diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a9dbcdc..d0d7b5b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -5,6 +5,7 @@
 
 
 add_library(trrep
+  logger.cpp
   provider.cpp
   client_context.cpp
   server_context.cpp
@@ -15,6 +16,7 @@ target_link_libraries(trrep wsrep pthread dl)
 add_executable(trrep_test
   mock_client_context.cpp
   mock_utils.cpp
+  client_context_test.cpp
   server_context_test.cpp
   transaction_context_test.cpp
   trrep_test.cpp
diff --git a/src/client_context.cpp b/src/client_context.cpp
index ed3c393..de7f540 100644
--- a/src/client_context.cpp
+++ b/src/client_context.cpp
@@ -33,30 +33,29 @@ int trrep::client_context::before_command()
         }
     }
     state(lock, s_exec);
-    if (transaction_.state() == trrep::transaction_context::s_must_abort)
+    if (transaction_.state() == trrep::transaction_context::s_must_abort ||
+        transaction_.state() == trrep::transaction_context::s_aborted)
     {
         return 1;
     }
     return 0;
 }
 
-int trrep::client_context::after_command()
+void trrep::client_context::after_command()
 {
-    int ret(0);
     trrep::unique_lock<trrep::mutex> lock(mutex_);
     if (transaction_.state() == trrep::transaction_context::s_must_abort)
     {
         lock.unlock();
         rollback(transaction_);
         lock.lock();
-        ret = 1;
     }
     state(lock, s_idle);
-    return ret;
 }
 
 int trrep::client_context::before_statement()
 {
+    trrep::unique_lock<trrep::mutex> lock(mutex_);
 #if 0
     /*!
      * \todo It might be beneficial to implement timed wait for
@@ -68,18 +67,25 @@ int trrep::client_context::before_statement()
         return 1;
     }
 #endif // 0
+
+    if (transaction_.state() == trrep::transaction_context::s_must_abort)
+    {
+        lock.unlock();
+        rollback(transaction_);
+        lock.lock();
+        return 1;
+    }
     return 0;
 }
 
-int trrep::client_context::after_statement()
+void trrep::client_context::after_statement()
 {
 #if 0
     /*!
      * \todo Check for replay state, do rollback if requested.
      */
 #endif // 0
-    transaction_.after_statement();
-    return 0;
+    (void)transaction_.after_statement();
 }
 
 // Private
diff --git a/src/client_context.hpp b/src/client_context.hpp
index 56d17fd..5e0c61a 100644
--- a/src/client_context.hpp
+++ b/src/client_context.hpp
@@ -148,7 +148,7 @@ namespace trrep
          * If overridden, the implementation should call base
          * class metods after any implementation specifict operations.
          */
-        virtual int after_command();
+        virtual void after_command();
 
         /*!
          * Before statement execution operations.
@@ -174,7 +174,7 @@ namespace trrep
          * If overridden by the implementation, base class method
          * should be called after any implementation specific operations.
          */
-        virtual int after_statement();
+        virtual void after_statement();
 
         int start_transaction(const trrep::transaction_id& id)
         {
@@ -314,6 +314,7 @@ namespace trrep
                                             trrep::transaction_context&,
                                             const trrep::data&);
         friend class client_context_switch;
+        friend class client_applier_mode;
         friend class transaction_context;
 
         /*!
@@ -383,8 +384,7 @@ namespace trrep
         /*!
          * Replay the transaction.
          */
-        virtual int replay(trrep::unique_lock<trrep::mutex>&,
-                           trrep::transaction_context& tc) = 0;
+        virtual int replay(trrep::transaction_context& tc) = 0;
 
 
         /*!
@@ -465,6 +465,24 @@ namespace trrep
         client_context& orig_context_;
         client_context& current_context_;
     };
+
+    class client_applier_mode
+    {
+    public:
+        client_applier_mode(trrep::client_context& client)
+            : client_(client)
+            , orig_mode_(client.mode_)
+        {
+            client_.mode_ = trrep::client_context::m_applier;
+        }
+        ~client_applier_mode()
+        {
+            client_.mode_ = orig_mode_;
+        }
+    private:
+        trrep::client_context& client_;
+        enum trrep::client_context::mode orig_mode_;
+    };
 }
 
 #endif // TRREP_CLIENT_CONTEXT_HPP
diff --git a/src/client_context_test.cpp b/src/client_context_test.cpp
new file mode 100644
index 0000000..5a5dab1
--- /dev/null
+++ b/src/client_context_test.cpp
@@ -0,0 +1,29 @@
+
+//
+// Copyright (C) 2018 Codership Oy <info@codership.com>
+//
+
+#include "mock_client_context.hpp"
+#include "mock_server_context.hpp"
+#include "mock_utils.hpp"
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_AUTO_TEST_CASE(client_context_test_error_codes)
+{
+    trrep::mock_server_context sc("s1", "s1", trrep::server_context::rm_async);
+    trrep::mock_client_context cc(sc,
+                                  trrep::client_id(1),
+                                  trrep::client_context::m_applier,
+                                  false);
+
+    trrep::transaction_context& tc(cc.transaction());
+    BOOST_REQUIRE(tc.active() == false);
+    tc.start_transaction(1);
+    trrep_mock::bf_abort_unordered(cc, tc);
+
+    BOOST_REQUIRE(cc.before_command());
+    BOOST_REQUIRE(cc.before_statement());
+    cc.after_statement();
+    cc.after_command();
+}
diff --git a/src/dbms_simulator.cpp b/src/dbms_simulator.cpp
index 0e65fbb..10297d2 100644
--- a/src/dbms_simulator.cpp
+++ b/src/dbms_simulator.cpp
@@ -16,17 +16,19 @@
 #include "provider.hpp"
 #include "condition_variable.hpp"
 #include "view.hpp"
+#include "logger.hpp"
 
