I have a model Tweet that I'd like to shard horizontally based on the
tweet author's id.
class Tweet(models.Model):
author_id = models.IntegreField()
text = models.TextField()
Let's say I set up 3 databases: shard0, shard1, shard2
I'd like to take the tweet author's id, do a modulo 3 and use the
result to determine which shard a tweet should be located in.
If I understand the documentation correctly, I'd do something like:
class TweetRouter(object):
N = 3
def db_for_read(self, model, **hints):
if model.__name__ == "Tweet" and hints['instance'].author_id %
N == 0:
return 'shard0'
if model.__name__ == "Tweet" and hints['instance'].author_id %
N == 1:
return 'shard1'
if model.__name__ == "Tweet" and hints['instance'].author_id %
N == 2:
return 'shard2'
return None
A couple of questions:
- Did I use the argument **hints correctly? I'm not entirely sure
- How is auto-increment PK being handled in a horizontal sharding
scenario like this?
Say I have 3 tweets with 3 author_id: 0, 1, 2
Those 3 tweets will live in 3 separate databases.
Each of them will get an auto-increment PK assigned by its database.
Since they all live in different databases, potentially they could all
get the same PK.
Does that mean if I shard a model horizontally I could get into a
situation where different model instances could have the same PK? How
is this being handled?
Thanks
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