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).

1 files changed, 26 insertions, 0 deletions

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;