CODEWITHSUNDEEP
pythongoogle-app-enginememcachedapp-engine-ndb
David Smith
David Smith

Reputation: 892

Why is there a memcache delete at the end of this NDB put operation?

I'm just experimenting with Appstats and NDB on Google App Engine.

I understand that the immediate get following the put would come from the local memory cache but why is there a memcache delete operation?

This is all the code:

import webapp2
from google.appengine.ext import ndb

class Specs(ndb.Model):
    make = ndb.StringProperty()
    model = ndb.StringProperty()
    doors = ndb.IntegerProperty()
    wheels = ndb.IntegerProperty()

class Car(ndb.Model):
    _use_memcache = True
    _use_cache = True
    specs = ndb.LocalStructuredProperty(Specs)

class MainHandler(webapp2.RequestHandler):
    def get(self):
        my_car = Car(id='some-car')
        specs = Specs(
          make = "Volvo",
          model = "240",
          doors = 5,
          wheels = 4
        )
        my_car.specs = specs
        result = my_car.put()

        my_car_by_get = result.get()

        self.response.write('Saved car')

app = webapp2.WSGIApplication([
    ('/', MainHandler),

], debug=True)

And the Appstats timeline:

Appstats timeline of an NDB put operation

Upvotes: 3

Views: 226

Answers (1)

Lipis
Lipis

Reputation: 21835

The memcache.Delete() is being called on every put() when you're using the NDB because of the automatic caching and this is by design. You can read more about the NDB caching if you want to have a better control or different behaviour when it comes to caching.

Upvotes: 1

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