Remember Partition Alignment

Kendra Little shows that truncating partitions in SQL Server 2016 requires all indexes be aligned to the partition:

If you have a non-aligned index on the table, you’ll see an error like this:

Msg 3756, Level 16, State 1, Line 1

TRUNCATE TABLE statement failed. Index ‘ix_FirstNameByBirthDate_pt_BirthYear_FirstNameId_nonaligned’ is not partitioned, but table ‘FirstNameByBirthDate_pt’ uses partition function ‘pf_fnbd’. Index and table must use an equivalent partition function.

This isn’t a bug, and it makes total sense from a logical point of view. “Non-aligned” indexes are not partitioned like the base table is– by definition they are either partitioned differently, or not partitioned at all. The chunk of data that you’re trying to truncate isn’t all in an easily identifiable partition that can be quickly marked as “data non grata”. There’s just no way to do a simple truncate when the data’s scattered all around.

Ideally, all indexes on a partitioned table would be partition-aligned, as it makes maintenance a lot easier.  That’s not always possible, though, so keep this in mind.

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