BUG#21474 (There is a rotation before the last table map):

Removing code to step the group log position and just stepping
the event log position.  If the group log position were stepped
one time too many, it might be that the group starts at a position
that is not possible, e.g., at a Rows_log_event, or between an
Intvar_log_event and the following associated Query_log_event.


sql/log_event.cc:
  Removing code to step the group log position and just stepping
  the event log position.  If the group log position were stepped
  one time too many, it might be that the group starts at a position
  that is not possible, e.g., at a Rows_log_event, or between an
  Intvar_log_event and the following associated Query_log_event.
sql/slave.cc:
  Removing code to step the group log position and just stepping
  the event log position when executing a Format_description_log_event.
  If the group log position were stepped one time too many, it might be that the group starts at a position
  that is not possible, e.g., at a Rows_log_event, or between an
  Intvar_log_event and the following associated Query_log_event.

1 files changed, 16 insertions, 11 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index f9645fc83e3..f9a847b9c26 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -3101,17 +3101,22 @@ static int exec_relay_log_event(THD* thd, RELAY_LOG_INFO* rli)
          type_code != START_EVENT_V3 && type_code!= FORMAT_DESCRIPTION_EVENT))
     {
       DBUG_PRINT("info", ("event skipped"));
-      if (thd->options & OPTION_BEGIN)
-        rli->inc_event_relay_log_pos();
-      else
-      {
-        rli->inc_group_relay_log_pos((type_code == ROTATE_EVENT ||
-                                      type_code == STOP_EVENT ||
-                                      type_code == FORMAT_DESCRIPTION_EVENT) ?
-                                     LL(0) : ev->log_pos,
-                                     1/* skip lock*/);
-        flush_relay_log_info(rli);
-      }
+      /*
+        We only skip the event here and do not increase the group log
+        position.  In the event that we have to restart, this means
+        that we might have to skip the event again, but that is a
+        minor issue.
+
+        If we were to increase the group log position when skipping an
+        event, it might be that we are restarting at the wrong
+        position and have events before that we should have executed,
+        so not increasing the group log position is a sure bet in this
+        case.
+
+        In this way, we just step the group log position when we
+        *know* that we are at the end of a group.
+       */
+      rli->inc_event_relay_log_pos();
 
       /*
         Protect against common user error of setting the counter to 1