标签：
今天帮助看了一个哥们的数据库，帮他抓了一下等待事件，刚好有一个sql在等待事件中，顺便看看
监控等待事件
select a.SID, a.EVENT, b.OSUSER, b.username, b.MACHINE, b.PROGRAM, b.MODULE, b.SQL_ID, b.sql_id from v$session_wait a, v$session b where a.sid = b.sid and a.sid in (select sid from v$session_wait where event not like ‘SQL%‘ and event not like ‘%message%‘ and event not like ‘Streams AQ%‘ and event not in (‘jobq slave wait‘, ‘class slave wait‘, ‘DIAG idle wait‘, ‘pmon timer‘, ‘ASM background timer‘, ‘smon timer‘)) select * from v$sql where sql_id=‘sql_id‘;
有问题的sql如下
SELECT count(*) AS rown FROM ( select t.KSGCXH,t.LSH,t.KSKM,t.KSXM,t.KSXH,t.XMKSXH,t.ZP, t.CS,to_char(t.ZPSJ,‘yyyy-mm-dd hh24:mi:ss‘) ZPSJ, to_char(t.XTZPSJ,‘yyyy-mm-dd hh24:mi:ss‘) XTZPSJ, t.CQBJ,t.JYW,t.FZJG, dbms_lob.getlength(zp) zplen from MON_ADMIN.DRV_MON_EXAM_PHOTO t where t.Fzjg=‘辽F‘ and zp is not null and dbms_lob.getlength(zp)<204800 and t.cqbj=‘1‘ and t.Xtzpsj>to_date(‘2015-09-17 10:38:22‘,‘yyyy-mm-dd hh24:mi:ss‘) and t.Xtzpsj<=to_date(‘2015-09-17 11:08:11‘,‘yyyy-mm-dd hh24:mi:ss‘)) pagetable
这个sql超级简单，就是简单的查询，连个多表连接都没有，运行4s，返回7行数据
那问题一看就是没有建立索引，并且全表扫描了
查看索引信息，发现现有的索引跟他鸟关系都没有
select * from dba_indexes where owner=‘MON_ADMIN‘ and table_name=‘DRV_MON_EXAM_PHOTO‘; select t.*,i.index_type from dba_ind_columns t,dba_indexes i where t.index_name = i.index_name and owner=‘MON_ADMIN‘ and t.table_name=‘DRV_MON_EXAM_PHOTO‘;
查看一下这个表的执行计划
SQL> select * from table(dbms_xplan.display); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Plan hash value: 2462891873 ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 101 | 29460 (1)| 00:05:54 | | 1 | SORT AGGREGATE | | 1 | 101 | | | |* 2 | TABLE ACCESS FULL| DRV_MON_EXAM_PHOTO | 1 | 101 | 29460 (1)| 00:05:54 | ----------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter("T"."XTZPSJ">TO_DATE(‘ 2015-09-17 10:38:22‘, ‘syyyy-mm-dd hh24:mi:ss‘) AND "T"."FZJG"=‘辽F‘ AND "DBMS_LOB"."GETLENGTH"("ZP")<204800 AND "T"."CQBJ"=‘1‘ AND "T"."XTZPSJ"<=TO_DATE(‘ 2015-09-17 11:08:11‘, ‘syyyy-mm-dd hh24:mi:ss‘)) 已选择17行。
果然走了全表扫描，查询这个表的总行数有5017932行，查询体积为896M
结果集返回7条数据，那么7/5017932约等于0，相当于全表扫描每一行数据才能找到这七条数据
我们知道全表扫描是多快读，读取1M的数据大概15ms，全读完大概13s，现在用时4s，看来还是很快的哦。哈哈哈
现在就是建立索引就可以解决问题
create index IDX_DRV_MON_EXAM_PHOTO3 on MON_ADMIN.DRV_MON_EXAM_PHOTO(Fzjg,cqbj,Xtzpsj,KSGCXH,LSH,KSKM,KSXM,KSXH,XMKSXH,CS,ZPSJ,JYW);
创建完索引之后再看执行计划
SQL> select * from table(dbms_xplan.display); PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Plan hash value: 2782271437 -------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 101 | 4 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 101 | | | |* 2 | TABLE ACCESS BY INDEX ROWID| DRV_MON_EXAM_PHOTO | 1 | 101 | 4 (0)| 00:00:01 | |* 3 | INDEX RANGE SCAN | IDX_DRV_MON_EXAM_PHOTO3 | 1 | | 3 (0)| 00:00:01 | -------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter("DBMS_LOB"."GETLENGTH"("ZP")<204800) 3 - access("T"."FZJG"=‘辽F‘ AND "T"."CQBJ"=‘1‘ AND "T"."XTZPSJ">TO_DATE(‘ 2015-09-17 10:38:22‘, ‘syyyy-mm-dd hh24:mi:ss‘) AND "T"."XTZPSJ"<=TO_DATE(‘ 2015-09-17 11:08:11‘, ‘syyyy-mm-dd hh24:mi:ss‘)) 已选择18行。
执行计划变成了索引范围扫描
运行时间有4s编程现在的0.03s，绝对秒杀
对于这种单表运行速度慢，主要看有没有建立索引。
标签：
原文地址：http://www.cnblogs.com/SUN-PH/p/4815969.html