 #include <boost/program_options.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/thread.hpp>
 
-#include <iostream>
 #include <memory>
 #include <map>
 #include <atomic>
 #include <chrono>
-// #include <thread>
+#include <iostream>
+#include <unordered_set>
+#include <thread>
 
 class dbms_server;
 
@@ -46,6 +48,83 @@ struct dbms_simulator_params
     { }
 };
 
+class dbms_storage_engine
+{
+public:
+    dbms_storage_engine()
+        : mutex_()
+        , transactions_()
+        , alg_freq_(1)
+        , bf_aborts_()
+    { }
+
+    class transaction
+    {
+    public:
+        transaction(dbms_storage_engine& se)
+            : se_(se)
+            , txc_()
+        {
+        }
+        void start(trrep::transaction_context* txc)
+        {
+            trrep::unique_lock<trrep::mutex> lock(se_.mutex_);
+            if (se_.transactions_.insert(txc).second == false)
+            {
+                ::abort();
+            }
+            txc_ = txc;
+
+        }
+
+        ~transaction()
+        {
+            if (txc_)
+            {
+                trrep::unique_lock<trrep::mutex> lock(se_.mutex_);
+                se_.transactions_.erase(txc_);
+            }
+        }
+
+        transaction(const transaction&) = delete;
+        transaction& operator=(const transaction&) = delete;
+
+    private:
+        dbms_storage_engine& se_;
+        trrep::transaction_context* txc_;
+    };
+
+    void bf_abort_some(const trrep::transaction_context& txc)
+    {
+        trrep::unique_lock<trrep::mutex> lock(mutex_);
+        if ((std::rand() % alg_freq_) == 0)
+        {
+            if (transactions_.empty() == false)
+            {
+                auto* victim_txc(*transactions_.begin());
+                trrep::unique_lock<trrep::mutex> victim_txc_lock(
+                    victim_txc->mutex());
+                lock.unlock();
+                if (victim_txc->bf_abort(victim_txc_lock, txc))
+                {
+                    trrep::log() << "BF aborted " << victim_txc->id().get();
+                    ++bf_aborts_;
+                }
+            }
+        }
+    }
+
+    long long bf_aborts()
+    {
+        return bf_aborts_;
+    }
+private:
+    trrep::default_mutex mutex_;
+    std::unordered_set<trrep::transaction_context*> transactions_;
+    size_t alg_freq_;
+    std::atomic<long long> bf_aborts_;
+};
+
 class dbms_simulator
 {
 public:
@@ -65,21 +144,7 @@ public:
                     const std::string& req, const wsrep_gtid_t& gtid, bool);
     const dbms_simulator_params& params() const
     { return params_; }
-    std::string stats() const
-    {
-        size_t transactions(params_.n_servers * params_.n_clients
-                            * params_.n_transactions);
-        auto duration(std::chrono::duration<double>(
-                          clients_stop_ - clients_start_).count());
-        std::ostringstream os;
-        os << "Number of transactions: " << transactions
-           << "\n"
-           << "Seconds: " << duration
-           << " \n"
-           << "Transactions per second: " << transactions/duration
-           << "\n";
-        return os.str();
-    }
+    std::string stats() const;
 private:
     std::string server_port(size_t i) const
     {
@@ -93,7 +158,7 @@ private:
     const dbms_simulator_params& params_;
     std::map<size_t, std::unique_ptr<dbms_server>> servers_;
     std::chrono::time_point<std::chrono::steady_clock> clients_start_;
-        std::chrono::time_point<std::chrono::steady_clock> clients_stop_;
+    std::chrono::time_point<std::chrono::steady_clock> clients_stop_;
 };
 
 class dbms_client;
@@ -110,6 +175,7 @@ public:
                                 name, id, address, name + "_data",
                                 trrep::server_context::rm_async)
         , simulator_(simulator)
+        , storage_engine_()
         , mutex_()
         , cond_()
         , last_client_id_(0)
@@ -162,6 +228,15 @@ public:
         return (last_transaction_id_.fetch_add(1) + 1);
     }
 
+    dbms_storage_engine& storage_engine() { return storage_engine_; }
+
+    int apply_to_storage_engine(const trrep::transaction_context& txc,
+                                const trrep::data&)
+    {
+        storage_engine_.bf_abort_some(txc);
+        return 0;
+    }
+
     void start_clients();
     void stop_clients();
     void client_thread(const std::shared_ptr<dbms_client>& client);
@@ -170,6 +245,7 @@ private:
     void start_client(size_t id);
 
     dbms_simulator& simulator_;
+    dbms_storage_engine storage_engine_;
     trrep::default_mutex mutex_;
     trrep::default_condition_variable cond_;
     std::atomic<size_t> last_client_id_;
@@ -192,7 +268,10 @@ public:
         , n_transactions_(n_transactions)
     { }
 
