如何监控Oracle索引的使用完全解析

2/9/2008来源:Oracle教程人气:6831

研究发现,Oracle数据库使用的索引不会超过总数的25%,或者不易他们期望被使用的方式使用。通过 监控数据库索引的使用,释放那些未被使用的索引,从而节省维护索引的开销,优化性能。 1、在oracle8i中,确定使用了那个索引的方法意味着要对存在语共享SQL区中的所有语句运行EXPLIAN PALN,然后查询计划表中的OperaTION列,从而识别有OBJECT_OWNER和OBJECT_NAME列所确定的那个索引上的索引访问。 下面是一个监控索引使用的脚本,这个脚本仅仅是一个样品,在某种条件下成立: 条件: 运行这个脚本的用户拥有权限解释所有的v$sqlarea中的sql,除了不是被SYS装载的。plan_table.remarks能够别用来决定与特权习惯的错误。对所有的共享池中SQL,参数OPTIMIZER_GOAL是一个常量,无视v$sqlarea.optimizer_mode。两次快照之间,统计资料被再次分析过。没有语句别截断。所有的对象都是局部的。所有被引用的表或视图或者是被运行脚本的用户所拥有,或者完全有资格的名字或同义词被使用。自从上次快照以来,没有不受"欢迎"的语句被冲洗出共享池(例如,在装载)。对于所有的语句,v$sqlarea.version_count = 1 (children)。 脚本:
  Code: [Copy to clipboard]   set echo off   Rem Drop and recreate PLAN_TABLE for EXPLAIN PLAN   drop table plan_table;   create table PLAN_TABLE (   statement_id     varchar2(30),   timestamp      date,   remarks       varchar2(80),   operation      varchar2(30),   options        varchar2(255),   object_node     varchar2(128),   object_owner     varchar2(30),   object_name     varchar2(30),   object_instance    numeric,   object_type     varchar2(30),   optimizer      varchar2(255),   search_columns     number,   id            numeric,   parent_id        numeric,   position        numeric,   cost        numeric,   cardinality        numeric,   bytes        numeric,   other_tag      varchar2(255),   partition_start   varchar2(255),   partition_stop   varchar2(255),   partition_id    numeric,   other        long,   distribution    varchar2(30),   cpu_cost        numeric,   io_cost        numeric,   temp_space        numeric,   access_PRedicates  varchar2(4000),   filter_predicates  varchar2(4000));      Rem Drop and recreate SQLTEMP for taking a snapshot of the SQLAREA   drop table sqltemp;   create table sqltemp  (   ADDR         VARCHAR2 (16),   SQL_TEXT         VARCHAR2 (2000),   DISK_READS        NUMBER,   EXECUTIONS        NUMBER,   PARSE_CALLS     NUMBER);      set echo on   Rem Create procedure to populate the plan_table by executing   Rem explain plan...for 'sqltext' dynamically   create or replace procedure do_explain (   addr IN varchar2, sqltext IN varchar2)   as dummy varchar2 (1100);   mycursor integer;   ret integer;   my_sqlerrm varchar2 (85);   begin dummy:='EXPLAIN PLAN SET STATEMENT_ID=' ;   dummy:=dummy''''addr'''' ' FOR 'sqltext;   mycursor := dbms_sql.open_cursor;   dbms_sql.parse(mycursor,dummy,dbms_sql.v7);   ret := dbms_sql.execute(mycursor);   dbms_sql.close_cursor(mycursor);   commit;   exception -- Insert errors into PLAN_TABLE...   when others then my_sqlerrm := substr(sqlerrm,1,80);   insert into plan_table(statement_id,
