add partition endpoint for views

[garrensmith]

Add partition endpoints for view queries. Support /db/_partition/:partitionkey/_designdoc/name/_view/viewname queries

[rnewson]

couldn't we just use DbName from path_parts above?

[rnewson]

this will be a 500 Server Error? I think you need a different shape to get a 400 Bad Request.

[wohali]

I know this is for user-specified partitions, but I wonder what endpoint we're exposing for per-shards at :5984 (necessary to deprecate :5986 once and for all), and whether this endpoint will cause confusion.

[wohali]

08:48 <garren> Wohali: I don't quite follow what you mean here
               https://github.com/apache/couchdb/pull/1480#issuecomment-409554240
08:51 <-- ASFBot (~ASFBot@apache/bot/asfbot) has quit (Ping timeout: 260 seconds)
08:51 <@Wohali> I mean, rnewson and i have had a long standing discussiona bout
                introducing a new endpoint on 5984 for shard-level queries
08:52 <@Wohali> we haven't been able to come up with the right endpoint yet
08:52 <@Wohali> but it eventually needs to exist
08:52 <@Wohali> and i just want to ensure that by introducing the new concept of a
                _partition we aren't further confusing people
08:52 <@Wohali> because I wouldn't be surprised to see an endpoint like
                /db/_shard/000000-1ffffff/...
08:53 <@Wohali> and then the question becomes: is this a db partition, or a view partition
                you are proposing?
08:53 <@Wohali> if the latter, then why not /db/_ddoc/name/_view/viewname/_partition
08:53 <@Wohali> i'm trying not to bikeshed, but our ui is already somewhat complex, and
                it's only going to get worse, that's all
08:53 <@Wohali> does that make sense?
08:55 <garren> Yes that makes sense thanks.
08:55 <@Wohali> i 100% guarantee you that people will not understand the difference
                between a db shard and a db partition if we introduce both concepts
                without careful thought :)
08:55 <garren> THe one thing is that a shard can hold multiple partitions. So they are
               related but not that related to shards
08:55 <@Wohali> subtle.
08:55 <garren> Yeah I agree 100%
08:57 <@rnewson> hasn't the partition proposal been on dev@ yet?
08:57 <@rnewson> cause I'm deep into implementation at this point and so is garren
08:57 <@Wohali> changing the endpoint is minor
08:57 <@Wohali> i'm fine with the concept
08:58 <@Wohali> i am not happy with the partition being at the 2nd level in the route,
                though
08:58 <@Wohali> i am not happy with the partition being at the 2nd level in the route,
                though
08:58 <@rnewson> can you respond to the thread saying so then?
08:58 <@Wohali> yes