32.读书笔记收获不止Oracle之表链接的驱动顺序
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32.读书笔记收获不止Oracle之表链接的驱动顺序 1. 嵌套循环驱动顺序T1和T2表草考前面笔记。 SQL>Alter session set statistics_level=all; 1.1实验1SQL>select /*+leading(t1) use_nl(t2)*/ * from t1,t2 wheret1.id=t2.t1_id and t1.n=19; SQL> select * from table(dbms_xplan.display_cursor(null,null,'allstatslast')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID 2w8kmgu3tmxhq,child number 0 ------------------------------------- select /*+leading(t1) use_nl(t2)*/ * fromt1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 1967407726 -------------------------------------------------------------------------------- ----- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buff PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- ers | -------------------------------------------------------------------------------- ----- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 1 014 | | 1| NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 1 014 | PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- |* 2| TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 8 | |* 3| TABLE ACCESS FULL| T2 | 1 | 1 | 1 |00:00:00.01 | 1 006 | -------------------------------------------------------------------------------- ----- Predicate Information (identified byoperation id): PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- --------------------------------------------------- 2- filter("T1"."N"=19) 3- filter("T1"."ID"="T2"."T1_ID") 22 rows selected. 1.2实验2SQL>select /*+leading(t2) use_nl(t1)*/ * from t1,t2 wheret1.id=t2.t1_id and t1.n=19; SQL> select * fromtable(dbms_xplan.display_cursor(null,'allstats last')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID axb2hvwr253j8,child number 0 ------------------------------------- select /*+leading(t2) use_nl(t1)*/ * fromt1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 4016936828 -------------------------------------------------------------------------------- ----- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buff PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- ers | -------------------------------------------------------------------------------- ----- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.93 | 701K| | 1| NESTED LOOPS | | 1 | 1 | 1 |00:00:00.93 | 701K| PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- | 2| TABLE ACCESS FULL| T2 | 1 | 100K| 100K|00:00:00.01 | 1 006 | |* 3| TABLE ACCESS FULL| T1 |100K| 1 | 1 |00:00:00.89 | 700K| -------------------------------------------------------------------------------- ----- Predicate Information (identified byoperation id): PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- --------------------------------------------------- 3- filter(("T1"."ID"="T2"."T1_ID" AND"T1"."N"=19)) 21 rows selected. 采用不同的驱动表，使用的BUFFER是不一样的，t1为驱动表的时候是1014，t2为驱动表的话使用了701k大小。 T1作为驱动表访问的情况下，T2表只被访问了1次。而t2 表作为驱动表被访问的情况下，T1表被访问了10000次，因为T1结果返回1条记录，而T2结构返回10000条记录。 嵌套循环连接要注意驱动表的顺序。 2. 哈希连接的表驱动顺序2.1实验1SQL>select /*+leading(t1) use_hash(t2)*/ * from t1,'allstatslast')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID 0x20q3zf8pn79,child number 0 ------------------------------------- select /*+leading(t1) use_hash(t2)*/ * fromt1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 1838229974 -------------------------------------------------------------------------------- -------------------------------- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buff PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- ers |OMem | 1Mem | Used-Mem | -------------------------------------------------------------------------------- -------------------------------- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.05 | 1 013 | | | | |* 1| HASH JOIN | | 1 | 1 | 1 |00:00:00.05 | 1 013 | 960K| 960K|403K (0)| PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- |* 2| TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7 | | | | | 3| TABLE ACCESS FULL| T2 | 1 | 100K| 100K|00:00:00.01 | 1 006 | | | | -------------------------------------------------------------------------------- -------------------------------- Predicate Information (identified byoperation id): PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- --------------------------------------------------- 1- access("T1"."ID"="T2"."T1_ID") 2- filter("T1"."N"=19) 22 rows selected. 