tree 8917b9a22b17625856affebf8c34db7099675cf9
parent 3ce28641c85af0d5054df47e9ac7de917a9d33cd
author Benjamin Anderson <b@banjiewen.net> 1468790722 -0700
committer Benjamin Anderson <b@banjiewen.net> 1468791775 -0700

Replace `stale` with `stable` and `update`

The `stale` mechanism for view queries conflates two independent
concerns:

1. Whether or not the view results should be returned from a "stable"
   set of shards; i.e., mem3:ushards. This semantic is new in 2.0,
   having originated in Cloudant code in 2011[1].

2. Whether or not the view in question should be updated prior to
   responding to the user, i.e., the pre-2.0 semantics.

Both of these concerns represent consistency/availability tradeoffs, but
they're addressing rather different aspects of that continuum. As such,
the "stale" mechanism limits flexibility.

For example, it's quite likely that a user would want to retrieve
"stale" view responses from the fastest available shards - the
"available/available" choice - and this choice is not available with the
existing "stale" mechanism. A similar argument could be made for the
"consistent/consistent" choice.

This patch introduces two new view API keywords - "stable" and "update"
- to address concerns #1 and #2, respectively. The semantics of the
"stale" mechanism is implemented in terms of these new keywords.

COUCHDB-3063

[1]: apache/couchdb-fabric@93923fda51c714c015b8621e41f3c425bfb3e61a