auto_update class attribute added for AbstractWhoosheer

[clime]

Decides if a whoosheer should be updated by on_commit method.

Default value is True and it can be changed in a user-specified whoosheer:

@whooshee.register_whoosheer
class CoprWhoosheer(AbstractWhoosheer):
   schema = whoosh.fields.Schema(
        copr_id=whoosh.fields.NUMERIC(stored=True, unique=True)
   )

  auto_update = False

The rationale for this feature is that index updates in our system can take a long time (around 0.8s) and if there are several concurrent requests to update the search index, some of them occasionally time out with 'LockError'. That's why we need to switch from continuous auto-updating of the search index to updating in batches (every hour, e.g.) and only for those records that have been modified (this is covered by a piece of custom logic).

The optimization here is that if a db record was modified many times in the passed hour, the search index record will be modified only once. Also search index updating will become sequential and hence proof to lock errors caused by many concurrent accesses.

Our index has become very large lately and that is why we need this. I'll add README and tests if you will agree with this feature.

[bkabrda]

Sorry for responding so late to this issue, I didn't notice the notification in my inbox...

Yeah, this makes perfect sense to me. If you can provide docs and tests, it will be absolutely awesome (feel free to describe the whole usecase in README, so that readers understand why this was implemented and what problem it solves).

[clime]

Docs & tests added.

[bkabrda]

LGTM, finally merging! :) thanks and sorry for the delay.

[bkabrda]

Released as part of flask-whooshee 0.5.0: https://pypi.python.org/pypi/flask-whooshee/0.5.0