Azure Cosmos DB for MongoDB: Enabling runtime collation on find/aggregate

David Huynh 0 Reputation points
2026-10-07T17:19:44.6566667+00:00

Problem description

I am trying to enable runtime collation (find/aggregate) on my Azure Cosmos DB for MongoDB clusters in East US to match the behavior of an existing cluster. Currently, some newer clusters reject collation-based queries with error code 115 (CommandNotSupported), while an older cluster accepts similar queries. I want to understand if runtime collation support can be enabled on these clusters, or if there is a way to align their configurations.

Environment

Azure Cosmos DB for MongoDB (vCore), three clusters in East US, application using .NET Core with SDK v10.

What I've already tried

I compared behavior across clusters with the same application workload. The working cluster accepts collation in find and aggregate commands, while the newer clusters return errors. I reviewed the application logs and the commands sent, including the collation document. I also verified the MongoDB compatibility version for all clusters, which is 8.0. All clusters report the same version. I tested the same find and aggregate commands with the collation option removed; the failing clusters succeed without collation, indicating the issue is tied to collation support.

Current status

Currently, the two newer clusters in East US are still rejecting collation in find and aggregate commands with error code 115, while the older cluster accepts these commands. I am seeking guidance on whether runtime collation support can be enabled on the failing clusters, or if there are configuration steps to align their behavior with the working cluster.

Azure Cosmos DB
Azure Cosmos DB

An Azure NoSQL database service for app development.

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  1. Rukshan edirisinghe 1,235 Reputation points
    2026-10-08T03:23:16.7+00:00

    Hi @David Huynh

    The difference between your clusters is most likely a preview flag. In the service release notes, runtime collation for find and aggregate was released as a gated preview, and the notes say preview items need a support request to be turned on for each cluster. So your older cluster probably had it enabled at some point, and the newer ones never did.

    To line them up:

    1. In the Azure portal, open Help + support and create a support request for Azure Cosmos DB for MongoDB (vCore).
    2. Ask them to enable "runtime support of collation with find/aggregate" and list all the clusters that need it in the ticket (not here), so they can do them together.
    3. Once they confirm, rerun one of the queries that failed with error 115 to check it now goes through.

    Is the older cluster that works in the same subscription, or was it created by a different team or account?

    If this resolved your issue, please consider accepting it as the answer. If the clusters still behave differently after that, let me know and I'll be happy to keep helping.

    Reference:

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