Check point refers to a particular point of time. Searching the entire log is time-consuming. We unnecessarily redo transactions which have already output their updates to the database. So, we use check-point records in log files.
At the checkpoint the contents of the database are copied to some storage. That storage can be secondary storage like a hard disk or tertiary storage such as external hard-disk.
After every 10 minutes the database administrator will look after the period of check point.
Let’s see the steps how check-points are created how it is helpful in data storage during transactions −
Step 1 − scan backwards to find the most recent check-point record.
Step 2 − consider the most recent transaction Ti that started before the check-point.
Step 3 − Scan forward in the log:
If a transaction has <Ti commit> , perform redo(Ti)
If a transaction has no <Ti, commit> Perform undo(Ti).
Check-point is one of the techniques that is used to recover from failure. We all know that recovery means to get back the information, which is lost. It helps to maintain database consistency in case of failure.
Given below is an example of check point −