diff --git a/libraries/chain/db_block.cpp b/libraries/chain/db_block.cpp
index 65f10cc7..d49f1dc5 100644
--- a/libraries/chain/db_block.cpp
+++ b/libraries/chain/db_block.cpp
@@ -162,10 +162,13 @@ void database::check_transaction_for_duplicated_operations(const signed_transact
       existed_operations_digests.insert( proposed_operations_digests.begin(), proposed_operations_digests.end() );
    });
 
-   for (auto& pending_transaction: _pending_tx)
    {
-      auto proposed_operations_digests = gather_proposed_operations_digests(pending_transaction);
-      existed_operations_digests.insert(proposed_operations_digests.begin(), proposed_operations_digests.end());
+      const std::lock_guard<std::mutex> pending_tx_lock{_pending_tx_mutex};
+      for (auto &pending_transaction : _pending_tx)
+      {
+         auto proposed_operations_digests = gather_proposed_operations_digests(pending_transaction);
+         existed_operations_digests.insert(proposed_operations_digests.begin(), proposed_operations_digests.end());
+      }
    }
 
    auto proposed_operations_digests = gather_proposed_operations_digests(trx);
@@ -187,7 +190,12 @@ bool database::push_block(const signed_block& new_block, uint32_t skip)
    bool result;
    detail::with_skip_flags( *this, skip, [&]()
    {
-      detail::without_pending_transactions( *this, std::move(_pending_tx),
+      std::vector<processed_transaction> pending_tx = [this] {
+         const std::lock_guard<std::mutex> pending_tx_lock{_pending_tx_mutex};
+         return std::move(_pending_tx);
+      }();
+
+      detail::without_pending_transactions( *this, std::move(pending_tx),
       [&]()
       {
          result = _push_block(new_block);
@@ -387,17 +395,26 @@ processed_transaction database::_push_transaction( const signed_transaction& trx
 {
    // If this is the first transaction pushed after applying a block, start a new undo session.
    // This allows us to quickly rewind to the clean state of the head block, in case a new block arrives.
-   if( !_pending_tx_session.valid() )
-      _pending_tx_session = _undo_db.start_undo_session();
+   {
+      const std::lock_guard<std::mutex> pending_tx_session_lock{_pending_tx_session_mutex};
+      if (!_pending_tx_session.valid()) {
+         const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
+         _pending_tx_session = _undo_db.start_undo_session();
+      }
+   }
 
    // Create a temporary undo session as a child of _pending_tx_session.
    // The temporary session will be discarded by the destructor if
    // _apply_transaction fails.  If we make it to merge(), we
    // apply the changes.
 
+   const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
    auto temp_session = _undo_db.start_undo_session();
-   auto processed_trx = _apply_transaction( trx );
-   _pending_tx.push_back(processed_trx);
+   auto processed_trx = _apply_transaction(trx);
+   {
+      const std::lock_guard<std::mutex> pending_tx_lock{_pending_tx_mutex};
+      _pending_tx.push_back(processed_trx);
+   }
 
    // notify_changed_objects();
    // The transaction applied successfully. Merge its changes into the pending block session.
@@ -410,6 +427,7 @@ processed_transaction database::_push_transaction( const signed_transaction& trx
 
 processed_transaction database::validate_transaction( const signed_transaction& trx )
 {
+   const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
    auto session = _undo_db.start_undo_session();
    return _apply_transaction( trx );
 }
@@ -509,47 +527,52 @@ signed_block database::_generate_block(
    // the value of the "when" variable is known, which means we need to
    // re-apply pending transactions in this method.
    //
-   _pending_tx_session.reset();
-   _pending_tx_session = _undo_db.start_undo_session();
+   {
+      const std::lock_guard<std::mutex> pending_tx_session_lock{_pending_tx_session_mutex};
+      _pending_tx_session.reset();
+      _pending_tx_session = _undo_db.start_undo_session();
+   }
 
    uint64_t postponed_tx_count = 0;
    // pop pending state (reset to head block state)
-   for( const processed_transaction& tx : _pending_tx )
    {
-      size_t new_total_size = total_block_size + fc::raw::pack_size( tx );
+      const std::lock_guard<std::mutex> pending_tx_lock{_pending_tx_mutex};
+      for (const processed_transaction &tx : _pending_tx) {
+         size_t new_total_size = total_block_size + fc::raw::pack_size(tx);
 
-      // postpone transaction if it would make block too big
-      if( new_total_size >= maximum_block_size )
-      {
-         postponed_tx_count++;
-         continue;
-      }
+         // postpone transaction if it would make block too big
+         if (new_total_size >= maximum_block_size) {
+            postponed_tx_count++;
+            continue;
+         }
 
