Oracle学习笔记（四）

Oracle中的体系结构：

oracle体系结构中的进程：

共享池相关的优化：

drop table t purge;
create table t as select  * from dba_objects;

set linesize 1000
set autotrace on
set timing on 

--第1次执行

select count(*) from t;

--第2次执行
--该命令只是为了先不考虑解析的优化,单纯考虑第2次执行物理读减少带来的优化效应
alter system flush shared_pool;
select count(*) from t;

　　

绑定变量带来的性能飞跃：

begin
    for i in 1 .. 100000
    loop
        execute immediate
        'insert into t values (:x)' using i;
    end loop;
        commit;
end;
/

select t.sql_text, t.sql_id, t.executions, t.parse_calls
  from v$sql t
 where sql_text like 'insert into t values%';

select t.sql_text, t.sql_id, t.executions, t.parse_calls
  from v$sql t
 where sql_text like 'insert into t values (:x)%';

SQL>--未使用绑定变量

SQL> begin
  2      for i in 1 .. 100000
  3      loop
  4          execute immediate
  5          'insert into t values ( '||i||')';
  6      end loop;
  7      commit;
  8  end;
  9  /

PL/SQL 过程已成功完成。

已用时间:  00: 00: 43.50

SQL>--使用绑定变量

SQL> begin
  2      for i in 1 .. 100000
  3      loop
  4          execute immediate
  5          'insert into t values ( :x )' using i;
  6      end loop;
  7          commit;
  8  end;
  9  /

PL/SQL 过程已成功完成。

已用时间:  00: 00: 04.77

　　硬解析次数和执行次数：

实验1
drop table t purge;
create table t ( x int );
alter system flush shared_pool;
exec dbms_workload_repository.create_snapshot();
set timing on
begin
    for i in 1 .. 100000
    loop
        execute immediate
        'insert into t values ( '||i||')';
    end loop;
    commit;
end;
/

exec dbms_workload_repository.create_snapshot();  

@?/rdbms/admin/awrrpt.sql

实验2

drop table t purge;
create table t ( x int );
alter system flush shared_pool;
exec dbms_workload_repository.create_snapshot();
set timing on
begin
    for i in 1 .. 100000
    loop
        execute immediate
        'insert into t values ( :x )' using i;
    end loop;
    commit;
end;
/

exec dbms_workload_repository.create_snapshot();  

@?/rdbms/admin/awrrpt.sql

　　

执行语句：

drop table t purge;
create table t ( x int );
set linesize 266
set pagesize 5000
alter system flush shared_pool;
alter system flush buffer_cache;
alter session set events '10046 trace name context  forever,level 12';

begin
    for i in 1 .. 10000
    loop
        execute immediate
        'insert into t values ( '||i||')';
    end loop;
    commit;
end;
alter session set events '10046 trace name context off';

--通过如下命令可以查出生成的trc文件

select d.value
|| '/'
|| LOWER (RTRIM(i.INSTANCE, CHR(0)))
|| '_ora_'
|| p.spid
|| '.trc' trace_file_name
from (select p.spid
      from v$mystat m,v$session s, v$process p
      where  m.statistic#=1 and s.sid=m.sid and p.addr=s.paddr) p,
      (select t.INSTANCE
       FROM v$thread t,v$parameter v
       WHERE v.name='thread'
       AND(v.VALUE=0 OR t.thread#=to_number(v.value))) i,
       (select value
       from v$parameter
       where name='user_dump_dest') d;

exit

　　生成报表：

tkprof  d:\oracle\diag\rdbms\test11g\test11g\trace/test11g_ora_4516.trc  d:\10046_no_bind.txt  sys=no sort=prsela,exeela,fchela

　　

