Page compression not working? I have created a table where I have around 100 partitions (per month), all of them are configured to use page compression. After that I'm inserting data to this table month by month.

I now would expect SQL Server to apply the page compression. However using sp_estimate_data_compression_savings it doesn't look like it. (I would have savings of around 40%-50%.)

Did I miss something in configuring page compression?

The problem with this is that I have now large files, 70-80 GB per partition. When I compress them, they are half empty. Regaining this disk space is impossible because if I try to shrink the data file that is behind the partition I end up with a fragmented clustered index.

How can I avoid this disk space waste party?
If you're using big fields like VARCHAR(MAX), you'll discover that off-page data isn't compressed with page compression. (Hey, go figure.)

To see how much data of your table is being stored off-page, use the free open source script sp_BlitzIndex (disclaimer: I'm a coauthor on that). You can run it at the table level like this:

EXEC sp_BlitzIndex @DatabaseName = 'mydb', @SchemaName = 'dbo', @TableName = 'whywontthiscompress'


Then, in the top result set where it lists the indexes, look at the amount of LOB data stored on the table. If it's a lot, that's probably why compression isn't working. (And you can post a screenshot of the top result set in your question if you'd like more help/clarifications on this.)