diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9eb708d..9a400b8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -56,6 +56,7 @@ set(HEADERS
   serializer_stdstring.hpp
   serializer_qstring.hpp
   serializer_qbytearray.hpp
+  operators.hpp
 )
 
 if (BUILD_STATIC)
diff --git a/cache.h b/cache.h
index 00e3042..6f7042c 100644
--- a/cache.h
+++ b/cache.h
@@ -45,8 +45,12 @@ public:
     virtual bool checkRecord(const K& key) const override;
     virtual V getRecord(const K& key) const override;
     virtual uint32_t count() const override;
+
+    using DataBase::Table<K, V>::drop;
     virtual int drop(MDB_txn * transaction) override;
     virtual std::map<K, V> readAll() const override;
+    virtual void replaceAll(const std::map<K, V>& data) override;
+    virtual uint32_t addRecords(const std::map<K, V>& data, bool overwrite = false) override;
 
 protected:
     Mode* mode;
diff --git a/cache.hpp b/cache.hpp
index 89011ae..503b2f4 100644
--- a/cache.hpp
+++ b/cache.hpp
@@ -102,11 +102,10 @@ void DataBase::Cache<K, V>::changeRecord(const K& key, const V& value) {
 
         try {
             Table<K, V>::changeRecord(key, value);
-            typename std::map<K, V>::iterator itr = cache->find(key);
-            if (itr != cache->end()) {
-                itr->second = value;
+            typename std::pair<typename std::map<K, V>::iterator, bool> res = cache->insert(std::make_pair(key, value));
+            if (!res.second) {
+                res.first->second = value;
             } else {
-                cache->insert(std::make_pair(key, value));
                 handleMode();
             }
         } catch (const NotFound& error) {
@@ -188,6 +187,44 @@ std::map<K, V> DataBase::Cache<K, V>::readAll() const {
     return *cache;
 }
 
+template<class K, class V>
+void DataBase::Cache<K, V>::replaceAll(const std::map<K, V>& data) {
+    DataBase::Table<K, V>::replaceAll(data);
+    *cache = data;
+}
+
+template<class K, class V>
+uint32_t DataBase::Cache<K, V>::addRecords(const std::map<K, V>& data, bool overwrite) {
+    uint32_t newSize = DataBase::Table<K, V>::addRecords(data, overwrite);
+
+    Mode& m = *mode;
+    if (m == Mode::nothing) {
+        m = Mode::size;
+    }
+    std::map<K, V>& c = *cache;
+    std::set<K>& a = *abscent;
+    for (const std::pair<const K, V>& pair : data) {
+        std::pair<typename std::map<K, V>::iterator, bool> res = c.insert(pair);
+        if (!res.second) {
+            if (overwrite) {
+                res.first->second = pair.second;
+            }
+        } else if (m != Mode::full) {
+            a.erase(pair.first);
+        }
+    }
+
+    if (m != Mode::full) {
+        *sizeDifference = newSize - c.size();
+        if (*sizeDifference == 0) {
+            *mode = Mode::full;
+            abscent->clear();
+        }
+    }
+
+    return newSize;
+}
+
 template<class K, class V>
 void DataBase::Cache<K, V>::removeRecord(const K& key) {
     if (!DataBase::Table<K, V>::db->opened) {
diff --git a/database.h b/database.h
index b1903b5..005c1d9 100644
--- a/database.h
+++ b/database.h
@@ -80,6 +80,7 @@ private:
 };
 
 #include "exceptions.h"
+#include "operators.hpp"
 
