Merge pull request #13665 from vespa-engine/toregge/check-brute-force-limit-in-nearest-neighbor-blueprint

Check brute force limit in nearest neighbor blueprint.

2 files changed, 26 insertions, 9 deletions

diff --git a/searchlib/src/tests/attribute/tensorattribute/tensorattribute_test.cpp b/searchlib/src/tests/attribute/tensorattribute/tensorattribute_test.cpp
index 6608959662f..c698a1d612b 100644
--- a/searchlib/src/tests/attribute/tensorattribute/tensorattribute_test.cpp
+++ b/searchlib/src/tests/attribute/tensorattribute/tensorattribute_test.cpp
@@ -887,13 +887,13 @@ public:
         return std::unique_ptr<QueryTensor>(tensor);
     }
 
-    std::unique_ptr<NearestNeighborBlueprint> make_blueprint() {
+    std::unique_ptr<NearestNeighborBlueprint> make_blueprint(double brute_force_limit = 0.05) {
         search::queryeval::FieldSpec field("foo", 0, 0);
         auto bp = std::make_unique<NearestNeighborBlueprint>(
             field,
             as_dense_tensor(),
             createDenseTensor(vec_2d(17, 42)),
-            3, true, 5, 0.05);
+            3, true, 5, brute_force_limit);
         EXPECT_EQUAL(11u, bp->getState().estimate().estHits);
         EXPECT_TRUE(bp->may_approximate());
         return bp;
@@ -938,4 +938,16 @@ TEST_F("NN blueprint handles weak filter", NearestNeighborBlueprintFixture)
     EXPECT_TRUE(bp->may_approximate());
 }
 
+TEST_F("NN blueprint handles strong filter triggering brute force search", NearestNeighborBlueprintFixture)
+{
+    auto bp = f.make_blueprint(0.2);
+    auto filter = search::BitVector::create(11);
+    filter->setBit(3);
+    filter->invalidateCachedCount();
+    auto strong_filter = GlobalFilter::create(std::move(filter));
+    bp->set_global_filter(*strong_filter);
+    EXPECT_EQUAL(11u, bp->getState().estimate().estHits);
+    EXPECT_FALSE(bp->may_approximate());
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/searchlib/src/vespa/searchlib/queryeval/nearest_neighbor_blueprint.cpp b/searchlib/src/vespa/searchlib/queryeval/nearest_neighbor_blueprint.cpp
index fcf8b78056d..2cf6e7e29c4 100644
--- a/searchlib/src/vespa/searchlib/queryeval/nearest_neighbor_blueprint.cpp
+++ b/searchlib/src/vespa/searchlib/queryeval/nearest_neighbor_blueprint.cpp
@@ -98,15 +98,20 @@ NearestNeighborBlueprint::set_global_filter(const GlobalFilter &global_filter)
         if (_global_filter->has_filter()) {
             uint32_t max_hits = _global_filter->filter()->countTrueBits();
             LOG(debug, "set_global_filter getNumDocs: %u / max_hits %u", est_hits, max_hits);
-            if (max_hits * 10 < est_hits) {
-                LOG(debug, "too many hits filtered out, consider using brute force implementation");
+            double max_hit_ratio = static_cast<double>(max_hits) / est_hits;
+            if (max_hit_ratio < _brute_force_limit) {
+                _approximate = false;
+                LOG(debug, "too many hits filtered out, using brute force implementation");
+            } else {
+                est_hits = std::min(est_hits, max_hits);
             }
-            est_hits = std::min(est_hits, max_hits);
         }
-        est_hits = std::min(est_hits, _target_num_hits);
-        setEstimate(HitEstimate(est_hits, false));
-        perform_top_k();
-        LOG(debug, "perform_top_k found %zu hits", _found_hits.size());
+        if (_approximate) {
+            est_hits = std::min(est_hits, _target_num_hits);
+            setEstimate(HitEstimate(est_hits, false));
+            perform_top_k();
+            LOG(debug, "perform_top_k found %zu hits", _found_hits.size());
+        }
     }
 }