On Thu, Oct 1, 2009 at 4:20 PM, mably <fm2...@mably.com> wrote: > > In fact my update rate might be pretty high. > > In the case of a timestamp field : are the servers/instances clocks > perfectly synchronized (millisecond/precision of a date object in > java) ? >
No. It's not possible to get clocks 'perfectly' synchronized, and short of dedicated hardware, millisecond precision is likewise impractical. Distributed monotonic counters are a great unsolved problem in computer science. Clocks on machines App Engine apps run on are synchronized with NTP, as reliably as is practical. -Nick Johnson > On 1 oct, 17:10, "Nick Johnson (Google)" <nick.john...@google.com> > wrote: > > Hi mably, > > If your update rate is low (less than 1 QPS), you can use a counter > entity, > > updating it in each transaction. If you don't need your sequence IDs to > be > > unique - only incrementing - you can do a best effort fetch for the > highest > > existing ID, and set your new entity to one more than that value. > Otherwise, > > your best option is a timestamp field. > > > > -Nick Johnson > > > > > > > > > > > > On Thu, Oct 1, 2009 at 4:08 PM, mably <fm2...@mably.com> wrote: > > > > > Thanx for your answer, so no way to get a kind of sequence besides > > > using Date fields I guess... > > > > > On 1 oct, 17:04, "Nick Johnson (Google)" <nick.john...@google.com> > > > wrote: > > > > Hi mably, > > > > > > On Thu, Oct 1, 2009 at 4:00 PM, mably <fm2...@mably.com> wrote: > > > > > > > Hi everybody, > > > > > > > Is there any way to create/emulate a "sequence" with the datastore > ? > > > > > > > I first thought that entity IDs where sequentially created, I was > > > > > wrong : old IDs can be reused. > > > > > > Old IDs are never reused. IDs allocated by the datastore are always > > > unique, > > > > but may not be sequential - so IDs could be numbered in the following > > > order: > > > > > > 1 > > > > 2 > > > > 1001 > > > > 3 > > > > 1002 > > > > > > -Nick Johnson > > > > > > > So no way to sort by IDs to fetch the last inserted one. > > > > > > > I could sort by a Date field but could get some conflicts, I could > had > > > > > a suffix in such cases though. > > > > > > > Does anybody have a better idea ? > > > > > > > Thanx in advance. > > > > > > > François > > > > > Bordeaux, FRANCE > > > > > > -- > > > > Nick Johnson, Developer Programs Engineer, App Engine > > > > Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration > > > Number: > > > > 368047 > > > > -- > > Nick Johnson, Developer Programs Engineer, App Engine > > Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration > Number: > > 368047 > > > -- Nick Johnson, Developer Programs Engineer, App Engine 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 -~----------~----~----~----~------~----~------~--~---
