Thanks, Jeff! And one more thing, it's pretty clear from the doc, but let me make sure anyway. The same is true for ancestor queries, they guarantee strong consistency even when not performed inside a transaction, right?
Thomas On Mon, Aug 3, 2015 at 8:48 PM, Jeff Schnitzer <j...@infohazard.org> wrote: > Yes, that is correct. By default, if you perform a low-level get-by-key > operation, it is strongly consistent whether or not you put it in a > transaction. > > Note that you can, if you want, explicitly request an eventually > consistent get-by-key operation in the low-level api. It does return faster > since it does not require a quorum response. However, this is a pretty > obscure feature. > > Jeff > > On Mon, Aug 3, 2015 at 7:30 PM, Thomas Becker <walkswiththeb...@gmail.com> > wrote: > >> Thanks for your detailed and thoughtful answer, Jeff. I was aware of the >> fact that within a transaction, all reads will return the original value >> even if one writes it within the transaction. That was not the problem, but >> thanks for pointing it out anyway, it's easy to forget! >> >> Other than that, after reading everything on the subject of GAE datastore >> consistency under JDO, I have decided to fall back to low-level access in >> those cases where strong consistency is of the essence. At the risk of >> sounding acerbic or snarky, it seems clear to me that nobody knows what's >> going on in JDO when it comes to consistency. >> >> So just to confirm, it is true that the low-level get-by-key guarantees >> strong consistency even *when performed outside of a transaction*, >> correct? >> >> Thanks again for your thoughtful answer. Very refreshing indeed. >> >> Thomas >> >> On Mon, Aug 3, 2015 at 8:13 PM, Jeff Schnitzer <j...@infohazard.org> >> wrote: >> >>> I'm no expert on JDO, but the low-level api does guarantee strong >>> consistency for get-by-key operations (that is, unless you explicitly ask >>> for eventual consistency). One of those SO responses suggested it is >>> possible to have the GAE/JDO plugin log its low-level operations - that >>> should at least point you in the right direction. >>> >>> One other thing that might be related: In the low-level API, within a >>> single transaction, all reads will return the original value even if you >>> write it within the transaction. I don't know what JDO does with this; I >>> would expect that subsequent reads would return a session-cached instance >>> and hide this little quirk. But maybe it's related to what you are seeing? >>> >>> Jeff >>> >>> On Mon, Aug 3, 2015 at 1:52 PM, Thomas Becker < >>> walkswiththeb...@gmail.com> wrote: >>> >>>> Thanks for your quick reply, Ryan. I have found several postings on the >>>> Web that describe the same problem, namely, GetObjectById returning stale >>>> data. Here are two from StackOverflow: >>>> >>>> >>>> http://stackoverflow.com/questions/26377347/inconsistent-fetch-from-google-app-engine-datastore >>>> >>>> >>>> http://stackoverflow.com/questions/22005349/appengine-jdo-with-multiple-server-instances-loses-transaction-updates-on-entiti >>>> >>>> Under the circumstances, I don't think it would be a good use of my >>>> time to make a demo app. It seems clear to me that the issue exists. >>>> Besides, the problem is so intermittent that a demo app is of very limited >>>> value. I would be perfectly happy with a statement of the kind, >>>> "GetObjectById() does not guarantee strong consistency, that's how it is, >>>> and here's what you do instead to get strongly consistent data." I just >>>> need to know what's going on. >>>> >>>> On Mon, Aug 3, 2015 at 2:32 PM, Ryan (Cloud Platform Support) < >>>> rbruy...