From: Sarah Hoffmann <lonvia@denofr.de>
Date: Wed, 25 Oct 2017 20:34:29 +0000 (+0200)
Subject: restrict number of results for reverse queries
X-Git-Tag: v3.1.0~29
X-Git-Url: https://git.openstreetmap.org./nominatim.git/commitdiff_plain/adbbb1ce02649e7acfefa2156f836bf04dd68a55

restrict number of results for reverse queries

When given a coordinate off the coast of a large town, the entire
town may end up in the potential results during the reverse query.
Postgres then needs to sort tens of thousands of results before it
can determine the clostest one. Given that the results at such a
large search radius are bound to be imprecise anyway, restrict
the number of results postgres should consider to 1000.
---

diff --git a/lib/ReverseGeocode.php b/lib/ReverseGeocode.php
index 31ebe717..ce2ee5e5 100644
--- a/lib/ReverseGeocode.php
+++ b/lib/ReverseGeocode.php
@@ -121,9 +121,17 @@ class ReverseGeocode
 
             $sSQL = 'select place_id,parent_place_id,rank_search,country_code,';
             $sSQL .= '  ST_distance('.$sPointSQL.', geometry) as distance';
-            $sSQL .= ' FROM placex';
-            $sSQL .= ' WHERE ST_DWithin('.$sPointSQL.', geometry, '.$fSearchDiam.')';
-            $sSQL .= ' and rank_search != 28 and rank_search >= '.$iMaxRank;
+            $sSQL .= ' FROM ';
+            if ($fSearchDiam < 0.01) {
+                $sSQL .= ' placex';
+                $sSQL .= '   WHERE ST_DWithin('.$sPointSQL.', geometry, '.$fSearchDiam.')';
+                $sSQL .= '   AND';
+            } else {
+                $sSQL .= ' (SELECT * FROM placex ';
+                $sSQL .= '   WHERE ST_DWithin('.$sPointSQL.', geometry, '.$fSearchDiam.')';
+                $sSQL .= '   LIMIT 1000) as p WHERE';
+            }
+            $sSQL .= ' rank_search != 28 and rank_search >= '.$iMaxRank;
             $sSQL .= ' and (name is not null or housenumber is not null)';
             $sSQL .= ' and class not in (\'waterway\',\'railway\',\'tunnel\',\'bridge\',\'man_made\')';
             $sSQL .= ' and indexed_status = 0 ';
diff --git a/test/bdd/api/reverse/queries.feature b/test/bdd/api/reverse/queries.feature
index bc88db06..b3ad20b2 100644
--- a/test/bdd/api/reverse/queries.feature
+++ b/test/bdd/api/reverse/queries.feature
@@ -45,3 +45,9 @@ Feature: Reverse geocoding
         Then result addresses contain
           | house_number | road |
           | 5            | Clasingstraße |
+
+    Scenario: Location off the coast
+        When sending jsonv2 reverse coordinates 54.046489113,8.5546870529
+        Then results contain
+         | display_name |
+         | Freie und Hansestadt Hamburg, Deutschland |