MDEV-19801: Change defaults for CHANGE MASTER TO so that GTID-based replication is used by default if master supports it

This commit makes replicas crash-safe by default by changing the
Using_Gtid value to be Slave_Pos on a fresh slave start and after
RESET SLAVE is issued. If the primary server does not support GTIDs
(i.e., version < 10), the replica will fall back to Using_Gtid=No on
slave start and after RESET SLAVE.

The following additional informational messages/warnings are added:

 1. When Using_Gtid is automatically changed. That is, if RESET
SLAVE reverts Using_Gtid back to Slave_Pos, or Using_Gtid is
inferred to No from a CHANGE MASTER TO given with log coordinates
without MASTER_USE_GTID.
 2. If options are ignored in CHANGE MASTER TO. If CHANGE MASTER TO
is given with log coordinates, yet also specifies
MASTER_USE_GTID=Slave_Pos, a warning message is given that the log
coordinate options are ignored.

Additionally, an MTR macro has been added for RESET SLAVE,
reset_slave.inc, which provides modes/options for resetting a slave
in log coordinate or gtid modes. When in log coordinates mode, the
macro will execute CHANGE MASTER TO MASTER_USE_GTID=No after the
RESET SLAVE command. When in GTID mode, an extra parameter,
reset_slave_keep_gtid_state, can be set to reset or preserve the
value of gtid_slave_pos.

Reviewed By:
===========
Andrei Elkin <andrei.elkin@mariadb.com>

5 files changed, 72 insertions, 3 deletions

diff --git a/sql/rpl_mi.cc b/sql/rpl_mi.cc
index 2283f91ba02..b4331c9efc5 100644
--- a/sql/rpl_mi.cc
+++ b/sql/rpl_mi.cc
@@ -39,12 +39,12 @@ Master_info::Master_info(LEX_CSTRING *connection_name_arg,
    clock_diff_with_master(0),
    sync_counter(0), heartbeat_period(0), received_heartbeats(0),
    master_id(0), prev_master_id(0),
-   using_gtid(USE_GTID_NO), events_queued_since_last_gtid(0),
+   using_gtid(USE_GTID_SLAVE_POS), events_queued_since_last_gtid(0),
    gtid_reconnect_event_skip_count(0), gtid_event_seen(false),
    in_start_all_slaves(0), in_stop_all_slaves(0), in_flush_all_relay_logs(0),
    users(0), killed(0),
    total_ddl_groups(0), total_non_trans_groups(0), total_trans_groups(0),
-   is_shutdown(false)
+   is_shutdown(false), master_supports_gtid(true)
 {
   char *tmp;
   host[0] = 0; user[0] = 0; password[0] = 0;
@@ -211,7 +211,10 @@ void init_master_log_pos(Master_info* mi)
 
   mi->master_log_name[0] = 0;
   mi->master_log_pos = BIN_LOG_HEADER_SIZE;             // skip magic number
-  mi->using_gtid= Master_info::USE_GTID_NO;
+  if (mi->master_supports_gtid)
+  {
+    mi->using_gtid= Master_info::USE_GTID_SLAVE_POS;
+  }
   mi->gtid_current_pos.reset();
   mi->events_queued_since_last_gtid= 0;
   mi->gtid_reconnect_event_skip_count= 0;
diff --git a/sql/rpl_mi.h b/sql/rpl_mi.h
index b8135b8b55f..fa3327873c4 100644
--- a/sql/rpl_mi.h
+++ b/sql/rpl_mi.h
@@ -361,6 +361,13 @@ class Master_info : public Slave_reporting_capability
     at time its alter info struct is about to be appened to the list.
   */
   bool is_shutdown;
+
+  /*
+    A replica will default to Slave_Pos for using Using_Gtid; however, we
+    first need to test if the master supports GTIDs. If not, fall back to 'No'.
+    Cache the value so future RESET SLAVE commands don't revert to Slave_Pos.
+  */
+  bool master_supports_gtid;
 };
 
