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Rework the stats_ext test
As suggested by Tom Lane, avoid printing specific estimated cost values, because they vary across architectures; instead, verify plan shapes (in this case, HashAggregate vs. GroupAggregate), as we do in other planner tests. We can now remove expected/stats_ext_1.out. Author: Tomas Vondra
This commit is contained in:
Alvaro Herrera
parent
70ec3f1f8f
commit
bed9ef5a16
@ -1,4 +1,10 @@
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-- Generic extended statistics support
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-- Generic extended statistics support
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-- We will be checking execution plans without/with statistics, so
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-- let's make sure we get simple non-parallel plans. Also set the
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-- work_mem low so that we can use small amounts of data.
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SET max_parallel_workers = 0;
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SET max_parallel_workers_per_gather = 0;
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SET work_mem = '128kB';
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-- Ensure stats are dropped sanely
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-- Ensure stats are dropped sanely
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CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
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CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
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CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
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CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
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@ -49,6 +55,67 @@ CREATE TABLE ndistinct (
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c INT,
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c INT,
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d INT
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d INT
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);
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);
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-- over-estimates when using only per-column statistics
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INSERT INTO ndistinct (a, b, c, filler1)
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SELECT i/100, i/100, i/100, cash_words((i/100)::money)
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FROM generate_series(1,30000) s(i);
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ANALYZE ndistinct;
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-- Group Aggregate, due to over-estimate of the number of groups
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: a, b
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-> Sort
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Sort Key: a, b
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: b, c
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-> Sort
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Sort Key: b, c
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: a, b, c
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-> Sort
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Sort Key: a, b, c
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: a, b, c, d
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-> Sort
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Sort Key: a, b, c, d
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: b, c, d
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-> Sort
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Sort Key: b, c, d
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-> Seq Scan on ndistinct
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(5 rows)
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-- unknown column
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-- unknown column
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CREATE STATISTICS s10 ON (unknown_column) FROM ndistinct;
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CREATE STATISTICS s10 ON (unknown_column) FROM ndistinct;
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ERROR: column "unknown_column" referenced in statistics does not exist
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ERROR: column "unknown_column" referenced in statistics does not exist
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@ -63,100 +130,184 @@ CREATE STATISTICS s10 ON (a, a, b) FROM ndistinct;
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ERROR: duplicate column name in statistics definition
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ERROR: duplicate column name in statistics definition
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-- correct command
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-- correct command
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CREATE STATISTICS s10 ON (a, b, c) FROM ndistinct;
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CREATE STATISTICS s10 ON (a, b, c) FROM ndistinct;
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-- perfectly correlated groups
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ANALYZE ndistinct;
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SELECT staenabled, standistinct
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FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
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staenabled | standistinct
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------------+------------------------------------------------------------------------------------------------
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{d} | [{(b 3 4), 301.000000}, {(b 3 6), 301.000000}, {(b 4 6), 301.000000}, {(b 3 4 6), 301.000000}]
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(1 row)
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-- Hash Aggregate, thanks to estimates improved by the statistic
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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QUERY PLAN
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-----------------------------
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HashAggregate
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Group Key: a, b
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-> Seq Scan on ndistinct
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(3 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
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QUERY PLAN
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-----------------------------
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HashAggregate
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Group Key: b, c
