Re: What happens when I combine the view query params sorted=false with startkey & endkey?

[Jan Lehnardt <ja...@apache.org>]

Heya Thilo,

startkey and endkey are applied first, so you are guaranteed to get all results within your specified range, but you are not guaranteed to get it in the sorted order defined by the second link you sent.

Imagine a sharded database. When making a view query, CouchDB makes an internal query with the same options (including startkey/endkey) to each shard. To ensure a sorted result (the default), the results from each shard get streamed to the node that handles the query, and that node does an in-flight merge of the incoming results.

The sorted=false option just returns all the result rows as they come in from the shards.

The potential performance gain is that some shards might reply faster than others, but to ensure an in-order result, those shard-results have to wait before they can be streamed to the client because a row from a slower shard might have logical precedence.

If you can sort on the client, or if the order doesn’t matter (just the startkey/endkey selection), then sorted=false can give you some potential speedup on a sharded database. You won’t go faster than your slowest shard, however, you might just get other shards’ results sooner.

Best
Jan
—

> On 9. Apr 2020, at 17:40, Thilo from Cobot <th...@cobot.me> wrote:
> 
> Hi there,
> 
> I was looking into speeding up queries to the database. I found under
> https://docs.couchdb.org/en/stable/api/ddoc/views.html#db-design-design-doc-view-view-name
> that I can disable sorting of results with sorted=false. I wonder what happens if I combine that with the startkey/endkey parameters.
> 
> What I understood from https://docs.couchdb.org/en/stable/api/ddoc/views.html#api-ddoc-view-sorting
> sorting is applied before filtering. I assume the result is undetermined, it might include some docs that are between start and endkey but not all or none, so its not wise to combine sorted=false with any filters. Is this correct?
> 
> Thanks for any insights.
> 
> Cheers
> Thilo
> 
> --
> more time for your coworkers: https://cobot.me