-    ~dbms_client() { }
+    ~dbms_client()
+    {
+        trrep::unique_lock<trrep::mutex> lock(mutex_);
+    }
 
     void start()
     {
@@ -205,10 +284,9 @@ public:
 
 private:
     bool do_2pc() const override { return false; }
-    int apply(trrep::transaction_context&, const trrep::data&) override
+    int apply(trrep::transaction_context& txc, const trrep::data& data) override
     {
-        // std::cerr << "applying" << "\n";
-        return 0;
+        return server_.apply_to_storage_engine(txc, data);
     }
     int commit(trrep::transaction_context& transaction_context) override
     {
@@ -216,26 +294,24 @@ private:
         ret = transaction_context.before_commit();
         ret = ret || transaction_context.ordered_commit();
         ret = ret || transaction_context.after_commit();
-        // std::cerr << "commit" << "\n";
         return 0;
     }
     int rollback(trrep::transaction_context& transaction_context) override
     {
-        std::cerr << "rollback: " << transaction_context.id().get()
-                  << "state: " << trrep::to_string(transaction_context.state())
-                  << "\n";
+        trrep::log() << "rollback: " << transaction_context.id().get()
+                     << "state: "
+                     << trrep::to_string(transaction_context.state());
         transaction_context.before_rollback();
         transaction_context.after_rollback();
         return 0;
     }
 
     void will_replay(trrep::transaction_context&) override { }
-    int replay(trrep::unique_lock<trrep::mutex>& lock,
-               trrep::transaction_context& tc) override
+    int replay(trrep::transaction_context& txc) override
     {
-        tc.state(lock, trrep::transaction_context::s_replaying);
-        tc.state(lock, trrep::transaction_context::s_committed);
-        return 0;
+        trrep::log() << "replay: " << txc.id().get();
+        trrep::client_applier_mode applier_mode(*this);
+        return provider().replay(&txc.ws_handle(), this);
     }
     void wait_for_replayers(trrep::unique_lock<trrep::mutex>&) const override
     { }
@@ -248,59 +324,75 @@ private:
 
     void run_one_transaction()
     {
-        before_command();
-        before_statement();
-        start_transaction(server_.next_transaction_id());
-        after_statement();
+        int err(before_command());
+        dbms_storage_engine::transaction se_trx(server_.storage_engine());
+        if (err == 0)
+        {
+            err = before_statement();
+            if (err == 0)
+            {
+                err = start_transaction(server_.next_transaction_id());
+                se_trx.start(&transaction());
+            }
+            after_statement();
+        }
         after_command();
-
-        int err(0);
+        std::this_thread::sleep_for(std::chrono::milliseconds(10));
         for (int i(0); i < 1 && err == 0; ++i)
         {
             std::ostringstream os;
-            before_command();
-            before_statement();
-            int data(std::rand() % 10000000);
-            os << data;
-            trrep::key key;
-            key.append_key_part("dbms", 4);
-            wsrep_conn_id_t client_id(id().get());
-            key.append_key_part(&client_id, sizeof(client_id));
-            key.append_key_part(&data, sizeof(data));
-            err = append_key(key);
-            err = err || append_data(trrep::data(os.str().c_str(), os.str().size()));
-            after_statement();
+            err = before_command();
+            if (err == 0)
+            {
+                err = before_statement();
+                if (err == 0)
+                {
+                    int data(std::rand() % 10000000);
+                    os << data;
+                    trrep::key key;
+                    key.append_key_part("dbms", 4);
+                    wsrep_conn_id_t client_id(id().get());
+                    key.append_key_part(&client_id, sizeof(client_id));
+                    key.append_key_part(&data, sizeof(data));
+                    err = append_key(key);
+                    err = append_data(trrep::data(os.str().c_str(), os.str().size()));
+                }
+                after_statement();
+            }
             after_command();
         }
-
-        before_command();
-        before_statement();
-        // std::cout << "append_data: " << err << "\n";
-        if (err == 0 && do_2pc())
+        std::this_thread::sleep_for(std::chrono::milliseconds(10));
+        if (err == 0)
         {
-            err = err || before_prepare();
-            // std::cout << "before_prepare: " << err << "\n";
-            err = err || after_prepare();
-            // std::cout << "after_prepare: " << err << "\n";
+            err = before_command();
+            if (err == 0)
+            {
+                err = before_statement();
+
+                if (err == 0 && do_2pc())
+                {
+                    err = err || before_prepare();
+                    err = err || after_prepare();
+                }
+                err = err || before_commit();
+                err = err || ordered_commit();
+                err = err || after_commit();
+                after_statement();
+            }
+            after_command();
         }
-        err = err || before_commit();
-        // std::cout << "before_commit: " << err << "\n";
-        err = err || ordered_commit();
-        // std::cout << "ordered_commit: " << err << "\n";
-        err = err || after_commit();
-        // std::cout << "after_commit: " << err << "\n";
-        after_statement();
-        after_command();
+        assert(transaction().state() == trrep::transaction_context::s_committed
+               ||
+               transaction().state() == trrep::transaction_context::s_aborted);
     }
 
