Repo created

libs/search/stats_cache.hpp

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+#pragma once
+
+#include "base/logging.hpp"
+
+#include <cstddef>
+#include <string>
+#include <unordered_map>
+#include <utility>
+
+namespace search
+{
+template <class Key, class Value>
+class Cache
+{
+  std::unordered_map<Key, Value> m_map;
+
+  /// query statistics
+  size_t m_accesses;
+  size_t m_misses;
+
+  size_t m_emptyQueriesCount;  /// empty queries count at a row
+  std::string m_name;          /// cache name for print functions
+
+public:
+  explicit Cache(std::string const & name) : m_accesses(0), m_misses(0), m_emptyQueriesCount(0), m_name(name) {}
+
+  std::pair<Value &, bool> Get(Key const & key)
+  {
+    auto r = m_map.insert(std::make_pair(key, Value()));
+
+    ++m_accesses;
+    if (r.second)
+      ++m_misses;
+
+    return std::pair<Value &, bool>(r.first->second, r.second);
+  }
+
+  void Clear()
+  {
+    m_map.clear();
+    m_accesses = m_misses = 0;
+    m_emptyQueriesCount = 0;
+  }
+
+  /// Called at the end of every search query.
+  void ClearIfNeeded()
+  {
+    if (m_accesses != 0)
+    {
+      LOG(LDEBUG,
+          ("Cache", m_name, "Queries =", m_accesses, "From cache =", m_accesses - m_misses, "Added =", m_misses));
+      m_accesses = m_misses = 0;
+      m_emptyQueriesCount = 0;
+    }
+    else if (++m_emptyQueriesCount > 5)
+    {
+      LOG(LDEBUG, ("Clearing cache", m_name));
+      Clear();
+    }
+  }
+};
+}  // namespace search