2.2实验2SQL>select /*+leading(t2) use_hash(t1)*/* from t1,t2 where t1.id=t2.t1_id and t1.n=19; SQL> select * fromtable(dbms_xplan.display_cursor(null,'allstats last')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID 1m1vnuurcxcm3,child number 0 ------------------------------------- select /*+leading(t2) use_hash(t1)*/ * fromt1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 2959412835 -------------------------------------------------------------------------------- -------------------------------- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buff PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- ers |OMem | 1Mem | Used-Mem | -------------------------------------------------------------------------------- -------------------------------- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.04 | 1 013 | | | | |* 1| HASH JOIN | | 1 | 1 | 1 |00:00:00.04 | 1 013 | 11M| 2469K| 12M (0)| PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- | 2| TABLE ACCESS FULL| T2 | 1 | 100K| 100K|00:00:00.01 | 1 005 | | | | |* 3| TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 8 | | | | -------------------------------------------------------------------------------- -------------------------------- Predicate Information (identified byoperation id): PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- --------------------------------------------------- 1- access("T1"."ID"="T2"."T1_ID") 3- filter("T1"."N"=19) 22 rows selected. 使用的BUFFER是一致的，Used-Mem 实验1是403k,实验2是12M。 在哈希连接中驱动表的顺序也是非常重要的。 3. 排序合拼连接的表驱动顺序3.1实验1SQL>select /*+leading(t1) use_merge(t2)*/ * from t1,'allstats last')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID afuusm6140307,child number 0 ------------------------------------- select /*+leading(t1) use_merge(t2)*/ *from t1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 412793182 -------------------------------------------------------------------------------- --------------------------------- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time| Buf PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- fers | OMem| 1Mem | Used-Mem | -------------------------------------------------------------------------------- --------------------------------- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.07 | 1012 | | | | | 1| MERGE JOIN | | 1 | 1 | 1 |00:00:00.07 | 1012 | | | | PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- | 2| SORT JOIN | | 1 | 1 | 1 |00:00:00.01 | 7| 2048 | 2048 | 2048 (0)| |* 3| TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7| | | | |* 4| SORT JOIN | | 1 | 100K| 1|00:00:00.07 | 1005 | 9762K| 1209K| 8677K (0)| | 5| TABLE ACCESS FULL| T2 | 1 | 100K| 100K|00:00:00.02 | 1005 | | | | PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- --------------------------------- Predicate Information (identified byoperation id): --------------------------------------------------- 3- filter("T1"."N"=19) 4- access("T1"."ID"="T2"."T1_ID") filter("T1"."ID"="T2"."T1_ID") PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- 25 rows selected. 3.2实验2SQL>select /*+leading(t2) use_merge(t1)*/ * from t1,'allstats last')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- SQL_ID dz2rnd44fg2jb,child number 0 ------------------------------------- select /*+leading(t2) use_merge(t1)*/ *from t1,t2 where t1.id=t2.t1_id and t1.n=19 Plan hash value: 1792967693 -------------------------------------------------------------------------------- --------------------------------- | Id| Operation | Name | Starts | E-Rows | A-Rows | A-Time| Buf PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- fers | OMem| 1Mem | Used-Mem | -------------------------------------------------------------------------------- --------------------------------- | 0| SELECT STATEMENT | | 1 | | 1 |00:00:00.06 | 1012 | | | | | 1| MERGE JOIN | | 1 | 1 | 1 |00:00:00.06 | 1012 | | | | PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- | 2| SORT JOIN | | 1 | 100K| 20|00:00:00.06 | 1005 | 9762K| 1209K| 8677K (0)| | 3| TABLE ACCESS FULL| T2 | 1 | 100K| 100K|00:00:00.01 | 1005 | | | | |* 4| SORT JOIN | | 20 | 1 | 1 |00:00:00.01 | 7| 2048 | 2048 | 2048 (0)| |* 5| TABLE ACCESS FULL| T1 | 1 | 1 | 1 |00:00:00.01 | 7| | | | PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- --------------------------------- Predicate Information (identified byoperation id): --------------------------------------------------- 4- access("T1"."ID"="T2"."T1_ID") filter("T1"."ID"="T2"."T1_ID") 5- filter("T1"."N"=19) PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- 25 rows selected. 排序合并连接实验1和实验2 的效率是一样的， 小结：嵌套循环连接和哈希连接有驱动顺序，驱动表的顺序不同将影响表连接的性能，而排序合并连接没有驱动的概念，无论哪张表在前都无妨。 （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |