how to minimize the massive message delay paho mqtt - python-3.x

Question

I have seven raspberry pi's as clients a and one raspberry pi as client b which are transferring messages between each other via mqtt. It's working well so far, but there is a massive delay of over 2s sometimes. Most of the times the the delay is arround 0,02-0,2s but sometimes there are some delay-peaks with over 2s of delay.
I think it appears as soon as client b gets too many messages at the same time from the a clients.
Has anybody of you guys an idea what's the reason for this and how I can solve this?
Thanks and stay healthy!
When the run() is called, client a publishes to client b
client a
from datetime import datetime
import time
import paho.mqtt.client as mqtt
class CarClient:
def __init__(self, id):
self.client = mqtt.Client(id)
self.client.connect("192.168.178.41", 1883, 60) # connect to broker
self.newSpeed = 0
self.holdSpeedTime = 5
self.speedDuration = 0
self.id = id
self.time_sent = 0
def on_connect(self, mqttc, obj, flags, rc):
print("connected" + str(rc))
def on_message(self, mqttc, obj, msg):
answerTuple = eval(msg.payload)
self.newSpeed = int(answerTuple[0])
self.holdSpeedTime = answerTuple[1]
self.client.unsubscribe("test_channel")
time_feedback = time.time()
delay = time_feedback - self.time_sent
print(str(delay))
def on_disconnect(self, mqttc, flags, rc):
print("disconnected" + str(rc))
def on_publish(self, mqttc, obj, mid):
print("Data published " + str(mid))
print("published")
def on_subscribe(self, mqttc, obj, mid, granted_qos):
print("Subscribed: " + str(mid) + " " + str(granted_qos))
def on_unsubscribe(self, mqttc, flags, rc):
print("unsubscribed" + str(rc))
def on_log(self, mqttc, obj, level, string):
print(string)
def run(self, carID, connectionPoint):
self.time_sent = time.time()
self.tuple = (carID, connectionPoint)
# assining functions to callback
self.client.on_disconnect = self.on_disconnect
self.client.on_connect = self.on_connect
self.client.on_message = self.on_message
# self.client.on_subscribe = self.on_subscribe
# self.client.on_unsubscribe = self.on_unsubscribe
self.client.loop_start()
self.client.subscribe(str(self.id), 0) # subscribe topic
self.client.publish("test_channel1", str(self.tuple))
time.sleep(1)
carFeedback = (self.newSpeed, self.holdSpeedTime)
self.newSpeed = 0
self.holdSpeedTime = 5
return carFeedback
client b
import paho.mqtt.client as mqtt
import time
crossingList = []
def on_subscribe(client, userdata, mid, granted_qos): # create function for callback
print("subscribed with qos", granted_qos, "\n")
def on_disconnect(client, userdata, rc=0):
print("disconnected")
def on_connect(client, userdata, flags, rc):
print("connected")
def on_message(client, userdata, message):
dataTuple = eval(message.payload) # message is a tuple of (carID, connectionPoint)
print(str(dataTuple))
addToList(dataTuple)
def on_publish(client, userdata, mid):
print("published")
def addToList(dataTuple):
carID = dataTuple[0]
connectionPoint = dataTuple[1]
crossingList.append((carID, connectionPoint))
def logic():
carID = crossingList.__getitem__(0)[0]
connectionPoint = crossingList.__getitem__(0)[1]
if connectionPoint == 600:
newSpeed = 400
holdTime = 5
client.publish( carID, str((newSpeed, holdTime)))
del crossingList[0]
else:
newSpeed = 500
holdTime = 3
client.publish(carID, str((newSpeed, holdTime)))
del crossingList[0]
client = mqtt.Client("Logic") # create client object
client.on_subscribe = on_subscribe # assign function to callback
client.on_disconnect = on_disconnect # assign function to callback
client.on_connect = on_connect # assign function to callback
client.on_message = on_message
client.connect("192.168.178.41", 1883, 60) # establish connection
time.sleep(0.1)
client.loop_start()
client.subscribe("test_channel1")
count = 1
while True: # runs forever break with CTRL+C
if len(crossingList) != 0:
logic()
else:
count = count + 1