oracle数据块pctfree变化查看

这篇文章对文章ORACLE空间管理实验6：块管理之ASSM下插入操作--高水位的影响及大并发插入的性能问题中第实验二：查看pctfree变化，做个实验补充。

思路：

1、创建一个表t1

2、通过t1表的segment的segment_header找到L2 -> L1从而查看L1中的pctfree变化

3、让数据块pctfree变化的方法是插入数据再删除数据

SQL> create table t1(name varchar2(1000)) tablespace test1;

Table created.

SQL> insert into t1 select rpad('A', 999, 'A') from dual;

1 row created.

SQL> commit;

Commit complete.

SQL> alter system checkpoint;

System altered.

SQL> select OWNER, SEGMENT_NAME, HEADER_FILE, HEADER_BLOCK from dba_segments where SEGMENT_NAME='T1' and owner='TEST';

OWNER  SEGMENT_NAME  HEADER_FILE HEADER_BLOCK
------ ------------- ----------- ------------
TEST   T1                      9          146

SQL> alter system dump datafile 9 block 146;

System altered.

通过dump文件信息找到L2块号

Segment Type: 1 nl2: 1 blksz: 8192 fbsz: 0

L2 Array start offset: 0x00001434

First Level 3 BMB: 0x00000000

L2 Hint for inserts: 0x02400091

Last Level 1 BMB: 0x02400090

Last Level II BMB: 0x02400091

Last Level III BMB: 0x00000000

Map Header:: next 0x00000000 #extents: 1 obj#: 17370 flag: 0x10000000

Inc # 0

从上面可以看到L2块号是 0x91 -> 145(十进制)

再dump 9号文件145号块

SQL> alter system dump datafile 9 block 146;

System altered.

下面是对我有用的信息

Dump of Second Level Bitmap Block

number: 1 nfree: 1 ffree: 0 pdba: 0x02400092

Inc #: 0 Objd: 17370

opcode:0

xid:

L1 Ranges :

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

0x02400090 Free: 5 Inst: 1



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

End dump data blocks tsn: 8 file#: 9 minblk 145 maxblk 145

从上面我们看到L1号块时 0x90 -> 144(十进制)

再dump 9号文件144号块

SQL> alter system dump datafile 9 block 144;

System altered.

下面是对我们有用的信息

Dump of First Level Bitmap Block

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

nbits : 4 nranges: 1 parent dba: 0x02400091 poffset: 0

unformatted: 0 total: 8 first useful block: 3

owning instance : 1

instance ownership changed at 08/24/2014 18:42:49

Last successful Search 08/24/2014 18:42:49

Freeness Status: nf1 0 nf2 0 nf3 0 nf4 5
--nf4 5 ：代表 <75-100% free>类型的快有5个



Extent Map Block Offset: 4294967295

First free datablock : 3

Bitmap block lock opcode 0

Locker xid: : 0x0000.000.00000000

Dealloc scn: 0.0

Flag: 0x00000001 (-/-/-/-/-/HWM)

Inc #: 0 Objd: 17370

HWM Flag: HWM Set

Highwater:: 0x02400098 ext#: 0 blk#: 8 ext size: 8

#blocks in seg. hdr's freelists: 0

#blocks below: 5

mapblk 0x00000000 offset: 0

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

DBA Ranges :

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

0x02400090 Length: 8 Offset: 0



0:Metadata 1:Metadata 2:Metadata 3:75-100% free

4:75-100% free 5:75-100% free 6:75-100% free 7:75-100% free --看出有五块的pctfree都是在 <75-100% free>类型中

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

这时我们向表t1中插入数据查看 以上两处的变化

SQL> insert into t1 select rpad('B', 999, 'B') from dual;

1 row created.

SQL> commit;

Commit complete.

SQL> alter system checkpoint;

System altered.

SQL> alter system dump datafile 9 block 144;

System altered.

Dump of First Level Bitmap Block

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

nbits : 4 nranges: 1 parent dba: 0x02400091 poffset: 0

unformatted: 0 total: 8 first useful block: 3

owning instance : 1

instance ownership changed at 08/24/2014 18:42:49

Last successful Search 08/24/2014 18:42:49

Freeness Status: nf1 0 nf2 0 nf3 1 nf4 4
--看到有一个块变化了在nf3类型中<50-75% free>



Extent Map Block Offset: 4294967295

First free datablock : 3

Bitmap block lock opcode 0

Locker xid: : 0x0000.000.00000000

Dealloc scn: 0.0

Flag: 0x00000001 (-/-/-/-/-/HWM)

Inc #: 0 Objd: 17370

HWM Flag: HWM Set

Highwater:: 0x02400098 ext#: 0 blk#: 8 ext size: 8

#blocks in seg. hdr's freelists: 0

#blocks below: 5

mapblk 0x00000000 offset: 0

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

DBA Ranges :

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

0x02400090 Length: 8 Offset: 0



0:Metadata 1:Metadata 2:Metadata 3:75-100% free

4:75-100% free 5:75-100% free 6:75-100% free
7:50-75% free
--看到一个块pctfree已经发生变化

下面我们再删除一行看看块的pctfree变化

SQL> delete from t1 where name like '%B%';

1 row deleted.

SQL> commit;

Commit complete.

SQL> alter system checkpoint;

System altered.

SQL> alter system dump datafile 9 block 144;

System altered.

下面是对我们有用的信息

Dump of First Level Bitmap Block

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

nbits : 4 nranges: 1 parent dba: 0x02400091 poffset: 0

unformatted: 0 total: 8 first useful block: 3

owning instance : 1

instance ownership changed at 08/24/2014 18:42:49

Last successful Search 08/24/2014 18:42:49

Freeness Status: nf1 0 nf2 0 nf3 0 nf4 5
--变回原来的样子



Extent Map Block Offset: 4294967295

First free datablock : 3

Bitmap block lock opcode 0

Locker xid: : 0x0000.000.00000000

Dealloc scn: 0.0

Flag: 0x00000001 (-/-/-/-/-/HWM)

Inc #: 0 Objd: 17370

HWM Flag: HWM Set

Highwater:: 0x02400098 ext#: 0 blk#: 8 ext size: 8

#blocks in seg. hdr's freelists: 0

#blocks below: 5

mapblk 0x00000000 offset: 0

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

DBA Ranges :

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

0x02400090 Length: 8 Offset: 0



0:Metadata 1:Metadata 2:Metadata 3:75-100% free

4:75-100% free 5:75-100% free 6:75-100% free 7:75-100% free --pctfree变回原来的样子