Shrinking old partitions

Question

I have a large partitioned time series table where each partition is stored in it's own file. Since it's time series based partitioning divided by week and I'm only storing data that is new I have never more than 2 partitions I'm actively writing to at once. I have a FILLFACTOR set to 75 on the index since the data is coming in somewhat randomly.

The old data partitions are taking up quite a bit of space, utilizing only about 60-70% of that space. Is it possible to automatically change the FILLFACTOR on said partitions, rebuild the indexes and shrink the files? Since I'm not writing to those partitions anymore they shouldn't grow back in size.

Answer 1

Yes, this is possible. Here is how

1. Create a copy of the table (you can use the partition management tool for that: https://sqlpartitionmgmt.codeplex.com/)
2. Switch the partition you want to "compress" into the copy
3. Rebuild the indexes on the copy with FF = 100.
4. Switch the partition back into the original table

It should be pretty trivial to automate this with a SQL agent job.

Step 3 is best done in this order:

• Drop all secondary indexes
• Rebuild the cluster index with FF = 100
• Create all the secondary indexes again with FF=100

Also, if you have SQL Server Enterprise Edition, you could compress the data with PAGE compression. This would require a different process:

1. Create a copy of that table as above
2. Switch the data you want to compress into the copy
3. Compress the data by rebuilding indexes as above
4. ALTER the original table to enable page compression on the now empty partitions (the ones you switched out)
5. SWITCH the compressed data back into the original table.

With SQL Server 2014 Enteprise Edition, you can do the above as an online operation directly on the partition you want to compress. However, it is still a good idea to drop the secondary indexes in a copy first, because it will typically give you better data layout on the disk.