Hi,
The truth is "During checkpoint ,dirty buffers are written to the disk".From Oracle 7.3 ,there is a event called the checkpoint event.This event occurs because DBWR is very lazy in writing the dirty database buffers from database buffer cache to the datafiles.Whenever a checkpoint happens,LGWR writes the contents of the redolog buffer to the online redolog files.It then signals DBWR to write the contents of the database buffer cache to the datafiles. Also checkpoint occurs due to various situations such as a log switch,when the database is shutdown normal,transactional or immediate option,when u put ur tablespace in read-only mode or when you take ur tablespace offline with normal option or through checkpoint parameters in ur init.ora parameter file i.e LOG_CHECKPOINT_TIMEOUT and LOG_CHECKPOINT_INTERVAL.


Regards,
Rohit nirkhe,oracle/Apps DBA,OCP 8i
[email protected]