Make max document size configurable

Hello,

We're seeing that document size highly affect sub-doc operations (bigger document, the most likely we'll receive timeout on operation) and we would like to decrease max document size. Unfortunately for now it is not possible on database side and current not configurable value is not acceptable in terms of performing sub-doc operations in efficient time.

We can check how big is document on insert/update and reject big docs, but couldn't find a way to prevent it in case of subdoc API operations (e.g. 1k updates of different subdocument paths, how can I detect that any of update will cause configured document size exceed ?).

I think it will be beneficial to give an option to configure max document size per bucket to allow tune it according to sub-doc operations response time.

Ticket issued after discussion in couchbase forum topic: https://forums.couchbase.com/t/how-can-i-change-the-max-document-size/16053