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-> Seq Scan on ndistinct
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(3 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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QUERY PLAN
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-----------------------------
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HashAggregate
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Group Key: a, b, c
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-> Seq Scan on ndistinct
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(3 rows)
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-- last two plans keep using Group Aggregate, because 'd' is not covered
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-- by the statistic and while it's NULL-only we assume 200 values for it
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: a, b, c, d
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-> Sort
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Sort Key: a, b, c, d
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: b, c, d
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-> Sort
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Sort Key: b, c, d
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-> Seq Scan on ndistinct
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(5 rows)
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TRUNCATE TABLE ndistinct;
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-- under-estimates when using only per-column statistics
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INSERT INTO ndistinct (a, b, c, filler1)
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INSERT INTO ndistinct (a, b, c, filler1)
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SELECT i/100, i/100, i/100, cash_words(i::money)
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SELECT mod(i,50), mod(i,51), mod(i,32),
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cash_words(mod(i,33)::int::money)
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FROM generate_series(1,10000) s(i);
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FROM generate_series(1,10000) s(i);
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ANALYZE ndistinct;
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ANALYZE ndistinct;
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SELECT staenabled, standistinct
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SELECT staenabled, standistinct
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FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
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FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
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staenabled | standistinct
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staenabled | standistinct
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------------+------------------------------------------------------------------------------------------------
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------------+----------------------------------------------------------------------------------------------------
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{d} | [{(b 3 4), 101.000000}, {(b 3 6), 101.000000}, {(b 4 6), 101.000000}, {(b 3 4 6), 101.000000}]
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{d} | [{(b 3 4), 2550.000000}, {(b 3 6), 800.000000}, {(b 4 6), 1632.000000}, {(b 3 4 6), 10000.000000}]
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(1 row)
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(1 row)
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-- plans using Group Aggregate, thanks to using correct esimates
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EXPLAIN (COSTS off)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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QUERY PLAN
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QUERY PLAN
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-----------------------------
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-----------------------------------
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HashAggregate
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GroupAggregate
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Group Key: a, b
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Group Key: a, b
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-> Sort
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Sort Key: a, b
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-> Seq Scan on ndistinct
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-> Seq Scan on ndistinct
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(3 rows)
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(5 rows)
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EXPLAIN (COSTS off)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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QUERY PLAN
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QUERY PLAN
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-----------------------------
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-----------------------------------
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HashAggregate
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GroupAggregate
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Group Key: a, b, c
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Group Key: a, b, c
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-> Sort
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Sort Key: a, b, c
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-> Seq Scan on ndistinct
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-> Seq Scan on ndistinct
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(3 rows)
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(5 rows)
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EXPLAIN (COSTS off)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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QUERY PLAN
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QUERY PLAN
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-----------------------------------
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GroupAggregate
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Group Key: a, b, c, d
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-> Sort
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Sort Key: a, b, c, d
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-> Seq Scan on ndistinct
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(5 rows)
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
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QUERY PLAN
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-----------------------------
