Explain howthe commit of a transaction is implemented within the logging system.

What will be an ideal response?

When a transaction commits, it writes a commit record to the log. If it aborts, it rolls back its updates and then writes an abort record to the log. Using these records, the backward scan can record the identity of transactions that completed prior to the crash, and ignore their update records as they are subsequently encountered. If, during the backward scan, the first record relating to T is an update record, T was active when the crash occurred and must be aborted.
A transaction is committed if and only if its commit record has been successfully appended to the log.