四, Show_space 统计SEGMENT的空间使用具体情况。

ORACLE深入 第一章ORACLE DBA常用语句和脚本(2)

空间管理 绑定变量 读一致性 flashback

日月明王BLOG：http://sunmoonking.spaces.live.com

四 , Show_space 统计 SEGMENT 的空间使用具体情况。

create or replace procedure show_space

( p_segname in varchar2, --SGEMENT的NAME

p_owner in varchar2 default user, --默任是当前用户

p_type in varchar2 default 'TABLE', --SEGMENT 的TYPE

p_partition in varchar2 default NULL ) --PARTITION的NAME

-- this procedure uses authid current user so it can query DBA_*

-- views using privileges from a ROLE, and so it can be installed

-- once per database, instead of once per user who wanted to use it

authid current_user

as

l_free_blks number;

l_total_blocks number;

l_total_bytes number;

l_unused_blocks number;

l_unused_bytes number;

l_LastUsedExtFileId number;

l_LastUsedExtBlockId number;

l_LAST_USED_BLOCK number;

l_segment_space_mgmt varchar2(255);

l_unformatted_blocks number;

l_unformatted_bytes number;

l_fs1_blocks number; l_fs1_bytes number;

l_fs2_blocks number; l_fs2_bytes number;

l_fs3_blocks number; l_fs3_bytes number;

l_fs4_blocks number; l_fs4_bytes number;

l_full_blocks number; l_full_bytes number;

-- inline procedure to print out numbers nicely formatted

-- with a simple label

procedure p( p_label in varchar2, p_num in number )

is

begin

dbms_output.put_line( rpad(p_label,40,'.') ||

to_char(p_num,'999,999,999,999') );

end;

begin

-- this query is executed dynamically in order to allow this procedure

-- to be created by a user who has access to DBA_SEGMENTS/TABLESPACES

-- via a role as is customary.

-- NOTE: at runtime, the invoker MUST have access to these two

-- views!

-- this query determines if the object is an ASSM object or not

begin

execute immediate

'select ts.segment_space_management

from dba_segments seg, dba_tablespaces ts

where seg.segment_name = :p_segname

and (:p_partition is null or

seg.partition_name = :p_partition)

and seg.owner = :p_owner

and seg.tablespace_name = ts.tablespace_name'

into l_segment_space_mgmt

using p_segname, p_partition, p_partition, p_owner;

exception

when too_many_rows then

dbms_output.put_line

( 'This must be a partitioned table, use p_partition => ');

return;

end;

-- if the object is in an ASSM tablespace, we must use this API

-- call to get space information, otherwise we use the FREE_BLOCKS

-- API for the user-managed segments

if l_segment_space_mgmt = 'AUTO'

then

dbms_space.space_usage

( p_owner, p_segname, p_type, l_unformatted_blocks,

l_unformatted_bytes, l_fs1_blocks, l_fs1_bytes,

l_fs2_blocks, l_fs2_bytes, l_fs3_blocks, l_fs3_bytes,

l_fs4_blocks, l_fs4_bytes, l_full_blocks, l_full_bytes, p_partition);

p( 'Unformatted Blocks ', l_unformatted_blocks );

p( 'FS1 Blocks (0-25) ', l_fs1_blocks );

p( 'FS2 Blocks (25-50) ', l_fs2_blocks );

p( 'FS3 Blocks (50-75) ', l_fs3_blocks );

p( 'FS4 Blocks (75-100)', l_fs4_blocks );

p( 'Full Blocks ', l_full_blocks );

else

dbms_space.free_blocks(

segment_owner => p_owner,

segment_name => p_segname,

segment_type => p_type,

freelist_group_id => 0,

free_blks => l_free_blks);

p( 'Free Blocks', l_free_blks );

end if;

-- and then the unused space API call to get the rest of the

-- information

dbms_space.unused_space

( segment_owner => p_owner,

segment_name => p_segname,

segment_type => p_type,

partition_name => p_partition,

total_blocks => l_total_blocks,

total_bytes => l_total_bytes,

unused_blocks => l_unused_blocks,

unused_bytes => l_unused_bytes,

LAST_USED_EXTENT_FILE_ID => l_LastUsedExtFileId,

LAST_USED_EXTENT_BLOCK_ID => l_LastUsedExtBlockId,

LAST_USED_BLOCK => l_LAST_USED_BLOCK );

p( 'Total Blocks', l_total_blocks );

p( 'Total Bytes', l_total_bytes );

p( 'Total MBytes', trunc(l_total_bytes/1024/1024) );

p( 'Unused Blocks', l_unused_blocks );

p( 'Unused Bytes', l_unused_bytes );

p( 'Last Used Ext FileId', l_LastUsedExtFileId );

p( 'Last Used Ext BlockId', l_LastUsedExtBlockId );

p( 'Last Used Block', l_LAST_USED_BLOCK );

end;

SQL> desc show_space

PROCEDURE show_space

参数名称 类型 输入 / 输出默认值 ?

