In the dev appserver with --high_replication, if I do this: 1. Create a blank entity 2. Edit that entity 3. put that entity 4. Generate a list of entities
That list, more often than not, shows me the blank entity. The entity is in the index, but it does not reflect the put in step #3. This is consistent with the "eventual consistency" model I've read about. If, in step 4, I generate a list of all entity KEYS, and then db.get() those entities, I never see the blank entity. This is also consistent with the documentation. So, I believe that while my pattern requires an extra db roundtrip, it is much less like to show information that will lead to a support call. -Joshua On Sep 8, 2011, at 12:47 AM, Robert Kluin wrote: > This is done on the backend, if I remember correctly. It doesn't gain > you anything. > > > > On Wed, Sep 7, 2011 at 19:28, Joshua Smith <[email protected]> wrote: >> Continuing the dialog with myself :) >> >> I've added this method to one of my classes that extends db.Model() and it >> is working well with the dev appserver in --high_replication mode: >> >> @classmethod >> def gql_with_get(cls, query_string, *args, **kwds): >> return db.get(db.GqlQuery('SELECT __key__ FROM %s %s' % (cls.kind(), >> query_string), *args, **kwds)) >> >> You use it just like gql().fetch(). For example: >> >> boards = BoardModel.gql_with_get("WHERE towns = :1 ORDER BY name", tid) >> >> It doesn't fix the index (things might be out of order, for instance), but >> otherwise, it cures the problem of seeing stale data in HR. >> >> On Sep 7, 2011, at 12:22 PM, Joshua Smith wrote: >> >>> Another thought: The reason I was doing only one meeting per request was >>> because of the old 30 second limit on crons. But cron handlers can be 10 >>> minutes now, which is plenty of time to schedule all the meetings. >>> Therefore, I suppose I could do this, right? >>> >>> now = datetime.datetime.now() >>> for schedule in db.get(db.gql("SELECT __key__ FROM ScheduleModel WHERE >>> next != :1 AND next < :2", None, now)): >>> if schedule.next and schedule.next < now: >>> schedule.cronAuto() >>> >>> Is wrapping a GET around a KEYS-ONLY query guaranteed to get me the >>> real-deal results (except, of course, for the fact that the index might be >>> out-of-date, so I might miss recent changes to who is in/out of the query >>> parameters)? Is this an efficient way to express this, or should I be >>> doing a fetch() on the gql first? >>> >>> It seems like it's possible to use a technique like this to get a >>> more-consistent result in cases where that's desirable. It at least would >>> get you a consistent data for a subset of things matching your query. In >>> principle, you could even re-sort the results if there is an ORDER clause. >>> Seems like this would be something useful in the db API... >>> >>> -Joshua >>> >>> On Sep 7, 2011, at 11:18 AM, Joshua Smith wrote: >>> >>>> >>>> I'm trying to port my existing M/S app to HR because I have a gun to my >>>> head with "Threaded Python Only for HR Apps" written on the bullets. >>>> >>>> My system will schedule meetings automatically. Scheduling a meeting can >>>> take some time, because a bunch of records are created, and a bunch of >>>> emails need to go out. So the code to schedule one looked like this: >>>> >>>> class MeetingAutoHandler(webapp.RequestHandler): >>>> def get(self): >>>> schedule = ScheduleModel.gql("WHERE next != :1 AND next < :2", None, >>>> datetime.datetime.now()).get() >>>> if schedule: >>>> schedule.cronAuto() >>>> taskqueue.add(url='/admin/meetingAuto', method='GET', countdown=1) >>>> >>>> The query looks for a schedule object that needs a meeting to to be >>>> scheduled now. There might be a few of these when the cron runs. So it >>>> does the hard work for one of them (in cronAuto()), and schedules another >>>> call to itself to get the next one using the task queue. >>>> >>>> This isn't going to work in HR because that query is going to keep finding >>>> the same meeting. I could trivially tweak this by setting the >>>> countdown=60, but I've yet to hear any of our google overlords commit to a >>>> maximum value of when "eventually" happens in "eventually consistent". I >>>> presume there might be cases, like during data center transitions, when >>>> "eventually" could be a very long time indeed. It is essentially >>>> unbounded. Right? >>>> >>>> But I like the pattern I'm using here, and I'm trying to change as little >>>> code as possible, so I want to put together a HR-resilient version. >>>> Here's what I came up with: >>>> >>>> class MeetingAutoHandler(webapp.RequestHandler): >>>> def get(self): >>>> now = datetime.datetime.now() >>>> for s in db.gql("SELECT __key__ FROM ScheduleModel WHERE next != :1 AND >>>> next < :2", None, now): >>>> schedule = db.get(s) >>>> if schedule.next and schedule.next < now: >>>> schedule.cronAuto() >>>> taskqueue.add(url='/admin/meetingAuto', method='GET', countdown=5) >>>> return >>>> >>>> So I'm doing a keys-only query and then doing a get() on the key. (I've >>>> never done a keys-only GQL query before, but I think I got it right. Note >>>> to google: There should be an option to Model.gql() to do keys-only >>>> queries!) >>>> >>>> The way I understand HR, that get is going to get the real Model, which >>>> might not meet the criteria in the gql, because the index might be out of >>>> date. Right? >>>> >>>> So I check that the model meets the criteria that I just specified. (Note >>>> to google: It'd be cool if there was a way to test an object against a >>>> query, so I don't have to write the same code twice!) >>>> >>>> Finally, I pushed the next task out a bit, to make it less likely that >>>> I'll have to look at the same objects over and over. >>>> >>>> So what do you think? Any suggestions? (I have a couple things that work >>>> this way, so I want to choose a good design pattern to apply to each of >>>> them.) >>>> >>>> The complexity would be lessened if I could to this: >>>> >>>> class MeetingAutoHandler(webapp.RequestHandler): >>>> def get(self): >>>> q = ScheduleModel.gql_keys_only("WHERE next != :1 AND next < :2", None, >>>> datetime.datetime.now()) >>>> for s in q: >>>> schedule = db.get(s) >>>> if q.matches(schedule): >>>> schedule.cronAuto() >>>> taskqueue.add(url='/admin/meetingAuto', method='GET', countdown=5) >>>> return >>>> >>>> This would require two changes: the db.Model would need to support >>>> gql_keys_only (that's probably trivial); GqlQuery would need a matches() >>>> method (that's probably not trivial). >>>> >>>> It's still a few more lines, but the complexity is about the same as the >>>> old one. >>>> >>>> Worth the trouble of a couple feature request issues? >>>> >>>> -Joshua >>>> >>>> -- >>>> You received this message because you are subscribed to the Google Groups >>>> "Google App Engine" group. >>>> To post to this group, send email to [email protected]. >>>> To unsubscribe from this group, send email to >>>> [email protected]. >>>> For more options, visit this group at >>>> http://groups.google.com/group/google-appengine?hl=en. >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "Google App Engine" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]. >>> For more options, visit this group at >>> http://groups.google.com/group/google-appengine?hl=en. >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Google App Engine" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/google-appengine?hl=en. >> >> > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. 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