触发DBWn写的条件-from 9i sg

DBWn defers writing to the data files until one of thefollowing events occurs:
? Incremental or normalcheckpoint
? The number of dirty buffers reaches a threshold value
? A process scans a specified number of blocks when scanning forfree buffers and
cannot find any
? Timeout occurs
? A ping request in Real Application Clusters (RAC)environment
? Placing a normal or temporary tablespace offline
? Placing a tablespace in read-only mode
? Dropping or truncating a table

 ---- 会写system 表空间的数据文件
? ALTER TABLESPACE tablespace name  BEGINBACKUP