I am building a search page with Azure Search. On my page, I have a search box. I want to provide suggestions to the users. In an attempt to do this, I'm using the Suggestions endpoint on my index. At this time, I have a request that includes the following query string:
search=sta&suggesterName=sites&$top=3
My question is, how does top determine which three results to return? Is it the first three matches it encounters when going through the search index? Or is it something else? Based on the URL structure, I don't think it's using a scoring profile. So, I ruled out relevancy. But then I started reading about the minimumCoverage field and I got confused.
If the suggest endpoint just returns the first [top] matches it encounters, then why is the minimumCoverage field even needed?
In general, $top will give you the top N results based on whatever order the rest of the query specifies. For queries with no $orderby, the sort order is descending by relevance score. This applies to both Suggest and Search.
Note that just because you don't have a scoring profile (such as with Suggest), that doesn't mean Azure Search doesn't calculate relevance scores for each document. Scoring profiles can influence the score, but they do not completely define it.
For queries with an $orderby, the order of results is defined first by the fields in the $orderby, and then by score if there are any ties to be broken.
minimumCoverage has nothing to do with ordering or $top. It has to do with the way search queries are distributed. Every query is executed concurrently against different subsets of the index (this happens regardless of whether or not you have multiple search units). Sometimes one of these subsets fails to execute for whatever reason, usually when your search service is under heavy load. The minimumCoverage parameter provides a way to relax the rule that normally says "X% of the index must successfully execute the query in order to consider the overall query a success" (X is 100 by default for Search and 80 by default for Suggest). This is a way to tradeoff completeness of search results for higher availability in case of heavy load or partial outages.