Partition expansion

Use CreatePartitionsAsync to increase a topic's partition count. TotalCount is the final total, including existing partitions. Existing partition replica assignments remain unchanged.

using Dekaf.Admin;

await using var admin = new AdminClientBuilder()
    .WithBootstrapServers("localhost:9092")
    .Build();

// A topic with 3 partitions and replication factor 2 grows to 5 partitions.
var expansion = new Dictionary<string, NewPartitions>
{
    ["orders"] = new()
    {
        TotalCount = 5,
        ReplicaAssignments = [[2, 1], [1, 3]]
    }
};

await admin.CreatePartitionsAsync(expansion, new CreatePartitionsOptions
{
    ValidateOnly = true,
    TimeoutMs = 10_000
});

// Apply the same specification after successful validation.
await admin.CreatePartitionsAsync(expansion);

Assignments describe only additional partitions, in ascending partition order. In this example, partition 3 prefers broker 2 and partition 4 prefers broker 1. Replica ordering is preserved. Leave ReplicaAssignments null to let the controller choose replicas. Each assignment must contain unique, nonnegative broker IDs and have the same replication factor. The controller checks assignment count, replication factor, broker availability and current topic state.

ValidateOnly performs broker validation without creating partitions. A successful validation does not reserve the expansion: cluster state can change before it is applied. Validation retries never infer success from an earlier ambiguous mutation. TimeoutMs controls the broker operation timeout; pass a cancellation token to bound the caller's entire operation, including initialization and retries.

The original count-only overload remains available:

await admin.CreatePartitionsAsync(new Dictionary<string, int> { ["orders"] = 5 });

Typed expansion is an optional IPartitionExpansionAdminClient capability implemented by the built-in AdminClient and InMemoryAdminClient. The in-memory client supports validation-only requests and explicit assignments to its single broker, ID 0; other broker IDs are rejected. Extensions expose it through IAdminClient without adding required members to existing custom implementations. Clients without this capability throw NotSupportedException for the typed overload.

See Kafka's NewPartitions contract and CreatePartitionsOptions.