Re: Parallel Seq Scan - Mailing list pgsql-hackers
| From | Pavel Stehule |
|---|---|
| Subject | Re: Parallel Seq Scan |
| Date | |
| Msg-id | CAFj8pRBF-i=qDg9b5nZrXYfChzBEZWmthxYPhidQvwoMOjHtzg@mail.gmail.com Whole thread Raw |
| In response to | Re: Parallel Seq Scan (Pavel Stehule <pavel.stehule@gmail.com>) |
| Responses |
Re: Parallel Seq Scan
Re: Parallel Seq Scan Re: Parallel Seq Scan |
| List | pgsql-hackers |
Hi
I have a first querypostgres=# 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)
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