Store a limited number of posting list indexes in countHits() to

reduce amount of dictionary entry filtering in fillArray()
and fillBitVector() for regexp search and fuzzy search.

4 files changed, 70 insertions, 10 deletions

diff --git a/searchlib/src/tests/attribute/searchcontext/searchcontext_test.cpp b/searchlib/src/tests/attribute/searchcontext/searchcontext_test.cpp
index 40d4b20aaf2..ac1042dda6c 100644
--- a/searchlib/src/tests/attribute/searchcontext/searchcontext_test.cpp
+++ b/searchlib/src/tests/attribute/searchcontext/searchcontext_test.cpp
@@ -4,6 +4,7 @@
 #include <vespa/searchlib/attribute/attributefactory.h>
 #include <vespa/searchlib/attribute/attributeiterators.h>
 #include <vespa/searchlib/attribute/flagattribute.h>
+#include <vespa/searchlib/attribute/postinglistsearchcontext.h>
 #include <vespa/searchlib/attribute/searchcontextelementiterator.h>
 #include <vespa/searchlib/attribute/singleboolattribute.h>
 #include <vespa/searchlib/attribute/stringbase.h>
@@ -1424,6 +1425,25 @@ SearchContextTest::testPrefixSearch(const vespalib::string& name, const Config&
             }
         }
     }
+
+    // Long range of prefixes with unique strings that causes
+    // PostingListFoldedSearchContextT<DataT>::countHits() to populate
+    // partial vector of posting indexes, with scan resumed by
+    // fillArray or fillBitVector.
+    auto& vec = dynamic_cast<StringAttribute &>(*attr.get());
+    uint32_t old_size = attr->getNumDocs();
+    constexpr uint32_t longrange_values = search::attribute::PostingListFoldedSearchContextT<int32_t>::MAX_POSTING_INDEXES_SIZE + 100;
+    attr->addDocs(longrange_values);
+    DocSet exp_longrange;
+    for (uint32_t i = 0; i < longrange_values; ++i) {
+        vespalib::asciistream ss;
+        ss << "lpref" << i;
+        vespalib::string sss(ss.str());
+        exp_longrange.put(old_size + i);
+        vec.update(old_size + i, vespalib::string(ss.str()).c_str());
+    }
+    attr->commit();
+    performSearch(*attr, "lpref", exp_longrange, TermType::PREFIXTERM);
 }
 
 
diff --git a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.cpp b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.cpp
index 12c887eb407..2b1d4fa3286 100644
--- a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.cpp
+++ b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.cpp
@@ -27,7 +27,8 @@ PostingListSearchContext(const IEnumStoreDictionary& dictionary, bool has_btree_
       _FSTC(0.0),
       _PLSTC(0.0),
       _hasWeight(hasWeight),
-      _useBitVector(useBitVector)
+      _useBitVector(useBitVector),
+      _counted_hits()
 {
 }
 
diff --git a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.h b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.h
index 7e2002f95fd..9a4dbdd9c61 100644
--- a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.h
+++ b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.h
@@ -153,9 +153,14 @@ protected:
 template <class DataT>
 class PostingListFoldedSearchContextT : public PostingListSearchContextT<DataT>
 {
+public:
+    static constexpr uint32_t MAX_POSTING_INDEXES_SIZE = 10000;
+
 protected:
     using Parent = PostingListSearchContextT<DataT>;
     using Dictionary = typename Parent::Dictionary;
+    using DictionaryConstIterator = Dictionary::ConstIterator;
+    using EntryRef = vespalib::datastore::EntryRef;
     using PostingList = typename Parent::PostingList;
     using Parent::_counted_hits;
     using Parent::_docIdLimit;
@@ -167,9 +172,13 @@ protected:
     using Parent::singleHits;
     using Parent::use_dictionary_entry;
 
