Cosmos DB Partition Query and RU Charges

Question

I'm using the Volcano JSON sample with 1571 documents. I created one container (using the Cosmos DB Emulator) partitioned by ID and one container partitioned by Country. I expected to see that when I ran these queries:

select *
from VolcanoesById c
where c.Country = 'Japan'


select *
from VolcanoesByCountry c
where c.Country = 'Japan'

The RU cost listed in the emulator has the same charge:

Partitioned by ID:

• Request Charge - 6.25 RUs
• Results - 111
• Retrieved document size - 56255 bytes
• Output document count - 111
• Output document size - 56416 bytes
• Index hit document count - 111
• Index lookup time - 0.13 ms
• Document load time - 0.5 ms
• Query engine execution time - 0.09 ms

Vs the partition by country:

• Request Charge - 6.25 RUs
• Results - 111
• Retrieved document size - 56255 bytes
• Output document count - 111
• Output document size - 56416 bytes
• Index hit document count - 111
• Index lookup time - 10.96 ms
• Document load time - 0.46 ms
• Query engine execution time - 0.11 ms

Shouldn't the query by country partitioned on country be a smaller RU result?

Answer 1

The reason could be that the Container you created has a single physical partition.

Try creating in the Emulator containers with multiple physical partitions (you can achieve that by provisioning more than 10K RU) and repeating the same exercise.