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如何监控Oracle索引的使用完全解析

 2007-05-09 12:14:15 来源:WEB开发网   
核心提示:研究发现,oracle数据库使用的索引不会超过总数的25%,如何监控Oracle索引的使用完全解析,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,在装载),对于所有的语句,释放那些未被使用的索引,从而节省维护索引的开销

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;

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