Does using post_save and post_delete methods slow down over all Django project speed?

I want to keep track of number of database entries. I do not want to use (in my case) Book.objects.all().count(). I know it works quite fast, but I do not think it is the good way. I have implemented Tracker class and I will be working with that singleton type of class if the numbers are needed.

Question: Does using post_save and post_delete slow down my Django project?

my source code

models.py

from django.db.models.signals import post_save, post_delete
from django.db import models


class Singleton(object):
    _instance = None

    def __new__(class_, *args, **kwargs):
        if not isinstance(class_._instance, class_):
            class_._instance = object.__new__(class_, *args, **kwargs)
        return class_._instance


class Book(models.Model):
    name = models.CharField(max_length=255)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name


class Tracker(Singleton):
    def __init__(self):
        self.__count = self.__get_numbers()

    def __get_numbers(self):
        print("I am getting records")
        return Book.objects.all().count()

    @property
    def count(self):
        return self.__count


def update_record_count(sender, **kwargs):
    tracker = Tracker()
    print("Database entries: {}".format(tracker.count))


post_save.connect(update_record_count, sender=Book)
post_delete.connect(update_record_count, sender=Book)

What I have written above is truely imaginative, just for learning purposes