--查询10046.txt,发现总共是花费4.38秒，其中解析时间占用了3.3秒

---用10046来跟踪另外一个使用绑定变量的写法，如下：
drop table t purge;
create table t ( x int );
set linesize 266
set pagesize 5000
alter system flush shared_pool;
alter system flush buffer_cache;
alter session set events '10046 trace name context  forever,level 12';
begin
    for i in 1 .. 10000
    loop
        execute immediate
        'insert into t values ( :x )' using i;
    end loop;
        commit;
end;
/
alter session set events '10046 trace name context off';

select d.value
|| '/'
|| LOWER (RTRIM(i.INSTANCE, CHR(0)))
|| '_ora_'
|| p.spid
|| '.trc' trace_file_name
from (select p.spid
      from v$mystat m,v$session s, v$process p
      where  m.statistic#=1 and s.sid=m.sid and p.addr=s.paddr) p,
      (select t.INSTANCE
       FROM v$thread t,v$parameter v
       WHERE v.name='thread'
       AND(v.VALUE=0 OR t.thread#=to_number(v.value))) i,
       (select value
       from v$parameter
       where name='user_dump_dest') d;

tkprof  d:\oracle\diag\rdbms\test11g\test11g\trace/test11g_ora_2908.trc d:\10046_bind.txt  sys=no sort=prsela,exeela,fchela

--查询10046.txt,发现总共是花费2.75秒，其中解析时间占用了0.03秒

　　静态sql自动绑定变量：

drop table t purge;
create table t(x int);
alter system flush shared_pool;
select * from v$mystat where rownum=1;
set timing on 

begin
    for i in 1 .. 100000
    loop
        insert into t values (i);
    end loop;
        commit;
end;
/

select t.sql_text, t.sql_id, t.executions, t.parse_calls
  from v$sql t
 where lower(sql_text) like 'insert into t values%';

　　参数对Sql性能的影响：

drop table t purge;
create table t ( x int );
set timing on

alter session set session_cached_cursors=0;
--使用绑定变量
begin
    for i in 1 .. 100000
    loop
        execute immediate
        'insert into t values ( :x )' using i;
    end loop;
    commit;
end;
/

drop table t purge;
create table t ( x int );
set timing on
alter session set session_cached_cursors=50;
--使用绑定变量
begin
    for i in 1 .. 100000
    loop
        execute immediate
        'insert into t values ( :x )' using i;
    end loop;
    commit;
end;
/

说明：
oracle有一个概念，那就是session cursor cache,中文描述就是有一块内存区域，用来存储关闭了的cursor。
当一个cursor关闭之后，oracle会检查这个cursor的request次数是否超过3次，如果超过了三次，就会放入session cursor cache。
这样在下次parse的时候，就可以从session cursor cache中找到这个statement, session cursor cache的管理也是使用LRU。
session_cached_cursors这个参数是控制session cursor cache的大小的。
session_cached_cursors定义了session cursor cache中存储的cursor的个数。这个值越大，则会消耗的内存越多。

　　

drop table t purge;
create table t   as select * from dba_objects;
insert into t  select * from t;
insert into t  select * from t;
insert into t  select * from t;
insert into t  select * from t;
commit;

--测试普通插入
drop table test;
create table test   as select * from dba_objects where 1=2;
set timing on
insert into test select * from t;
commit;

--注意这个普通方式插入试验输出的物理读（首次读）
set autotrace traceonly
select count(*) from test;

--测试直接路径读方式
drop table test;
create table test  as select * from dba_objects where 1=2;
set timing on
insert  /*+ append */ into test select * from t;
commit;
--注意这个直接路径方式插入试验输出的物理读（首次读）
set autotrace traceonly
select count(*) from test;

批量提交与否性能差异：

set serveroutput on size 100000
drop table t purge;
create table t(x int);
set timing on 

begin
    for i in 1 .. 100000 loop
       insert into t1 values (i);
      commit;
    end loop;
end;
/
drop table t purge;
create table t(x int);

begin
    for i in 1 .. 100000  loop
       insert into t values (i);
    end loop;
  commit;
end;
/

　　日志关闭与否对性能的影响：

--环境准备(构造一个记录有400万左右的表）
drop table t purge;
create table t   as select * from dba_objects;
insert into t  select * from t;
insert into t  select * from t;
insert into t  select * from t;
insert into t  select * from t;
--多插几次，让数据大一点
insert into t  select * from t;
insert into t  select * from t;
commit;

--测试直接路径读方式
drop table test;
create table test  as select * from dba_objects where 1=2;
set timing on
insert  /*+ append */ into test select * from t;
commit;

--测试nolgging关闭日志+直接路径读方式
drop table test;
create table test  as select * from dba_objects where 1=2;
alter table test nologging;
set timing on
insert  /*+ append */ into test select * from t;
commit;