oracle 11g checkpoint (ckpt)
Checkpoint (ckpt) -
1) Checkpoint is a process, responsible for when to allow dbwn (database writer process) to write all modified
blocks from buffer to disk. A successful checkpoint all dirty blocks are written from buffer to disk.
2) After allowing dbwn process to write into disk, checkpoint process update datafile header and control file to record checkpoint details including time when the checkpoint was performed
NOTE- checkpoint record consists of a list of all active transactions and the address of the most
recent log record for those transactions
3) purpose of checkpoint is sync data between buffer and disk.
4) checkpoint participate in the following activities
a) Flushing/moving the contents of the redo log buffers to the redo log files
b) Writing a checkpoint record to the redo log file
c) Flushing the contents of the database buffer cache to disk
d) Updating the datafile headers and the control files after the checkpoint completes
5) database writer processes write all modified blocks to disk at checkpoints, the more frequent the checkpoints, the less data will need to be recovered when the instance crashes.checkpoint operation required extra resources thats why oracle provides automatic checkpoint tuning so that checkpoint operate in a very efficient manner.
Checkpoint happen in following situation --
a) Consistent database shutdown
b) By issuing the command alter system checkpoint'
c) Online redo log switch (or by issuing the command alter system switch logfile')
d) By issuing the command alter database begin backup
sql ALTER SYSTEM CHECKPOINT
select * from v$datafile;