Steve Malley (3/5/2013)
Can someone explain how data compression works at the index level? If I compress a primary key, am I compressing the whole table [since the data pages are leaf pages]?
Depends whether the primary key is clustered or not. There's no requirement that it is.
If you compress the clustered index, you are compressing the table, if you compress a nonclustered index, you're compressing just the index.
Have a look for the performance benchmarks microsoft did (cat team I think). They got performance gains in all but one case, even when compressing active, in-use portions of the database. Less data to be moved around, less memory required resulted in improved performance.
I'll see if I can find the link in the morning.
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