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标签归档:_optimizer_batch_table_access_by_rowid
Oracle 12C TABLE ACCESS BY INDEX ROWID BATCHED
从Oracle 12C开始执行计划中可能会出现TABLE ACCESS BY INDEX ROWID BATCHED,官方的解释:TABLE ACCESS BY INDEX ROWID BATCHED:means that the database retrieves a few rowids from the index, and then attempts to access rows in block order to improve the clustering and reduce the number of times that the database must access a block.主要意思:对于一个块中多个rowid,通过批量减少访问快的次数.而作为12.1的新特性,数据库是通过_optimizer_batch_table_access_by_rowid来控制的
数据库版本12.1
SQL> select * from v$version; BANNER CON_ID -------------------------------------------------------------------------------- ---------- Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production 0 PL/SQL Release 12.1.0.2.0 - Production 0 CORE 12.1.0.2.0 Production 0 TNS for IBM/AIX RISC System/6000: Version 12.1.0.2.0 - Production 0 NLSRTL Version 12.1.0.2.0 - Production 0
TABLE ACCESS BY INDEX ROWID BATCHED执行计划
SQL> set autot traceonly exp stat; SQL> var b1 number; SQL> set lines 150 SQL> set pages 10000 SQL> exec :b1:=18868701138; PL/SQL procedure successfully completed. SQL> SELECT BRAND_ID FROM T_USERTYPE_FULLNO WHERE BILL_ID= LTRIM(:B1 ,'0') AND ROWNUM < 2; Execution Plan ---------------------------------------------------------- Plan hash value: 942613467 ----------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 15 | 2 (0)| 00:00:01 | |* 1 | COUNT STOPKEY | | | | | | | 2 | TABLE ACCESS BY INDEX ROWID BATCHED| XIFENFEI | 1 | 15 | 2 (0)| 00:00:01 | |* 3 | INDEX RANGE SCAN | IND_XIFENFEI | 1 | | 2 (0)| 00:00:01 | ----------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(ROWNUM<2) 3 - access("BILL_ID"=LTRIM(:B1,'0')) Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 5 consistent gets 0 physical reads 0 redo size 559 bytes sent via SQL*Net to client 552 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed
_optimizer_batch_table_access_by_rowid参数为true
SQL> col name for a32 SQL> col value for a24 col description for a70 set linesize 150 select a.ksppinm name,b.ksppstvl value,a.ksppdesc description SQL> SQL> SQL> 2 from x$ksppi a,x$ksppcv b 3 where a.inst_id = USERENV ('Instance') 4 and b.inst_id = USERENV ('Instance') 5 and a.indx = b.indx 6 and upper(a.ksppinm) LIKE upper('%¶m%') 7 order by name 8 / Enter value for param: _optimizer_batch_table_access_by_rowid old 6: and upper(a.ksppinm) LIKE upper('%¶m%') new 6: and upper(a.ksppinm) LIKE upper('%_optimizer_batch_table_access_by_rowid%') NAME VALUE DESCRIPTION ------------------------------------- ------------------------ ---------------------------------------------- _optimizer_batch_table_access_by_rowid TRUE enable table access by ROWID IO batching
设置_optimizer_batch_table_access_by_rowid为false,执行计划由TABLE ACCESS BY INDEX ROWID BATCHED变为TABLE ACCESS BY INDEX ROWID
SQL> set autot traceonly exp stat; SQL> var b1 number; SQL> set lines 150 SQL> set pages 10000 SQL> exec :b1:=18868701138; PL/SQL procedure successfully completed. SQL> alter session set "_optimizer_batch_table_access_by_rowid"=false; Session altered. SQL> SELECT BRAND_ID FROM XIFENFEI WHERE BILL_ID= LTRIM(:B1 ,'0') AND ROWNUM < 2; Execution Plan ---------------------------------------------------------- Plan hash value: 2797551150 --------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 15 | 2 (0)| 00:00:01 | |* 1 | COUNT STOPKEY | | | | | | | 2 | TABLE ACCESS BY INDEX ROWID| XIFENFEI | 1 | 15 | 2 (0)| 00:00:01 | |* 3 | INDEX RANGE SCAN | IND_XIFENFEI | 1 | | 2 (0)| 00:00:01 | --------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(ROWNUM<2) 3 - access("BILL_ID"=LTRIM(:B1,'0')) Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 5 consistent gets 0 physical reads 0 redo size 559 bytes sent via SQL*Net to client 552 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed
optimizer_features_enable修改为11.2之后,_optimizer_batch_table_access_by_rowid会联锁变为fasle
SQL> alter session set optimizer_features_enable = '11.2.0.3'; Session altered. SQL> col name for a52 col value for a24 col description for a50 set linesize 150 select a.ksppinm name,b.ksppstvl value,a.ksppdesc description from x$ksppi a,x$ksppcv b where a.inst_idSQL> SQL> SQL> SQL> 2 3 = USERENV ('Instance') and b.inst_id = USERENV ('Instance') and a.indx = b.indx and upper(a.ksppinm) LIKE upper('%¶m%') order by name 4 5 6 7 8 / Enter value for param: _optimizer_batch_table_access_by old 6: and upper(a.ksppinm) LIKE upper('%¶m%') new 6: and upper(a.ksppinm) LIKE upper('%_optimizer_batch_table_access_by%') NAME VALUE DESCRIPTION ------------------------------------------ -------------- ----------------------------------------- _optimizer_batch_table_access_by_rowid FALSE enable table access by ROWID IO batching
这里可以看出来,在调整optimizer_features_enable参数后,会直接影响某些数据库相关的优化器参数,例如:_optimizer_batch_table_access_by_rowid