CODEWITHSUNDEEP
androidcouchdb
Amruta
Amruta

Reputation: 469

How to optimize views in couchdb?

I'm writing android using couchdb. I have around 1000 documents. Every DB operation invokes a view,my view is taking a lot of time. Is there a way to optimize views in couch db? If there are less documents then fetching documents is working fast.

Upvotes: 0

Views: 1200

Answers (3)

Noah
Noah

Reputation: 34303

Emit the smallest amount of data as possible in your document in the map function. You can access the entire document using the include_docs=true url parameter if you actually need the entire document

Good

{
  map: function(doc) {
    emit(doc._id, null)
  }
}

Bad

{
  map: function(doc) {
    emit(doc._id, doc)
  }
}

Upvotes: 0

Tim Perry
Tim Perry

Reputation: 13216

The main things to note with views are that both map and reduce values are cached in the view index (see http://horicky.blogspot.co.uk/2008/10/couchdb-implementation.html for details), that views are only rebuilt when you look at them, and that the CouchDB JavaScript engine is not particularly fast.

There's a few options to use all this for actual performance improvements:

  • Accept stale data in your views, and periodically rebuild the view index asynchronously. You can query views with ?stale=ok to immediately return the currently cached view index, from the last time the view was built, and then have some other background task querying with stale != ok to actually do the rebuild. The typical strategies for this are either to rebuild the view every X minutes or watch /db/_changes rebuild the view after every Y changes. Depends on your application.

  • Accept stale data and then always immediately rebuild the view asynchronously afterwards. This uses ?stale=update_after, which I believe will immediately return you a value and then do the view rebuild in the background. Whether to do this or the above depends on your use case and how important up to date values are to you; this might end up with your rebuilding the view far more than is really necessary, and thereby actually slowing down your queries. This does seem easier than the previous option though.

  • Push as much of your code into your map function as possible. This should improve performance in quickly changing databases, because map values are cached and don't need updating until the underlying document changes, whereas reduces need recalculating whenever one of a larger set of documents changes. I'm not sure exactly how reduce recalculation is tuned in CouchDB, i.e. how big the set that needs recalculating is, but it's definitely going to happen more the map recalculations, and potentially much much more.

  • Use built-in reduce functions (see http://wiki.apache.org/couchdb/Built-In_Reduce_Functions) instead of rewriting them in JavaScript. These fulfil many standard reduce cases, and are much much faster than writing the equivalent function yourself.

  • Rewrite your map/reduce in Erlang. See http://wiki.apache.org/couchdb/EnableErlangViews. This does require you to learn Erlang, but should just take away big percentage of your view rebuilding time.

Upvotes: 4

brdlph
brdlph

Reputation: 619

The map function in a view is executed only once per document (plus as many times as you update the document). This happens at the first time you query the view. After that the result of the map function does not have to be computed anymore and therefore the query to the view should be extremely fast. As views are already efficient there is no general way to optimize them further.

This is not the case for temporary views. If you are using these, please store them in a design document to turn them into regular views.

Upvotes: 1

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