ah well, glad to hear that ! It certainly can be more of a core element if it
had some more dedicated maintainers. I haven't actually used it in a real
project so i can't vouch strongly for it. It also might be a nice
third-party project. Sharding is very tough and there's lots of complex cases
that come up pretty fast.
On Apr 20, 2011, at 8:05 PM, can xiang wrote:
> Thanks anyway.
>
> It's sad horizontal shard extension is only considered as a example. I hardly
> believe it, because it works so great in some of my simple use case. I really
> hope there would be more work on this extension or more docs on how to do it.
>
> Best regards!
> can
>
> On Thu, Apr 21, 2011 at 3:19 AM, Michael Bayer <mike...@zzzcomputing.com>
> wrote:
>
> On Apr 20, 2011, at 4:37 AM, can xiang wrote:
>
> > Hi,
> >
> > I have a problem of bulk deleting from a sharded session, I tried to
> > search the previous posts without any finding.
> >
> > I have the following table:
> >
> > usersession_table = Table('kg_usersession', meta,
> > Column('session_id', String(32),
> > primary_key=True),
> > Column('user_id', BigInteger, index=True,
> > nullable=False),
> > Column('create_time', DateTime, index=True),
> > Column('expire_time', DateTime, index=True),
> > Column('site', String(10)),
> > mysql_engine='MyISAM'
> > )
> >
> > I use horizontal sharding by "session_id", with the following shard
> > chooser:
> >
> > def shard_chooser(mapper, instance, clause=None):
> > if instance:
> > return shard_value(instance.session_id)
> >
> > Then, I want to delete all record earlier than a given expire_time,
> > with the following code:
> >
> > session.query(UserSession).filter(UserSession.expire_time<=expire_time).delete();
>
> range deletions are not supported by the ShardedSession extension right now.
> You'd need to implement your own delete() onto ShardedQuery.
>
> Note that the horizontal shard extension really should have been an example,
> not a full extension. It's really just a proof of concept and real-world
> horizontal sharding scenarios will usually need to tweak it for specific use
> cases.
>
>
>
>
>
> >
> > It raises an error:
> >
> > Traceback (most recent call last):
> > File "delete_expire_session.py", line 20, in <module>
> > delete_expire_session(expire_time)
> > File "delete_expire_session.py", line 13, in delete_expire_session
> >
> > session.query(UserSession).filter(UserSession.expire_time<=expire_time).delete();
> > File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> > py2.6.egg/sqlalchemy/orm/query.py", line 2142, in delete
> > result = session.execute(delete_stmt, params=self._params)
> > File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> > py2.6.egg/sqlalchemy/orm/session.py", line 726, in execute
> > engine = self.get_bind(mapper, clause=clause, **kw)
> > File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> > py2.6.egg/sqlalchemy/ext/horizontal_shard.py", line 73, in get_bind
> > return self.__binds[shard_id]
> > KeyError: None
> >
> > I guess shard_chooser return None because of "instance" is None at
> > runtime. I read from the docs: shard_chooser maybe in "some round-
> > robin scheme". But I don't have any idea what does it exactly mean in
> > my case.
> >
> > I appreciate any advice.
> >
> > Best regards!
> > can
> >
> >
> > PS: you can access partial source code in the gist:
> > https://gist.github.com/930708
> >
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> >
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