------
100 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c');
estimated | actual
-----------+--------
100 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
estimated | actual
-----------+--------
100 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
estimated | actual
-----------+--------
200 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
estimated | actual
-----------+--------
200 | 11
(1 row)
-- correct command
CREATE STATISTICS s10 ON a, b, c FROM ndistinct;
ANALYZE ndistinct;
SELECT stxkind, stxndistinct
FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
stxkind | stxndistinct
---------+---------------------------------------------------------
{d,f,m} | {"3, 4": 301, "3, 6": 301, "4, 6": 301, "3, 4, 6": 301}
stxkind | stxndistinct
---------+-----------------------------------------------------
{d,f,m} | {"3, 4": 11, "3, 6": 11, "4, 6": 11, "3, 4, 6": 11}
(1 row)
-- Hash Aggregate, thanks to estimates improved by the statistic
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, b
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: b, c
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, b, c
-> Seq Scan on ndistinct
(3 rows)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
estimated | actual
-----------+--------
11 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c');
estimated | actual
-----------+--------
11 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
estimated | actual
-----------+--------
11 | 11
(1 row)
-- last two plans keep using Group Aggregate, because 'd' is not covered
-- by the statistic and while it's NULL-only we assume 200 values for it
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b, c, d
-> Sort
Sort Key: a, b, c, d
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: b, c, d
-> Sort
Sort Key: b, c, d
-> Seq Scan on ndistinct
(5 rows)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
estimated | actual
-----------+--------
200 | 11
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
estimated | actual
-----------+--------
200 | 11
(1 row)
TRUNCATE TABLE ndistinct;
-- under-estimates when using only per-column statistics
INSERT INTO ndistinct (a, b, c, filler1)
SELECT mod(i,50), mod(i,51), mod(i,32),
cash_words(mod(i,33)::int::money)
FROM generate_series(1,10000) s(i);
FROM generate_series(1,5000) s(i);
ANALYZE ndistinct;
SELECT stxkind, stxndistinct
FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
stxkind | stxndistinct
---------+-------------------------------------------------------------
{d,f,m} | {"3, 4": 2550, "3, 6": 800, "4, 6": 1632, "3, 4, 6": 10000}
(1 row)
-- plans using Group Aggregate, thanks to using correct esimates
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b
-> Sort
Sort Key: a, b
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b, c
-> Sort
Sort Key: a, b, c
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
QUERY PLAN
-----------------------------------
GroupAggregate
Group Key: a, b, c, d
-> Sort
Sort Key: a, b, c, d
-> Seq Scan on ndistinct
(5 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: b, c, d
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, d
-> Seq Scan on ndistinct
(3 rows)
stxkind | stxndistinct
---------+------------------------------------------------------------
{d,f,m} | {"3, 4": 2550, "3, 6": 800, "4, 6": 1632, "3, 4, 6": 5000}
(1 row)
-- correct esimates
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
estimated | actual
-----------+--------
2550 | 2550
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
estimated | actual
-----------+--------
5000 | 5000
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
estimated | actual
-----------+--------
5000 | 5000
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
estimated | actual
-----------+--------
1632 | 1632
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d');
estimated | actual
-----------+--------
500 | 50
(1 row)
DROP STATISTICS s10;
SELECT stxkind, stxndistinct
@ -339,52 +291,36 @@ SELECT stxkind, stxndistinct
---------+--------------
(0 rows)
-- dropping the statistics switches the plans to Hash Aggregate,
-- due to under-estimates
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, b
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, b, c
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, b, c, d
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: b, c, d
-> Seq Scan on ndistinct
(3 rows)
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
QUERY PLAN
-----------------------------
HashAggregate
Group Key: a, d
-> Seq Scan on ndistinct
(3 rows)
-- dropping the statistics results in under-estimates
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
estimated | actual
-----------+--------
500 | 2550
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
estimated | actual
-----------+--------
500 | 5000
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
estimated | actual
-----------+--------
500 | 5000
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
