Hi Ikai, Thanks for the follow up. I can't say for sure, and the following is my crystal ball guess of what's happening.
The problem only occurred when I was developing my email webhook. It has since stopped happening (I think). When developing my webhook, often I had exceptions thrown as a result of not parsing the Multiparts correctly. On the surface, it looks like when an exception is thrown, the email is marked as undelivered and AppEngine retries to send again later. This is further complicated when on some requests, I was processing a plain text email as a MultiPart email, which resulted in OutOfMemoryErrors. Due to the high CPU usage, AppEngine temporarily shuts down my app. Not sure what happens next, but it would appear the SMTP server retries whilst my app is down/suspended or otherwise broken and ends up failing to deliver each time. Something gets out of sync then, because it would build up a backlog of failed deliveries and retries for each failed delivery! The other side effect was my app would never stay up - AppEngine would restart it and then it would immediately get shut down again (due to the high CPU usage from the OutOfMemoryErrors). Once I fixed my code, I noticed lots of repeated emails coming through (and getting processed/saved to the datastore). I let it run for several hours for it to clear the backlog of emails. It has since stopped delivering these dups. Does this make sense? Plausible? Prior to using AppEngine's inbound mail funtionality, I was using http://smtp2web.com which had a nice feature in that if an exception is thrown when calling the webhook, it would send a bounce email to the sender and stop trying. This was nice I thought because there was user feedback that the mail didn't get through. Your thoughts? dave AppEngine may opt to suspend the app (eg due to high CPU usage). This in turn could be signalling to the SMTP server that the mail delivery has failed and signal it to try again later. However, what gets placed in the queue may be a duplicate, so there might be a reference to two copies of the same email that needs to be delivered. After a certain timeout, AppEngine restarts the app, which fails to restart properly because it immediately fails again due to the email resend. This is further complicated if a new version is deployed with changes to the email webhook - so some requests would succeed and others fail. On Nov 19, 8:35 am, "Ikai L (Google)" <ika...@google.com> wrote: > Hi Dave, > > Have you had any luck reproducing this? If so, what did you do? > > > > > > On Tue, Nov 17, 2009 at 4:45 AM, Dave Cheong <d...@davecheong.com> wrote: > > Hi all, > > > I'm observing a situation where my email webhook (/_ah/mail/*) is > > being invoked multiple times (seemingly randomly) for a given email. > > Not sure the pattern, but I'm definitely seeing log messages with the > > same email content multiple times, in no particular order or pattern. > > > I'm not sure if a red herring, but it does appear to be somewhat > > related to the fact that I am deploying new versions and restarting > > the app constantly, as I tweak my code which handles the inbound > > email. > > > Has anyone observed this behaviour? Can someone in Google help > > diagnose why my email webhook is being called repeatedly? > > > Any help is appreciated. > > > thanks, > > dave > > > -- > > > You received this message because you are subscribed to the Google Groups > > "Google App Engine for Java" group. > > To post to this group, send email to > > google-appengine-j...@googlegroups.com. > > To unsubscribe from this group, send email to > > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2B > > unsubscr...@googlegroups.com> > > . > > For more options, visit this group at > >http://groups.google.com/group/google-appengine-java?hl=. > > -- > Ikai Lan > Developer Programs Engineer, Google App Engine -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. To post to this group, send email to google-appengine-j...@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=.
