Oracle TABLE ACCESS BY INDEX ROWID 说明

一. 测试环境

SQL> select * from v$version where rownum=1; BANNER--------------------------------------------------------------------------------Oracle Database 11g Enterprise Edition Release11.2.0.3.0 - 64bit Production SQL> create table dave as selectobject_id,object_name,object_type,created,timestamp,status from all_objects;表已创建。 SQL> create table dave2 as select * from dave;表已创建。 --收集统计信息，这里没有收集直方图：SQL> exec dbms_stats.gather_table_stats（ownname=>"SYS",tabname =>"DAVE",estimate_percent => 10 ,method_opt =>"FORCOLUMNS size 1",degree=>10,cascade => true）; PL/SQL 过程已成功完成。 SQL> exec dbms_stats.gather_table_stats（ownname=>"SYS",tabname =>"DAVE2",estimate_percent => 10 ,method_opt =>"FORCOLUMNS size 1",degree=>10,cascade => true）; PL/SQL 过程已成功完成。 --避免其他影响，先刷新buffer cache：SQL> alter system flush buffer_cache; 系统已更改。 --查看全表扫描时的执行计划：SQL> set autot traceonly SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id; 已选择72762行。执行计划----------------------------------------------------------Plan hash value: 3613449503 ------------------------------------------------------------------------------------| Id |Operation | Name | Rows | Bytes |TempSpc| Cost （%CPU）| Time |------------------------------------------------------------------------------------| 0 |SELECT STATEMENT | | 72520 | 3824K| | 695 （1）| 00:00:09 ||* 1 | HASH JOIN | | 72520 | 3824K| 2536K| 695 （1）| 00:00:09 || 2 | TABLE ACCESS FULL| DAVE2 | 71990 | 1687K| | 213 （1）| 00:00:03 || 3 | TABLE ACCESS FULL| DAVE | 72520 | 2124K| | 213 （1）| 00:00:03 |------------------------------------------------------------------------------------ Predicate Information （identified by operation id）:--------------------------------------------------- 1 -access（"D1"."OBJECT_ID"="D2"."OBJECT_ID"）统计信息---------------------------------------------------------- 0 recursive calls 0 db block gets 6353 consistent gets 1558 physical reads 0 redo size 3388939 bytes sent via SQL*Net toclient 53874 bytes received via SQL*Netfrom client 4852 SQL*Net roundtrips to/fromclient 0 sorts （memory） 0 sorts （disk） 72762 rows processed--这里产生了1558的物理读SQL> --在object_id上创建索引： SQL> create index idx_dave_object_idon dave（object_id）;索引已创建。SQL> create index idx_dave_object_id2 ondave2（object_id）;索引已创建。 --在次查看执行计划： SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id; 已选择72762行。执行计划----------------------------------------------------------Plan hash value: 3613449503 ------------------------------------------------------------------------------------| Id |Operation | Name | Rows | Bytes |TempSpc| Cost （%CPU）| Time |------------------------------------------------------------------------------------| 0 |SELECT STATEMENT | | 72520 | 3824K| | 695 （1）| 00:00:09 ||* 1 | HASH JOIN | | 72520 | 3824K| 2536K| 695 （1）| 00:00:09 || 2 | TABLE ACCESS FULL| DAVE2 | 71990 | 1687K| | 213 （1）| 00:00:03 || 3 | TABLE ACCESS FULL| DAVE | 72520 | 2124K| | 213 （1）| 00:00:03 |------------------------------------------------------------------------------------ Predicate Information （identified by operation id）:--------------------------------------------------- 1 -access（"D1"."OBJECT_ID"="D2"."OBJECT_ID"）统计信息---------------------------------------------------------- 1 recursive calls 0 db block gets 6353 consistent gets 0 physical reads 0 redo size 3388939 bytes sent via SQL*Net toclient 53874 bytes received via SQL*Netfrom client 4852 SQL*Net roundtrips to/fromclient 0 sorts （memory） 0 sorts （disk） 72762 rows processed 这里的物理读为0. 但是还是走的是全表扫描。 --刷新一下buffer，增加索引条件：SQL> alter system flush buffer_cache; 系统已更改。 SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id and d1.object_id <100; 已选择98行。执行计划----------------------------------------------------------Plan hash value: 504164237 ----------------------------------------------------------------------------------------------------| Id |Operation | Name | Rows | Bytes | Cost （%CPU）| Time |----------------------------------------------------------------------------------------------------| 0 |SELECT STATEMENT | | 3600 | 189K| 23 （5）| 00:00:01 ||* 1 | HASH JOIN | | 3600 | 189K| 23 （5）| 00:00:01 || 2 | TABLE ACCESS BY INDEX ROWID| DAVE2 | 3600 | 86400 | 11 （0）| 00:00:01 ||* 3 | INDEX RANGE SCAN | IDX_DAVE_OBJECT_ID2 | 648 | | 3 （0）| 00:00:01 || 4 | TABLE ACCESS BY INDEX ROWID| DAVE | 3626 | 106K| 11 （0）| 00:00:01 ||* 5 | INDEX RANGE SCAN | IDX_DAVE_OBJECT_ID | 653| | 3 （0）| 00:00:01 |---------------------------------------------------------------------------------------------------- Predicate Information （identified by operation id）:--------------------------------------------------- 1 -access（"D1"."OBJECT_ID"="D2"."OBJECT_ID"） 3 -access（"D2"."OBJECT_ID"<100） 5 -access（"D1"."OBJECT_ID"<100）统计信息---------------------------------------------------------- 1 recursive calls 0 db block gets 20 consistent gets 6 physical reads 0 redo size 3317 bytes sent via SQL*Net toclient 590 bytes received via SQL*Netfrom client 8 SQL*Net roundtrips to/fromclient 0 sorts （memory） 0 sorts （disk） 98 rows processedSQL> 走索引之后，物理读从1558降到6.

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