Do not give an error when the user does START SLAVE on an already

running slave, just give a warning. Same thing for STOP SLAVE.
This will make scripts writing easier for users.

include/mysqld_error.h

@@ -268,4 +268,6 @@
 #define ER_NOT_SUPPORTED_AUTH_MODE    1249
 #define ER_SPATIAL_CANT_HAVE_NULL 1250
 #define ER_COLLATION_CHARSET_MISMATCH 1251
-#define ER_ERROR_MESSAGES 252
+#define ER_SLAVE_WAS_RUNNING 1252
+#define ER_SLAVE_WAS_NOT_RUNNING 1253
+#define ER_ERROR_MESSAGES 254

mysql-test/include/master-slave.inc

@@ -3,8 +3,11 @@ connect (master1,127.0.0.1,root,,test,$MASTER_MYPORT,);
 connect (slave,127.0.0.1,root,,test,$SLAVE_MYPORT,);
 connect (slave1,127.0.0.1,root,,test,$SLAVE_MYPORT,);
 connection slave;
---error 0,1199
-!stop slave;
+#we expect STOP SLAVE to produce a warning as the slave is stopped
+#(the server was started with skip-slave-start)
+--disable_warnings
+stop slave;
+--enable_warnings
 @r/slave-stopped.result show status like 'Slave_running';
 connection master;
 --disable_warnings

sql/share/czech/errmsg.txt

@@ -262,3 +262,5 @@ v/*
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/danish/errmsg.txt

@@ -256,3 +256,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/dutch/errmsg.txt

@@ -264,3 +264,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/english/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/estonian/errmsg.txt

@@ -258,3 +258,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/french/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/german/errmsg.txt

@@ -263,3 +263,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client",
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/greek/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/hungarian/errmsg.txt

@@ -255,3 +255,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/italian/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/japanese/errmsg.txt

@@ -255,3 +255,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/korean/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/norwegian-ny/errmsg.txt

@@ -255,3 +255,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/norwegian/errmsg.txt

@@ -255,3 +255,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/polish/errmsg.txt

@@ -257,3 +257,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/portuguese/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/romanian/errmsg.txt

@@ -257,3 +257,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/russian/errmsg.txt

@@ -256,3 +256,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/serbian/errmsg.txt

@@ -249,3 +249,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/slovak/errmsg.txt

@@ -261,3 +261,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/spanish/errmsg.txt

@@ -254,3 +254,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/swedish/errmsg.txt

@@ -253,3 +253,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/share/ukrainian/errmsg.txt

@@ -258,3 +258,5 @@
 "Client does not support authentication protocol requested by server. Consider upgrading MySQL client"
 "All parts of a SPATIAL KEY must be NOT NULL"
 "COLLATION '%s' is not valid for CHARACTER SET '%s'"
+"The slave was already running"
+"The slave was already stopped"

sql/sql_repl.cc

@@ -622,7 +622,7 @@ Increase max_allowed_packet on master";
 
 int start_slave(THD* thd , MASTER_INFO* mi,  bool net_report)
 {
-  int slave_errno = 0;
+  int slave_errno;
   if (!thd)
     thd = current_thd;
   int thread_mask;
@@ -631,10 +631,17 @@ int start_slave(THD* thd , MASTER_INFO* mi,  bool net_report)
   if (check_access(thd, SUPER_ACL, any_db))
     DBUG_RETURN(1);
   lock_slave_threads(mi);  // this allows us to cleanly read slave_running
+  // Get a mask of _stopped_ threads
   init_thread_mask(&thread_mask,mi,1 /* inverse */);
+  /*
+    Below we will start all stopped threads.
+    But if the user wants to start only one thread, do as if the other thread
+    was running (as we don't wan't to touch the other thread), so set the
+    bit to 0 for the other thread
+  */
   if (thd->lex.slave_thd_opt)
     thread_mask &= thd->lex.slave_thd_opt;
-  if (thread_mask)
+  if (thread_mask) //some threads are stopped, start them
   {
     if (init_master_info(mi,master_info_file,relay_log_info_file, 0))
       slave_errno=ER_MASTER_INFO;
@@ -648,7 +655,12 @@ int start_slave(THD* thd , MASTER_INFO* mi,  bool net_report)
       slave_errno = ER_BAD_SLAVE;
   }
   else
-    slave_errno = ER_SLAVE_MUST_STOP;
+  {
+    //no error if all threads are already started, only a warning
+    slave_errno= 0;
+    push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE, ER_SLAVE_WAS_RUNNING,
+                 ER(ER_SLAVE_WAS_RUNNING));
+  }
   
   unlock_slave_threads(mi);
   
@@ -667,7 +679,7 @@ int start_slave(THD* thd , MASTER_INFO* mi,  bool net_report)
 
 int stop_slave(THD* thd, MASTER_INFO* mi, bool net_report )
 {
-  int slave_errno = 0;
+  int slave_errno;
   if (!thd)
     thd = current_thd;
 
@@ -676,12 +688,29 @@ int stop_slave(THD* thd, MASTER_INFO* mi, bool net_report )
   thd->proc_info = "Killing slave";
   int thread_mask;
   lock_slave_threads(mi);
+  // Get a mask of _running_ threads
   init_thread_mask(&thread_mask,mi,0 /* not inverse*/);
+  /*
+    Below we will stop all running threads.
+    But if the user wants to stop only one thread, do as if the other thread
+    was stopped (as we don't wan't to touch the other thread), so set the
+    bit to 0 for the other thread
+  */
   if (thd->lex.slave_thd_opt)
     thread_mask &= thd->lex.slave_thd_opt;
-  slave_errno = (thread_mask) ?
-    terminate_slave_threads(mi,thread_mask,
-			    1 /*skip lock */) :    ER_SLAVE_NOT_RUNNING;
+
+  if (thread_mask)
+  {
+    slave_errno= terminate_slave_threads(mi,thread_mask,
+                                         1 /*skip lock */);
+  }
+  else
+  {
+    //no error if both threads are already stopped, only a warning
+    slave_errno= 0;
+    push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE, ER_SLAVE_WAS_NOT_RUNNING,
+                 ER(ER_SLAVE_WAS_NOT_RUNNING));
+  }
   unlock_slave_threads(mi);
   thd->proc_info = 0;