[Couchdb Wiki] Update of "DocumentRevisions" by JimLindley

[Apache Wiki <wi...@apache.org>]

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Couchdb Wiki" for change notification.

The following page has been changed by JimLindley:
http://wiki.apache.org/couchdb/DocumentRevisions

The comment on the change is:
initial document revisions 

New page:
== Overview ==

CouchDB does not overwrite updated documents in place, instead it creates a new document at the end of the database file, with the same `_id` but a new `_revision` identifier. Document revisions are also used to handle conflicting updates. Outdated revisions are not exposed to views. Conflicts may be resolved by your application, the default conflict resolution scheme is to use the potential candidate that made the most changes to the subject document.

The storage system is disk-wasteful so ["Compaction"] is needed. The revisions are not, at least at this point, meant to implement revision control systems, they rather exists for the optimistic concurrency control that allows any number of parallel readers while serialised writes are happening and to power replication.