dsmiley commented on a change in pull request #1501:
URL: https://github.com/apache/lucene-solr/pull/1501#discussion_r422539014
##########
File path: solr/solr-ref-guide/src/common-query-parameters.adoc
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@@ -361,3 +361,42 @@ This is what happens if a similar request is sent that
adds `echoParams=all` to
}
}
----
+
+== minExactHits Parameter
Review comment:
Wouldn't "minNumFoundExact" be a better parameter name because it aligns
with the "numFound" that we expose? I searched for "hits" in Solr string
literals and the ref guide. It's not used much; more often refers to cache
hits.
##########
File path: solr/solr-ref-guide/src/common-query-parameters.adoc
##########
@@ -361,3 +361,42 @@ This is what happens if a similar request is sent that
adds `echoParams=all` to
}
}
----
+
+== minExactHits Parameter
+When this parameter is used, Solr will count the number of hits accurately at
least until this value. After that, Solr can skip over documents that don't
have a score high enough to enter in the top N. This can greatly improve
performance o search queries. On the other hand, when this parameter is used,
the `numFound` may not be exact, and may instead be an approximation.
+The `numFoundExact` boolean attribute is included in all responses, indicating
if the `numFound` value is exact or an approximation. If it's an approximation,
the real number of hits for the query is guaranteed to be greater or equal
`numFound`.
+
+More about approximate document counting and `minExactHits`:
+* The documents returned in the response are guaranteed to be the docs with
the top scores. This parameter will not skip documents that are to be returned
in the response, it will only skip counting docs that, while they match the
query, their score is low enough to not be in the top N.
+* Providing `minExactHits` doesn't guarantee that Solr will use approximate
hit counting (and thus, provide the speedup). Some types of queries, or other
parameters (like if facets are requested) will require accurate counting. The
value of `numFoundExact` indicates if the approximation was used or not.
+* Approximate counting can only be used when sorting by `score desc` first
(which is the default sort in Solr). Other fields can be used after `score
desc`, but if any other type of sorting is used before score, then the
approximation won't be applied.
+* When doing distributed queries across multiple shards, each shard will
accurately count hits until `minExactHits` (which means the query could be
hitting `numShards * minExactHits` docs and `numFound` in the response would
still be accurate)
+For example:
+
+[source,text]
+q=quick brown fox&minExactHits=100&rows=10
+
+[source,json]
+----
+"response": {
+ "numFound": 153,
+ "start": 0,
+ "hitCountExact": false,
Review comment:
didn't we agree on "numFoundExact" ?
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