multiple key ranges as parameters to a couchdb view

Question

is there a way to send multiple startKey/endKey pairs to a view, akin to the keys: [] array that can be posted for keys?

the underlying problem - let's say my documents have "categories" and timestamps. if i want all documents in the "foo" category that have a timestamp that's within the last two hours, it's simple:

function (doc) {
  emit([doc.category, doc.timestamp], null);
}

and then query as

GET server:5894/.../myview?startKey=[foo, |now - 2 hours|]&endkey=[foo, |now|]

the problem comes when i want something in categories foo or bar, within the last two hours. if i didn't care about time, i could just pull directly by key through the keys collection. unfortunately, i have no such option with ranges.

what i ended up doing in the meantime is rounding the timestamp to two-hour blocks, and then multiplexing the query out:

POST server:5894/.../myview
keys=[[foo, 0 hours], [foo, 2 hours], [bar, 0 hours], [bar, 2 hours]]

it works, but will get messy if i want to go back a large amount of time (in relationship to the blocksize)

Answer 1

Your probably better off just doing two queries. CouchDB can handle multiple simultaneous queries pretty well so spin off several processes/threads and query for foo and bar docs seperately.

CouchDB does not currently support multiple range queries. ORing and ANDing keys is pretty much not doable in one query.

Answer 2

There is a CouchDB issue request to let you do just that. I've attached a simple, no guarantees patch to 0.10.1 to that ticket which may work for you. It works for me and lets me do things like:

{
    "keys": [
        {
            "startkey": ["0240286524","2010","03","01"],
            "endkey": ["0240286524","2010","03","07",{}]
        },
        {
            "startkey": ["0442257276","2010","03","01"],
            "endkey": ["0442257276","2010","03","07",{}]
        }
    ]
}

in the POST body, which lets me get all the data across multiple tracking ids, for a range of dates. I call with group=true&group_level=1 to have the results grouped by tracking id. Deeper group levels would allow me to group by tracking id|year, tracking id|year|month etc.

Multiple connections were an unscalable overhead for me as I'd be looking to make 2000 concurrently :) (No, a new view is not an option - we're already at 400GB for data plus one view!)

The issue and patch is at https://issues.apache.org/jira/browse/COUCHDB-523 .