They are very different. The "facet" expression sends a request to the JSON facet API which pushes the aggregation into the search engine. In most scenarios this is the preferred method because it only streams aggregated results. I would always try the "facet" expression first before going to rollup.
The "rollup" expression rolls up aggregations over a sorted stream of tuples. It almost always involves exporting and sorting entire result sets with the /export handler. There are only two reasons to use this approach: 1) Very high cardinality faceting. By very high I mean millions of facet values are being returned in the same query. 2) Rollups following any kind of relational algebra. For example a rollup on top of a hashJoin. Joel Bernstein http://joelsolr.blogspot.com/ On Tue, Oct 16, 2018 at 8:54 AM RAUNAK AGRAWAL <agrawal.rau...@gmail.com> wrote: > Hi Guys, > > I am trying to do an aggregation (sum) using streaming API. I have around > 10 billion documents in my collection and every document has around 10 > docValues. > > So streaming facet is taking close to 6 secs to respond with aggregation on > 10 fields while streaming rollup is returning the response in 2 secs. > > So my questions are: > > 1. What is the fundamental difference between streaming facet and rollUp. > 2. When to use facet and when to use rollUp. > > Thanks >
