diff --git a/include/wsrep/server_service.hpp b/include/wsrep/server_service.hpp
new file mode 100644
index 0000000..5c4fe64
--- /dev/null
+++ b/include/wsrep/server_service.hpp
@@ -0,0 +1,97 @@
+//
+// Copyright (C) 2018 Codership Oy <info@codership.com>
+//
+
+/** @file server_service.hpp
+ *
+ * An abstract interface for a DBMS server services.
+ * The interface will define methods which will be called from
+ * the wsrep-lib.
+ */
+
+namespace wsrep
+{
+    class client_state;
+    class server_service
+    {
+        /**
+         * Create client state instance which acts only locally, i.e. does
+         * not participate in replication. However, local client
+         * state may execute transactions which require ordering,
+         * as when modifying local SR fragment storage requires
+         * strict commit ordering.
+         *
+         * @return Pointer to Client State.
+         */
+        virtual wsrep::client_state* local_client_state() = 0;
+
+        /**
+         * Create an applier state for streaming transaction applying.
+         *
+         * @return Pointer to streaming applier client state.
+         */
+        virtual wsrep::client_state* streaming_applier_client_state() = 0;
+
+        /**
+         * Release a client state allocated by either local_client_state()
+         * or streaming_applier_client_state().
+         */
+        virtual void release_client_state(wsrep::client_state*) = 0;
+
+        /**
+         * Perform a background rollback for a transaction.
+         */
+        virtual void background_rollback(wsrep::client_state&) = 0;
+
+        /**
+         * Log a dummy write set. A dummy write set is usually either
+         * a remotely generated write set which failed certification in
+         * provider and had a GTID assigned or a streaming replication
+         * rollback write set. If the DBMS implements logging for
+         * applied transactions, logging dummy write sets which do not
+         * commit any transaction is neeeded to keep the GTID sequence
+         * continuous in the server.
+         */
+        virtual void log_dummy_write_set(wsrep::client_state& client_state,
+                                         const wsrep::ws_meta& ws_meta) = 0;
+
+        /**
+         * Log a cluster view change event.
+         */
+        virtual void log_view(wsrep::client_state&, const wsrep::view&) = 0;
+
+        /**
+         * Determine if the configured SST method requires SST to be
+         * performed before DBMS storage engine initialization.
+         *
+         * @return True if the SST must happen before storage engine init,
+         *         otherwise false.
+         */
+        virtual bool sst_before_init() const = 0;
+
+        /**
+         * Return SST request which provides the donor server enough
+         * information how to donate the snapshot.
+         *
+         * @return A string containing a SST request.
+         */
+        virtual std::string sst_request() = 0;
+
+        /**
+         * Start a SST process.
+         *
+         * @param sst_request A string containing the SST request from
+         *                   the joiner
+         * @param gtid A GTID denoting the current replication position
+         * @param bypass Boolean bypass flag.
+         *
+         * @return Zero if the SST transfer was succesfully started,
+         *         non-zero otherwise.
+         */
+        virtual int start_sst(const std::string& sst_request,
+                              const wsrep::gtid& gtid,
+                              bool bypass) = 0;
+
+
+    };
+}
diff --git a/include/wsrep/server_state.hpp b/include/wsrep/server_state.hpp
index e9ff0c7..dbf620f 100644
--- a/include/wsrep/server_state.hpp
+++ b/include/wsrep/server_state.hpp
@@ -203,10 +203,6 @@ namespace wsrep
 
         /**
          * Create applier context for streaming transaction.
-         *
-         * @param server_id Server id of the origin of the SR transaction.
-         * @param transaction_id Transaction ID of the SR transaction on the
-         *        origin server.
          */
         virtual client_state* streaming_applier_client_state() = 0;
 
@@ -247,6 +243,8 @@ namespace wsrep
          * @return Reference to provider
          *
          * @throw wsrep::runtime_error if provider has not been loaded
+         *
+         * @todo This should not be virtual.
          */
         virtual wsrep::provider& provider() const
         {
@@ -382,16 +380,34 @@ namespace wsrep
          *
          * @return True if the statement is allowed for streaming
          *         replication, false otherwise.
+         *
+         * @todo Move to client service interface.
          */
         virtual bool statement_allowed_for_streaming(
             const wsrep::client_state& client_state,
             const wsrep::transaction& transaction) const;
 
+        /**
+         * Set server wide wsrep debug logging level.
+         *
+         * Log levels are
+         * - 0 - No debug logging.
+         * - 1..n - Debug logging with increasing verbosity.
+         */
         void debug_log_level(int level) { debug_log_level_ = level; }
+
+        /**
+         *
+         */
         int debug_log_level() const { return debug_log_level_; }
 
+        /**
+         * @todo Set filter for debug logging.
+         */
+        void debug_log_filter(const std::string&);
+
     protected:
-        /** Server Context constructor
+        /** Server state constructor
          *
          * @param mutex Mutex provided by the DBMS implementation.
          * @param name Human Readable Server Name.