下面开始探讨内部细节
由于压缩是以block为单位的，因此在批插入的时候若数据本身不超过1 block容量是不会压缩的 （未严格证明，如下面例子，
若插入数据100条可存放在block中则不会产生压缩）
SQL> create table test1(a varchar2(20),b varchar2(20),c varchar2(20)) compress;
SQL> select TABLESPACE_NAME ,EXTENT_ID ,blocks from dba_extents where segment_name = 'TEST1';
TABLESPACE_NAME EXTENT_ID BLOCKS
------------------------------ ---------- ----------
USERS 0 8
SQL> select file_id,block_id from dba_extents where segment_name = 'TEST1';
FILE_ID BLOCK_ID
---------- ----------
11 769
SQL> insert /*+ append */ into test1 select 'AAAAAAAAAAAAAAAAAAAA','BBBBBBBBBBBBBBBBBBBB','CCCCCCCCCCCCCCCCCCCC' from dba_objects where rownum < 1001;
1000 rows created.
SQL> commit;
Commit complete.
SQL> alter system dump datafile 11 block min 769 block max 771;
System altered.
trace 部分内容
data_block_dump,data header at 0xadb4674
===============
tsiz: 0x1f88
hsiz: 0x5ce
pbl: 0x0adb4674
bdba: 0x02c00302
76543210
flag=-0------
ntab=2
nrow=724
frre=-1
fsbo=0x5ce
fseo=0x1127
avsp=0xd
tosp=0xd
r0_9ir2=0x0
mec_kdbh9ir2=0x1
r1_9ir2=0x0
76543210
flag_9ir2=-------C
fcls_9ir2[4]={ 0 32768 32768 32768 }
0x1e: pti[0] nrow=1 offs=0
0x22: pti[1] nrow=723 offs=1
0x26: pri[0] offs=0x1f46
0x28: pri[1] offs=0x1f41
0x2a: pri[2] offs=0x1f3c
0x2c: pri[3] offs=0x1f37
x5b6: pri[712] offs=0x115e
0x5b8: pri[713] offs=0x1159
0x5ba: pri[714] offs=0x1154
0x5bc: pri[715] offs=0x114f
0x5be: pri[716] offs=0x114a
0x5c0: pri[717] offs=0x1145
0x5c2: pri[718] offs=0x1140
0x5c4: pri[719] offs=0x113b
0x5c6: pri[720] offs=0x1136
0x5c8: pri[721] offs=0x1131
0x5ca: pri[722] offs=0x112c
0x5cc: pri[723] offs=0x1127 总记录条数724条，每条消耗5字节
block_row_dump:
tab 0, row 0, @0x1f46
tl: 66 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 02 d3 03 dc 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 dc 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 dc 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
这部分为集中存储
tab 1, row 0, @0x1f41
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00 这里的5个字节就是实际存储内容，03 表示压缩了3个字段,估计这里最后00表示指针指向第一个存储了完全数据的 ROW 0
tab 1, row 1, @0x1f3c
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00
tab 1, row 2, @0x1f37
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00
tab 1, row 3, @0x1f32
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00
tab 1, row 4, @0x1f2d
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00
tab 1, row 5, @0x1f28
tl: 5 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41
col 1: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 2: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 2c 00 01 03 00
tab 1, row 6, @0x1f23
SQL> truncate table test1;
Table truncated.
SQL> conn test/test
Connected.
SQL> insert /*+ append */ into test1 select rownum,'BBBBBBBBBBBBBBBBBBBB','CCCCCCCCCCCCCCCCCCCC' from dba_objects where rownum < 1001;
1000 rows created.
SQL> commit;
Commit complete.
SQL> alter system dump datafile 11 block min 769 block max 771;
System altered.
data_block_dump,data header at 0xadb4674
===============
tsiz: 0x1f88
hsiz: 0x5b2
pbl: 0x0adb4674
bdba: 0x02c00302
76543210
flag=-0------
ntab=2
nrow=709
frre=-1
fsbo=0x5b2
fseo=0x6e3
avsp=0xc5
tosp=0xc5
r0_9ir2=0x0
mec_kdbh9ir2=0x1
r1_9ir2=0x0
76543210
flag_9ir2=------OC
fcls_9ir2[3]={ 0 32768 32768 }
perm_9ir2[3]={ 2 0 1 } 这部分很关键，表示下面的实际存储字段顺序
也就是说，后面物理存储的顺序COL2,COL0,COL1对应数据字典中列的顺序应该是col0,col1,col2
0x20: pti[0] nrow=1 offs=0
0x24: pti[1] nrow=708 offs=1
0x28: pri[0] offs=0x1f5b
0x2a: pri[1] offs=0x1f54
0x2c: pri[2] offs=0x1f4d
0x2e: pri[3] offs=0x1f46
0x30: pri[4] offs=0x1f3f
0x32: pri[5] offs=0x1f38
0x34: pri[6] offs=0x1f31
0x36: pri[7] offs=0x1f2a
0x38: pri[8] offs=0x1f23
x25c: pri[282] offs=0x1571
0x25e: pri[283] offs=0x1568
0x260: pri[284] offs=0x155f
0x262: pri[285] offs=0x1556
0x264: pri[286] offs=0x154d
0x266: pri[287] offs=0x1544
0x268: pri[288] offs=0x153b
0x26a: pri[289] offs=0x1532
0x26c: pri[290] offs=0x1529
0x26e: pri[291] offs=0x1520
0x270: pri[292] offs=0x1516
block_row_dump:
tab 0, row 0, @0x1f5b
tl: 45 fb: --H-FL-- lb: 0x0 cc: 2
col 0: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 1: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
bindmp: 01 24 02 dc 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 dc 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
tab 1, row 0, @0x1f52
tl: 9 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42
col 1: [20] 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43 43
col 2: [ 3] 37 30 39
bindmp: 2c 00 02 02 00 cb 37 30 39 我们注意这里的02表示压缩2字段，本来的插入的rownum对应数据字典中表创建顺序最前的字段被存储在最末尾
tab 1, row 1, @0x1f49
tl: 9 fb: --H-FL-- lb: 0x0 cc: 3
col 0: [20] 42 42 42 42 42 42 42 42 42 42 42 42 4
【责编:admin】
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