+    mutable DictionaryConstIterator _resume_scan_itr;
+    mutable std::vector<EntryRef>   _posting_indexes;
+
     PostingListFoldedSearchContextT(const IEnumStoreDictionary& dictionary, uint32_t docIdLimit, uint64_t numValues,
                                     bool hasWeight, const PostingList &postingList,
                                     bool useBitVector, const ISearchContext &baseSearchCtx);
+    ~PostingListFoldedSearchContextT() override;
 
     bool fallback_to_approx_num_hits() const override;
     size_t countHits() const override;
diff --git a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.hpp b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.hpp
index 714da9997bb..c479bbfcd06 100644
--- a/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.hpp
+++ b/searchlib/src/vespa/searchlib/attribute/postinglistsearchcontext.hpp
@@ -264,11 +264,16 @@ PostingListFoldedSearchContextT<DataT>::
 PostingListFoldedSearchContextT(const IEnumStoreDictionary& dictionary, uint32_t docIdLimit, uint64_t numValues,
                                 bool hasWeight, const PostingList &postingList,
                                 bool useBitVector, const ISearchContext &searchContext)
-    : Parent(dictionary, docIdLimit, numValues, hasWeight, postingList, useBitVector, searchContext)
+    : Parent(dictionary, docIdLimit, numValues, hasWeight, postingList, useBitVector, searchContext),
+      _resume_scan_itr(),
+      _posting_indexes()
 {
 }
 
 template <typename DataT>
+PostingListFoldedSearchContextT<DataT>::~PostingListFoldedSearchContextT() = default;
+
+template <typename DataT>
 bool
 PostingListFoldedSearchContextT<DataT>::fallback_to_approx_num_hits() const
 {
@@ -283,12 +288,27 @@ PostingListFoldedSearchContextT<DataT>::countHits() const
         return _counted_hits.value();
     }
     size_t sum(0);
-    for (auto it(_lowerDictItr); it != this->_upperDictItr;) {
+    bool overflow = false;
+    for (auto it(_lowerDictItr); it != _upperDictItr;) {
         if (use_dictionary_entry(it)) {
-            sum += _postingList.frozenSize(it.getData().load_acquire());
+            auto pidx = it.getData().load_acquire();
+            if (pidx.valid()) {
+                sum += _postingList.frozenSize(pidx);
+                if (!overflow) {
+                    if (_posting_indexes.size() < MAX_POSTING_INDEXES_SIZE) {
+                        _posting_indexes.emplace_back(pidx);
+                    } else {
+                        overflow = true;
+                        _resume_scan_itr = it;
+                    }
+                }
+            }
             ++it;
         }
     }
+    if (!overflow) {
+        _resume_scan_itr = _upperDictItr;
+    }
     _counted_hits = sum;
     return sum;
 }
@@ -297,10 +317,15 @@ template <typename DataT>
 void
 PostingListFoldedSearchContextT<DataT>::fillArray()
 {
-    for (auto it(_lowerDictItr); it != _upperDictItr;) {
+    for (auto pidx : _posting_indexes) {
+        _merger.addToArray(PostingListTraverser<PostingList>(_postingList, pidx));
+    }
+    for (auto it(_resume_scan_itr); it != _upperDictItr;) {
         if (use_dictionary_entry(it)) {
-            _merger.addToArray(PostingListTraverser<PostingList>(_postingList,
-                                                                 it.getData().load_acquire()));
+            auto pidx = it.getData().load_acquire();
+            if (pidx.valid()) {
+                _merger.addToArray(PostingListTraverser<PostingList>(_postingList, pidx));
+            }
             ++it;
         }
     }
@@ -311,10 +336,15 @@ template <typename DataT>
 void
 PostingListFoldedSearchContextT<DataT>::fillBitVector()
 {
-    for (auto it(_lowerDictItr); it != _upperDictItr;) {
+    for (auto pidx : _posting_indexes) {
+        _merger.addToBitVector(PostingListTraverser<PostingList>(_postingList, pidx));
+    }
+    for (auto it(_resume_scan_itr); it != _upperDictItr;) {
         if (use_dictionary_entry(it)) {
-            _merger.addToBitVector(PostingListTraverser<PostingList>(_postingList,
-                                                                     it.getData().load_acquire()));
+            auto pidx = it.getData().load_acquire();
+            if (pidx.valid()) {
+                _merger.addToBitVector(PostingListTraverser<PostingList>(_postingList, pidx));
+            }
             ++it;
         }
     }