Fix for BUG#1870

    "CHANGE MASTER makes SQL thread restart from coordinates of I/O thread".
    So, in CHANGE MASTER:
    when it seems reasonable that the user did not want to discontinue
    its replication (i.e. when he is not specifying host or port or master_log_file
    or master_log_pos; this will be documented), set the coordinates of the
    I/O thread to those of the SQL thread. This way, the SQL thread will see
    no discontinuity in the relay log (i.e. will skip no events), because
    the I/O thread will fill the brand new relay log with the events which
    are just after the position where the SQL thread had stopped
    (before CHANGE MASTER was issued).
    And a new test for this bug.


mysql-test/r/rpl_loaddata.result:
  Now, after CHANGE MASTER the coordinates of the I/O thread are the last ones of the SQL thread, so result update.
sql/sql_repl.cc:
  Fix for BUG#1870
  "CHANGE MASTER makes SQL thread restart from coordinates of I/O thread".
  So, in CHANGE MASTER:
  when it seems reasonable that the user did not want to discontinue
  its replication (i.e. when he is not specifying host or port or master_log_file
  or master_log_pos; this will be documented), set the coordinates of the
  I/O thread to those of the SQL thread. This way, the SQL thread will see
  no discontinuity in the relay log (i.e. will skip no events), because
  the I/O thread will fill the brand new relay log with the events which
  are just after the position where the SQL thread had stopped
  (before CHANGE MASTER was issued).

3 files changed, 59 insertions, 1 deletions

diff --git a/mysql-test/r/rpl_change_master.result b/mysql-test/r/rpl_change_master.result
new file mode 100644
index 00000000000..be2aec616b0
--- /dev/null
+++ b/mysql-test/r/rpl_change_master.result
@@ -0,0 +1,32 @@
+slave stop;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+slave start;
+select get_lock("a",5);
+get_lock("a",5)
+1
+create table t1(n int);
+insert into t1 values(1+get_lock("a",10)*0);
+insert into t1 values(2);
+stop slave;
+select * from t1;
+n
+1
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	9306	1	master-bin.001	273	slave-relay-bin.002	255	master-bin.001	No	No			0		0	214	314
+change master to master_user='root';
+show slave status;
+Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
+127.0.0.1	root	9306	1	master-bin.001	214	slave-relay-bin.001	4	master-bin.001	No	No			0		0	214	4
+select release_lock("a");
+release_lock("a")
+1
+start slave;
+select * from t1;
+n
+1
+2
+drop table t1;
diff --git a/mysql-test/r/rpl_loaddata.result b/mysql-test/r/rpl_loaddata.result
index 8b910d0d183..268e383ce69 100644
--- a/mysql-test/r/rpl_loaddata.result
+++ b/mysql-test/r/rpl_loaddata.result
@@ -43,7 +43,7 @@ change master to master_user='test';
 change master to master_user='root';
 show slave status;
 Master_Host	Master_User	Master_Port	Connect_retry	Master_Log_File	Read_Master_Log_Pos	Relay_Log_File	Relay_Log_Pos	Relay_Master_Log_File	Slave_IO_Running	Slave_SQL_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter	Exec_master_log_pos	Relay_log_space
-127.0.0.1	root	MASTER_PORT	1	master-bin.001	1442	slave-relay-bin.001	4	master-bin.001	No	No			0		0	1442	4
+127.0.0.1	root	MASTER_PORT	1	master-bin.001	1419	slave-relay-bin.001	4	master-bin.001	No	No			0		0	1419	4
 set global sql_slave_skip_counter=1;
 start slave;
 set sql_log_bin=0;
diff --git a/mysql-test/t/rpl_change_master.test b/mysql-test/t/rpl_change_master.test
new file mode 100644
index 00000000000..61de22fe57b
--- /dev/null
+++ b/mysql-test/t/rpl_change_master.test
@@ -0,0 +1,26 @@
+source include/master-slave.inc;
+
+connection slave;
+select get_lock("a",5);
+connection master;
+create table t1(n int);
+insert into t1 values(1+get_lock("a",10)*0);
+insert into t1 values(2);
+save_master_pos;
+connection slave;
+sleep 3; # can't sync_with_master as we should be blocked
+stop slave;
+select * from t1;
+show slave status;
+change master to master_user='root';
+show slave status;
+# Will restart from after the values(2), which is bug
+select release_lock("a");
+start slave;
+sync_with_master;
+select * from t1;
+connection master;
+drop table t1;
+save_master_pos;
+connection slave;
+sync_with_master;