Hi I have a first query
I looked on EXPLAIN ANALYZE output and the numbers of filtered rows are differen postgres=# set max_parallel_degree to 4; SET Time: 0.717 ms postgres=# EXPLAIN ANALYZE select count(*) from xxx where a % 10 = 0; ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ │ QUERY PLAN │ ╞═══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╡ │ Aggregate (cost=9282.50..9282.51 rows=1 width=0) (actual time=142.541..142.541 rows=1 loops=1) │ │ -> Gather (cost=1000.00..9270.00 rows=5000 width=0) (actual time=0.633..130.926 rows=100000 loops=1) │ │ Number of Workers: 2 │ │ -> Parallel Seq Scan on xxx (cost=0.00..7770.00 rows=5000 width=0) (actual time=0.052..411.303 rows=169631 loops=1) │ │ Filter: ((a % 10) = 0) │ │ Rows Removed by Filter: 1526399 │ │ Planning time: 0.167 ms │ │ Execution time: 144.519 ms │ └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘ (8 rows) Time: 145.374 ms postgres=# set max_parallel_degree to 1; SET Time: 0.706 ms postgres=# EXPLAIN ANALYZE select count(*) from xxx where a % 10 = 0; ┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐ │ QUERY PLAN │ ╞════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╡ │ Aggregate (cost=14462.50..14462.51 rows=1 width=0) (actual time=163.355..163.355 rows=1 loops=1) │ │ -> Gather (cost=1000.00..14450.00 rows=5000 width=0) (actual time=0.485..152.827 rows=100000 loops=1) │ │ Number of Workers: 1 │ │ -> Parallel Seq Scan on xxx (cost=0.00..12950.00 rows=5000 width=0) (actual time=0.043..309.740 rows=145364 loops=1) │ │ Filter: ((a % 10) = 0) │ │ Rows Removed by Filter: 1308394 │ │ Planning time: 0.129 ms │ │ Execution time: 165.102 ms │ └────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘ (8 rows) Rows removed by filter: 1308394 X 1526399. Is it expected?