 template <class K, class V>
 DataBase::Table<K, V>* DataBase::addTable(const std::string& p_name) {
diff --git a/operators.hpp b/operators.hpp
new file mode 100644
index 0000000..c4010ff
--- /dev/null
+++ b/operators.hpp
@@ -0,0 +1,209 @@
+// Squawk messenger.
+// Copyright (C) 2019  Yury Gubich <blue@macaw.me>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#ifndef CORE_OPERATORS_HPP
+#define CORE_OPERATORS_HPP
+
+#include <map>
+#include <set>
+#include <vector>
+#include <list>
+#include <deque>
+
+#include <QDataStream>
+
+template <class K, class V>
+QDataStream& operator << (QDataStream &out, const std::map<K, V>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const std::pair<const K, V>& pair : container) {
+        out << pair;
+    }
+
+    return out;
+}
+
+template <class K, class V>
+QDataStream& operator >> (QDataStream &in, std::map<K, V>& container) {
+    uint32_t size;
+    in >> size;
+    for (uint32_t i = 0; i < size; ++i) {
+        std::pair<K, V> pair;
+        in >> pair;
+        container.insert(pair);
+    }
+
+    return in;
+}
+
+template <class K, class V>
+QDataStream& operator << (QDataStream &out, const std::multimap<K, V>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const std::pair<const K, V>& pair : container) {
+        out << pair;
+    }
+
+    return out;
+}
+
+template <class K, class V>
+QDataStream& operator >> (QDataStream &in, std::multimap<K, V>& container) {
+    uint32_t size;
+    in >> size;
+    for (uint32_t i = 0; i < size; ++i) {
+        std::pair<K, V> pair;
+        in >> pair;
+        container.insert(pair);
+    }
+
+    return in;
+}
+
+template <class K, class V>
+QDataStream& operator << (QDataStream &out, const std::pair<K, V>& pair) {
+    out << pair.first;
+    out << pair.second;
+
+    return out;
+}
+
+template <class K, class V>
+QDataStream& operator >> (QDataStream &in, std::pair<K, V>& container) {
+    in >> container.first;
+    in >> container.second;
+
+    return in;
+}
+
+template <class K>
+QDataStream& operator << (QDataStream &out, const std::set<K>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const K& value : container) {
+        out << value;
+    }
+
+    return out;
+}
+
+template <class K>
+QDataStream& operator >> (QDataStream &in, std::set<K>& container) {
+    uint32_t size;
+    in >> size;
+    for (uint32_t i = 0; i < size; ++i) {
+        K value;
+        in >> value;
+        container.insert(value);
+    }
+
+    return in;
+}
+
+template <class K>
+QDataStream& operator << (QDataStream &out, const std::multiset<K>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const K& value : container) {
+        out << value;
+    }
+
+    return out;
+}
+
+template <class K>
+QDataStream& operator >> (QDataStream &in, std::multiset<K>& container) {
+    uint32_t size;
+    in >> size;
+    for (uint32_t i = 0; i < size; ++i) {
+        K value;
+        in >> value;
+        container.insert(value);
+    }
+
+    return in;
+}
+
+template <class K>
+QDataStream& operator << (QDataStream &out, const std::vector<K>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const K& value : container) {
+        out << value;
+    }
+
+    return out;
+}
+
+template <class K>
+QDataStream& operator >> (QDataStream &in, std::vector<K>& container) {
+    uint32_t size;
+    in >> size;
+    container.resize(size);
+    for (uint32_t i = 0; i < size; ++i) {
+        in >> container[i];
+    }
+
+    return in;
+}
+
+template <class K>
+QDataStream& operator << (QDataStream &out, const std::deque<K>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const K& value : container) {
+        out << value;
+    }
+
+    return out;
+}
+
+template <class K>
+QDataStream& operator >> (QDataStream &in, std::deque<K>& container) {
+    uint32_t size;
+    in >> size;
+    container.resize(size);
+    for (uint32_t i = 0; i < size; ++i) {
+        in >> container[i];
+    }
+
+    return in;
+}
+
+template <class K>
+QDataStream& operator << (QDataStream &out, const std::list<K>& container) {
+    uint32_t size = container.size();
+    out << size;
+    for (const K& value : container) {
+        out << value;
+    }
+
+    return out;
+}
+
+template <class K>
+QDataStream& operator >> (QDataStream &in, std::list<K>& container) {
+    uint32_t size;
+    in >> size;
+    for (uint32_t i = 0; i < size; ++i) {
+        typename std::list<K>::iterator itr = container.emplace(container.end());
+        in >> *itr;
+    }
+
+    return in;
+}
+
+#endif //CORE_OPERATORS_HPP
diff --git a/table.cpp b/table.cpp
index 141df13..80ac7bc 100644
--- a/table.cpp
+++ b/table.cpp
@@ -35,10 +35,12 @@ void DataBase::_Table::drop()
     MDB_txn *txn;
     int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
     if (rc) {
+        mdb_txn_abort(txn);
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
     rc = drop(txn);
     if (rc) {
+        mdb_txn_abort(txn);
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
 
@@ -61,6 +63,7 @@ uint32_t DataBase::_Table::count() const
     int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
     rc = mdb_stat(txn, dbi, &stat);
     if (rc) {
+        mdb_txn_abort(txn);
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
     uint32_t amount = stat.ms_entries;
diff --git a/table.h b/table.h
index 8803e2e..8279237 100644
--- a/table.h
+++ b/table.h
@@ -54,6 +54,7 @@ protected:
     ~Table() override;
 
 public:
+    using DataBase::_Table::drop;
     virtual void addRecord(const K& key, const V& value);
     virtual bool forceRecord(const K& key, const V& value);     //returns true if there was addition, false if change
     virtual void changeRecord(const K& key, const V& value);
@@ -61,6 +62,8 @@ public:
     virtual bool checkRecord(const K& key) const;               //checks if there is a record with given key
     virtual V getRecord(const K& key) const;
     virtual std::map<K, V> readAll() const;
+    virtual void replaceAll(const std::map<K, V>& data);
+    virtual uint32_t addRecords(const std::map<K, V>& data, bool overwrite = false);
 