-      try
-      {
-         auto temp_session = _undo_db.start_undo_session();
-         processed_transaction ptx = _apply_transaction( tx );
-         temp_session.merge();
+         try {
+            auto temp_session = _undo_db.start_undo_session();
+            processed_transaction ptx = _apply_transaction(tx);
+            temp_session.merge();
 
-         // We have to recompute pack_size(ptx) because it may be different
-         // than pack_size(tx) (i.e. if one or more results increased
-         // their size)
-         total_block_size += fc::raw::pack_size( ptx );
-         pending_block.transactions.push_back( ptx );
-      }
-      catch ( const fc::exception& e )
-      {
-         // Do nothing, transaction will not be re-applied
-         wlog( "Transaction was not processed while generating block due to ${e}", ("e", e) );
-         wlog( "The transaction was ${t}", ("t", tx) );
+            // We have to recompute pack_size(ptx) because it may be different
+            // than pack_size(tx) (i.e. if one or more results increased
+            // their size)
+            total_block_size += fc::raw::pack_size(ptx);
+            pending_block.transactions.push_back(ptx);
+         } catch (const fc::exception &e) {
+            // Do nothing, transaction will not be re-applied
+            wlog("Transaction was not processed while generating block due to ${e}", ("e", e));
+            wlog("The transaction was ${t}", ("t", tx));
+         }
       }
    }
+
    if( postponed_tx_count > 0 )
    {
       wlog( "Postponed ${n} transactions due to block size limit", ("n", postponed_tx_count) );
    }
 
-   _pending_tx_session.reset();
+   {
+      const std::lock_guard<std::mutex> pending_tx_session_lock{_pending_tx_session_mutex};
+      _pending_tx_session.reset();
+   }
 
    // We have temporarily broken the invariant that
    // _pending_tx_session is the result of applying _pending_tx, as
@@ -597,7 +620,11 @@ signed_block database::_generate_block(
  */
 void database::pop_block()
 { try {
-   _pending_tx_session.reset();
+   {
+      const std::lock_guard<std::mutex> pending_tx_session_lock{_pending_tx_session_mutex};
+      _pending_tx_session.reset();
+   }
+
    auto head_id = head_block_id();
    optional<signed_block> head_block = fetch_block_by_id( head_id );
    GRAPHENE_ASSERT( head_block.valid(), pop_empty_chain, "there are no blocks to pop" );
@@ -611,6 +638,8 @@ void database::pop_block()
 
 void database::clear_pending()
 { try {
+   const std::lock_guard<std::mutex> pending_tx_lock{_pending_tx_mutex};
+   const std::lock_guard<std::mutex> pending_tx_session_lock{_pending_tx_session_mutex};
    assert( (_pending_tx.size() == 0) || _pending_tx_session.valid() );
    _pending_tx.clear();
    _pending_tx_session.reset();
diff --git a/libraries/chain/db_init.cpp b/libraries/chain/db_init.cpp
index e9f3b9f5..82d7fde1 100644
--- a/libraries/chain/db_init.cpp
+++ b/libraries/chain/db_init.cpp
@@ -374,7 +374,9 @@ void database::initialize_hardforks()
 void database::initialize_indexes()
 {
    reset_indexes();
-   _undo_db.set_max_size( GRAPHENE_MIN_UNDO_HISTORY );
+
+   const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
+   _undo_db.set_max_size(GRAPHENE_MIN_UNDO_HISTORY);
 
    //Protocol object indexes
    add_index< primary_index<asset_index, 13> >(); // 8192 assets per chunk
@@ -474,7 +476,9 @@ void database::init_genesis(const genesis_state_type& genesis_state)
    FC_ASSERT(genesis_state.initial_active_witnesses <= genesis_state.initial_witness_candidates.size(),
              "initial_active_witnesses is larger than the number of candidate witnesses.");
 
+   const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
    _undo_db.disable();
+
    struct auth_inhibitor {
       auth_inhibitor(database& db) : db(db), old_flags(db.node_properties().skip_flags)
       { db.node_properties().skip_flags |= skip_authority_check; }
diff --git a/libraries/chain/db_management.cpp b/libraries/chain/db_management.cpp
index 4a3b519f..dea75bc6 100644
--- a/libraries/chain/db_management.cpp
+++ b/libraries/chain/db_management.cpp
@@ -112,6 +112,7 @@ void database::reindex( fc::path data_dir )
    uint32_t undo_point = last_block_num < 50 ? 0 : last_block_num - 50;
 
    ilog( "Replaying blocks, starting at ${next}...", ("next",head_block_num() + 1) );
+   const std::lock_guard<std::mutex> undo_db_lock{_undo_db_mutex};
    auto_undo_enabler undo(_slow_replays, _undo_db);
    if( head_block_num() >= undo_point )
    {
diff --git a/libraries/chain/include/graphene/chain/database.hpp b/libraries/chain/include/graphene/chain/database.hpp
index eeb25167..2a432732 100644
--- a/libraries/chain/include/graphene/chain/database.hpp
+++ b/libraries/chain/include/graphene/chain/database.hpp
@@ -520,6 +520,7 @@ namespace graphene { namespace chain {
          void notify_changed_objects();
 
       private:
+         std::mutex                             _pending_tx_session_mutex;
          optional<undo_database::session>       _pending_tx_session;
          vector< unique_ptr<op_evaluator> >     _operation_evaluators;
 
