Hi all again,
Trying to deploy polymorphic inheritance, I am now hit by what may be
another bug: it seems like getting polymorphic objects may be 100
times slower than regular ones.
I reproduce the problem in the copy-pastable script below, using a
single table polymorphic inheritance scenario. On my machine, the
output of this script gives me:
The non-polymorphic loop took 0.082 seconds
The polymorphic loop took 7.916 seconds
The polymorphic loop was 96 times slower
I know that there may be *some* overhead in using polymorphism, but 96
times slower sounds way too much, so I am suspecting some form of bug.
Is this a known issue? Is there a work around?
Thank you for your help!
### BEGIN: polymorphic_inheritance_slowness_test.py ###
from sqlalchemy import *
db = create_engine('sqlite://', echo=False)
__meta__ = BoundMetaData(db)
person_table = Table("persons", __meta__,
Column("id", Integer, primary_key=True),
Column("ptype", String(80)), # Polymorphic ID field
Column("name", String(80)),
)
class Person(object):
def __init__(self, name):
self.name = name
class Employee(Person): pass
__meta__.create_all()
person_mapper = mapper(Person, person_table,
polymorphic_on=person_table.c.ptype)
mapper(Employee, person_table, inherits=person_mapper,
polymorphic_identity='EMPLOYEE')
person_insert = person_table.insert()
# Alice is just a Person (non-polymorphic)
person_insert.execute(id=1, ptype=None, name='alice')
# Bob is an Employee (polymorphic)
person_insert.execute(id=2, ptype='EMPLOYEE', name='bob')
session = create_session()
query = session.query(Person)
# Now timing loops getting our 2 objects:
from time import time
start1 = time()
# Non-polymorphic get loop
for i in range(5000):
dummy = query.get(1)
time1 = time() - start1
start2 = time()
# Polymorphic get loop
for i in range(5000):
dummy = query.get(2)
time2 = time() - start2
print """The non-polymorphic loop took %0.3f seconds
The polymorphic loop took %0.3f seconds
The polymorphic loop was %i times slower""" % (time1, time2, time2/
time1)
### END ###
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