Checkpoints in Database Management system

[Ainsley]

I was practicing on oracle database and I found some error like DBWR not recognizes the file.I had restarted the database but nothing happened after that,What the problem may be please suggest me. Hello sir ! Can you suggest me to solve the problem regarding Checkpoint and its different behavior.

[Zecho]

Checkpoints:

Checkpoint is another a background process which perform the synchronization of database and happens through the SCN number of the database.
It performs three operations:
1. The dirty blocks of buffer cache is written when it signals.
2. It writes the SCN number on the header of the data file.
3. The same SCN number is written on control file also.

[Reegan]

Hi friends
You are opening your database and it occur some error like DBWR is unable to recognize to open the file. So its very simple to understand that your database is not synchronized means the SCN number is not written on the header of both the file datafile and controfile.

You should mount your database and shutdown properly,There are some events on which the database can be synchronized.Now open the database if it is not being start then you need to perform media recovery.It can ask you for instance recovery,simply enter the recover database command and try to open it currently or after mounting the database.

[opaper]

Events to triggering the checkpoints:
There are four ways through which the database can perform checkpoints.Three are listed which is performed by the instance itself and fourth one is user dependent using commands forcefully.
They are as follows:
1. When a Redo log file swithes to another.
2. When the value of LOG_CHECKPOINT_TIMEOUT parameter has expired.
3. When LOG_CHECKPOINT_INTERVAL is reached to is maximum.
4. Its depends on the Administrator using ALTER .... command.