@@ -602,6 +603,7 @@ namespace graphene { namespace chain {
          ///@}
          ///@}
 
+         std::mutex                             _pending_tx_mutex;
          vector< processed_transaction >        _pending_tx;
          fork_database                          _fork_db;
 
diff --git a/libraries/db/include/graphene/db/object_database.hpp b/libraries/db/include/graphene/db/object_database.hpp
index fa2109aa..e76e5a83 100644
--- a/libraries/db/include/graphene/db/object_database.hpp
+++ b/libraries/db/include/graphene/db/object_database.hpp
@@ -29,6 +29,7 @@
 #include <fc/log/logger.hpp>
 
 #include <map>
+#include <mutex>
 
 namespace graphene { namespace db {
 
@@ -144,6 +145,7 @@ namespace graphene { namespace db {
          fc::path get_data_dir()const { return _data_dir; }
 
          /** public for testing purposes only... should be private in practice. */
+         mutable std::mutex                     _undo_db_mutex;
          undo_database                          _undo_db;
      protected:
          template<typename IndexType>
diff --git a/libraries/plugins/account_history/account_history_plugin.cpp b/libraries/plugins/account_history/account_history_plugin.cpp
index 60ce64f8..a47496f4 100644
--- a/libraries/plugins/account_history/account_history_plugin.cpp
+++ b/libraries/plugins/account_history/account_history_plugin.cpp
@@ -85,6 +85,7 @@ void account_history_plugin_impl::update_account_histories( const signed_block&
       vector<optional< operation_history_object > >& hist = db.get_applied_operations();
       bool is_first = true;
       auto skip_oho_id = [&is_first,&db,this]() {
+         const std::lock_guard<std::mutex> undo_db_lock{db._undo_db_mutex};
          if( is_first && db._undo_db.enabled() ) // this ensures that the current id is rolled back on undo
          {
             db.remove( db.create<operation_history_object>( []( operation_history_object& obj) {} ) );
diff --git a/libraries/plugins/elasticsearch/elasticsearch_plugin.cpp b/libraries/plugins/elasticsearch/elasticsearch_plugin.cpp
index e306054a..fae54da2 100644
--- a/libraries/plugins/elasticsearch/elasticsearch_plugin.cpp
+++ b/libraries/plugins/elasticsearch/elasticsearch_plugin.cpp
@@ -127,6 +127,7 @@ bool elasticsearch_plugin_impl::update_account_histories( const signed_block& b
    const vector<optional< operation_history_object > >& hist = db.get_applied_operations();
    bool is_first = true;
    auto skip_oho_id = [&is_first,&db,this]() {
+      const std::lock_guard<std::mutex> undo_db_lock{db._undo_db_mutex};
       if( is_first && db._undo_db.enabled() ) // this ensures that the current id is rolled back on undo
       {
          db.remove( db.create<operation_history_object>( []( operation_history_object& obj) {} ) );
diff --git a/libraries/plugins/peerplays_sidechain/peerplays_sidechain_plugin.cpp b/libraries/plugins/peerplays_sidechain/peerplays_sidechain_plugin.cpp
index b52f9906..27784720 100644
--- a/libraries/plugins/peerplays_sidechain/peerplays_sidechain_plugin.cpp
+++ b/libraries/plugins/peerplays_sidechain/peerplays_sidechain_plugin.cpp
@@ -87,6 +87,7 @@ private:
    std::mutex access_db_mutex;
    std::mutex access_approve_prop_mutex;
    std::mutex access_son_down_prop_mutex;
+   std::mutex access_son_deregister_prop_mutex;
 
    std::map<sidechain_type, bool> sidechain_enabled;
    std::map<sidechain_type, std::unique_ptr<sidechain_net_handler>> net_handlers;
@@ -463,7 +464,7 @@ void peerplays_sidechain_plugin_impl::heartbeat_loop() {
       //! Check that son is active (at least for one sidechain_type)
       bool is_son_active = false;
       for (const auto &active_sidechain_type : active_sidechain_types) {
-         if(sidechain_enabled.at(active_sidechain_type)) {
+         if (sidechain_enabled.at(active_sidechain_type)) {
             if (is_active_son(active_sidechain_type, son_id))
                is_son_active = true;
          }
@@ -501,8 +502,13 @@ void peerplays_sidechain_plugin_impl::schedule_son_processing() {
    const auto next_wakeup = now + std::chrono::microseconds(time_to_next_son_processing);
 
