We say that a transaction has been committed when its commit log record has been output to stable storage. At that point, all the earlier records have already been output to stable storage.

Using checkpoints reduces overhead because the search process is time consuming and searching for transactions does not take place if we use checkpoints.

The most widely used structure for recording database modification is called as a log. The log is a sequence of log records recording all the update activities in the database.

If the database modifications occur while the transaction is still active, the transaction is said to use the immediate modification technique. Deferred modification has overhead whereas immediate modification doesn’t have any overhead.

The value of the data item prior to the write is called as old value. This is stored in the update log record.

A fuzzy checkpoint is a checkpoint where transactions are allowed to perform updates even while buffer blocks are being written out.

An update log record describes a single database write. It has four fields in it which are, transaction identifier, data-item identifier, old value, new value.

The unique identifier of the transaction that performed the write operation is called as transaction identifier. This is a field in the update log record.

If a transaction does not modify the database until it has committed it is said to use a deferred modification technique. Deferred modification has the overhead that transactions need to make local copies of all updated data items.

An update log record describes a single database write. It has four fields in it. The update log record has a transaction identifier, data-item identifier, old value, new value.