SCN概念
The SCN is a stamp that defines a committed version of a database at a point in time. Oracle assigns every committed transaction a unique SCN. The value of a SCN is the logical point in time at which changes are made to a database. This number is utilized by Oracle to log the changes made to the database.
更多详情请参考Oracle SCN
SCN = (SCN_WRAP * 4294967296) + SCN_BASE.
SCN is a 6 Byte (48 bit) number whose value is 281,474,976,710,656 and represented as 2 parts - SCN_BASE and SCN_WRAP.
SCN_BASE is a 4 Byte (32 bit) number
SCN_WRAP is a 2 Byte (16 bit) number. Whenever SCN_BASE reaches its maximum (2 power 32 = 4294967296 ), SCN_WRAP is increased by one and SCN_BASE will be reset to 0. This continues until SCN_WRAP reaches its maximum, i.e. 2 power 16 = 65536.
AODU功能
AODU> scn 0x001f.00233d44
scn: 0x001f.00233d44=133146295620
scn wrap: 0x001f=31
scn base: 00233d44=2309444
AODU>
