This was reported on the puppet-users list here:
I don't know the specific context in which the user is encountering it, but I'm able to reproduce this issue by creating and storing a very large array-valued structured fact with map-valued elements, then updating the fact by inserting an element at the front of the array to force recomputation of all the paths. This problem was encountered on 2.3.7, but it affects master/3.x as well.
We'll need to coordinate with the user to figure out what's going on with his particular setup. If this relates to a large array-valued structured fact, reformulating the top-level structure as a map would likely fix the issue. Ultimately, if we want to support arbitrarily large structured facts we'll want to expose jdbc's max message size as a tunable. Alternatively we should document our limits.