estimated | actual
-----------+--------
500 | 1632
(1 row)
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d');
estimated | actual
-----------+--------
500 | 50
(1 row)
-- functional dependencies tests
CREATE TABLE functional_dependencies (
@ -396,51 +332,38 @@ CREATE TABLE functional_dependencies (
c INT,
d TEXT
);
SET random_page_cost = 1.2;
CREATE INDEX fdeps_ab_idx ON functional_dependencies (a, b);
CREATE INDEX fdeps_abc_idx ON functional_dependencies (a, b, c);
-- random data (no functional dependencies)
INSERT INTO functional_dependencies (a, b, c, filler1)
SELECT mod(i, 23), mod(i, 29), mod(i, 31), i FROM generate_series(1,5000) s(i);
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
-> Bitmap Index Scan on fdeps_abc_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(4 rows)
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
-----------------------------------------------------------
Index Scan using fdeps_abc_idx on functional_dependencies
Index Cond: ((a = 1) AND (b = '1'::text) AND (c = 1))
(2 rows)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
estimated | actual
-----------+--------
8 | 8
(1 row)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
1 | 1
(1 row)
-- create statistics
CREATE STATISTICS func_deps_stat (dependencies) ON a, b, c FROM functional_dependencies;
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
-> Bitmap Index Scan on fdeps_abc_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(4 rows)
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
-----------------------------------------------------------
Index Scan using fdeps_abc_idx on functional_dependencies
Index Cond: ((a = 1) AND (b = '1'::text) AND (c = 1))
(2 rows)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
estimated | actual
-----------+--------
8 | 8
(1 row)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
1 | 1
(1 row)
-- a => b, a => c, b => c
TRUNCATE functional_dependencies;
@ -448,92 +371,48 @@ DROP STATISTICS func_deps_stat;
INSERT INTO functional_dependencies (a, b, c, filler1)
SELECT mod(i,100), mod(i,50), mod(i,25), i FROM generate_series(1,5000) s(i);
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
QUERY PLAN
-----------------------------------------------------------
Index Scan using fdeps_abc_idx on functional_dependencies
Index Cond: ((a = 1) AND (b = '1'::text))
(2 rows)
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
-----------------------------------------------------------
Index Scan using fdeps_abc_idx on functional_dependencies
Index Cond: ((a = 1) AND (b = '1'::text) AND (c = 1))
(2 rows)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
estimated | actual
-----------+--------
1 | 50
(1 row)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
1 | 50
(1 row)
-- create statistics
CREATE STATISTICS func_deps_stat (dependencies) ON a, b, c FROM functional_dependencies;
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
-> Bitmap Index Scan on fdeps_abc_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(4 rows)
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
Filter: (c = 1)
-> Bitmap Index Scan on fdeps_ab_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(5 rows)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
estimated | actual
-----------+--------
50 | 50
(1 row)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
50 | 50
(1 row)
-- check change of column type doesn't break it
ALTER TABLE functional_dependencies ALTER COLUMN c TYPE numeric;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
Filter: (c = '1'::numeric)
-> Bitmap Index Scan on fdeps_ab_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(5 rows)
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
50 | 50
(1 row)
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
QUERY PLAN
---------------------------------------------------
Bitmap Heap Scan on functional_dependencies
Recheck Cond: ((a = 1) AND (b = '1'::text))
Filter: (c = '1'::numeric)
-> Bitmap Index Scan on fdeps_ab_idx
Index Cond: ((a = 1) AND (b = '1'::text))
(5 rows)
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
$$
declare
ln text;
tmp text[];
first_row bool := true;
begin
for ln in
execute format('explain analyze %s', $1)
loop
if first_row then
first_row := false;
tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)');
return query select tmp[1]::int, tmp[2]::int;
end if;
end loop;
end;
$$;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
estimated | actual
-----------+--------
50 | 50
(1 row)
-- MCV lists
CREATE TABLE mcv_lists (
filler1 TEXT,
@ -728,7 +607,6 @@ SELECT m.* FROM pg_statistic_ext,
0 | {1, 2, 3} | {f,f,f} | 1 | 1
(1 row)
RESET random_page_cost;
-- mcv with arrays
CREATE TABLE mcv_lists_arrays (
a TEXT[],

150
src/test/regress/sql/stats_ext.sql
Unescape View File

@ -3,9 +3,27 @@
-- We will be checking execution plans without/with statistics, so
-- let's make sure we get simple non-parallel plans. Also set the
-- work_mem low so that we can use small amounts of data.