     void report_progress(size_t i) const
     {
         if ((i % 100) == 0)
         {
-            std::cout << "client: " << id().get()
-                      << " transactions: " << i
-                      << " " << 100*double(i)/n_transactions_ << "%"
-                      << std::endl;
+            trrep::log() << "client: " << id().get()
+                         << " transactions: " << i
+                         << " " << 100*double(i)/n_transactions_ << "%";
         }
     }
     trrep::default_mutex mutex_;
@@ -316,7 +408,7 @@ void dbms_server::applier_thread()
     dbms_client applier(*this, client_id,
                         trrep::client_context::m_applier, 0);
     wsrep_status_t ret(provider().run_applier(&applier));
-    std::cout << "Applier thread exited with error code " << ret << "\n";
+    trrep::log() << "Applier thread exited with error code " << ret;
 }
 
 trrep::client_context* dbms_server::local_client_context()
@@ -362,10 +454,10 @@ void dbms_server::start_client(size_t id)
 
 void dbms_simulator::start()
 {
-    std::cout << "Provider: " << params_.wsrep_provider << "\n";
+    trrep::log() << "Provider: " << params_.wsrep_provider;
 
     std::string cluster_address(build_cluster_address());
-    std::cout << "Cluster address: " << cluster_address << "\n";
+    trrep::log() << "Cluster address: " << cluster_address;
     for (size_t i(0); i < params_.n_servers; ++i)
     {
         std::ostringstream name_os;
@@ -406,7 +498,7 @@ void dbms_simulator::start()
     }
 
     // Start client threads
-    std::cout << "####################### Starting client load" << "\n";
+    trrep::log() << "####################### Starting client load";
     clients_start_ = std::chrono::steady_clock::now();
     for (auto& i : servers_)
     {
@@ -423,20 +515,20 @@ void dbms_simulator::stop()
         server.stop_clients();
     }
     clients_stop_ = std::chrono::steady_clock::now();
-    std::cout << "######## Stats ############\n";
-    std::cout << stats();
-    std::cout << "######## Stats ############\n";
+    trrep::log() << "######## Stats ############";
+    trrep::log()  << stats();
+    trrep::log() << "######## Stats ############";
     // REMOVEME: Temporary shortcut
     // exit(0);
     for (auto& i : servers_)
     {
         dbms_server& server(*i.second);
-        std::cout << "Status for server: " << server.id() << "\n";
+        trrep::log() << "Status for server: " << server.id();
         auto status(server.provider().status());
         for_each(status.begin(), status.end(),
                  [](const trrep::provider::status_variable& sv)
                  {
-                     std::cout << sv.name() << " = " << sv.value() << "\n";
+                     trrep::log() << sv.name() << " = " << sv.value();
                  });
 
         server.disconnect();
@@ -445,6 +537,29 @@ void dbms_simulator::stop()
     }
 }
 
+std::string dbms_simulator::stats() const
+{
+    size_t transactions(params_.n_servers * params_.n_clients
+                        * params_.n_transactions);
+    auto duration(std::chrono::duration<double>(
+                      clients_stop_ - clients_start_).count());
+    long long bf_aborts(0);
+    for (const auto& s : servers_)
+    {
+        bf_aborts += s.second->storage_engine().bf_aborts();
+    }
+    std::ostringstream os;
+    os << "Number of transactions: " << transactions
+       << "\n"
+       << "Seconds: " << duration
+       << " \n"
+       << "Transactions per second: " << transactions/duration
+       << "\n"
+       << "BF aborts: "
+       << bf_aborts;
+    return os.str();
+}
+
 void dbms_simulator::donate_sst(dbms_server& server,
                                 const std::string& req,
                                 const wsrep_gtid_t& gtid,
@@ -461,7 +576,7 @@ void dbms_simulator::donate_sst(dbms_server& server,
     }
     if (bypass == false)
     {
-        std::cout << "SST " << server.id() << " -> " << id << "\n";
+        trrep::log() << "SST " << server.id() << " -> " << id;
     }
     i->second->sst_received(gtid);
     server.sst_sent(gtid);
@@ -514,7 +629,7 @@ int main(int argc, char** argv)
 
         if (vm.count("help"))
         {
-            std::cout << desc << "\n";
+            std::cerr << desc << "\n";
             return 1;
         }
 
@@ -526,17 +641,17 @@ int main(int argc, char** argv)
         }
         catch (const std::exception& e)
         {
-            std::cerr << "Caught exception: " << e.what();
+            trrep::log() << "Caught exception: " << e.what();
         }
         stats = sim.stats();
     }
     catch (const std::exception& e)
     {
-        std::cerr << e.what() << "\n";
+        trrep::log() << e.what();
         return 1;
     }
 
