some debug, some idea how to utilize home hints of data by cache

cache.h

@@ -25,27 +25,31 @@
 template <class K, class V>
 class DataBase::Cache : public DataBase::Table<K, V> {
     friend class DataBase;
-    enum class Mode {
-        nothing,
-        size,
-        full
+    enum class Mode {       //it's a cache state when we:
+        nothing,            //  - know nothing about records in database on disk
+        size,               //  - know just an amount of records
+        full                //  - shure that our cache is equal to the database on disk
     };
 protected:
     Cache(const std::string& name, DataBase* parent);
     ~Cache() override;
 
+private:
+    void handleMode() const;
+
 public:
     virtual void addRecord(const K& key, const V& value) override;
     virtual void changeRecord(const K& key, const V& value) override;
     virtual void removeRecord(const K& key) override;
     virtual V getRecord(const K& key) const override;
-    //virtual uint32_t count() const;
-    //virtual void drop();
+    virtual uint32_t count() const override;
+    virtual void drop() override;
 
 protected:
-    Mode mode;
+    Mode* mode;
     std::map<K, V>* cache;
     std::set<K>* abscent;
+    uint32_t* sizeDifference;
 };
 
 #include "cache.hpp"

cache.hpp

@@ -23,14 +23,19 @@
 template<class K, class V>
 DataBase::Cache<K, V>::Cache(const std::string& p_name, DataBase* parent):
     DataBase::Table<K, V>(p_name, parent),
-    mode(Mode::nothing),
+    mode(new Mode),
     cache(new std::map<K, V>()),
-    abscent(new std::set<K>())
+    abscent(new std::set<K>()),
+    sizeDifference(new uint32_t)
 {
+    *mode = Mode::nothing;
+    *sizeDifference = 0;
 }
 
 template<class K, class V>
 DataBase::Cache<K, V>::~Cache() {
+    delete sizeDifference;
+    delete mode;
     delete cache;
     delete abscent;
 }
@@ -50,24 +55,37 @@ void DataBase::Cache<K, V>::addRecord(const K& key, const V& value) {
 }
 
 
-
 template<class K, class V>
 void DataBase::Cache<K, V>::changeRecord(const K& key, const V& value) {
     if (!DataBase::Table<K, V>::db->opened) {
         throw Closed("changeRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
     }
 
-    typename std::map<K, V>::iterator itr = cache->find(key);
-    if (itr == cache->end() || abscent->count(key) > 0) {
-        throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
-    }
-
-    try {
+    if (*mode == Mode::full) {
+        typename std::map<K, V>::iterator itr = cache->find(key);
+        if (itr != cache->end()) {
+            throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
+        }
         Table<K, V>::changeRecord(key, value);
         itr->second = value;
-    } catch (const NotFound& error) {
-        abscent->insert(key);
-        throw error;
+    } else {
+        if (abscent->count(key) > 0) {
+            throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
+        }
+
+        try {
+            Table<K, V>::changeRecord(key, value);
+            typename std::map<K, V>::iterator itr = cache->find(key);
+            if (itr != cache->end()) {
+                itr->second = value;
+            } else {
+                cache->insert(std::make_pair(key, value));
+                handleMode();
+            }
+        } catch (const NotFound& error) {
+            abscent->insert(key);
+            throw error;
+        }
     }
 }
 
@@ -82,13 +100,14 @@ V DataBase::Cache<K, V>::getRecord(const K& key) const {
         return itr->second;
     }
 
-    if (abscent->count(key) == 0) {
+    if (*mode == Mode::full || abscent->count(key) == 0) {
         throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
     }
 
     try {
         V value = Table<K, V>::getRecord(key);
         cache->insert(std::make_pair(key, value));
+        handleMode();
         return value;
     } catch (const NotFound& error) {
         abscent->insert(key);
@@ -107,8 +126,55 @@ void DataBase::Cache<K, V>::removeRecord(const K& key) {
         throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
     }
 
-    cache->erase(key);
     Table<K, V>::removeRecord(key);
+    if (cache->erase(key) == 0) {   //if it was not cached and we are now in size mode then the sizeDifference would decrease
+        handleMode();
+    }
+    if (*mode != Mode::full) {
+        abscent->insert(key);
+    }
+}
+
+template<class K, class V>
+uint32_t DataBase::Cache<K, V>::count() const {
+    switch (*mode) {
+        case Mode::nothing:
+        {
+            uint32_t sz = DataBase::Table<K, V>::count();
+            *sizeDifference = sz - cache->size();
+            if (sz == 0) {
+                *mode = Mode::full;
+                abscent->clear();
+            } else {
+                *mode = Mode::size;
+            }
+            return sz;
+        }
+        case Mode::size:
+            return cache->size() + *sizeDifference;
+        case Mode::full:
+            return cache->size();
+    }
+}
+
+template<class K, class V>
+void DataBase::Cache<K, V>::handleMode() const {
+    if (*mode == Mode::size) {
+        --(*sizeDifference);
+        if (*sizeDifference == 0) {
+            *mode = Mode::full;
+            abscent->clear();
+        }
+    }
+}
+
+template<class K, class V>
+void DataBase::Cache<K, V>::drop() {
+    DataBase::Table<K, V>::drop();
+    cache->clear();
+    abscent->clear();
+    *mode = Mode::full;
+    *sizeDifference = 0;
 }
 
 #endif //DATABASE_CACHE_HPP