launchpad-dev team mailing list archive

[Bjorn Tillenius <bjorn@xxxxxxxxxxxxx>]

On Tue, Feb 23, 2010 at 03:43:42PM +0700, stuart.bishop@xxxxxxxxxxxxx wrote:
> Hi. There were some inquiries recently on how to get scripts using slave databases, in order to reduce load on the master databases. I've taken this opportunity to improve the syntax and write improved documentation. The new documentation is in lib/canonical/launchpad/doc/db-policy.txt and is reproduced below.
> 
> Storm Stores & Database Policies
> ================================
> 
> Launchpad has multiple master and slave databases. Changes to data are
> made on the master and replicated asynchronously to the slave
> databases. Slave databases will usually lag a few seconds behind their
> master. Under high load they may lag a few minutes behind, during
> maintenance they may lag a few hours behind and if things explode
> while admins are on holiday they may lag days behind.
> 
> If know your code needs to change data, or must have the latest posible
> information, you retrieve objects from the master databases that stores
> the data for your database class.
> 
>    >>> from canonical.launchpad.interfaces.lpstorm import IMasterStore
>    >>> from lp.registry.model.person import Person
>    >>> import transaction
> 
>    >>> writable_janitor = IMasterStore(Person).find(
>    ...     Person, Person.name == 'janitor').one()

All these examples deal with the Person class directly. A lot of scripts
use getUtility(IFooSet) to get security proxied objects. Can you give an
example of how that works?




-- 
Björn Tillenius | https://launchpad.net/~bjornt