-    std::cout << "Stats:\n" << stats << "\n";
+    trrep::log() << "Stats:\n" << stats << "\n";
 
     return 0;
 }
diff --git a/src/lock.hpp b/src/lock.hpp
index 2084cb7..d37ebdb 100644
--- a/src/lock.hpp
+++ b/src/lock.hpp
@@ -24,8 +24,10 @@ namespace trrep
         }
         ~unique_lock()
         {
-            assert(locked_);
-            mutex_.unlock();
+            if (locked_)
+            {
+                unlock();
+            }
         }
 
         void lock()
diff --git a/src/logger.cpp b/src/logger.cpp
new file mode 100644
index 0000000..c53da18
--- /dev/null
+++ b/src/logger.cpp
@@ -0,0 +1,8 @@
+
+#include "logger.hpp"
+
+#include <iostream>
+
+std::ostream& trrep::log::os_ = std::cout;
+static trrep::default_mutex log_mutex_;
+trrep::mutex& trrep::log::mutex_ = log_mutex_;
diff --git a/src/logger.hpp b/src/logger.hpp
new file mode 100644
index 0000000..11882ae
--- /dev/null
+++ b/src/logger.hpp
@@ -0,0 +1,39 @@
+//
+// Copyright (C) 2018 Codership Oy <info@codership.com>
+//
+
+#ifndef TRREP_LOGGER_HPP
+#define TRREP_LOGGER_HPP
+
+#include "mutex.hpp"
+#include "lock.hpp"
+
+#include <iosfwd>
+#include <sstream>
+
+namespace trrep
+{
+    class log
+    {
+    public:
+        log()
+            : oss_()
+        { }
+        ~log()
+        {
+            trrep::unique_lock<trrep::mutex> lock(mutex_);
+            os_ << oss_.str() << "\n";
+        }
+        template <typename T>
+        std::ostream& operator<<(const T& val)
+        {
+            return (oss_ << val);
+        }
+    private:
+        std::ostringstream oss_;
+        static trrep::mutex& mutex_;
+        static std::ostream& os_;
+    };
+}
+
+#endif // TRREP_LOGGER_HPP
diff --git a/src/mock_client_context.hpp b/src/mock_client_context.hpp
index 385a2ec..0805df4 100644
--- a/src/mock_client_context.hpp
+++ b/src/mock_client_context.hpp
@@ -37,10 +37,11 @@ namespace trrep
         int rollback(trrep::transaction_context&);
         bool do_2pc() const { return do_2pc_; }
         void will_replay(trrep::transaction_context&) TRREP_OVERRIDE { }
-        int replay(trrep::unique_lock<trrep::mutex>& lock,
-                   trrep::transaction_context& tc) TRREP_OVERRIDE
+        int replay(trrep::transaction_context& tc) TRREP_OVERRIDE
         {
-            tc.state(lock, trrep::transaction_context::s_replaying);
+            trrep::unique_lock<trrep::mutex> lock(mutex_);
+            tc.state(lock, trrep::transaction_context::s_committing);
+            tc.state(lock, trrep::transaction_context::s_ordered_commit);
             tc.state(lock, trrep::transaction_context::s_committed);
             return 0;
         }
diff --git a/src/mock_provider.hpp b/src/mock_provider.hpp
index 982da81..80fe8c8 100644
--- a/src/mock_provider.hpp
+++ b/src/mock_provider.hpp
@@ -103,6 +103,8 @@ namespace trrep
                                const wsrep_trx_meta_t*) { return 0;}
         int release(wsrep_ws_handle_t*) { return 0; }
 
+        int replay(wsrep_ws_handle_t*, void*) { ::abort(); /* not impl */}
+
         // Methods to modify mock state
 
         // Inject BF abort event into the provider.
diff --git a/src/provider.hpp b/src/provider.hpp
index 63eb1c8..af808cd 100644
--- a/src/provider.hpp
+++ b/src/provider.hpp
@@ -53,15 +53,16 @@ namespace trrep
         certify(wsrep_conn_id_t, wsrep_ws_handle_t*,
                 uint32_t,
                 wsrep_trx_meta_t*) = 0;
-        //!
-        //! BF abort a transaction inside provider.
-        //!
-        //! @param[in] bf_seqno Seqno of the aborter transaction
-        //! @param[in] victim_txt Transaction identifier of the victim
-        //! @param[out] victim_seqno Sequence number of the victim transaction
-        //!              or WSREP_SEQNO_UNDEFINED if the victim was not ordered
-        //!
-        //! @return wsrep_status_t
+        /*!
+         * BF abort a transaction inside provider.
+         *
+         * @param[in] bf_seqno Seqno of the aborter transaction
+         * @param[in] victim_txt Transaction identifier of the victim
+         * @param[out] victim_seqno Sequence number of the victim transaction
+         * or WSREP_SEQNO_UNDEFINED if the victim was not ordered
+         *
+         * @return wsrep_status_t
+         */
         virtual wsrep_status_t bf_abort(wsrep_seqno_t bf_seqno,
                                         wsrep_trx_id_t victim_trx,
                                         wsrep_seqno_t* victim_seqno) = 0;
@@ -72,6 +73,13 @@ namespace trrep
                                        const wsrep_trx_meta_t*) = 0;
         virtual int release(wsrep_ws_handle_t*) = 0;
 
+        /*!
+         * Replay a transaction.
+         *
+         * @return Zero in case of success, non-zero on failure.
+         */
+        virtual int replay(wsrep_ws_handle_t* ws_handle, void* applier_ctx) = 0;
+
         virtual int sst_sent(const wsrep_gtid_t&, int) = 0;
         virtual int sst_received(const wsrep_gtid_t&, int) = 0;
 
diff --git a/src/server_context.cpp b/src/server_context.cpp
index 907d2f8..eaa2959 100644
--- a/src/server_context.cpp
+++ b/src/server_context.cpp
@@ -6,6 +6,7 @@
 #include "client_context.hpp"
 #include "transaction_context.hpp"
 #include "view.hpp"
+#include "logger.hpp"
 #include "compiler.hpp"
 