@google.com> wrote: >>>> >>>>> If you can create a sample app that shows this post on it on the PIT >>>>> <https://code.google.com/p/googleappengine/issues/entry> so I can >>>>> investigate this further. >>>>> >>>>> On Saturday, August 1, 2015 at 6:24:55 PM UTC-4, Thomas Becker wrote: >>>>>> >>>>>> I am using the app engine datastore with Java JDO. According to the >>>>>> documentation, ancestor queries are always strongly consistent. Recently, >>>>>> however, I've been seeing a lot of stale data from ancestor queries. It >>>>>> seems to happen randomly. A query may return the most recent data, and a >>>>>> moment later, the same query returns stale data. >>>>>> >>>>> -- >>>>> You received this message because you are subscribed to a topic in the >>>>> Google Groups "Google App Engine" group. >>>>> To unsubscribe from this topic, visit >>>>> https://groups.google.com/d/topic/google-appengine/1re1FtqllnQ/unsubscribe >>>>> . >>>>> To unsubscribe from this group and all its topics, send an email to >>>>> google-appengine+unsubscr...@googlegroups.com. >>>>> To post to this group, send email to google-appengine@googlegroups.com >>>>> . >>>>> Visit this group at http://groups.google.com/group/google-appengine. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/google-appengine/9723734e-0b14-49c0-8c31-3407df8454ad%40googlegroups.com >>>>> <https://groups.google.com/d/msgid/google-appengine/9723734e-0b14-49c0-8c31-3407df8454ad%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Google App Engine" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to google-appengine+unsubscr...@googlegroups.com. >>>> To post to this group, send email to google-appengine@googlegroups.com. >>>> Visit this group at http://groups.google.com/group/google-appengine. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/google-appengine/CAPxj-GA3OKiGfjwgYgKmvZ%3DSi7ZXG3VLvts7%2BjWZ7c2CsC693Q%40mail.gmail.com >>>> <https://groups.google.com/d/msgid/google-appengine/CAPxj-GA3OKiGfjwgYgKmvZ%3DSi7ZXG3VLvts7%2BjWZ7c2CsC693Q%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >>> You received this message because you are subscribed to a topic in the >>> Google Groups "Google App Engine" group. >>> To unsubscribe from this topic, visit >>> https://groups.google.com/d/topic/google-appengine/1re1FtqllnQ/unsubscribe >>> . >>> To unsubscribe from this group and all its topics, send an email to >>> google-appengine+unsubscr...@googlegroups.com. >>> To post to this group, send email to google-appengine@googlegroups.com. >>> Visit this group at http://groups.google.com/group/google-appengine. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/google-appengine/CADK-0uh4Q8kswYMhD5RcxeQJnO3rFshgkfGEbB%2BXzHVXQLbGiw%40mail.gmail.com >>> <https://groups.google.com/d/msgid/google-appengine/CADK-0uh4Q8kswYMhD5RcxeQJnO3rFshgkfGEbB%2BXzHVXQLbGiw%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Google App Engine" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to google-appengine+unsubscr...@googlegroups.com. >> To post to this group, send email to google-appengine@googlegroups.com. >> Visit this group at http://groups.google.com/group/google-appengine. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/google-appengine/CAPxj-GApGFORBdvJd88QvitX_bHLGvAtiQ943WBd0V3Ro9onZw%40mail.gmail.com >> <https://groups.google.com/d/msgid/google-appengine/CAPxj-GApGFORBdvJd88QvitX_bHLGvAtiQ943WBd0V3Ro9onZw%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- > You received this message because you are subscribed to a topic in the > Google Groups "Google App Engine" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/google-appengine/1re1FtqllnQ/unsubscribe > . > To unsubscribe from this group and all its topics, send an email to > google-appengine+unsubscr...@googlegroups.com. > To post to this group, send email to google-appengine@googlegroups.com. > Visit this group at http://groups.google.com/group/google-appengine. > To view this discussion on the web visit > https://groups.google.com/d/msgid/google-appengine/CADK-0ujMaP_xRg6Pjht%3DsCR%3Dc-3hGEJvhXGtOT0h1vcMKhQBqQ%40mail.gmail.com > <https://groups.google.com/d/msgid/google-appengine/CADK-0ujMaP_xRg6Pjht%3DsCR%3Dc-3hGEJvhXGtOT0h1vcMKhQBqQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. 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