Hi, I am running a Django app on appengine, but I am constantly
hitting the roof with read operations.
I have not found an easy way to find what's causing this, so I am
trying to find it out myself.
To me, it seems that even if I use all().filter(..) or get(), the
database is queried for all instances.
I wrote a custom manager like this:
class LoggingManager(models.Manager):
def get_query_set(self):
query_set = super(SignalsManager, self).get_query_set()
logging.debug("Got the following queryset from the backend:")
logging.debug(query_set)
if query_set.count():
key = "num_of_reads_for_" + str(type(query_set[0]))
num_of_calls_so_far = memcache.get(key) or 0
num_of_calls_so_far += query_set.count()
memcache.delete(key)
memcache.add(key, num_of_calls_so_far )
logging.debug("++++++++++++++++++++++++++++++++++")
logging.debug("total number of reads for " + key)
logging.debug(num_of_calls_so_far)
logging.debug("----------------------------------")
return query_set
I then created a class:
class Foo(models.Model):
bar = models.CharField(max_length=10)
objects = LoggingManager()
When I tried this in the shell I got:
>>> Foo(bar="Hi").save()
>>> Foo(bar="there").save()
>>> Foo.objects.get(bar="Hi")
DEBUG:root:Got the following queryset from the backend:
DEBUG:root:[<Foo: Foo object>, <Foo: Foo object>]
DEBUG:root:++++++++++++++++++++++++++++++++++
DEBUG:root:total number of reads for num_of_reads_for_<class
'models.Foo'>
DEBUG:root:2
DEBUG:root:----------------------------------
<Foo: Foo object>
>>> Foo.objects.all().filter(bar="Hi")
DEBUG:root:Got the following queryset from the backend:
DEBUG:root:[<Foo: Foo object>, <Foo: Foo object>]
DEBUG:root:++++++++++++++++++++++++++++++++++
DEBUG:root:total number of reads for num_of_reads_for_<class
'models.Foo'>
DEBUG:root:4
DEBUG:root:----------------------------------
[<Foo: Foo object>]
>>> Foo.objects.all().filter(bar="NotExisting")
DEBUG:root:Got the following queryset from the backend:
DEBUG:root:[<Foo: Foo object>, <Foo: Foo object>]
DEBUG:root:++++++++++++++++++++++++++++++++++
DEBUG:root:total number of reads for num_of_reads_for_<class
'models.Foo'>
DEBUG:root:6
DEBUG:root:----------------------------------
[]
According to the Django documentation, 'the act of creating a QuerySet
doesn't involve any database activity'.
But since the queryset contains two instances of Foo object when I use
the get() method or all().filter(), isn't the database queried for all
Foo instances? And then the queryset is filtered?
Am I doing something wrong here? Is there a better way to do this?
And does anybody know how this would affect App Engines Quote Details,
since they have a limit of number of operations?
I am using:
Python 2.5.1,
Django (1, 3, 0, 'alpha', 1)
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