Mistake: compressing first and measuring later. Page compression may consume extra CPU without shrinking a table whose GUIDs and generated strings share little commonality. Estimate the result before changing a large table, especially on an I/O-bound instance with spare processor capacity. section 10.9
Estimate an alternative compression state
For the dbo.ImpressionsArchive clustered index, estimate the size without compression before rebuilding it: EXEC sp_estimate_data_compression_savings @schema_name = 'dbo', @object_name = 'ImpressionsArchive', @index_id = 1, @partition_number = NULL, @data_compression = 'none'; Compare the estimate with the current table and with row or page compression before implementation. In the ImpressionArchive scenario, page compression provided no additional reduction over row compression while requiring more decompression CPU. section 10.9
