Signal Forge ADR-010: gRPC server-streaming via AsAsyncEnumerable (not ToListAsync)

Signal Forge ADR-010: gRPC server-streaming via AsAsyncEnumerable (not ToListAsync)

Status: Accepted

Decision: [[projects/app-signal-forge/api/grpc|GetOrdersByProject]] streams rows directly from the PostgreSQL cursor using AsAsyncEnumerable(), writing each row to the gRPC stream as it is fetched.

Code pattern:

await foreach (var order in _db.Orders
    .Where(o => o.ProjectId == request.ProjectId)
    .OrderByDescending(o => o.CreatedAt)
    .AsAsyncEnumerable()
    .WithCancellation(context.CancellationToken))
{
    await responseStream.WriteAsync(MapToResponse(order), context.CancellationToken);
}

Rationale:

• ToListAsync() loads all matching rows into a List<Order> in application memory before streaming begins. For large result sets this causes OOM.
• AsAsyncEnumerable() uses the database cursor: one row is fetched, sent over gRPC, then the next is fetched. Memory usage is O(1) regardless of result set size.
• CancellationToken is threaded through so the DB query is cancelled if the gRPC client disconnects.

Alternative considered: ToListAsync() — rejected due to unbounded memory growth.