 // Todo: refactor into provider factory
@@ -15,7 +16,6 @@
 #include <wsrep_api.h>
 
 #include <cassert>
-
 #include <sstream>
 
 namespace
@@ -116,7 +116,7 @@ namespace
         assert(client_context->mode() == trrep::client_context::m_applier);
 
         trrep::data data(buf->ptr, buf->len);
-        if (client_context->start_transaction(*wsh, *meta, flags))
+        if (client_context->transaction().state() != trrep::transaction_context::s_replaying && client_context->start_transaction(*wsh, *meta, flags))
         {
             ret = WSREP_CB_FAILURE;
         }
@@ -174,7 +174,7 @@ namespace
 int trrep::server_context::load_provider(const std::string& provider_spec,
                                          const std::string& provider_options)
 {
-    std::cout << "Loading provider " << provider_spec << "\n";
+    trrep::log() << "Loading provider " << provider_spec;
     if (provider_spec == "mock")
     {
         provider_ = new trrep::mock_provider;
@@ -252,27 +252,27 @@ void trrep::server_context::wait_until_state(
 
 void trrep::server_context::on_connect()
 {
-    std::cout << "Server " << name_ << " connected to cluster" << "\n";
+    trrep::log() << "Server " << name_ << " connected to cluster";
     trrep::unique_lock<trrep::mutex> lock(mutex_);
     state(lock, s_connected);
 }
 
 void trrep::server_context::on_view(const trrep::view& view)
 {
-    std::cout << "================================================\nView:\n"
-              << "id: " << view.id() << "\n"
-              << "status: " << view.status() << "\n"
-              << "own_index: " << view.own_index() << "\n"
-              << "final: " << view.final() << "\n"
-              << "members: \n";
+    trrep::log() << "================================================\nView:\n"
+                 << "id: " << view.id() << "\n"
+                 << "status: " << view.status() << "\n"
+                 << "own_index: " << view.own_index() << "\n"
+                 << "final: " << view.final() << "\n"
+                 << "members";
     const std::vector<trrep::view::member>& members(view.members());
     for (std::vector<trrep::view::member>::const_iterator i(members.begin());
          i != members.end(); ++i)
     {
-        std::cout << "id: " << i->id() << " "
-                  << "name: " << i->name() << "\n";
+        trrep::log() << "id: " << i->id() << " "
+                     << "name: " << i->name();
     }
-    std::cout << "=================================================\n";
+    trrep::log() << "=================================================";
     trrep::unique_lock<trrep::mutex> lock(mutex_);
     if (view.final())
     {
@@ -282,7 +282,7 @@ void trrep::server_context::on_view(const trrep::view& view)
 
 void trrep::server_context::on_sync()
 {
-    std::cout << "Synced with group" << "\n";
+    trrep::log() << "Server " << name_ << " synced with group";
     trrep::unique_lock<trrep::mutex> lock(mutex_);
     if (state_ != s_synced)
     {
@@ -299,8 +299,11 @@ int trrep::server_context::on_apply(
     if (starts_transaction(transaction_context.flags()) &&
         commits_transaction(transaction_context.flags()))
     {
-        assert(transaction_context.active() == false);
-        transaction_context.start_transaction();
+        if (transaction_context.state() != trrep::transaction_context::s_replaying)
+        {
+            assert(transaction_context.active() == false);
+            transaction_context.start_transaction();
+        }
         if (client_context.apply(transaction_context, data))
         {
             ret = 1;
@@ -360,8 +363,8 @@ void trrep::server_context::state(
 
     if (allowed[state_][state])
     {
-        std::cout << "server " << name_ << " state change: "
-                  << state_ << " -> " << state;
+        trrep::log() << "server " << name_ << " state change: "
+                     << state_ << " -> " << state;
         state_ = state;
         cond_.notify_all();
         while (state_waiters_[state_])
diff --git a/src/transaction_context.cpp b/src/transaction_context.cpp
index ef22bd5..dbba2d0 100644
--- a/src/transaction_context.cpp
+++ b/src/transaction_context.cpp
@@ -7,9 +7,9 @@
 #include "server_context.hpp"
 #include "key.hpp"
 #include "data.hpp"
+#include "logger.hpp"
 #include "compiler.hpp"
 
-#include <iostream> // TODO: replace with proper logging utility
 #include <sstream>
 #include <memory>
 
@@ -33,7 +33,8 @@ trrep::transaction_context::transaction_context(
 
 
 trrep::transaction_context::~transaction_context()
-{ }
+{
+}
 
 int trrep::transaction_context::start_transaction(
     const trrep::transaction_id& id)
@@ -179,8 +180,10 @@ int trrep::transaction_context::before_commit()
 
     trrep::unique_lock<trrep::mutex> lock(client_context_.mutex());
     debug_log_state("before_commit_enter");
-    assert(state() == s_executing || state() == s_committing ||
-           state() == s_must_abort);
+    assert(state() == s_executing ||
+           state() == s_committing ||
+           state() == s_must_abort ||
+           state() == s_replaying);
 
     switch (client_context_.mode())
     {
@@ -246,6 +249,10 @@ int trrep::transaction_context::before_commit()
                 state(lock, s_certifying);
                 state(lock, s_committing);
             }
+            else if (state() == s_replaying)
+            {
+                state(lock, s_committing);
+            }
         }
         break;
     }
@@ -405,7 +412,11 @@ int trrep::transaction_context::after_statement()
     case s_aborted:
         break;
     case s_must_replay:
-        ret = client_context_.replay(lock, *this);
+        state(lock, s_replaying);
+        lock.unlock();
+        ret = client_context_.replay(*this);
+        lock.lock();
+        provider_.release(&ws_handle_);
         break;
     default:
         assert(0);
@@ -432,9 +443,62 @@ int trrep::transaction_context::after_statement()
     }
 
     debug_log_state("after_statement_leave");
+    assert(ret == 0 || state() == s_aborted);
     return ret;
 }
 