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-----------------------------
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HashAggregate
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HashAggregate
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Group Key: a, b, c, d
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Group Key: b, c, d
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-> Seq Scan on ndistinct
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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TRUNCATE TABLE ndistinct;
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EXPLAIN (COSTS off)
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-- partially correlated groups
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SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
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INSERT INTO ndistinct (a, b, c)
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QUERY PLAN
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SELECT i/50, i/100, i/200 FROM generate_series(1,10000) s(i);
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-----------------------------
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ANALYZE ndistinct;
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HashAggregate
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Group Key: a, d
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-> Seq Scan on ndistinct
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(3 rows)
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DROP STATISTICS s10;
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SELECT staenabled, standistinct
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SELECT staenabled, standistinct
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FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
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FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
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staenabled | standistinct
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staenabled | standistinct
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------------+------------------------------------------------------------------------------------------------
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------------+--------------
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{d} | [{(b 3 4), 201.000000}, {(b 3 6), 201.000000}, {(b 4 6), 101.000000}, {(b 3 4 6), 201.000000}]
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(0 rows)
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(1 row)
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EXPLAIN
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-- dropping the statistics switches the plans to Hash Aggregate,
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-- due to under-estimates
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
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QUERY PLAN
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QUERY PLAN
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---------------------------------------------------------------------
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-----------------------------
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HashAggregate (cost=230.00..232.01 rows=201 width=16)
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HashAggregate
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Group Key: a, b
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Group Key: a, b
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-> Seq Scan on ndistinct (cost=0.00..155.00 rows=10000 width=8)
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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EXPLAIN
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
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QUERY PLAN
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QUERY PLAN
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----------------------------------------------------------------------
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-----------------------------
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HashAggregate (cost=255.00..257.01 rows=201 width=20)
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HashAggregate
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Group Key: a, b, c
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Group Key: a, b, c
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-> Seq Scan on ndistinct (cost=0.00..155.00 rows=10000 width=12)
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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EXPLAIN
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
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QUERY PLAN
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QUERY PLAN
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----------------------------------------------------------------------
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-----------------------------
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HashAggregate (cost=280.00..290.00 rows=1000 width=24)
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HashAggregate
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Group Key: a, b, c, d
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Group Key: a, b, c, d
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-> Seq Scan on ndistinct (cost=0.00..155.00 rows=10000 width=16)
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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EXPLAIN
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
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SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
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QUERY PLAN
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QUERY PLAN
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----------------------------------------------------------------------
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-----------------------------
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HashAggregate (cost=255.00..265.00 rows=1000 width=20)
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HashAggregate
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Group Key: b, c, d
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Group Key: b, c, d
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-> Seq Scan on ndistinct (cost=0.00..155.00 rows=10000 width=12)
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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EXPLAIN
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EXPLAIN (COSTS off)
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SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
