diff --git a/mysql-test/r/events_bugs.result b/mysql-test/r/events_bugs.result
index b6b77101874..b0de2358777 100644
--- a/mysql-test/r/events_bugs.result
+++ b/mysql-test/r/events_bugs.result
@@ -3,6 +3,10 @@ drop database if exists mysqltest_db1;
 drop database if exists mysqltest_db2;
 create database events_test;
 use events_test;
+select * from information_schema.global_variables where variable_name like 'event_scheduler';
+VARIABLE_NAME	VARIABLE_VALUE
+EVENT_SCHEDULER	ON
+SET GLOBAL event_scheduler = 'OFF';
 CREATE EVENT lower_case ON SCHEDULE EVERY 1 MINUTE DO SELECT 1;
 CREATE EVENT Lower_case ON SCHEDULE EVERY 2 MINUTE DO SELECT 2;
 ERROR HY000: Event 'Lower_case' already exists
diff --git a/mysql-test/r/kill.result b/mysql-test/r/kill.result
index a08be429a83..8376eb7c0de 100644
--- a/mysql-test/r/kill.result
+++ b/mysql-test/r/kill.result
@@ -125,3 +125,12 @@ drop function bug27563;
 drop procedure proc27563;
 PREPARE stmt FROM 'EXPLAIN SELECT * FROM t1,t2,t3,t4,t5,t6,t7,t8,t9,t10,t11,t12,t13,t14,t15,t16,t17,t18,t19,t20,t21,t22,t23,t24,t25,t26,t27,t28,t29,t30,t31,t32,t33,t34,t35,t36,t37,t38,t39,t40 WHERE a1=a2 AND a2=a3 AND a3=a4 AND a4=a5 AND a5=a6 AND a6=a7 AND a7=a8 AND a8=a9 AND a9=a10 AND a10=a11 AND a11=a12 AND a12=a13 AND a13=a14 AND a14=a15 AND a15=a16 AND a16=a17 AND a17=a18 AND a18=a19 AND a19=a20 AND a20=a21 AND a21=a22 AND a22=a23 AND a23=a24 AND a24=a25 AND a25=a26 AND a26=a27 AND a27=a28 AND a28=a29 AND a29=a30 AND a30=a31 AND a31=a32 AND a32=a33 AND a33=a34 AND a34=a35 AND a35=a36 AND a36=a37 AND a37=a38 AND a38=a39 AND a39=a40  ';
 EXECUTE stmt;
+#
+# Bug#19723: kill of active connection yields different error code
+# depending on platform.
+#
+
+# Connection: con2.
+KILL CONNECTION_ID();
+SELECT 1;
+ERROR HY000: Lost connection to MySQL server during query
diff --git a/mysql-test/r/no-threads.result b/mysql-test/r/no-threads.result
index 50e52138be8..aefecd0f7bc 100644
--- a/mysql-test/r/no-threads.result
+++ b/mysql-test/r/no-threads.result
@@ -4,3 +4,6 @@ select 1+1;
 select 1+2;
 1+2
 3
+SHOW GLOBAL VARIABLES LIKE 'thread_handling';
+Variable_name	Value
+thread_handling	no-threads
diff --git a/mysql-test/t/events_bugs-master.opt b/mysql-test/t/events_bugs-master.opt
new file mode 100644
index 00000000000..f93413a61e5
--- /dev/null
+++ b/mysql-test/t/events_bugs-master.opt
@@ -0,0 +1 @@
+--event-scheduler
diff --git a/mysql-test/t/events_bugs.test b/mysql-test/t/events_bugs.test
index ebd86f3a3d2..efdb67349ec 100644
--- a/mysql-test/t/events_bugs.test
+++ b/mysql-test/t/events_bugs.test
@@ -9,6 +9,21 @@ drop database if exists mysqltest_db2;
 create database events_test;
 use events_test;
 
+#
+# START:  Bug #31332 --event-scheduler option misbehaving
+#
+
+# NOTE!! this test must come first! It's testing that the --event-scheduler
+# option with no argument in events_bugs-master.opt turns the scheduler on.
+
+select * from information_schema.global_variables where variable_name like 'event_scheduler';
+
+SET GLOBAL event_scheduler = 'OFF';
+
+#
+# END: Bug #31332
+#
+
 #
 # START - 16415: Events: event names are case sensitive
 #
diff --git a/mysql-test/t/information_schema.test b/mysql-test/t/information_schema.test
index 1987d9d5773..55334916913 100644
--- a/mysql-test/t/information_schema.test
+++ b/mysql-test/t/information_schema.test
@@ -1142,6 +1142,7 @@ END$$
 