+bool trrep::transaction_context::bf_abort(
+    trrep::unique_lock<trrep::mutex>& lock TRREP_UNUSED,
+    const trrep::transaction_context& txc)
+{
+    bool ret(false);
+    assert(lock.owns_lock());
+    switch (state())
+    {
+    case s_executing:
+    case s_preparing:
+    case s_certifying:
+    case s_committing:
+    {
+        wsrep_seqno_t victim_seqno(WSREP_SEQNO_UNDEFINED);
+        wsrep_status_t status(client_context_.provider().bf_abort(
+                                  txc.seqno(), id_.get(), &victim_seqno));
+        switch (status)
+        {
+        case WSREP_OK:
+            trrep::log() << "Seqno " << txc.seqno()
+                         << " succesfully BF aborted " << id_.get()
+                         << " victim_seqno " << victim_seqno;
+            state(lock, s_must_abort);
+            ret = true;
+            break;
+        default:
+            trrep::log() << "Seqno " << txc.seqno()
+                         << " failed to BF abort " << id_.get()
+                         << " with status " << status
+                         << " victim_seqno " << victim_seqno;
+            break;
+        }
+        break;
+    }
+    default:
+        trrep::log() << "BF abort not allowed in state "
+                     << trrep::to_string(state()) << "\n";
+        break;
+    }
+
+    if (client_context_.server_context().rollback_mode() == trrep::server_context::rm_sync)
+    {
+        //! \todo Launch background rollbacker.
+        assert(0);
+    }
+    return ret;
+}
+
+trrep::mutex& trrep::transaction_context::mutex()
+{
+    return client_context_.mutex();
+}
 // Private
 
 void trrep::transaction_context::state(
@@ -455,13 +519,10 @@ void trrep::transaction_context::state(
             { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0}, /* ab */
             { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* ad */
             { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}, /* mr */
-            { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0}  /* re */
+            { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0}  /* re */
         };
     if (allowed[state_][next_state])
     {
-        // std::cerr << "state transition: " << trrep::to_string(state_)
-        //         << " -> " << trrep::to_string(next_state)
-        //         << "\n";
         state_hist_.push_back(state_);
         state_ = next_state;
     }
@@ -471,7 +532,7 @@ void trrep::transaction_context::state(
         os << "unallowed state transition for transaction "
            << id_.get() << ": " << trrep::to_string(state_)
            << " -> " << trrep::to_string(next_state);
-        std::cerr << os.str() << "\n";
+        trrep::log() << os.str();
         throw trrep::runtime_error(os.str());
     }
 }
@@ -565,6 +626,7 @@ int trrep::transaction_context::certify_commit(
 
     state(lock, s_certifying);
 
+    flags(flags() | WSREP_FLAG_TRX_END);
     lock.unlock();
 
     trrep::data data;
@@ -586,7 +648,7 @@ int trrep::transaction_context::certify_commit(
 
     wsrep_status cert_ret(provider_.certify(client_context_.id().get(),
                                             &ws_handle_,
-                                            flags() | WSREP_FLAG_TRX_END,
+                                            flags(),
                                             &trx_meta_));
 
     lock.lock();
@@ -594,7 +656,6 @@ int trrep::transaction_context::certify_commit(
     assert(state() == s_certifying || state() == s_must_abort);
     client_context_.debug_sync("wsrep_after_replication");
 
-    // std::cout << "seqno: " << trx_meta_.gtid.seqno << "\n";
     int ret(1);
     switch (cert_ret)
     {
@@ -640,7 +701,10 @@ int trrep::transaction_context::certify_commit(
         // transaction or to determine failed certification status.
         assert(ordered());
         client_context_.will_replay(*this);
-        state(lock, s_must_abort);
+        if (state() != s_must_abort)
+        {
+            state(lock, s_must_abort);
+        }
         state(lock, s_must_replay);
         break;
     case WSREP_TRX_FAIL:
@@ -653,7 +717,12 @@ int trrep::transaction_context::certify_commit(
         break;
     case WSREP_CONN_FAIL:
     case WSREP_NODE_FAIL:
-        state(lock, s_must_abort);
+        // Galera provider may return CONN_FAIL if the trx is
+        // BF aborted O_o
+        if (state() != s_must_abort)
+        {
+            state(lock, s_must_abort);
+        }
         client_context_.override_error(trrep::e_error_during_commit);
         break;
     case WSREP_FATAL:
@@ -687,6 +756,7 @@ void trrep::transaction_context::cleanup()
 {
     debug_log_state("cleanup_enter");
     id_ = trrep::transaction_id::invalid();
+    ws_handle_.trx_id = -1;
     if (is_streaming())
     {
         state_ = s_executing;
@@ -702,13 +772,13 @@ void trrep::transaction_context::cleanup()
 }
 
