MSSQL2008 Backup of Log does not reduce log size

Question

I did a full backup of my database in MSSQL2008 and then performed a backup of the Log. I expected the transaction log file to change in size, but when I checked the file on disk, it remains the same. Note: Database is in FULL recovery mode. What am i doing wrong?

Answer 1

SQL Server will not automatically shrink the physical size of the log after a backup.

Continually shrinking and regrowing the log after each backup would cause unnecessary performance issues (growing requires zeroing out the newly allocated space).

After the transaction log backup the log can be automatically truncated (not shrunk) which just marks any no longer required VLFs as available to be over written.