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SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
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QUERY PLAN
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QUERY PLAN
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---------------------------------------------------------------------
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-----------------------------
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HashAggregate (cost=230.00..240.00 rows=1000 width=16)
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HashAggregate
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Group Key: a, d
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Group Key: a, d
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-> Seq Scan on ndistinct (cost=0.00..155.00 rows=10000 width=8)
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-> Seq Scan on ndistinct
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(3 rows)
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(3 rows)
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DROP TABLE ndistinct;
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DROP TABLE ndistinct;
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@ -1,155 +0,0 @@
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-- Generic extended statistics support
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-- Ensure stats are dropped sanely
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CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
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CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
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DROP STATISTICS ab1_a_b_stats;
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CREATE SCHEMA regress_schema_2;
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CREATE STATISTICS regress_schema_2.ab1_a_b_stats ON (a, b) FROM ab1;
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DROP STATISTICS regress_schema_2.ab1_a_b_stats;
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-- Ensure statistics are dropped when columns are
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CREATE STATISTICS ab1_b_c_stats ON (b, c) FROM ab1;
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CREATE STATISTICS ab1_a_b_c_stats ON (a, b, c) FROM ab1;
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CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
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ALTER TABLE ab1 DROP COLUMN a;
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\d ab1
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Table "public.ab1"
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Column | Type | Collation | Nullable | Default
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--------+---------+-----------+----------+---------
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b | integer | | |
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c | integer | | |
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Statistics:
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"public.ab1_b_c_stats" WITH (ndistinct) ON (b, c)
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DROP TABLE ab1;
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-- Ensure things work sanely with SET STATISTICS 0
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CREATE TABLE ab1 (a INTEGER, b INTEGER);
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ALTER TABLE ab1 ALTER a SET STATISTICS 0;
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INSERT INTO ab1 SELECT a, a%23 FROM generate_series(1, 1000) a;
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CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
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ANALYZE ab1;
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ERROR: extended statistics could not be collected for column "a" of relation public.ab1
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HINT: Consider ALTER TABLE "public"."ab1" ALTER "a" SET STATISTICS -1
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ALTER TABLE ab1 ALTER a SET STATISTICS -1;
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ANALYZE ab1;
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DROP TABLE ab1;
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-- n-distinct tests
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CREATE TABLE ndistinct (
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filler1 TEXT,
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filler2 NUMERIC,
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a INT,
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b INT,
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filler3 DATE,
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c INT,
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d INT
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);
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-- unknown column
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CREATE STATISTICS s10 ON (unknown_column) FROM ndistinct;
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ERROR: column "unknown_column" referenced in statistics does not exist
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-- single column
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CREATE STATISTICS s10 ON (a) FROM ndistinct;
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ERROR: statistics require at least 2 columns
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-- single column, duplicated
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CREATE STATISTICS s10 ON (a,a) FROM ndistinct;
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ERROR: duplicate column name in statistics definition
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-- two columns, one duplicated
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CREATE STATISTICS s10 ON (a, a, b) FROM ndistinct;
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ERROR: duplicate column name in statistics definition
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-- correct command
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CREATE STATISTICS s10 ON (a, b, c) FROM ndistinct;
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-- perfectly correlated groups
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INSERT INTO ndistinct (a, b, c, filler1)
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SELECT i/100, i/100, i/100, cash_words(i::money)
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FROM generate_series(1,10000) s(i);
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ANALYZE ndistinct;
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SELECT staenabled, standistinct
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|
||||||
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
|
||||||
staenabled | standistinct
