Home Database Mysql Tutorial Oracle 中关于超过253列内部数据的存储

Oracle 中关于超过253列内部数据的存储

Jun 07, 2016 pm 05:21 PM

建表语句declare v_sql varchar2(32767) ;begin v_sql :=

建表语句
declare
  v_sql varchar2(32767) ;
begin
  v_sql := 'create table test ( ' ;
  for i in 1..500 loop
    v_sql := v_sql || 'name'||i||' varchar2(2000) ,' ;
  end loop ;
  v_sql := substr(v_sql,1,length(v_sql)-1) ;
  v_sql := v_sql || ');' ;
  dbms_output.put_line(v_sql) ;
end ;
复制粘贴创建表

_dex@DAVID> desc test
Name                                                  Null?    Type
----------------------------------------------------- -------- ------------------------------------
NAME1                                                          VARCHAR2(2000)
NAME2                                                          VARCHAR2(2000)
NAME3                                                          VARCHAR2(2000)
.....
NAME500                                                        VARCHAR2(2000)

_dex@DAVID> insert into test (name500) values (lpad(1,300,'d')) ;

1 row created.


_dex@DAVID> select
  2  length(t.name500),
  3  dbms_rowid.rowid_relative_fno(t.rowid) as "FNO#",
  4  dbms_rowid.rowid_block_number(t.rowid) as "BLK#",
  5  dbms_rowid.rowid_row_number(t.rowid) as "ROW#"
  6  from dex.test t
  7  /

LENGTH(T.NAME500)      FNO#      BLK#      ROW#
----------------- ---------- ---------- ----------
              300          4        925          1
                1          4        925          3
              300          4        925          5


使用bbed查看

首先看row#为1长度为300的数据
BBED> set dba 4,925
        DBA            0x0100039d (16778141 4,925)

BBED> p kdbr
sb2 kdbr[0]                                @142      7504
sb2 kdbr[1]                                @144      7250
sb2 kdbr[2]                                @146      6991
sb2 kdbr[3]                                @148      6737
sb2 kdbr[4]                                @150      6177
sb2 kdbr[5]                                @152      5923

BBED> p *kdbr[1]
rowdata[1327]
-------------
ub1 rowdata[1327]                          @7374    0x28

BBED> dump /v offset 7374 count 128
File: /u01/apps/Oracle/oradata/david/users01.dbf (4)
Block: 925    Offsets: 7374 to 7501  Dba:0x0100039d
-------------------------------------------------------
2801f501 00039d00 00ffffff ffffffff l (.õ.............
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................

这些是row piece header
2801f501 00039d00 00

1个字节的flag=28
16进制28=二进制00101000=--H-F---=head of rowpiece + first data piece
1个字节的lb(itl slot)=01
1个字节的cc column count=f5=245 (因为最后一列name500不为空,所以null都需要使用ff来表示,也就是说需要存储500列的数据)

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