Search: improve queries (#12569)

- Set some values for fuzzyness. Search terms like `webdav~` timeout ES,
with these settings now the query resolves between 400-800ms. Not great,
but at least doesn't kill ES.
- Enforce a limit of 3 results for inner hits (blocks).
- Move the filter query so it's at the top (according to chatgpt this is
an improvement).

I tested several queries on ES, and all of them take around 200ms, even
the simplest one... Sometimes some queries do take more time (randomly).
My guess is that some other slow queries add some overhead to the
server, so all queries get affected. Other theories are the index size,
and using the wrong tokenizer/analyzer for the type of queries users
want.

Author: stsewd

readthedocs/search/faceted_search.py

@@ -113,10 +113,15 @@ def _get_text_queries(self, *, query, fields):
         is_advanced_query = self.use_advanced_query or self._is_advanced_query(query)
         for operator in self.operators:
             if is_advanced_query:
+                # See all valid options at:
+                # https://www.elastic.co/docs/reference/query-languages/query-dsl/query-dsl-simple-query-string-query.
                 query_string = SimpleQueryString(
                     query=query,
                     fields=fields,
                     default_operator=operator,
+                    # Restrict fuzziness to avoid timeouts with complex queries.
+                    fuzzy_prefix_length=1,
+                    fuzzy_max_expansions=15,
                 )
             else:
                 query_string = self._get_fuzzy_query(
@@ -283,13 +288,13 @@ def _get_projects_query(self):
 
         if isinstance(self.projects, dict):
             versions_query = [
-                Bool(filter=[Term(project=project), Term(version=version)])
+                Bool(must=[Term(project=project), Term(version=version)])
                 for project, version in self.projects.items()
             ]
             return Bool(should=versions_query)
 
         if isinstance(self.projects, list):
-            return Bool(filter=Terms(project=self.projects))
+            return Terms(project=self.projects)
 
         raise ValueError("projects must be a list or a dict!")
 
@@ -312,13 +317,14 @@ def query(self, search, query):
             query=query,
             path="sections",
             fields=self._section_fields,
+            limit=3,
         )
         queries.append(sections_nested_query)
         bool_query = Bool(should=queries)
 
         projects_query = self._get_projects_query()
         if projects_query:
-            bool_query = Bool(must=[bool_query, projects_query])
+            bool_query = Bool(must=[bool_query], filter=projects_query)
 
         final_query = FunctionScore(
             query=bool_query,
@@ -327,7 +333,7 @@ def query(self, search, query):
         search = search.query(final_query)
         return search
 
-    def _get_nested_query(self, *, query, path, fields):
+    def _get_nested_query(self, *, query, path, fields, limit=3):
         """Generate a nested query with passed parameters."""
         queries = self._get_queries(
             query=query,
@@ -348,7 +354,7 @@ def _get_nested_query(self, *, query, path, fields):
 
         return Nested(
             path=path,
-            inner_hits={"highlight": highlight},
+            inner_hits={"highlight": highlight, "size": limit},
             query=bool_query,
         )