 void trrep::transaction_context::debug_log_state(
-    const std::string& context TRREP_UNUSED)
-    const
+    const std::string& context TRREP_UNUSED) const
 {
 #if 0
-    std::cout << context
-              << ": client: " << client_context_.id().get()
-              << " trx: " << int64_t(id_.get())
-              << " state: " << trrep::to_string(state_) << "\n";
+    trrep::log() << context
+                 << ": server: " << client_context_.server_context().name()
+                 << ": client: " << client_context_.id().get()
+                 << " trx: " << int64_t(id_.get())
+                 << " state: " << trrep::to_string(state_);
 #endif /* 0 */
 }
diff --git a/src/transaction_context.hpp b/src/transaction_context.hpp
index 172c8ef..fd4424e 100644
--- a/src/transaction_context.hpp
+++ b/src/transaction_context.hpp
@@ -75,9 +75,13 @@ namespace trrep
         // fragment succeeded
         bool certified() { return certified_; }
 
+        wsrep_seqno_t seqno() const
+        {
+            return trx_meta_.gtid.seqno;
+        }
         // Return true if the last fragment was ordered by the
         // provider
-        bool ordered() { return (trx_meta_.gtid.seqno > 0); }
+        bool ordered() const { return (trx_meta_.gtid.seqno > 0); }
 
         bool is_streaming() const
         {
@@ -125,20 +129,29 @@ namespace trrep
 
         int after_statement();
 
+        bool bf_abort(trrep::unique_lock<trrep::mutex>& lock,
+                      const transaction_context& txc);
+
         uint32_t flags() const
         {
             return flags_;
         }
+
+        trrep::mutex& mutex();
+
+        wsrep_ws_handle_t& ws_handle() { return ws_handle_; }
     private:
         transaction_context(const transaction_context&);
         transaction_context operator=(const transaction_context&);
 
+        void flags(uint32_t flags) { flags_ = flags; }
         int certify_fragment(trrep::unique_lock<trrep::mutex>&);
         int certify_commit(trrep::unique_lock<trrep::mutex>&);
         void remove_fragments();
         void clear_fragments();
         void cleanup();
         void debug_log_state(const std::string&) const;
+
         trrep::provider& provider_;
         trrep::client_context& client_context_;
         trrep::transaction_id id_;
diff --git a/src/wsrep_provider_v26.cpp b/src/wsrep_provider_v26.cpp
index d7df699..739333c 100644
--- a/src/wsrep_provider_v26.cpp
+++ b/src/wsrep_provider_v26.cpp
@@ -93,6 +93,15 @@ wsrep_status_t trrep::wsrep_provider_v26::certify(wsrep_conn_id_t conn_id,
     return wsrep_->certify(wsrep_, conn_id, wsh, flags, meta);
 }
 
+wsrep_status_t trrep::wsrep_provider_v26::bf_abort(
+    wsrep_seqno_t bf_seqno,
+    wsrep_trx_id_t victim_id,
+    wsrep_seqno_t *victim_seqno)
+{
+    return wsrep_->abort_certification(
+        wsrep_, bf_seqno, victim_id, victim_seqno);
+}
+
 wsrep_status_t trrep::wsrep_provider_v26::commit_order_enter(
     const wsrep_ws_handle_t* wsh,
     const wsrep_trx_meta_t* meta)
@@ -112,6 +121,12 @@ int trrep::wsrep_provider_v26::release(wsrep_ws_handle_t* wsh)
     return (wsrep_->release(wsrep_, wsh) != WSREP_OK);
 }
 
+int trrep::wsrep_provider_v26::replay(wsrep_ws_handle_t* wsh,
+                                      void* applier_ctx)
+{
+    return (wsrep_->replay_trx(wsrep_, wsh, applier_ctx) != WSREP_OK);
+}
+
 int trrep::wsrep_provider_v26::sst_sent(const wsrep_gtid_t& gtid, int err)
 {
     if (wsrep_->sst_sent(wsrep_, &gtid, err) != WSREP_OK)
diff --git a/src/wsrep_provider_v26.hpp b/src/wsrep_provider_v26.hpp
index d33f451..25a4c6f 100644
--- a/src/wsrep_provider_v26.hpp
+++ b/src/wsrep_provider_v26.hpp
@@ -31,13 +31,14 @@ namespace trrep
                 wsrep_trx_meta_t*);
         wsrep_status_t bf_abort(wsrep_seqno_t,
                                 wsrep_trx_id_t,
-                                wsrep_seqno_t*) { return WSREP_OK; }
-        int rollback(const wsrep_trx_id_t) { return 0; }
+                                wsrep_seqno_t*);
+        int rollback(const wsrep_trx_id_t) { ::abort(); return 0; }
         wsrep_status commit_order_enter(const wsrep_ws_handle_t*,
                                         const wsrep_trx_meta_t*);
         int commit_order_leave(const wsrep_ws_handle_t*,
                                const wsrep_trx_meta_t*);
         int release(wsrep_ws_handle_t*);
+        int replay(wsrep_ws_handle_t*, void*);
         int sst_sent(const wsrep_gtid_t&,int);
         int sst_received(const wsrep_gtid_t& gtid, int);