SET max_parallel_workers = 0;
SET max_parallel_workers_per_gather = 0;
SET work_mem = '128kB';
-- 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
$$
declare
ln text;
tmp text[];
first_row bool := true;
begin
for ln in
execute format('explain analyze %s', $1)
loop
if first_row then
first_row := false;
tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)');
return query select tmp[1]::int, tmp[2]::int;
end if;
end loop;
end;
$$;
-- Verify failures
CREATE STATISTICS tst;
@ -106,25 +124,20 @@ CREATE TABLE ndistinct (
-- over-estimates when using only per-column statistics
INSERT INTO ndistinct (a, b, c, filler1)
SELECT i/100, i/100, i/100, cash_words((i/100)::money)
FROM generate_series(1,30000) s(i);
FROM generate_series(1,1000) s(i);
ANALYZE ndistinct;
-- Group Aggregate, due to over-estimate of the number of groups
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
-- correct command
CREATE STATISTICS s10 ON a, b, c FROM ndistinct;
@ -135,22 +148,17 @@ SELECT stxkind, stxndistinct
FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
-- Hash Aggregate, thanks to estimates improved by the statistic
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
-- last two plans keep using Group Aggregate, because 'd' is not covered
-- by the statistic and while it's NULL-only we assume 200 values for it
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
TRUNCATE TABLE ndistinct;
@ -158,50 +166,39 @@ TRUNCATE TABLE ndistinct;
INSERT INTO ndistinct (a, b, c, filler1)
SELECT mod(i,50), mod(i,51), mod(i,32),
cash_words(mod(i,33)::int::money)
FROM generate_series(1,10000) s(i);
FROM generate_series(1,5000) s(i);
ANALYZE ndistinct;
SELECT stxkind, stxndistinct
FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
-- plans using Group Aggregate, thanks to using correct esimates
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
-- correct esimates
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d');
DROP STATISTICS s10;
SELECT stxkind, stxndistinct
FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
-- dropping the statistics switches the plans to Hash Aggregate,
-- due to under-estimates
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
-- dropping the statistics results in under-estimates
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d');
EXPLAIN (COSTS off)
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d');
-- functional dependencies tests
CREATE TABLE functional_dependencies (
@ -214,8 +211,6 @@ CREATE TABLE functional_dependencies (
d TEXT
);
SET random_page_cost = 1.2;
CREATE INDEX fdeps_ab_idx ON functional_dependencies (a, b);
CREATE INDEX fdeps_abc_idx ON functional_dependencies (a, b, c);
@ -225,22 +220,18 @@ INSERT INTO functional_dependencies (a, b, c, filler1)
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
-- create statistics
CREATE STATISTICS func_deps_stat (dependencies) ON a, b, c FROM functional_dependencies;
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
-- a => b, a => c, b => c
TRUNCATE functional_dependencies;
@ -251,56 +242,27 @@ INSERT INTO functional_dependencies (a, b, c, filler1)
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
-- create statistics
CREATE STATISTICS func_deps_stat (dependencies) ON a, b, c FROM functional_dependencies;
ANALYZE functional_dependencies;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1';
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1''');
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
-- check change of column type doesn't break it
ALTER TABLE functional_dependencies ALTER COLUMN c TYPE numeric;
EXPLAIN (COSTS OFF)
SELECT * FROM functional_dependencies WHERE a = 1 AND b = '1' AND c = 1;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
ANALYZE functional_dependencies;
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
$$
declare
ln text;
tmp text[];
first_row bool := true;
begin
for ln in
execute format('explain analyze %s', $1)
loop
if first_row then
first_row := false;
tmp := regexp_match(ln, 'rows=(\d*) .* rows=(\d*)');
return query select tmp[1]::int, tmp[2]::int;
end if;
end loop;
end;
$$;
SELECT * FROM check_estimated_rows('SELECT * FROM functional_dependencies WHERE a = 1 AND b = ''1'' AND c = 1');
-- MCV lists
CREATE TABLE mcv_lists (
@ -419,8 +381,6 @@ ANALYZE mcv_lists;
SELECT m.* FROM pg_statistic_ext,
pg_mcv_list_items(stxmcv) m WHERE stxname = 'mcv_lists_stats';
RESET random_page_cost;
-- mcv with arrays
CREATE TABLE mcv_lists_arrays (
a TEXT[],

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