潜水艇官方网站代理,鞍山SEO网站推广公司,金蝶软件有限公司,沈阳百度seo排名优化软件READ和WRITE并行性并不总是捆绑在一起.alter session disable parallel dml;仅禁用语句的WRITE部分的并行性. READ部分可能仍然并行运行.由于这是MERGE操作,因此并行提示请求读写并行写入.此外,并行提示覆盖alter session disable parallel query;,即使它不覆盖alter session d…READ和WRITE并行性并不总是捆绑在一起.alter session disable parallel dml;仅禁用语句的WRITE部分的并行性. READ部分可能仍然并行运行.由于这是MERGE操作,因此并行提示请求读写并行写入.此外,并行提示覆盖alter session disable parallel query;,即使它不覆盖alter session disable parallel dml;.并行服务器的数量将是所请求的并行度的两倍,以支持producer and consumer operations,以便充分利用互操作并行性.对结果进行分组或排序的查询将使用两倍的线程.在某些情况下,即使没有显式的GROUP BY或ORDER BY,也可能会发生这种情况,因为某些操作可能隐式需要排序.样本表create table bigtable_1(key number,value1 number);create table bigtable_2(key number,value1 number);并行读写注意操作#1的PX COORDINATOR.当该步骤高于MERGE时,意味着写入是并行完成的.rollback;alter session enable parallel dml;alter session enable parallel query;explain plan for merge /* parallel(a,8) */ into bigtable_1 a using bigtable_2 bon (a.key b.key) when matched then update set a.value1 b.value1;select * from table(dbms_xplan.display(format basic));Plan hash value: 827272579------------------------------------------------------| Id | Operation | Name |------------------------------------------------------| 0 | MERGE STATEMENT | || 1 | PX COORDINATOR | | | 2 | PX SEND QC (RANDOM) | :TQ10003 || 3 | MERGE | BIGTABLE_1 || 4 | PX RECEIVE | | | 5 | PX SEND HYBRID (ROWID PKEY)| :TQ10002 || 6 | VIEW | || 7 | HASH JOIN BUFFERED | || 8 | BUFFER SORT | || 9 | PX RECEIVE | || 10 | PX SEND HASH | :TQ10000 || 11 | TABLE ACCESS FULL | BIGTABLE_2 || 12 | PX RECEIVE | || 13 | PX SEND HASH | :TQ10001 || 14 | PX BLOCK ITERATOR | || 15 | TABLE ACCESS FULL | BIGTABLE_1 |------------------------------------------------------串行写入,并行读取现在,MERGE操作首先是PX …操作.写操作是串行完成的,但读操作仍然是并行完成的.rollback;alter session disable parallel dml;alter session disable parallel query;explain plan for merge /* parallel(a,8) */ into bigtable_1 a using bigtable_2 bon (a.key b.key) when matched then update set a.value1 b.value1;select * from table(dbms_xplan.display(format basic));Plan hash value: 1648019208------------------------------------------------| Id | Operation | Name |------------------------------------------------| 0 | MERGE STATEMENT | || 1 | MERGE | BIGTABLE_1 | | 2 | PX COORDINATOR | | | 3 | PX SEND QC (RANDOM) | :TQ10002 || 4 | VIEW | || 5 | HASH JOIN BUFFERED | || 6 | BUFFER SORT | || 7 | PX RECEIVE | || 8 | PX SEND HASH | :TQ10000 || 9 | TABLE ACCESS FULL| BIGTABLE_2 || 10 | PX RECEIVE | || 11 | PX SEND HASH | :TQ10001 || 12 | PX BLOCK ITERATOR | || 13 | TABLE ACCESS FULL| BIGTABLE_1 |------------------------------------------------
