anchor.diff:      member val NetworkDown        = Nullable<double>() with get, set
       member val Version            = Unchecked.defaultof<string> with get, set
       member val Status             = Unchecked.defaultof<byte []> with get, set
  -    
  +    member val HeartbeatRate      = Unchecked.defaultof<TimeSpan> with get, set
  +
       new () = new WorkerRecord(null, null)
   
       member this.GetCounters () : Utils.PerformanceMonitor.PerformanceInfo =
  
positive.code: open MBrace.Azure.Runtime.Utilities
  open MBrace.Runtime
  
  type WorkerRecord(pk, id) =
      inherit TableEntity(pk, id)
      
      member val Id                 = id with get, set
      member val Hostname           = Unchecked.defaultof<string> with get, set
  
negative.code:         member this.GetAvailableWorkers(): Async<WorkerState []> = 
              async { 
                  let! workers = this.GetAllWorkers()
                  return workers 
                         |> Seq.filter (fun w -> DateTime.UtcNow - w.LastHeartbeat <= maxHeartbeatTimespan)
                         |> Seq.filter (fun w -> match w.ExecutionStatus with
                                                 | WorkerJobExecutionStatus.Running -> true
                                                 | _ -> false)
                         |> Seq.toArray
              }
          
          member this.SubmitPerformanceMetrics(id: IWorkerId, perf: Utils.PerformanceMonitor.PerformanceInfo): Async<unit> = 
  