Columnstore Partitioning

Niko Neugebauer warns against partitioning small tables with clustered columnstore indexes:

Needless to say that looking at the execution plans you notice that the actual execution plan shows 10 times difference between them, even though both tables contain the very same data!
The query cost for the partitioned table is staggering – it is around 10 times bigger (~8.8) vs (~0.81) for the first query.
The execution times reflect in part this situation: 12 ms vs 91 ms. Non-partitioned table performs almost 9 times faster overall and the spent CPU time is reflecting it: 15 ms vs 94 ms. Remember, that both tables are Columnstore Indexes based ! Partitioning your table in a wrong way will contain a huge penalty that might not be directly detectable through the execution plan of the complex queries. Well, you might want to use the CISL, just saying

If you can’t fill a single rowgroup, your partition is too granular.  Even then, I’d like to see double-digit rowgroups per partition, though that’s just me.

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