Basic knowledge about block address

Basic knowledge about block address 1. block address (ondisk rba is voided after 9.2) 1.uba= Undofile BA 1 BA = dbfile file number, block number, row number rdba = tablespace Relative Database BA 2 BA = logfile serial number, logfile block number, offset length 2. low cache rba and low rba 1.low cache rba = checkpoint position = The DBWR write progress recorded by CKPT = the previous data file written by low cache rba 2. low scn (first_change #) of the current redo logfile #)

SQL> select sequence #, status, first_change # from v $ log; SEQUENCE # STATUS FIRST_CHANGE #5 INACTIVE5667516 CURRENT5898194 INACTIVE531541

 

First_change # indicates the low scn of the current redo log, and only the current redo log file will be used for instance recovery (cause: CKPT is triggered to write dirty blocks during log switching) 3. additional knowledge: next_change # indicates the high scn select sequence #, first_change # from v $ log; select sequence #, first_change from v $ log_history; the Redo log records the changes in the database in sequence. After a set of redo log files are fully written, they are automatically switched to the next set of redo log files. The high scn of the previous redo log is the low scn of the next redo log.