From 7fe19e2b100c9942889aece496580f9170b404ea Mon Sep 17 00:00:00 2001
From: Håvard Pettersen <havardpe@yahooinc.com>
Date: Mon, 31 Oct 2022 14:37:01 +0000
Subject: short-circuit filter evaluation if filter iterator is trivial

---
 .../queryeval/global_filter/global_filter_test.cpp | 18 +++++++
 .../vespa/searchlib/queryeval/global_filter.cpp    | 55 +++++++++++++++++-----
 2 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/searchlib/src/tests/queryeval/global_filter/global_filter_test.cpp b/searchlib/src/tests/queryeval/global_filter/global_filter_test.cpp
index a18fe010ad0..dcf175a6fdd 100644
--- a/searchlib/src/tests/queryeval/global_filter/global_filter_test.cpp
+++ b/searchlib/src/tests/queryeval/global_filter/global_filter_test.cpp
@@ -2,6 +2,7 @@
 
 #include <vespa/vespalib/gtest/gtest.h>
 #include <vespa/vespalib/util/require.h>
+#include <vespa/vespalib/util/classname.h>
 #include <vespa/vespalib/util/simple_thread_bundle.h>
 #include <vespa/searchlib/common/bitvector.h>
 #include <vespa/searchlib/queryeval/global_filter.h>
@@ -199,4 +200,21 @@ TEST(GlobalFilterTest, multi_threaded_global_filter_works_with_docid_limit_0) {
     verify(*filter, 2, 1);
 }
 
+TEST(GlobalFilterTest, global_filter_matching_any_document_becomes_invalid) {
+    SimpleThreadBundle thread_bundle(7);
+    AlwaysTrueBlueprint blueprint;
+    auto filter = GlobalFilter::create(blueprint, 100, thread_bundle);
+    EXPECT_FALSE(filter->is_active());
+}
+
+TEST(GlobalFilterTest, global_filter_not_matching_any_document_becomes_empty) {
+    SimpleThreadBundle thread_bundle(7);
+    EmptyBlueprint blueprint;
+    auto filter = GlobalFilter::create(blueprint, 100, thread_bundle);
+    auto class_name = vespalib::getClassName(*filter);
+    fprintf(stderr, "empty global filter class name: %s\n", class_name.c_str());
+    EXPECT_TRUE(class_name.find("EmptyFilter") < class_name.size());
+    verify(*filter, 1000, 100);
+}
+
 GTEST_MAIN_RUN_ALL_TESTS()
diff --git a/searchlib/src/vespa/searchlib/queryeval/global_filter.cpp b/searchlib/src/vespa/searchlib/queryeval/global_filter.cpp
index 04e4d154821..3ef28b461b8 100644
--- a/searchlib/src/vespa/searchlib/queryeval/global_filter.cpp
+++ b/searchlib/src/vespa/searchlib/queryeval/global_filter.cpp
@@ -9,6 +9,7 @@
 
 using vespalib::Runnable;
 using vespalib::ThreadBundle;
+using vespalib::Trinary;
 
 namespace search::queryeval {
 
@@ -21,6 +22,15 @@ struct Inactive : GlobalFilter {
     bool check(uint32_t) const override { abort(); }
 };
 
+struct EmptyFilter : GlobalFilter {
+    uint32_t docid_limit;
+    EmptyFilter(uint32_t docid_limit_in) : docid_limit(docid_limit_in) {}
+    bool is_active() const override { return true; }
+    uint32_t size() const override { return docid_limit; }
+    uint32_t count() const override { return 0; }
+    bool check(uint32_t) const override { return false; }
+};
+
 struct BitVectorFilter : public GlobalFilter {
     std::unique_ptr<BitVector> vector;
     BitVectorFilter(std::unique_ptr<BitVector> vector_in)
@@ -56,22 +66,38 @@ struct MultiBitVectorFilter : public GlobalFilter {
     }
 };
 
-std::unique_ptr<BitVector> make_part(Blueprint &blueprint, uint32_t begin, uint32_t end) {
+struct PartResult {
+    Trinary matches_any;
+    std::unique_ptr<BitVector> bits;
+    PartResult()
+      : matches_any(Trinary::False), bits() {}
+    PartResult(Trinary matches_any_in)
+      : matches_any(matches_any_in), bits() {}
+    PartResult(std::unique_ptr<BitVector> &&bits_in)
+      : matches_any(Trinary::Undefined), bits(std::move(bits_in)) {}
+};
+
+PartResult make_part(Blueprint &blueprint, uint32_t begin, uint32_t end) {
     bool strict = true;
     auto constraint = Blueprint::FilterConstraint::UPPER_BOUND;
-    auto filter_iterator = blueprint.createFilterSearch(strict, constraint);
-    filter_iterator->initRange(begin, end);
-    auto result = filter_iterator->get_hits(begin);
-    // count bits in parallel and cache the results for later
-    result->countTrueBits();
-    return result;
+    auto filter = blueprint.createFilterSearch(strict, constraint);
+    auto matches_any = filter->matches_any();
+    if (matches_any == Trinary::Undefined) {
+        filter->initRange(begin, end);
+        auto bits = filter->get_hits(begin);
+        // count bits in parallel and cache the results for later
+        bits->countTrueBits();
+        return PartResult(std::move(bits));
+    } else {
+        return PartResult(matches_any);
+    }
 }
 
 struct MakePart : Runnable {
     Blueprint &blueprint;
     uint32_t begin;
     uint32_t end;
-    std::unique_ptr<BitVector> result;
+    PartResult result;
     MakePart(Blueprint &blueprint_in, uint32_t begin_in, uint32_t end_in) noexcept
       : blueprint(blueprint_in), begin(begin_in), end(end_in), result() {}
     void run() override { result = make_part(blueprint, begin, end); }
@@ -146,13 +172,18 @@ GlobalFilter::create(Blueprint &blueprint, uint32_t docid_limit, ThreadBundle &t
     assert(parts.size() <= num_threads);
     assert((docid == docid_limit) || parts.empty());
     thread_bundle.run(parts);
-    if (parts.size() == 1) {
-        return create(std::move(parts[0].result));
-    }
     std::vector<std::unique_ptr<BitVector>> vectors;
     vectors.reserve(parts.size());
     for (MakePart &part: parts) {
-        vectors.push_back(std::move(part.result));
+        switch (part.result.matches_any) {
+        case Trinary::False: return std::make_unique<EmptyFilter>(docid_limit);
+        case Trinary::True: return create(); // filter not needed after all
+        case Trinary::Undefined:
+            vectors.push_back(std::move(part.result.bits));
+        }
+    }
+    if (vectors.size() == 1) {
+        return create(std::move(vectors[0]));
     }
     return create(std::move(vectors));
 }
-- 
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