OCI Streaming | Group Cursor | Clarification on Partition Assignment When Only One Consumer Instance is Present in Group

[MurugeshSandari]

Hi Team,

We’re integrating OCI Streaming using the .NET SDK and following the consumer group model. We would like clarification regarding how partitions are assigned when only one consumer instance is present in a consumer group, but the stream has multiple partitions (e.g., 4, 8, or more).

Specifically, we want to confirm the following behavior:

When a single consumer instance (with a unique instance Name and associated group Name) is created via the Group Cursor API:

• Will OCI assign all partitions to this single consumer?
• Will the consumer receive messages in a round-robin or interleaved fashion across the partitions?
• Are there any caveats or recommended limits when using a single consumer instance to read from many partitions?

Observed Behavior in POC :

• We did a proof-of-concept (POC) by running a job for 10 minutes:
• This job creates a group cursor and then enters a loop, fetching messages and processing them every 10–20 seconds.
• The fetch loop continues for the full 10-minute duration.
• We noticed that:

1. Sometimes all partitions were assigned to the consumer and messages from all were received.
2. But in other runs, only a subset of partitions seemed to be assigned and processed throughout the cycle.

This raises the question:
Is there a guarantee that OCI will allocate all available partitions to a single active group member (if only one exists)?

We are asking this to confirm:

• If this single-consumer pattern is production-safe for low-throughput cases.
• If there’s any hidden limitation or retry behavior we should be aware of while fetching from multiple partitions with a single group member.