Cosmos DB Cassandra API Indexes that span partitions

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Cosmos DB Cassandra API Indexes that span partitions

Eugene Arutchev 0

We are in the process of moving our application from on prem to Azure. We are currently using Cassandra and the plan is to use Cosmos DB Cassandra API in Azure. In Cassandra, the general rule of thumb is that an index should correspond to single partition, otherwise it is better to use Materialized Views or secondary tables.

Does the same hold true for Cosmos DB? If I have a query that would return ~20 rows of data that come from 20 different partitions, can I accomplish this by using an index (without incurring significant performance or cost penalties), or should I create a secondary table?

As an aside, I am aware that Cosmos DB Cassandra API has recently introduced Materialized Views, but since this feature is still in Preview, we are not going to use it.

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Answer 1

GeethaThatipatri-MSFT 29,542 Microsoft Employee Moderator

@Eugene Arutchev Welcome to the Microsoft Q&A forum, Thanks for posting your question.

This “rule of thumb” holds for any distributed database (i.e. one that supports transparent sharding/partitioning), including Cosmos DB. That said, cross-partition queries are not necessarily a disaster if you are not frequent, and the latency is tolerable for the user. If reviewing Cassandra, you may need to consider Cassandra Managed Instance: https://learn.microsoft.com/azure/managed-instance-apache-cassandra/

Regards

Geetha

Eugene Arutchev 0 Reputation points

2023-05-08T20:35:18.75+00:00

Thanks for the response, I understand that cross partition queries is an antipattern for all distributed databases. That was not my question. In Cassandra even creating cross partition indices is an antipattern. To make cross partition queries work in Cassandra, I would need to use secondary tables or Materialized Views.
My question is it ok to create cross partition indices in Cosmos DB Cassandra API? Would such indices be performant for high volume reads?

Unfortunately the decision to use Cosmos DB Cassandra API vs Cassandra Managed Instance is out of my hands.
GeethaThatipatri-MSFT 29,542 Reputation points Microsoft Employee Moderator

2023-05-09T15:49:37.09+00:00

@Eugene Arutchev on your additional ask I hope you got the answer from SO forum, however I am updating here so others from the community can refer

If by "cross partition indices" you mean creating an index on a field that is not the partition key, where the intention is to execute queries that filter on that field, but doesn't provide the partition key in the filter, then yes, those queries in Cosmos DB will incur similar issues as they would in Cassandra. With that said, in general reads are more efficient in Cosmos DB than Cassandra, because there are no read repairs, tombstones do not need to be skipped over, and SSTables do not need to be compacted. So even in your use case, performance may be better in Cosmos DB

Regards

Geetha

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Cosmos DB Cassandra API Indexes that span partitions

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