x=>log(x/min_parallel_table_scan_size)/log(3)+1worker 表比min_parallel_(index|table)_scan_size值每大3倍,PG增加一个worker进程。Workers进程个数不是基于成本的。循环依赖使得复杂的实现变得困难。相反,规划者使用简单的规则。 可以通过ALTER TABLE … SET (parallel_workers = N)来对某个表指定并行进...
Finalize Aggregate (cost=10000.00..10001.00 rows=1 width=8) -> Gather (cost=1000.00..10000.00 rows=4 width=8) Workers Planned: 2 -> Partial Aggregate (cost=0.00..2500.00 rows=2 width=8) -> Parallel Seq Scan on large_table (cost=0.00..2000.00 rows=500000 width=4) (5 rows...
-> Parallel Seq Scan on public.t_bit2 (cost=0.00..25029413.08rows=500000width=32) (actualtime=30941.191..30941.191rows=0loops=33) Output: id Filter: (bitand(t_bit2.id, B'1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010...
-> Parallel Seq Scan on test_jsonb (cost=0.00..52175.85 rows=838 width=134) (actual time=465.234..480.57 3 rows=3333 loops=3) Filter: (j_jsonb @> '{"kxhbsl": "索尼是大法官"}'::jsonb) Rows Removed by Filter: 666667 Planning time: 0.318 ms Execution time: 506.204 ms (8 rows)...
全表扫描在pgsql中叫做顺序扫描(seq scan),全表扫描就是把表的的所有的数据从头到尾读取一遍,然后从数据块中找到符合条件的数据块。 索引扫描 索引是为了加快数据查询的速度索引而增加的(Index Scan)。索引扫描也就是我们的查询条件使用到了我们创建的索引,当然什么是索引,自行查阅资料吧。
-> Parallel Seq Scan on test (cost=0.00..85914.57rows=4166657width=0) (actualtime=0.161..251.158rows=3333333loops=3) Planning Time: 0.057 ms JIT: Functions: 9 Options: Inliningtrue, Optimizationtrue, Expressionstrue, DeformingtrueTiming: Generation 1.096 ms, Inlining 109.551 ms, Optimization 22.20...
"Node Type": "Seq Scan", + "Parallel Aware": false, + "Relation Name": "playground",+ "Alias": "playground", + "Startup Cost": 0.00, + "Total Cost": 12.80, + "Plan Rows": 280, + "Plan Width": 262 + } + } + ]
WorkTable Scan,用于扫描Recursive Union 的中间数据 Foreign Scan,用于外键扫描 Custom Scan,用于用户自定义的扫描 其中,我们将重点介绍最常用的几个:Seq Scan、Index Scan、IndexOnly Scan、BitmapIndex Scan、BitmapHeap Scan。 Seq Scan Seq Scan 是全表顺序扫描,一般查询没有索引的表需要全表顺序扫描,例如下面的...
SharedTidBitmap Waiting to access a shared TID bitmap during a parallel bitmap index scan. SharedTupleStore Waiting to access a shared tuple store during parallel query. ShmemIndex Waiting to find or allocate space in shared memory. SInvalRead Waiting to retrieve messages f...
./sysbench_pg --test=lua/parallel_init_pg.lua \ --db-driver=pgsql \ --pgsql-host=xxx.xxx.xxx.xxx \ --pgsql-port=3432 \ --pgsql-user=digoal \ --pgsql-password=pwd \ --pgsql-db=postgres \ --oltp-tables-count=256 \ --oltp-table-size=1000000 \ --num-threads...