 struct start_alter_thd_args
diff --git a/sql/share/errmsg-utf8.txt b/sql/share/errmsg-utf8.txt
index e20dcec3b9f..0c05167823b 100644
--- a/sql/share/errmsg-utf8.txt
+++ b/sql/share/errmsg-utf8.txt
@@ -10074,3 +10074,7 @@ ER_INCONSISTENT_SLAVE_TEMP_TABLE
         eng "Replicated query '%s' table `%s.%s` can not be temporary"
 ER_VERS_HIST_PART_FAILED
         eng "Versioned table %`s.%`s: adding HISTORY partition(s) failed"
+WARN_OPTION_CHANGING
+        eng "%s is implicitly changing the value of '%s' from '%s' to '%s'"
+ER_CM_OPTION_MISSING_REQUIREMENT
+        eng "CHANGE MASTER TO option '%s=%s' is missing requirement %s"
diff --git a/sql/slave.cc b/sql/slave.cc
index 5c746271cf5..616e1248738 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -1775,6 +1775,9 @@ static int get_master_version_and_clock(MYSQL* mysql, Master_info* mi)
   }
   else
   {
+    DBUG_EXECUTE_IF("mock_mariadb_primary_v5_in_get_master_version",
+                    version= 5;);
+
     /*
       Note the following switch will bug when we have MySQL branch 30 ;)
     */
@@ -2358,6 +2361,14 @@ past_checksum:
 after_set_capability:
 #endif
 
+  if (!(mi->master_supports_gtid= version >= 10))
+  {
+    sql_print_information(
+        "Slave I/O thread: Falling back to Using_Gtid=No because "
+        "master does not support GTIDs");
+    mi->using_gtid= Master_info::USE_GTID_NO;
+  }
+
   if (mi->using_gtid != Master_info::USE_GTID_NO)
   {
     /* Request dump to start from slave replication GTID state. */
diff --git a/sql/sql_repl.cc b/sql/sql_repl.cc
index 90fdce1b56f..d4a455e9034 100644
--- a/sql/sql_repl.cc
+++ b/sql/sql_repl.cc
@@ -3420,6 +3420,16 @@ int reset_slave(THD *thd, Master_info* mi)
     goto err;
   }
 
+  if (mi->using_gtid != Master_info::USE_GTID_SLAVE_POS &&
+      mi->master_supports_gtid)
+  {
+    push_warning_printf(
+        thd, Sql_condition::WARN_LEVEL_NOTE, WARN_OPTION_CHANGING,
+        ER_THD(thd, WARN_OPTION_CHANGING), "RESET SLAVE", "Using_Gtid",
+        mi->using_gtid_astext(mi->using_gtid),
+        mi->using_gtid_astext(Master_info::USE_GTID_SLAVE_POS));
+  }
+
   /* Clear master's log coordinates and associated information */
   mi->clear_in_memory_info(thd->lex->reset_slave_info.all);
 
@@ -3816,7 +3826,41 @@ bool change_master(THD* thd, Master_info* mi, bool *master_info_added)
   else if (lex_mi->use_gtid_opt == LEX_MASTER_INFO::LEX_GTID_NO ||
            lex_mi->log_file_name || lex_mi->pos ||
            lex_mi->relay_log_name || lex_mi->relay_log_pos)
+  {
+    if (lex_mi->use_gtid_opt != LEX_MASTER_INFO::LEX_GTID_NO)
+    {
+      push_warning_printf(
+          thd, Sql_condition::WARN_LEVEL_NOTE, WARN_OPTION_CHANGING,
+          ER_THD(thd, WARN_OPTION_CHANGING), "CHANGE MASTER TO", "Using_Gtid",
+          mi->using_gtid_astext(mi->using_gtid),
+          mi->using_gtid_astext(Master_info::USE_GTID_NO));
+    }
     mi->using_gtid= Master_info::USE_GTID_NO;
+  }
+
+  /*
+    Warn about ignored options if there are GTID/log coordinate option
+    conflicts
+  */
+  if (mi->using_gtid != Master_info::USE_GTID_NO)
+  {
+    if (lex_mi->log_file_name)
+      push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                          WARN_OPTION_IGNORED,
+                          ER_THD(thd, WARN_OPTION_IGNORED), "MASTER_LOG_FILE");
+    if (lex_mi->pos)
+      push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                          WARN_OPTION_IGNORED,
+                          ER_THD(thd, WARN_OPTION_IGNORED), "MASTER_LOG_POS");
+    if (lex_mi->relay_log_name)
+      push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                          WARN_OPTION_IGNORED,
+                          ER_THD(thd, WARN_OPTION_IGNORED), "RELAY_LOG_FILE");
+    if (lex_mi->relay_log_pos)
+      push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                          WARN_OPTION_IGNORED,
+                          ER_THD(thd, WARN_OPTION_IGNORED), "RELAY_LOG_POS");
+  }
 
   do_ids= ((lex_mi->repl_do_domain_ids_opt ==
             LEX_MASTER_INFO::LEX_MI_ENABLE) ?