 DELIMITER ;$$
 
+let $wait_timeout= 300;
 let $wait_condition=select count(*) = 0 from information_schema.events where event_name='event_status';
 --source include/wait_condition.inc
 
diff --git a/mysql-test/t/kill.test b/mysql-test/t/kill.test
index 5d5095f7d61..219412e5afa 100644
--- a/mysql-test/t/kill.test
+++ b/mysql-test/t/kill.test
@@ -304,3 +304,19 @@ while ($i)
   dec $i ;
 }
 --enable_query_log
+
+###########################################################################
+
+--echo #
+--echo # Bug#19723: kill of active connection yields different error code
+--echo # depending on platform.
+--echo #
+
+--echo
+--echo # Connection: con2.
+--connection con2
+
+KILL CONNECTION_ID();
+
+--error 2013
+SELECT 1;
diff --git a/mysql-test/t/no-threads.test b/mysql-test/t/no-threads.test
index 806cf24e961..31ea6406ee9 100644
--- a/mysql-test/t/no-threads.test
+++ b/mysql-test/t/no-threads.test
@@ -3,3 +3,4 @@
 #
 select 1+1;
 select 1+2;
+SHOW GLOBAL VARIABLES LIKE 'thread_handling';
diff --git a/sql/events.cc b/sql/events.cc
index 262c62bdbc8..73b8f2cda84 100644
--- a/sql/events.cc
+++ b/sql/events.cc
@@ -146,7 +146,7 @@ bool
 Events::set_opt_event_scheduler(char *argument)
 {
   if (argument == NULL)
-    opt_event_scheduler= Events::EVENTS_DISABLED;
+    opt_event_scheduler= Events::EVENTS_ON;
   else
   {
     int type;
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 03c65c9d654..a7624c5bbcd 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -356,10 +356,35 @@ String *Item_func_concat::val_str(String *str)
       }
       else
       {						// Two big const strings
-	if (tmp_value.alloc(max_length) ||
-	    tmp_value.copy(*res) ||
-	    tmp_value.append(*res2))
+        /*
+          NOTE: We should be prudent in the initial allocation unit -- the
+          size of the arguments is a function of data distribution, which
+          can be any. Instead of overcommitting at the first row, we grow
+          the allocated amount by the factor of 2. This ensures that no
+          more than 25% of memory will be overcommitted on average.
+        */
+
+        uint concat_len= res->length() + res2->length();
+
+        if (tmp_value.alloced_length() < concat_len)
+        {
+          if (tmp_value.alloced_length() == 0)
+          {
+            if (tmp_value.alloc(concat_len))
+              goto null;
+          }
+          else
+          {
+            uint new_len = max(tmp_value.alloced_length() * 2, concat_len);
+
+            if (tmp_value.realloc(new_len))
+              goto null;
+          }
+        }
+
+	if (tmp_value.copy(*res) || tmp_value.append(*res2))
 	  goto null;
+
 	res= &tmp_value;
 	use_as_buff=str;
       }
@@ -679,8 +704,33 @@ String *Item_func_concat_ws::val_str(String *str)
     }
     else
     {						// Two big const strings
-      if (tmp_value.alloc(max_length) ||
-	  tmp_value.copy(*res) ||
+      /*
+        NOTE: We should be prudent in the initial allocation unit -- the
+        size of the arguments is a function of data distribution, which can
+        be any. Instead of overcommitting at the first row, we grow the
+        allocated amount by the factor of 2. This ensures that no more than
+        25% of memory will be overcommitted on average.
+      */
+
+      uint concat_len= res->length() + sep_str->length() + res2->length();
+
+      if (tmp_value.alloced_length() < concat_len)
+      {
+        if (tmp_value.alloced_length() == 0)
+        {
+          if (tmp_value.alloc(concat_len))
+            goto null;
+        }
+        else
+        {
+          uint new_len = max(tmp_value.alloced_length() * 2, concat_len);
+
+          if (tmp_value.realloc(new_len))
+            goto null;
+        }
+      }
+
+      if (tmp_value.copy(*res) ||
 	  tmp_value.append(*sep_str) ||
 	  tmp_value.append(*res2))
 	goto null;
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 4cf6e05751f..f65fee872ed 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -7745,12 +7745,13 @@ mysqld_get_one_option(int optid,
     break;
   }
   case OPT_ONE_THREAD:
-    global_system_variables.thread_handling= 2;
+    global_system_variables.thread_handling=
+      SCHEDULER_ONE_THREAD_PER_CONNECTION;
     break;
   case OPT_THREAD_HANDLING:
   {
     global_system_variables.thread_handling=
-      find_type_or_exit(argument, &thread_handling_typelib, opt->name);
+      find_type_or_exit(argument, &thread_handling_typelib, opt->name)-1;
     break;
   }
   case OPT_FT_BOOLEAN_SYNTAX:
diff --git a/sql/scheduler.h b/sql/scheduler.h
index 8351cefda4c..46bbd300cbb 100644
--- a/sql/scheduler.h
+++ b/sql/scheduler.h
@@ -40,7 +40,7 @@ public:
 
 enum scheduler_types
 {
-  SCHEDULER_ONE_THREAD_PER_CONNECTION=1,
+  SCHEDULER_ONE_THREAD_PER_CONNECTION=0,
   SCHEDULER_NO_THREADS,
   SCHEDULER_POOL_OF_THREADS
 };
diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index a904023cbff..368ed897a4d 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -818,7 +818,20 @@ void THD::awake(THD::killed_state state_to_set)
     if (!slave_thread)
       thread_scheduler.post_kill_notification(this);
 #ifdef SIGNAL_WITH_VIO_CLOSE
-    close_active_vio();
+    if (this != current_thd)
+    {
+      /*
+        In addition to a signal, let's close the socket of the thread that
+        is being killed. This is to make sure it does not block if the
+        signal is lost. This needs to be done only on platforms where
+        signals are not a reliable interruption mechanism.
+
+        If we're killing ourselves, we know that we're not blocked, so this
+        hack is not used.
+      */
+
+      close_active_vio();
+    }
 #endif    
   }
   if (mysys_var)