    for (const auto &active_sidechain_type : active_sidechain_types) {
+      if (_son_processing_task.count(active_sidechain_type) != 0 && _son_processing_task.at(active_sidechain_type).wait_for(std::chrono::seconds{0}) != std::future_status::ready) {
+         wlog("Son doesn't process in time for sidechain: ${active_sidechain_type}", ("active_sidechain_type", active_sidechain_type));
+         _son_processing_task.at(active_sidechain_type).wait();
+      }
+
       _son_processing_task[active_sidechain_type] = std::async(std::launch::async, [this, next_wakeup, active_sidechain_type] {
-         if(sidechain_enabled.at(active_sidechain_type)) {
+         if (sidechain_enabled.at(active_sidechain_type)) {
             std::this_thread::sleep_until(next_wakeup);
             son_processing(active_sidechain_type);
          }
@@ -613,7 +619,7 @@ bool peerplays_sidechain_plugin_impl::can_son_participate(sidechain_type sidecha
 std::map<sidechain_type, std::vector<std::string>> peerplays_sidechain_plugin_impl::get_son_listener_log() {
    std::map<sidechain_type, std::vector<std::string>> result;
    for (const auto &active_sidechain_type : active_sidechain_types) {
-      if(net_handlers.at(active_sidechain_type)) {
+      if (net_handlers.at(active_sidechain_type)) {
          result.emplace(active_sidechain_type, net_handlers.at(active_sidechain_type)->get_son_listener_log());
       }
    }
@@ -626,7 +632,7 @@ void peerplays_sidechain_plugin_impl::approve_proposals(sidechain_type sidechain
    // into problem of approving the same propsal since it might happens that previous
    // approved proposal didn't have time or chance to populate the list of available
    // active proposals which is consulted here in the code.
-   std::lock_guard<std::mutex> lck(access_approve_prop_mutex);
+   const std::lock_guard<std::mutex> lck{access_approve_prop_mutex};
    auto check_approve_proposal = [&](const chain::son_id_type &son_id, const chain::proposal_object &proposal) {
       if (!is_valid_son_proposal(proposal)) {
          return;
@@ -676,7 +682,7 @@ void peerplays_sidechain_plugin_impl::approve_proposals(sidechain_type sidechain
 }
 
 void peerplays_sidechain_plugin_impl::create_son_down_proposals(sidechain_type sidechain) {
-   std::lock_guard<std::mutex> lck(access_son_down_prop_mutex);
+   const std::lock_guard<std::mutex> lck{access_son_down_prop_mutex};
    auto create_son_down_proposal = [&](chain::son_id_type son_id, fc::time_point_sec last_active_ts) {
       chain::database &d = plugin.database();
       const chain::global_property_object &gpo = d.get_global_properties();
@@ -740,6 +746,7 @@ void peerplays_sidechain_plugin_impl::create_son_down_proposals(sidechain_type s
 }
 
 void peerplays_sidechain_plugin_impl::create_son_deregister_proposals(sidechain_type sidechain) {
+   const std::lock_guard<std::mutex> lck{access_son_down_prop_mutex};
    chain::database &d = plugin.database();
    std::set<son_id_type> sons_to_be_dereg = d.get_sons_to_be_deregistered();
    chain::son_id_type my_son_id = get_current_son_id(sidechain);
@@ -778,49 +785,49 @@ void peerplays_sidechain_plugin_impl::create_son_deregister_proposals(sidechain_
 }
 
 void peerplays_sidechain_plugin_impl::process_proposals(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->process_proposals();
    }
 }
 
 void peerplays_sidechain_plugin_impl::process_active_sons_change(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->process_active_sons_change();
    }
 }
 
 void peerplays_sidechain_plugin_impl::create_deposit_addresses(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->create_deposit_addresses();
    }
 }
 
 void peerplays_sidechain_plugin_impl::process_deposits(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->process_deposits();
    }
 }
 
 void peerplays_sidechain_plugin_impl::process_withdrawals(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->process_withdrawals();
    }
 }
 
 void peerplays_sidechain_plugin_impl::process_sidechain_transactions(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->process_sidechain_transactions();
    }
 }
 
 void peerplays_sidechain_plugin_impl::send_sidechain_transactions(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->send_sidechain_transactions();
    }
 }
 
 void peerplays_sidechain_plugin_impl::settle_sidechain_transactions(sidechain_type sidechain) {
-   if(net_handlers.at(sidechain)) {
+   if (net_handlers.at(sidechain)) {
       net_handlers.at(sidechain)->settle_sidechain_transactions();
    }
 }