diff --git a/src/sync-log.cc b/src/sync-log.cc
new file mode 100644
index 0000000..99b652c
--- /dev/null
+++ b/src/sync-log.cc
@@ -0,0 +1,219 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2013 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ *	   Zhenkai Zhu <zhenkai@cs.ucla.edu>
+ */
+
+#include "sync-log.h"
+
+#include <boost/make_shared.hpp>
+
+using namespace boost;
+using namespace std;
+
+HashPtr
+SyncLog::RememberStateInStateLog ()
+{
+  int res = sqlite3_exec (m_db, "BEGIN TRANSACTION;", 0,0,0);
+
+  res += sqlite3_exec (m_db, "\
+INSERT INTO SyncLog                                     \
+    (state_hash, last_update)                           \
+    SELECT                                              \
+       hash(device_name, seq_no), datetime('now')       \
+    FROM SyncNodes                                      \
+    ORDER BY device_name;                               \
+", 0,0,0);
+
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("1"));
+    }
+  
+  sqlite3_int64 rowId = sqlite3_last_insert_rowid (m_db);
+  
+  sqlite3_stmt *insertStmt;
+  res += sqlite3_prepare (m_db, "\
+INSERT INTO SyncStateNodes                              \
+      (state_id, device_id, seq_no)                     \
+      SELECT ?, device_id, seq_no                       \
+            FROM SyncNodes;                             \
+", -1, &insertStmt, 0);
+
+  res += sqlite3_bind_int64 (insertStmt, 1, rowId);
+  sqlite3_step (insertStmt);
+
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("4"));
+    }
+  sqlite3_finalize (insertStmt);
+  
+  sqlite3_stmt *getHashStmt;
+  res += sqlite3_prepare (m_db, "\
+SELECT state_hash FROM SyncLog WHERE state_id = ?\
+", -1, &getHashStmt, 0);
+  res += sqlite3_bind_int64 (getHashStmt, 1, rowId);
+
+  HashPtr retval;
+  int stepRes = sqlite3_step (getHashStmt);
+  if (stepRes == SQLITE_ROW)
+    {
+      retval = make_shared<Hash> (sqlite3_column_blob (getHashStmt, 0),
+                                  sqlite3_column_bytes (getHashStmt, 0));
+    }
+  sqlite3_finalize (getHashStmt);
+  res += sqlite3_exec (m_db, "COMMIT;", 0,0,0);
+
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("Some error with rememberStateInStateLog"));
+    }
+
+  return retval;
+}
+
+sqlite3_int64
+SyncLog::LookupSyncLog (const std::string &stateHash)
+{
+  return LookupSyncLog (*Hash::FromString (stateHash));
+}
+
+sqlite3_int64
+SyncLog::LookupSyncLog (const Hash &stateHash)
+{
+  sqlite3_stmt *stmt;
+  int res = sqlite3_prepare (m_db, "SELECT state_id FROM SyncLog WHERE state_hash = ?",
+                             -1, &stmt, 0);
+  
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("Cannot prepare statement"));
+    }
+
+  res = sqlite3_bind_blob (stmt, 1, stateHash.GetHash (), stateHash.GetHashBytes (), SQLITE_STATIC);
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("Cannot bind"));
+    }
+
+  sqlite3_int64 row = 0; // something bad
+
+  if (sqlite3_step (stmt) == SQLITE_ROW)
+    {
+      row = sqlite3_column_int64 (stmt, 0);
+    }
+
+  sqlite3_finalize (stmt);
+
+  return row;
+}
+
+void
+SyncLog::UpdateDeviceSeqno (const std::string &name, uint64_t seqNo)
+{
+  sqlite3_stmt *stmt;
+  // update is performed using trigger
+  int res = sqlite3_prepare (m_db, "INSERT INTO SyncNodes (device_name, seq_no) VALUES (?,?);", 
+                             -1, &stmt, 0);
+
+  res += sqlite3_bind_text  (stmt, 1, name.c_str (), name.size (), SQLITE_STATIC);
+  res += sqlite3_bind_int64 (stmt, 2, seqNo);
+  sqlite3_step (stmt);
+  
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("Some error with UpdateDeviceSeqno"));
+    }
+  sqlite3_finalize (stmt);
+}
+
+void
+SyncLog::FindStateDifferences (const std::string &oldHash, const std::string &newHash)
+{
+  FindStateDifferences (*Hash::FromString (oldHash), *Hash::FromString (newHash));
+}
+
+void
+SyncLog::FindStateDifferences (const Hash &oldHash, const Hash &newHash)
+{
+  sqlite3_stmt *stmt;
+
+  int res = sqlite3_prepare_v2 (m_db, "\
+SELECT sn.device_name, s_old.seq_no, s_new.seq_no                       \
+    FROM (SELECT *                                                      \
+            FROM SyncStateNodes                                         \
+            WHERE state_id=(SELECT state_id                             \
+                                FROM SyncLog                            \
+                                WHERE state_hash=:old_hash)) s_old      \
+    LEFT JOIN (SELECT *                                                 \
+                FROM SyncStateNodes                                     \
+                WHERE state_id=(SELECT state_id                         \
+                                    FROM SyncLog                        \
+                                    WHERE state_hash=:new_hash)) s_new  \
+                                                                        \
+        ON s_old.device_id = s_new.device_id                            \
+    JOIN SyncNodes sn ON sn.device_id = s_old.device_id                 \
+                                                                        \
+    WHERE s_new.seq_no IS NULL OR                                       \
+          s_old.seq_no != s_new.seq_no                                  \
+                                                                        \
+UNION ALL                                                               \
+                                                                        \
+SELECT sn.device_name, s_old.seq_no, s_new.seq_no                       \
+    FROM (SELECT *                                                      \
+            FROM SyncStateNodes                                         \
+            WHERE state_id=(SELECT state_id                             \
+                                FROM SyncLog                            \
+                                WHERE state_hash=:new_hash )) s_new     \
+    LEFT JOIN (SELECT *                                                 \
+                FROM SyncStateNodes                                     \
+                WHERE state_id=(SELECT state_id                         \
+                                    FROM SyncLog                        \
+                                    WHERE state_hash=:old_hash)) s_old  \
+                                                                        \
+        ON s_old.device_id = s_new.device_id                            \
+    JOIN SyncNodes sn ON sn.device_id = s_new.device_id                 \
+                                                                        \
+    WHERE s_old.seq_no IS NULL                                          \
+", -1, &stmt, 0);
+
+  if (res != SQLITE_OK)
+    {
+      BOOST_THROW_EXCEPTION (Error::Db ()
+                             << errmsg_info_str ("Some error with FindStateDifferences"));
+    }
+
+  res += sqlite3_bind_blob  (stmt, 1, oldHash.GetHash (), oldHash.GetHashBytes (), SQLITE_STATIC);
+  res += sqlite3_bind_blob  (stmt, 2, newHash.GetHash (), newHash.GetHashBytes (), SQLITE_STATIC);
+
+  while (sqlite3_step (stmt) == SQLITE_ROW)
+    {
+      std::cout << sqlite3_column_text (stmt, 0) <<
+        ": from "  << sqlite3_column_int64 (stmt, 1) <<
+        " to "     << sqlite3_column_int64 (stmt, 2) <<
+        std::endl;
+    }
+  sqlite3_finalize (stmt);  
+}