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. 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.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.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.--------------------------------
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.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
