Fix for MDEV-9670 server_id mysteriously set to 0

Problem was that in a circular replication setup the master remembers
position to events it has generated itself when reading from a slave.
If there are no new events in the queue from the slave, a
Gtid_list_log_event is generated to remember the last skipped event.
The problem happens if there is a network delay and we generate a
Gtid_list_log_event in the middle of the transaction, in which case there
will be an implicit comment and a new transaction with serverid=0 will be
logged.

The fix was to not generate any Gtid_list_log_events in the middle of a
transaction.

1 files changed, 29 insertions, 3 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index 8c3627514ac..4e61c161a93 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -2363,6 +2363,7 @@ static void write_ignored_events_info_to_relay_log(THD *thd, Master_info *mi)
     }
     if (rli->ign_gtids.count())
     {
+      DBUG_ASSERT(!rli->is_in_group());         // Ensure no active transaction
       glev= new Gtid_list_log_event(&rli->ign_gtids,
                                     Gtid_list_log_event::FLAG_IGN_GTIDS);
       rli->ign_gtids.reset();
@@ -5317,7 +5318,9 @@ static int queue_event(Master_info* mi,const char* buf, ulong event_len)
   bool gtid_skip_enqueue= false;
   bool got_gtid_event= false;
   rpl_gtid event_gtid;
-
+#ifndef DBUG_OFF
+  static uint dbug_rows_event_count= 0;
+#endif
   /*
     FD_q must have been prepared for the first R_a event
     inside get_master_version_and_clock()
@@ -5384,6 +5387,26 @@ static int queue_event(Master_info* mi,const char* buf, ulong event_len)
       (uchar)buf[EVENT_TYPE_OFFSET] != FORMAT_DESCRIPTION_EVENT /* a way to escape */)
     DBUG_RETURN(queue_old_event(mi,buf,event_len));
 
+#ifdef ENABLED_DEBUG_SYNC
+  /*
+    A (+d,dbug.rows_events_to_delay_relay_logging)-test is supposed to
+    create a few Write_log_events and after receiving the 1st of them
+    the IO thread signals to launch the SQL thread, and sets itself to
+    wait for a release signal.
+  */
+  DBUG_EXECUTE_IF("dbug.rows_events_to_delay_relay_logging",
+                  if ((buf[EVENT_TYPE_OFFSET] == WRITE_ROWS_EVENT_V1 ||
+                       buf[EVENT_TYPE_OFFSET] == WRITE_ROWS_EVENT) &&
+                      ++dbug_rows_event_count == 2)
+                  {
+                    const char act[]=
+                      "now SIGNAL start_sql_thread "
+                      "WAIT_FOR go_on_relay_logging";
+                    DBUG_ASSERT(debug_sync_service);
+                    DBUG_ASSERT(!debug_sync_set_action(current_thd,
+                                                       STRING_WITH_LEN(act)));
+                  };);
+#endif
   mysql_mutex_lock(&mi->data_lock);
 
   switch ((uchar)buf[EVENT_TYPE_OFFSET]) {
@@ -6588,9 +6611,12 @@ static Log_event* next_event(rpl_group_info *rgi, ulonglong *event_size)
           DBUG_RETURN(ev);
         }
 
-        if (rli->ign_gtids.count())
+        if (rli->ign_gtids.count() && !rli->is_in_group())
         {
-          /* We generate and return a Gtid_list, to update gtid_slave_pos. */
+          /*
+            We generate and return a Gtid_list, to update gtid_slave_pos,
+            unless being in the middle of a group.
+          */
           DBUG_PRINT("info",("seeing ignored end gtids"));
           ev= new Gtid_list_log_event(&rli->ign_gtids,
                                       Gtid_list_log_event::FLAG_IGN_GTIDS);