What Happens With Data Compression + Backup Compression

Jess Pomfret tests what happens when you enable backup compression for databases with already-compressed tables in SQL Server:

What happens if I use data compression and backup compression, do I get double compression?

This is a great question, and without diving too deeply into how backup compression works I’m going to do a simple experiment on the WideWorldImporters database.  I’ve restored this database to my local SQL Server 2016 instance and I’m simply going to back it up several times under different conditions.

After restoring the database it’s about 3GB in size, so our testing will be on a reasonably small database.  It would be interesting to see how the results change as the database size increases, perhaps a future blog post.

Click through for the answer.

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