|
|
||||||
------------+------------------------------------------------------------------------------------------------
|
|
||||||
{d} | [{(b 3 4), 101.000000}, {(b 3 6), 101.000000}, {(b 4 6), 101.000000}, {(b 3 4 6), 101.000000}]
|
|
||||||
(1 row)
|
|
||||||
|
|
||||||
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)
|
|
||||||
|
|
||||||
TRUNCATE TABLE ndistinct;
|
|
||||||
-- partially correlated groups
|
|
||||||
INSERT INTO ndistinct (a, b, c)
|
|
||||||
SELECT i/50, i/100, i/200 FROM generate_series(1,10000) s(i);
|
|
||||||
ANALYZE ndistinct;
|
|
||||||
SELECT staenabled, standistinct
|
|
||||||
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
|
||||||
staenabled | standistinct
|
|
||||||
------------+------------------------------------------------------------------------------------------------
|
|
||||||
{d} | [{(b 3 4), 201.000000}, {(b 3 6), 201.000000}, {(b 4 6), 101.000000}, {(b 3 4 6), 201.000000}]
|
|
||||||
(1 row)
|
|
||||||
|
|
||||||
EXPLAIN
|
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
|
||||||
QUERY PLAN
|
|
||||||
---------------------------------------------------------------------
|
|
||||||
HashAggregate (cost=225.00..227.01 rows=201 width=16)
|
|
||||||
Group Key: a, b
|
|
||||||
-> Seq Scan on ndistinct (cost=0.00..150.00 rows=10000 width=8)
|
|
||||||
(3 rows)
|
|
||||||
|
|
||||||
EXPLAIN
|
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
|
|
||||||
QUERY PLAN
|
|
||||||
----------------------------------------------------------------------
|
|
||||||
HashAggregate (cost=250.00..252.01 rows=201 width=20)
|
|
||||||
Group Key: a, b, c
|
|
||||||
-> Seq Scan on ndistinct (cost=0.00..150.00 rows=10000 width=12)
|
|
||||||
(3 rows)
|
|
||||||
|
|
||||||
EXPLAIN
|
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
|
||||||
QUERY PLAN
|
|
||||||
----------------------------------------------------------------------
|
|
||||||
HashAggregate (cost=275.00..285.00 rows=1000 width=24)
|
|
||||||
Group Key: a, b, c, d
|
|
||||||
-> Seq Scan on ndistinct (cost=0.00..150.00 rows=10000 width=16)
|
|
||||||
(3 rows)
|
|
||||||
|
|
||||||
EXPLAIN
|
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
|
||||||
QUERY PLAN
|
|
||||||
----------------------------------------------------------------------
|
|
||||||
HashAggregate (cost=250.00..260.00 rows=1000 width=20)
|
|
||||||
Group Key: b, c, d
|
|
||||||
-> Seq Scan on ndistinct (cost=0.00..150.00 rows=10000 width=12)
|
|
||||||
(3 rows)
|
|
||||||
|
|
||||||
EXPLAIN
|
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
|
|
||||||
QUERY PLAN
|
|
||||||
---------------------------------------------------------------------
|
|
||||||
HashAggregate (cost=225.00..235.00 rows=1000 width=16)
|
|
||||||
Group Key: a, d
|
|
||||||
-> Seq Scan on ndistinct (cost=0.00..150.00 rows=10000 width=8)
|
|
||||||
(3 rows)
|
|
||||||
|
|
||||||
DROP TABLE ndistinct;
|
|
||||||
@ -1,5 +1,12 @@
|
|||||||
-- Generic extended statistics support
|
-- Generic extended statistics support
|
||||||
|
|
||||||
|
-- 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';
|
||||||
|
|
||||||
-- Ensure stats are dropped sanely
|
-- Ensure stats are dropped sanely
|
||||||
CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
|
CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
|
||||||
CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
|
CREATE STATISTICS ab1_a_b_stats ON (a, b) FROM ab1;
|
||||||
@ -43,6 +50,29 @@ CREATE TABLE ndistinct (
|
|||||||
d INT
|
d INT
|
||||||
);
|
);
|
||||||
|
|
||||||
|
-- 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);
|
||||||
|
|
||||||
|
ANALYZE ndistinct;
|
||||||
|
|
||||||
|
-- Group Aggregate, due to over-estimate of the number of groups
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
||||||
|
|
||||||
-- unknown column
|
-- unknown column
|
||||||
CREATE STATISTICS s10 ON (unknown_column) FROM ndistinct;
|
CREATE STATISTICS s10 ON (unknown_column) FROM ndistinct;
|
||||||
|
|
||||||
@ -58,9 +88,35 @@ CREATE STATISTICS s10 ON (a, a, b) FROM ndistinct;
|
|||||||
-- correct command
|
-- correct command
|
||||||
CREATE STATISTICS s10 ON (a, b, c) FROM ndistinct;
|
CREATE STATISTICS s10 ON (a, b, c) FROM ndistinct;
|
||||||
|
|
||||||
-- perfectly correlated groups
|
ANALYZE ndistinct;
|
||||||
|
|
||||||
|
SELECT staenabled, standistinct
|
||||||
|
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
||||||
|
|
||||||
|
-- Hash Aggregate, thanks to estimates improved by the statistic
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
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;
|
||||||
|
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
||||||
|
|
||||||
|
TRUNCATE TABLE ndistinct;
|
||||||
|
|
||||||
|
-- under-estimates when using only per-column statistics
|
||||||
INSERT INTO ndistinct (a, b, c, filler1)
|
INSERT INTO ndistinct (a, b, c, filler1)
|
||||||
SELECT i/100, i/100, i/100, cash_words(i::money)
|
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(1,10000) s(i);
|
||||||
|
|
||||||
ANALYZE ndistinct;
|
ANALYZE ndistinct;
|
||||||
@ -68,6 +124,7 @@ ANALYZE ndistinct;
|
|||||||
SELECT staenabled, standistinct
|
SELECT staenabled, standistinct
|
||||||
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
||||||
|
|
||||||
|
-- plans using Group Aggregate, thanks to using correct esimates
|
||||||
EXPLAIN (COSTS off)
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
||||||
|
|
||||||
@ -77,30 +134,32 @@ EXPLAIN (COSTS off)
|
|||||||
EXPLAIN (COSTS off)
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
||||||
|
|
||||||
TRUNCATE TABLE ndistinct;
|
EXPLAIN (COSTS off)
|
||||||
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
||||||
|
|
||||||
-- partially correlated groups
|
EXPLAIN (COSTS off)
|
||||||
INSERT INTO ndistinct (a, b, c)
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
|
||||||
SELECT i/50, i/100, i/200 FROM generate_series(1,10000) s(i);
|
|
||||||
|
|
||||||
ANALYZE ndistinct;
|
DROP STATISTICS s10;
|
||||||
|
|
||||||
SELECT staenabled, standistinct
|
SELECT staenabled, standistinct
|
||||||
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
FROM pg_statistic_ext WHERE starelid = 'ndistinct'::regclass;
|
||||||
|
|
||||||
EXPLAIN
|
-- dropping the statistics switches the plans to Hash Aggregate,
|
||||||
|
-- due to under-estimates
|
||||||
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b;
|
||||||
|
|
||||||
EXPLAIN
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c;
|
||||||
|
|
||||||
EXPLAIN
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, b, c, d;
|
||||||
|
|
||||||
EXPLAIN
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
SELECT COUNT(*) FROM ndistinct GROUP BY b, c, d;
|
||||||
|
|
||||||
EXPLAIN
|
EXPLAIN (COSTS off)
|
||||||
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
|
SELECT COUNT(*) FROM ndistinct GROUP BY a, d;
|
||||||
|
|
||||||
DROP TABLE ndistinct;
|
DROP TABLE ndistinct;
|
||||||
|
|||||||
Loading…
x
Reference in New Issue
Block a user