欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  数据库

Oracle 中关于超过253列内部数据的存储

程序员文章站 2022-06-13 13:28:38
...

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)