I am new to Google Cloud Datastore. I have read that there is a write limit on 1 write per second on an entity group. Does it means that the main "guestbook" tutorial on app engine cannot scale to thousands of very active users?
2 Answers
4
votes
Indeed.
The tutorial is just a showcase. The writes per second limitation is due to the strong consistency guarantee for entities in the same group or ancestor. This limit can be exceed at the price of changing strong consistency by eventual consistency, meaning all datastore queries will show the same information at some point. This is due to App engine distributed design.
Please, have a look at https://cloud.google.com/appengine/articles/scaling/contention to avoid datastore contention issues. Hope it helps.
1
votes
Yes, I think it does mean that.
It might not be a problem if the greetings are all added to different guestbooks, but quickly adding Greetings to the same Guestbook is definitely not gonna scale. However, in practice it's often much faster than 1 write per second.
Perhaps you could work around this by using a taskqueue to add Greetings, but that might be overkill.
That guestbook tutorial is not a very good example in general. You shouldn't put logic in your jsp's like in that example (you probably shouldn't use jsp's at all). It's also not very practical to use the datastore at such a low level. Just use Objectify.
