[1]. PostgreSQL 并行表扫描分析 Gather Parallel Seq Scan https://www.mytecdb.com/blogDetail.php?id=22 [2]. Parallel Hash for PostgreSQL https://www.enterprisedb.com/blog/parallel-hash-postgresql [3]. Parallelism in PostgreSQL 11 https://2019.pgdu.org/static/presentations/Thomas-parallelism-po...
Hash Cond: (a.serial_key = serial.serial_key) -> Parallel Seq Scan on activity a (cost=904.75..6513564.40 rows=71339546width=16) Filter: (NOT (hashed SubPlan 1)) SubPlan 1 -> Seq Scan on serial_iswip (cost=0.00..860.00 rows=17900 width=8) -> Parallel Hash (cost=828614.46..828614....
Gather (cost=1000.00..58878.99 rows=1 width=18) (actual time=0.920..579.144 rows=1 loops=1) Workers Planned: 2# 计划的workerWorkers Launched: 2# 实际执行的worker-> Parallel Seq Scan on testtable1 (cost=0.00..57878.89 rows=1 width=18) (actual time=375.012..566.492 rows=0 loops=3) Fil...
Postgres选择慢得多的Seq扫描而不是索引扫描 我检查了每个数据库的default_statistics_target(都是100)和random_page_cost(都是4)。 我认识到将enable_seqscan设置为OFF不是一个永久的解决方案,但是它确实强制postgres 11实例返回与postgres 9.5实例相同的查询计划。 我通过设置max_parallel_workers_per_gather = 0进...
ParallelSeq Scanon test_bigl--这个代表这这个进行了并行的循序扫描 Planning time:0.098ms-->这个是sql生成执行计划的时间 Execution time:2961.299ms-->这个是sql实际执行时间 其实到这里你就发现我这个一直开启了并行度,现在我们关闭它 kingledb=>setmax_parallel_workers_per_gather=0;SET0代表关闭 ...
(actual time=6019.362..6019.364rows=1loops=3)Buffers:shared hit=12855read=326149dirtied=580I/OTimings:shared/local read=15953.695->Parallel Seq Scan onpages(cost=0.00..362738.57rows=2373457width=71)(actual time=2.644..5770.110rows=1878348loops=3)Buffers:shared hit=12855read=326149dirtied=580I/O...
(actual time=0.051..12.345 rows=8500 loops=1) Output: order_id, customer_id, order_date, order_amount Workers Planned: 2 Workers Launched: 2 Buffers: shared hit=50 read=1000 -> Parallel Seq Scan on public.orders (cost=0.00..9000.00 rows=4167 width=123) (actual time=0.028..10.045 rows...
5. 节点之间的关系:在示例中,Gather节点是Parallel Seq Scan节点的父节点,表示Gather节点在执行之前会等待Parallel Seq Scan节点的完成。 三、Explain结果的解析步骤 对于复杂的查询语句,Explain命令返回的结果可能会比较长。为了更好地理解查询计划,可以按照以下步骤进行解析: 1. 查看查询计划类型:首先,了解查询计划的...
-> Parallel Seq Scanonbar (cost=0.00..88695.29rows=2500029width=24) (5rows)Setwork_mem =256MB The initial query’s sort node has an estimated cost of 514431.86. A cost is an arbitrary unit of computation. For the above query, we have a work_mem of only 2MB. For testing ...
min_parallel_table_scan_size,8MB,Sets the minimum amount of table data for a parallel scan. min_wal_size,80MB,Sets the minimum size to shrink the WAL to. old_snapshot_threshold,-1,Time before a snapshot is too old to read pages changed after the snapshot was taken. ...