Hello again,
I'm getting errors in a certain case which lead me to suspect that I'm
missing some big picture sharding concept, so to better understand
sharding I'm playing with the SQLAlchemy sharding unit tests
(sqlalchemy/test/orm/sharding/test_shard.py).
Here's one of the investigative tests I've added in order to better
understand query_chooser:
def test_read(self):
session = create_session()
query = session.query(WeatherLocation)
print "get tokyo:"
# query_chooser returns: ['asia']
tokyo = query.filter_by(city='Tokyo').filter_by
(continent='Asia').first()
print "access tokyo:"
# query_chooser returns: ['north_america', 'asia', 'europe',
'south_america']
assert tokyo.city == "Tokyo"
My question: If we already have an instance of tokyo from the 'get
tokyo' code snippet, why is a new query_cls being instantiated to
rerfesh the tokyo object on access (thus having to traverse all 4
shards) rather than using shard_chooser and the got instance to
compute the shard based on its continent value? Is there some way I
can optimize this case, perhaps by setting the shard_id somewhere, so
that 4 queries aren't executed in this case? Hope that was clear
enough.
Thanks again for your time,
--diana
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