SQL Interview: 106 Database backup and log shrinking

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Administration Level: Intro

Question:

You successfully create a full backup of a database that is in full recovery model.

As part of the backup, is the transaction log shrunk?

Answer:

No — a full database backup does not shrink or truncate the transaction log.

A full database backup in the Full Recovery Model captures:

The entire data file contents (all pages), and
Enough of the transaction log to make the backup transactionally consistent — meaning it includes log records from the start of the backup through the end of the backup operation.

However, it does not clear, shrink, or truncate the transaction log.

In Full Recovery Model, SQL Server keeps the transaction log records until you perform a log backup.

This is because: