Read delay in App Engine Datastore after put()

Question

I write a code for a blog/news site. Main page has 10 most recent articles and also there is an archive section with all articles sorted by modification time descending. In

Answer 1

You're most likely being hit by "eventually consistent queries". When using the HR datastore, queries may use slightly old data, and it takes a while for data written by put() to be visible to queries (there is no such delay for get() by key or id). The delay is typically measured in seconds but I don't think we guarantee an upper bound -- if you're hit by an unfortunate network partition it might be hours, I imagine.

There are all sorts of partial solutions, from cheating when the author of the most recent writes is viewing the query results to using ancestor queries (which have their own share of limitations). You might simply give your cache a limited lifetime and update it on read instead of write.

Good luck!