 protected:
     Serializer<K>* keySerializer;
diff --git a/table.hpp b/table.hpp
index 573c828..49cb38e 100644
--- a/table.hpp
+++ b/table.hpp
@@ -43,8 +43,12 @@ void DataBase::Table<K, V>::addRecord(const K& key, const V& value) {
     MDB_val lmdbKey = keySerializer->setData(key);
     MDB_val lmdbData = valueSerializer->setData(value);
     MDB_txn *txn;
-    mdb_txn_begin(db->environment, NULL, 0, &txn);
-    int rc;
+    int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
+    if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
     rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, MDB_NOOVERWRITE);
     if (rc != 0) {
         mdb_txn_abort(txn);
@@ -68,8 +72,12 @@ bool DataBase::Table<K, V>::forceRecord(const K& key, const V& value) {
     MDB_val lmdbKey = keySerializer->setData(key);
     MDB_val lmdbData;
     MDB_txn *txn;
-    mdb_txn_begin(db->environment, NULL, 0, &txn);
-    int rc;
+    int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
+    if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
     rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
     if (rc == 0) {
         added = false;
@@ -100,8 +108,13 @@ void DataBase::Table<K, V>::changeRecord(const K& key, const V& value) {
     MDB_val lmdbKey = keySerializer->setData(key);
     MDB_val lmdbData = valueSerializer->setData(value);
     MDB_txn *txn;
-    mdb_txn_begin(db->environment, NULL, 0, &txn);
-    int rc;
+
+    int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
+    if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
     rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, 0);
     if (rc != 0) {
         mdb_txn_abort(txn);
@@ -123,8 +136,12 @@ V DataBase::Table<K, V>::getRecord(const K& key) const {
     MDB_val lmdbData;
 
     MDB_txn *txn;
-    int rc;
-    mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
+    int rc = mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
+    if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
     rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
     if (rc) {
         mdb_txn_abort(txn);
@@ -151,8 +168,12 @@ bool DataBase::Table<K, V>::checkRecord(const K& key) const {
     MDB_val lmdbData;
 
     MDB_txn *txn;
-    int rc;
-    mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
+    int rc = mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
+    if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
     rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
     mdb_txn_abort(txn);
 
@@ -179,10 +200,12 @@ std::map<K, V> DataBase::Table<K, V>::readAll() const {
     MDB_val lmdbKey, lmdbData;
     int rc = mdb_txn_begin(db->environment, NULL, MDB_RDONLY, &txn);
     if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
     rc = mdb_cursor_open(txn, dbi, &cursor);
     if (rc != MDB_SUCCESS) {
+        mdb_txn_abort(txn);
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
     rc = mdb_cursor_get(cursor, &lmdbKey, &lmdbData, MDB_FIRST);
@@ -193,6 +216,7 @@ std::map<K, V> DataBase::Table<K, V>::readAll() const {
         rc = mdb_cursor_get(cursor, &lmdbKey, &lmdbData, MDB_NEXT);
     }
 
+    mdb_txn_abort(txn);
     if (rc != MDB_NOTFOUND) {
         throw Unknown(db->name, mdb_strerror(rc), name);
     }
@@ -200,6 +224,75 @@ std::map<K, V> DataBase::Table<K, V>::readAll() const {
     return result;
 }
 
+template<class K, class V>
+void DataBase::Table<K, V>::replaceAll(const std::map<K, V>& data) {
+    if (!db->opened) {
+        throw Closed("replaceAll", db->name, name);
+    }
+
+    MDB_txn *txn;
+    int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
+    if (rc) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+    rc = drop(txn);
+    if (rc) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
+    MDB_val lmdbKey, lmdbData;
+    for (const std::pair<const K, V>& pair : data) {
+        lmdbKey = keySerializer->setData(pair.first);
+        lmdbData = valueSerializer->setData(pair.second);
+
+        rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, MDB_NOOVERWRITE);
+        if (rc != 0) {
+            mdb_txn_abort(txn);
+            throw Unknown(db->name, mdb_strerror(rc), name);
+        }
+    }
+    mdb_txn_commit(txn);
+}
+
+template<class K, class V>
+uint32_t DataBase::Table<K, V>::addRecords(const std::map<K, V>& data, bool overwrite) {
+    if (!db->opened) {
+        throw Closed("addRecords", db->name, name);
+    }
+
+    MDB_txn *txn;
+    int rc = mdb_txn_begin(db->environment, NULL, 0, &txn);
+    if (rc) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+
+    MDB_val lmdbKey, lmdbData;
+    for (const std::pair<const K, V>& pair : data) {
+        lmdbKey = keySerializer->setData(pair.first);
+        lmdbData = valueSerializer->setData(pair.second);
+
+        rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, overwrite ? 0 : MDB_NOOVERWRITE);
+        if (rc != 0) {
+            mdb_txn_abort(txn);
+            throw Unknown(db->name, mdb_strerror(rc), name);
+        }
+    }
+
+    MDB_stat stat;
+    rc = mdb_stat(txn, dbi, &stat);
+    if (rc) {
+        mdb_txn_abort(txn);
+        throw Unknown(db->name, mdb_strerror(rc), name);
+    }
+    uint32_t amount = stat.ms_entries;
+
+    mdb_txn_commit(txn);
+    return amount;
+}
+
 template<class K, class V>
 void DataBase::Table<K, V>::removeRecord(const K& key) {
     if (!db->opened) {