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3311ccc3d2
When a tablesample routine says that it is not repeatable across scans, set_tablesample_rel_pathlist will (usually) materialize it, confusing pg_plan_advice's plan walker machinery. To fix, update that machinery to view such Material paths as essentially an extension of the underlying scan. Reported-by: Alexander Lakhin <exclusion@gmail.com> Discussion: http://postgr.es/m/CA+TgmobOOmmXSJz3e+cjTY-bA1+W0dqVDqzxUBEvGtW62whYGg@mail.gmail.com
210 lines
9.5 KiB
PL/PgSQL
210 lines
9.5 KiB
PL/PgSQL
LOAD 'pg_plan_advice';
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SET max_parallel_workers_per_gather = 0;
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SET seq_page_cost = 0.1;
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SET random_page_cost = 0.1;
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SET cpu_tuple_cost = 0;
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SET cpu_index_tuple_cost = 0;
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CREATE TABLE scan_table (a int primary key, b text)
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WITH (autovacuum_enabled = false);
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INSERT INTO scan_table
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SELECT g, 'some text ' || g FROM generate_series(1, 100000) g;
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CREATE INDEX scan_table_b ON scan_table USING brin (b);
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VACUUM ANALYZE scan_table;
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-- Sequential scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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-- Index scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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-- Index-only scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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-- Bitmap heap scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE b > 'some text 8';
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-- TID scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE ctid = '(0,1)';
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-- TID range scan
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE ctid > '(1,1)' AND ctid < '(2,1)';
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-- Try forcing each of our test queries to use the scan type they
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-- wanted to use anyway. This should succeed.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'BITMAP_HEAP_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE b > 'some text 8';
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SET LOCAL pg_plan_advice.advice = 'TID_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE ctid = '(0,1)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE ctid > '(1,1)' AND ctid < '(2,1)';
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COMMIT;
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-- Try to force a full scan of the table to use some other scan type. All
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-- of these will fail. An index scan or bitmap heap scan could potentially
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-- generate the correct answer, but the planner does not even consider these
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-- possibilities due to the lack of a WHERE clause.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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SET LOCAL pg_plan_advice.advice = 'BITMAP_HEAP_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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SET LOCAL pg_plan_advice.advice = 'TID_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table;
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COMMIT;
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-- Try again to force index use. This should now succeed for the INDEX_SCAN
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-- and BITMAP_HEAP_SCAN, but the INDEX_ONLY_SCAN can't be forced because the
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-- query fetches columns not included in the index.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a > 0;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a > 0;
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SET LOCAL pg_plan_advice.advice = 'BITMAP_HEAP_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a > 0;
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COMMIT;
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-- We can force a primary key lookup to use a sequential scan, but we
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-- can't force it to use an index-only scan (due to the column list)
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-- or a TID scan (due to the absence of a TID qual). If we apply DO_NOT_SCAN
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-- here, we should get a valid plan anyway, but with the scan disabled.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'TID_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'DO_NOT_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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COMMIT;
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-- We can forcibly downgrade an index-only scan to an index scan, but we can't
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-- force the use of an index that the planner thinks is inapplicable.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table public.scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_b)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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COMMIT;
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-- We can force the use of a sequential scan in place of a bitmap heap scan,
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-- but a plain index scan on a BRIN index is not possible.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE b > 'some text 8';
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_b)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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COMMIT;
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-- We can force the use of a sequential scan rather than a TID scan or
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-- TID range scan.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(scan_table)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE ctid = '(0,1)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table
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WHERE ctid > '(1,1)' AND ctid < '(2,1)';
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COMMIT;
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-- Test more complex scenarios with index scans.
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BEGIN;
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-- Should still work if we mention the schema.
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table public.scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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-- But not if we mention the wrong schema.
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table cilbup.scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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-- It's OK to repeat the same advice.
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey scan_table scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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-- But it doesn't work if the index target is even notionally different.
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table scan_table_pkey scan_table public.scan_table_pkey)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT * FROM scan_table WHERE a = 1;
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COMMIT;
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-- Test assorted incorrect advice.
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BEGIN;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(nothing)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(nothing whatsoever)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_SCAN(scan_table bogus)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(nothing whatsoever)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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SET LOCAL pg_plan_advice.advice = 'INDEX_ONLY_SCAN(scan_table bogus)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE) SELECT a FROM scan_table WHERE a = 1;
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COMMIT;
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-- Test our ability to refer to multiple instances of the same alias.
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BEGIN;
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (generate_series(1,10) g LEFT JOIN scan_table s ON g = s.a) x
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LEFT JOIN scan_table s ON g = s.a;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (generate_series(1,10) g LEFT JOIN scan_table s ON g = s.a) x
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LEFT JOIN scan_table s ON g = s.a;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s#2)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (generate_series(1,10) g LEFT JOIN scan_table s ON g = s.a) x
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LEFT JOIN scan_table s ON g = s.a;
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s) SEQ_SCAN(s#2)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (generate_series(1,10) g LEFT JOIN scan_table s ON g = s.a) x
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LEFT JOIN scan_table s ON g = s.a;
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COMMIT;
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-- Test our ability to refer to scans within a subquery.
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0) x;
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0);
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BEGIN;
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-- Should not match.
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0) x;
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0);
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-- Should match first query only.
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s@x)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0) x;
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0);
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-- Should match second query only.
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SET LOCAL pg_plan_advice.advice = 'SEQ_SCAN(s@unnamed_subquery)';
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0) x;
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT * FROM (SELECT * FROM scan_table s WHERE a = 1 OFFSET 0);
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COMMIT;
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-- Test a non-repeatable tablesample method with a scan-level Materialize.
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CREATE EXTENSION tsm_system_time;
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CREATE TABLE scan_tsm (i int);
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT 1 FROM (SELECT i FROM scan_tsm TABLESAMPLE system_time (1000)),
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LATERAL (SELECT i LIMIT 1);
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-- Same, but with the scan-level Materialize on the inner side of a join.
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EXPLAIN (COSTS OFF, PLAN_ADVICE)
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SELECT 1 FROM (SELECT 1 AS x LIMIT 1),
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LATERAL (SELECT x FROM scan_tsm TABLESAMPLE system_time (1000));
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