don't be so aggressive about adding PINGs if we're already backed up; no need...

don't be so aggressive about adding PINGs if we're already backed up; no need to report QUIT as faulted if the socket died (that's always a race)

StackExchange.Redis/Message.cs

@@ -619,6 +619,8 @@ internal void SetException(Exception exception)
             resultBox?.SetException(exception);
         }
 
+        internal bool TrySetResult<T>(T value) => resultBox is ResultBox<T> typed && typed.TrySetResult(value);
+
         internal void SetEnqueued() => performance?.SetEnqueued();
 
         internal void SetRequestSent()

StackExchange.Redis/PhysicalBridge.cs

@@ -260,6 +260,7 @@ internal void KeepAlive()
                     }
                     break;
             }
+
             if (msg != null)
             {
                 msg.SetInternalCall();
@@ -460,7 +461,9 @@ internal void OnHeartbeat(bool ifConnectedOnly)
                                     OnDisconnected(ConnectionFailureType.SocketFailure, tmp, out bool ignore, out State oldState);
                                 }
                             }
-                            else if (tmp.GetSentAwaitingResponseCount() != 0)
+                            else if (writeEverySeconds <= 0 && tmp.IsIdle()
+                                && tmp.LastWriteSecondsAgo > 2
+                                && tmp.GetSentAwaitingResponseCount() != 0)
                             {
                                 // there's a chance this is a dead socket; sending data will shake that
                                 // up a bit, so if we have an empty unsent queue and a non-empty sent

StackExchange.Redis/PhysicalConnection.cs

@@ -399,13 +399,21 @@ void add(string lk, string sk, string v)
                 while (_writtenAwaitingResponse.Count != 0)
                 {
                     var next = _writtenAwaitingResponse.Dequeue();
-                    var ex = innerException is RedisException ? innerException : outerException;
-                    if (bridge != null)
+
+                    if (next.Command == RedisCommand.QUIT && next.TrySetResult(true))
+                    {
+                        // fine, death of a socket is close enough
+                    }
+                    else
                     {
-                        bridge.Trace("Failing: " + next);
-                        bridge.Multiplexer?.OnMessageFaulted(next, ex, origin);
+                        var ex = innerException is RedisException ? innerException : outerException;
+                        if (bridge != null)
+                        {
+                            bridge.Trace("Failing: " + next);
+                            bridge.Multiplexer?.OnMessageFaulted(next, ex, origin);
+                        }
+                        next.SetException(ex);
                     }
-                    next.SetException(ex);
                     bridge.CompleteSyncOrAsync(next);
                 }
             }

StackExchange.Redis/ResultBox.cs

@@ -82,6 +82,13 @@ public void SetResult(T value)
             this.value = value;
         }
 
+        internal bool TrySetResult(T value)
+        {
+            if (_exception != null) return false;
+            this.value = value;
+            return true;
+        }
+
         public override bool IsAsync => stateOrCompletionSource is TaskCompletionSource<T>;
 
         public override bool TryComplete(bool isAsync)