remarks) values (addr,my_sqlerrm);   -- close cursor if exception raised on EXPLAIN PLAN   dbms_sql.close_cursor(mycursor);   end;   /      Rem Start EXPLAINing all S/I/U/D statements in the shared pool   declare   -- exclude statements with v$sqlarea.parsing_schema_id = 0 (SYS)   cursor c1 is select address, sql_text, DISK_READS, EXECUTIONS, PARSE_CALLS   from v$sqlarea   where command_type in (2,3,6,7)   and parsing_schema_id != 0;   cursor c2 is select addr, sql_text from sqltemp;   addr2     varchar(16);   sqltext    v$sqlarea.sql_text%type;   dreads     v$sqlarea.disk_reads%type;   execs     v$sqlarea.executions%type;   pcalls     v$sqlarea.parse_calls%type;   begin open c1;   fetch c1 into addr2,sqltext, dreads,execs,pcalls;   while (c1%found) loop   insert into sqltemp values (addr2,sqltext,dreads,execs,pcalls);   commit;   fetch c1 into addr2, sqltext,dreads,execs,pcalls;   end  loop;   close c1;   open c2;   fetch c2 into addr2, sqltext;   while (c2%found) loop   do_explain(addr2,sqltext);   fetch c2 into addr2, sqltext;   end  loop;   close c2;   end;   /      Rem Generate a report of index usage based on the number of times   Rem a SQL statement using that index was executed   select p.owner, p.name, sum(s.executions) totexec   from sqltemp s,   (select distinct statement_id stid, object_owner owner, object_name name   from plan_table where operation = 'INDEX') p   where s.addr = p.stid   group by p.owner, p.name   order by 2 desc;      Rem Perform cleanup on exit (optional)   delete from plan_table   where statement_id in   ( select addr from sqltemp );   drop table sqltemp;
关于这个脚本,有几个重要的地方需要注重,即它可能一起明显的开销,因此,应该在仔细地进行 权衡后才把它应用到繁忙的生产应用系统中区。 2、oracle9i中如何确定索引的使用情况: 在oracle9i中,情况会简单得多,因为有一个新得字典视图V$SQL_PLAN存储了实际计划,这些计划用于执行共享SQL区中得语句。V$SQL_PLAN视图很类似与计划表,但V$SQL_PLAN使用ADDRESS和HASH_VALUE列 来识别语句, 而计划表使用用户提供得STATEMENT_ID来识别语句。下面的SQL显示了在一个oracle9i数据库中,由出现在共享SQL区中语句使用的所有索引。
   select object_owner, object_name, options, count(*)   from  v$sql_plan   where operation='INDEX'   and  object_owner!='SYS'   group by object_owner, object_name, operation, options   order by count(*) desc;
所有基于共享SQL区中的信心来识别索引使用情况的方法, 都可能会收集到不完整的信息。共享SQL区是一 个动态结构,除非能对它进行足够频繁的采样, 否则在有关索引使用的情况的信息被收集之前,SQL语句可 能就已经(因为老化)被移出缓存了。oracle9i提供了解决这个问题的方案,即它为alter index提供了一个monitoring usage子句。当启用monitoring usage 时,oralce记录简单的yes或no值,以指出在监控间隔 期间某个索引是否被使用。 为了演示这个新特性,你可以使用下面的例子:   (a) Create and populate a small test table   (b) Create Primary Key index on that table   (c) Query v$object_usage: the monitoring has not started yet   (d) Start monitoring of the index usage   (e) Query v$object_usage to see the monitoring in progress
  (f) Issue the SELECT statement which uses the index   (g) Query v$object_usage again to see that the index has been used   (h) Stop monitoring of the index usage   (i) Query v$object_usage to see that the monitoring sDetailed steps
     (a) Create and populate a small test table   create table prodUCts  (   prod_id number(3),   prod_name_code varchar2(5));      insert into products values(1,'aaaaa');   insert into products values(2,'bbbbb');   insert into products values(3,'ccccc');   insert into products values(4,'ddddd');   commit;      (b) Create Primary Key index on that table   alter table products  add (constraint products_pk primary key (prod_id));      (c) Query v$object_usage: the monitoring has not started yet   column