Finalize Aggregate -> Gather Workers Planned: 2 -> Partial Aggregate -> Parallel Hash Join Hash Cond: (lineitem.l_orderkey = orders.o_orderkey) -> Parallel Seq Scan on lineitem -> Parallel Hash -> Parallel Seq Scan on orders Filter: (o_totalprice > 5.00) 过程是: 1)每个worker并行扫...
postgres=# select name,setting from pg_settings where name like'%hash%'or name like'hash%'or name like'%hash';name|setting---+---enable_hashagg|on enable_hashjoin|on enable_parallel_hash|on hash_mem_multiplier|1 这里有是哪个部分,hash 聚合,hash join ,hash 并行 三个部分都可以进行开关,...
会话级设置enable_parallel_hash参数为off表示关闭并行哈希连接,测试性能有何变化,如下。 francs=>setenable_parallel_hash = off;SETfrancs=> EXPLAIN ANALYZE SELECT t_small.nameFROMt_big JOIN t_small ON (t_big.id = t_small.id)ANDt_small.id < 100; QUERY PLAN --- Gather (cost=151869.66..69048...
2、PostgreSQL 11 已经支持了parallel hash join,可以解决大数据量求交、差的性能问题。 《PostgreSQL 11 preview - parallel hash join(并行哈希JOIN) 性能极大提升》 原生求交、差性能 测试结构和数据 postgres=#createtabletbl(idint, c1int);CREATETABLEpostgres=#insertintotblselectgenerate_series(1,10000000), ...
postgres=# select name,setting from pg_settings where name like '%hash%' or name like 'hash%' or name like '%hash'; name | setting ---+--- enable_hashagg | on enable_hashjoin | on enable_parallel_hash | on hash_mem_multiplier | 1 1. 2. 3....
HashJoinTuplehj_CurTuple;//当前元组 TupleTableSlot*hj_OuterTupleSlot;//outer relation slot TupleTableSlot*hj_HashTupleSlot;//Hash tuple slot TupleTableSlot*hj_NullOuterTupleSlot;//用于外连接的outer虚拟slot TupleTableSlot*hj_NullInnerTupleSlot;//用于外连接的inner虚拟slot ...
-> Hash -> Seq Scan on orders Filter: (o_totalprice > 5.00) Using the development master branch, it can now also produce a query plan like this: Finalize Aggregate -> Gather Workers Planned: 2 -> Partial Aggregate -> Parallel Hash Join ...
-> Parallel Hash Join (cost=13743.46..56864.89 rows=416667 width=461) Hash Cond: (a.bid = b.bid) -> Parallel Seq Scan on pgbench_accounts a (cost=0.00..20560.67 rows=416667 width=97) -> Parallel Hash (cost=3092.65..3092.65 rows=176465 width=364) ...
-> Hash Join (cost=308310.48..570009.22 rows=9999977 width=0) (actual time=8483.284..16703.813 rows=3333333 loops=3) Hash Cond: (t1.id = t2.id) -> Parallel Seq Scan on t1 (cost=0.00..85914.87 rows=4166687 width=4) (actual time=0.575..741.057 rows=3333333 loops=3) -> Hash (cost...
max_parallel_workers:其次,查询执行器从max_parallel_workers池中可以获取workers的最大数。 max_worker_processes:这个是workers的顶级限制后台进程的总数(此参数谨慎修改,根据系统实际的cpu个数(核数)来设置)。 max_parallel_workers_per_gather:理解为每个用户去银行取钱金额。