On Thu, Jun 18, 2009 at 11:45 AM, Dennis <dennisf...@gmail.com> wrote:
> > I asked about this (datastore timeout exceptions) in yesterday's app > engine chat and just wanted to follow up. > > I'm trying to figure out an architecture to deal with the timeout > exceptions. > The "solution" of pushing the exception back to the end user is > actually ok for my app. > This works for read timeouts. > > For write timeouts, my code can be in the middle of storing a data > structure when the timeout happens. > Thus, I could have a corrupt data structure instance in my datastore. I presume by 'data structure', you mean multiple entities? Because individual entities (and entity groups inside transactions) will always be written atomically - all or nothing - and never 'corrupted' or partially written. > So, for fault-tolerant production code, any (later) access to any > datastore data structure should check > the integrity data structure before using it. > This is what Ken Ashcraft's google i/o 2008 talk recommended (without > referring specifically to timeout issues): > > http://sites.google.com/site/io/best-practices---building-a-production-quality-application-on-google-app-engine > > A bit troublesome but at least we know what to do: > every datastore read needs to do data structure integrity checking. > > > I just want to get feedback on whether this line of thinking and the > resulting coding style is what the appengine team recommends. > Also, it would be very helpful to know what google engineers do to > avoid this issue (do they use the same style or do they have internal > tools or libraries that hide this issue from them). More or less. If your write order is predictable, some of your queries will probably not care about incomplete data, or that they may see data that's only partially written. In general, though, the 'roll forward' approach works quite well. -Nick Johnson > > > Dennis > > search term: DatastoreTimeoutException > > > > On Jun 18, 6:01 pm, Iap <iap...@gmail.com> wrote: > > 2009/6/18 Nick Johnson (Google) nick.john...@google.com > > > > > > > > > For datastore puts and deletes, we currently automatically retry when > > > timeouts occur, and for datastore transactions, your user code is rerun > if a > > > timeout occurs. Gets and queries are currently not retried. > > > > It's exciting that the GAE inherites the "I'm feeling lucky" tradition of > > Google. >_* > > > > Why not retry the Get and Queires ? > > If the retry will eventually succeed, > > How about provide a decrator for convenience to do the things right. > > > > Iap > > > -- Nick Johnson, App Engine Developer Programs Engineer Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number: 368047 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
