1 files changed, 63 insertions, 0 deletions
diff --git a/search/stats_cache.hpp b/search/stats_cache.hpp
new file mode 100644
index 0000000000..946e12a7c7
--- /dev/null
+++ b/search/stats_cache.hpp
@@ -0,0 +1,63 @@
+#pragma once
+#include "base/logging.hpp"
+
+#include "std/unordered_map.hpp"
+#include "std/utility.hpp"
+
+namespace search
+{
+template <class TKey, class TValue>
+class Cache
+{
+  unordered_map<TKey, TValue> m_map;
+
+  /// query statistics
+  size_t m_accesses;
+  size_t m_misses;
+
+  size_t m_emptyQueriesCount;  /// empty queries count at a row
+  string m_name;               /// cache name for print functions
+
+public:
+  explicit Cache(string const & name)
+    : m_accesses(0), m_misses(0), m_emptyQueriesCount(0), m_name(name)
+  {
+  }
+
+  pair<TValue &, bool> Get(TKey const & key)
+  {
+    auto r = m_map.insert(make_pair(key, TValue()));
+
+    ++m_accesses;
+    if (r.second)
+      ++m_misses;
+
+    return pair<TValue &, 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