MDEV-4490: Old-style master position points at the last GTID event after slave restart

Now whenever we reach the GTID point requested from the slave (when using GTID
position to connect), we send a fake Gtid_list event. This event is used by
the slave to know the current old-style position for MASTER_POS_WAIT(), and
later the similar binlog position for MASTER_GTID_WAIT().

Without this fake event, if the slave is already fully up-to-date with the
master, there may be no events sent at the given position for an indeterminate
time.

1 files changed, 49 insertions, 23 deletions

diff --git a/sql/sql_repl.cc b/sql/sql_repl.cc
index 29f2897315c..283078203ed 100644
--- a/sql/sql_repl.cc
+++ b/sql/sql_repl.cc
@@ -1461,7 +1461,8 @@ send_event_to_slave(THD *thd, NET *net, String* const packet, ushort flags,
                     slave_connection_state *until_gtid_state,
                     enum_gtid_until_state *gtid_until_group,
                     rpl_binlog_state *until_binlog_state,
-                    bool slave_gtid_strict_mode, rpl_gtid *error_gtid)
+                    bool slave_gtid_strict_mode, rpl_gtid *error_gtid,
+                    bool *send_fake_gtid_list)
 {
   my_off_t pos;
   size_t len= packet->length();
@@ -1541,7 +1542,7 @@ send_event_to_slave(THD *thd, NET *net, String* const packet, ushort flags,
           if (event_gtid.server_id == gtid->server_id &&
               event_gtid.seq_no >= gtid->seq_no)
           {
-            if (event_gtid.seq_no > gtid->seq_no)
+            if (slave_gtid_strict_mode && event_gtid.seq_no > gtid->seq_no)
             {
               /*
                 In strict mode, it is an error if the slave requests to start
@@ -1549,24 +1550,21 @@ send_event_to_slave(THD *thd, NET *net, String* const packet, ushort flags,
                 exist, even though both the prior and subsequent seq_no exists
                 for same domain_id and server_id.
               */
-              if (slave_gtid_strict_mode)
-              {
-                my_errno= ER_GTID_START_FROM_BINLOG_HOLE;
-                *error_gtid= *gtid;
-                return "The binlog on the master is missing the GTID requested "
-                  "by the slave (even though both a prior and a subsequent "
-                  "sequence number does exist), and GTID strict mode is enabled.";
-              }
-            }
-            else
-            {
-              /*
-                Send a fake Gtid_list event to the slave.
-                This allows the slave to update its current binlog position
-                so MASTER_POS_WAIT() and MASTER_GTID_WAIT() can work.
-              */
-//              send_fake_gtid_list_event(until_binlog_state);
+              my_errno= ER_GTID_START_FROM_BINLOG_HOLE;
+              *error_gtid= *gtid;
+              return "The binlog on the master is missing the GTID requested "
+                "by the slave (even though both a prior and a subsequent "
+                "sequence number does exist), and GTID strict mode is enabled.";
             }
+
+            /*
+              Send a fake Gtid_list event to the slave.
+              This allows the slave to update its current binlog position
+              so MASTER_POS_WAIT() and MASTER_GTID_WAIT() can work.
+              The fake event will be sent at the end of this event group.
+            */
+            *send_fake_gtid_list= true;
+
             /*
               Delete this entry if we have reached slave start position (so we
               will not skip subsequent events and won't have to look them up
@@ -1818,6 +1816,7 @@ void mysql_binlog_send(THD* thd, char* log_ident, my_off_t pos,
   enum_gtid_until_state gtid_until_group= GTID_UNTIL_NOT_DONE;
   rpl_binlog_state until_binlog_state;
   bool slave_gtid_strict_mode;
+  bool send_fake_gtid_list= false;
 
   uint8 current_checksum_alg= BINLOG_CHECKSUM_ALG_UNDEF;
   int old_max_allowed_packet= thd->variables.max_allowed_packet;
@@ -2234,11 +2233,25 @@ impossible position";
                                         &gtid_state, &gtid_skip_group,
                                         until_gtid_state, &gtid_until_group,
                                         &until_binlog_state,
-                                        slave_gtid_strict_mode, &error_gtid)))
+                                        slave_gtid_strict_mode, &error_gtid,
+                                        &send_fake_gtid_list)))
       {
         errmsg= tmp_msg;
         goto err;
       }
+      if (unlikely(send_fake_gtid_list) && gtid_skip_group == GTID_SKIP_NOT)
+      {
+        Gtid_list_log_event glev(&until_binlog_state, 0);
+
+        if (reset_transmit_packet(thd, flags, &ev_offset, &errmsg) ||
+            fake_gtid_list_event(net, packet, &glev, &errmsg,
+                                 current_checksum_alg, my_b_tell(&log)))
+        {
+          my_errno= ER_UNKNOWN_ERROR;
+          goto err;
+        }
+        send_fake_gtid_list= false;
+      }
       if (until_gtid_state &&
           is_until_reached(thd, net, packet, &ev_offset, gtid_until_group,
                            event_type, current_checksum_alg, flags, &errmsg,
@@ -2426,13 +2439,26 @@ impossible position";
                                             using_gtid_state, &gtid_state,
                                             &gtid_skip_group, until_gtid_state,
                                             &gtid_until_group, &until_binlog_state,
-                                            slave_gtid_strict_mode, &error_gtid)))
+                                            slave_gtid_strict_mode, &error_gtid,
+                                            &send_fake_gtid_list)))
           {
             errmsg= tmp_msg;
             goto err;
           }
-          if (
-              until_gtid_state &&
+          if (unlikely(send_fake_gtid_list) && gtid_skip_group == GTID_SKIP_NOT)
+          {
+            Gtid_list_log_event glev(&until_binlog_state, 0);
+
+            if (reset_transmit_packet(thd, flags, &ev_offset, &errmsg) ||
+                fake_gtid_list_event(net, packet, &glev, &errmsg,
+                                     current_checksum_alg, my_b_tell(&log)))
+            {
+              my_errno= ER_UNKNOWN_ERROR;
+              goto err;
+            }
+            send_fake_gtid_list= false;
+          }
+          if (until_gtid_state &&
               is_until_reached(thd, net, packet, &ev_offset, gtid_until_group,
                                event_type, current_checksum_alg, flags, &errmsg,
                                &until_binlog_state, my_b_tell(&log)))