"The changes feed is just a listing of documents ordered by their current sequence numbers."
Succinctly put. B. On 23 August 2013 16:15, Jens Alfke <j...@couchbase.com> wrote: > > On Aug 23, 2013, at 1:01 AM, Jens Rantil <jens.ran...@gmail.com> wrote: > >> Just to be clear, does compaction influence the changes feed in any way? > > It may help to think of the changes feed this way: > > Every database has a last-sequence counter (similar to a SQL table’s > autoincrement counter.) > Every document has a sequence number*. > Whenever a document is updated (i.e. a revision is added) its sequence number > is changed to the next available sequence count. > The changes feed is just a listing of documents ordered by their current > sequence numbers. > (Under the hood, the database has a separate b-tree index that maps sequence > numbers to document IDs.) > > Thus the effect is that updating a document moves it to the end of the > changes feed, with a new sequence number. > > Compaction doesn’t have any effect on this at all; all it does is prune > intra-document revision data. > > —Other Jens ;) > > * This gets more complex with BigCouch/Cloudant, because it’s clustered. The > opaque sequence IDs it shows clients are actually aggregates of the sequence > numbers of all the nodes in the cluster.
