二、执行计划 2.1 Parallel Seq Scan 只有顺序扫描可以被修改为并行查询。因此,一个表扫描进入并行查询,通常使用的是Parallel Seq Scan(并行顺序扫描)。 关系表的块被分配给合作进程的每一个进程。块被一次分发出去,所以访问关系表依然是顺序的。每一个进程在请求一个新页之前,必须访问被分配页的每一个元组 2.2 Has
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...
[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...
Workers Planned:4Workers Launched:4->Partial Aggregate (cost=29199.62..29199.63rows=1width=8) (actual time=170.658..170.658rows=1loops=5)->ParallelIndexOnlyScan using index_test_biglontest_bigl (cost=0.56..28564.97rows=253860width=0) (actual time=0.114..142.576rows=200000loops=5)IndexCond: (...
{PLANNEDSTMT :commandType 1 :queryId 0 :hasReturning false :hasModifyingCTE false :canSetTag true :transientPlan false :dependsOnRole false :parallelModeNeeded false :jitFlags 0 :planTree {SEQSCAN :startup_cost 0.00 :total_cost 1.06 :plan_rows 6 :plan_width 10 :parallel_aware false :paral...
create table sort_random(id int, info text, tm timestamp default now()); insert into sort_random(id, info) select 10000000*random(), random_string(64) from generate_series(1,1000000); set trace_sort=on; set max_parallel_workers_per_gather = 0; --测试非并行的情况 explain (analyze,ver...
-> Parallel Seq Scan on t1 Filter: (c1 = (InitPlan 1).col1 Eliminated IS NOT NULL query restrictions on NOT NULL columns CREATE TABLE pred_tab (a int NOT NULL, b int, c int NOT NULL);EXPLAIN (COSTS OFF) SELECT * FROM pred_tab t WHERE t.a IS NOT NULL; QUERY PLAN --- ...
(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...
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...
EN谈到MySQL性能优化，查询优化作为优化的源头，它也是最能体现一个系统是否更快。 本章以及接下来的几...