------------------------------ ----------------------- ------ --------

P_SEGNAME VARCHAR2 IN

P_OWNER VARCHAR2 IN DEFAULT

P_TYPE VARCHAR2 IN DEFAULT

P_PARTITION VARCHAR2 IN DEFAULT

ASSM和user space managed tablespaces得到的结果不同,以下用user space managed tablespaces来说明

SQL> exec show_spacE('WWM');

Free Blocks............................. 2

Total Blocks............................ 5,120

Total Bytes............................. 41,943,040

Total MBytes............................ 40

Unused Blocks........................... 13

Unused Bytes............................ 106,496

Last Used Ext FileId.................... 1

Last Used Ext BlockId................... 46,473

Last Used Block......................... 115

FULL BLOCKS: full表示在没有变化之前不会再被分配出去。

Total Blocks, Total Bytes, Total MBytes: 整个分配给此SEGMENT的空间。

Unused Blocks, Unused Bytes:分配给SEGMENT，但是还没有使用，也就是说在HWM之上的空闲块。

Last Used Ext FileId: 最后一个extent所在的FILE ID.

Last Used Ext BlockId: 最后一个EXTENT 的BEGIN BLOCK ID.

FS1 Blocks – FS4 Blocks: 例如,0-25,表示在0-25%之间的空块.

做一个大表 , 以供测试使用

create table big_table

as

select rownum id, a.*

from all_objects a

where 1=0

/

alter table big_table nologging;

insert /*+ append */

into big_table

select rownum, a.*

from all_objects a;

已创建 29645 行。

1 insert /*+ append */

2 into big_table

3 select rownum+29646, a.*

4* from all_objects a

SQL> /

已创建 29645 行。

alter table big_table add constraint

big_table_pk primary key(id)

1 begin

2 dbms_stats.gather_table_stats

3 ( ownname => 'SYSTEM',

4 tabname => 'BIG_TABLE',

5 method_opt => 'for all indexed columns',

6 cascade => TRUE );

7* end;

五 , 绑定变量与非绑定变量

阅读本章可以参考我的 BIND VARIABLE

http://sunmoonking.spaces.live.com/blog/cns!E3BD9CBED01777CA!175.entry

测试表

create table t ( x int );

绑定变量

create or replace procedure proc1

as

begin

for i in 1 .. 10000

loop

execute immediate

'insert into t values ( :x )' using i;

end loop;

end;

/

非绑定变量

create or replace procedure proc2

as

begin

for i in 1 .. 10000

loop

execute immediate

'insert into t values ( '||i||')';

end loop;

end;

/

SQL> exec runstats_pkg.rs_start;

PL/SQL 过程已成功完成。

SQL> exec proc1

PL/SQL 过程已成功完成。

SQL> exec runstats_pkg.rs_middle;

PL/SQL 过程已成功完成。

SQL> exec proc2

PL/SQL 过程已成功完成。

SQL> exec runstats_pkg.rs_stop(1000); --差别大于1000的才输出

Run1 ran in 1622 hsecs

Run2 ran in 4378 hsecs

run 1 ran in 37.05% of the time

Name Run1 Run2 Diff

STAT...bytes received via SQL* 387 1,690 1,303

STAT...bytes sent via SQL*Net 276 1,798 1,522

STAT...parse count (hard) 5 10,009 10,004

…………………………………………………………………………….

Run1 latches total versus runs -- difference and pct

Run1 Run2 Diff Pct

313,680 1,625,995 1,312,315 19.29%

PL/SQL 过程已成功完成。

可以看到 PRO2基本上是PRO1的三倍,也就是说解析时间占完整运行完一条语句所耗时间的2/3，会多占用LATCH.可见,尽量减少硬解析能明显提高性能.

六 ,read-consistent

SQL> create table wwm as select * from all_users;

表已创建。

SQL> variable x refcursor

SQL> begin

2 open :x for select * from wwm;

3 end;

4 /

PL/SQL 过程已成功完成。

SQL> delete from wwm;

已删除 27 行。

SQL> commit;

提交完成。

SQL> print x

USERNAME USER_ID

------------------------------------------------------------ ----------

CREATED

--------------

BI 60

07-6 月 -06

。。。。。。。。。。。。。。。

注意，这是在一个 SESSION里做的实验。现建立一个表WWM，再OPEN一个CURSOR，再DELETE表WWM，甚至COMMIT之后还是可以PRINT CURSOR的原来的内容。

但是，需要明白的是，在 OPEN一个CURSOR的时候并不取得数据或把数据放到某个地方；而是在DELETE的时候才将你需要的数据给你保留到一个地方（UNDO SEGMENT或叫ROLLBACK SEGMENT）。

七 , flashback query .

SCN 是ORACLE内部时钟，

SQL> variable SCN number

SQL> exec :scn:=dbms_flashback.get_system_change_number

PL/SQL 过程已成功完成。

SQL> print scn

SCN

----------

1170636

SQL> select count(*) from wwm;

COUNT(*)

----------

0

SQL> desc wwm

名称 是否为空 ? 类型

----------------------------------------- -------- ----------------------------

USERNAME NOT NULL VARCHAR2(30)

USER_ID NOT NULL NUMBER

CREATED NOT NULL DATE

SQL> insert into wwm select * from all_users;

已创建 27 行。

SQL> select count(*) from wwm;

COUNT(*)

----------

27

SQL> select count(*) from wwm as of scn :scn;

COUNT(*)

----------

0

SQL> commit;

提交完成。

SQL> select count(*) from wwm as of scn :scn;

COUNT(*)

----------

0

甚至，我们可以用一个 SQL得到两个SCN点的值

SQL> select * from (select count(*) from wwm),

2 (select count(*) from wwm as of scn :scn);

COUNT(*) COUNT(*)

---------- ----------

27 0