MDEV-4605: Failing to load GTID slave position from rpl.gtid_slave_pos

There were several cases where the slave GTID position was not loaded
correctly before being used. This caused various failures such as
corrupting the position at slave start and empty values of
@@gtid_slave_pos and @@gtid_current_pos.

Fixed by adding more checks for loaded position, and by always loading
the position at server startup.

1 files changed, 73 insertions, 0 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index 10411f9a5a5..6b876c5e863 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -253,6 +253,66 @@ static void init_slave_psi_keys(void)
 }
 #endif /* HAVE_PSI_INTERFACE */
 
+
+static bool slave_init_thread_running;
+
+
+pthread_handler_t
+handle_slave_init(void *arg __attribute__((unused)))
+{
+  THD *thd;
+
+  my_thread_init();
+  thd= new THD;
+  thd->thread_stack= (char*) &thd;           /* Set approximate stack start */
+  mysql_mutex_lock(&LOCK_thread_count);
+  thd->thread_id= thread_id++;
+  mysql_mutex_unlock(&LOCK_thread_count);
+  thd->store_globals();
+
+  thd_proc_info(thd, "Loading slave GTID position from table");
+  if (rpl_load_gtid_slave_state(thd))
+    sql_print_warning("Failed to load slave replication state from table "
+                      "%s.%s: %u: %s", "mysql",
+                      rpl_gtid_slave_state_table_name.str,
+                      thd->stmt_da->sql_errno(), thd->stmt_da->message());
+
+  mysql_mutex_lock(&LOCK_thread_count);
+  delete thd;
+  mysql_mutex_unlock(&LOCK_thread_count);
+  my_thread_end();
+
+  mysql_mutex_lock(&LOCK_thread_count);
+  slave_init_thread_running= false;
+  mysql_cond_signal(&COND_thread_count);
+  mysql_mutex_unlock(&LOCK_thread_count);
+
+  return 0;
+}
+
+
+static int
+run_slave_init_thread()
+{
+  pthread_t th;
+
+  slave_init_thread_running= true;
+  if (mysql_thread_create(key_thread_slave_init, &th, NULL,
+                          handle_slave_init, NULL))
+  {
+    sql_print_error("Failed to create thread while initialising slave");
+    return 1;
+  }
+
+  mysql_mutex_lock(&LOCK_thread_count);
+  while (slave_init_thread_running)
+    mysql_cond_wait(&COND_thread_count, &LOCK_thread_count);
+  mysql_mutex_unlock(&LOCK_thread_count);
+
+  return 0;
+}
+
+
 /* Initialize slave structures */
 
 int init_slave()
@@ -264,6 +324,9 @@ int init_slave()
   init_slave_psi_keys();
 #endif
 
+  if (run_slave_init_thread())
+    return 1;
+
   /*
     This is called when mysqld starts. Before client connections are
     accepted. However bootstrap may conflict with us if it does START SLAVE.
@@ -3454,6 +3517,16 @@ pthread_handler_t handle_slave_io(void *arg)
   /* This must be called before run any binlog_relay_io hooks */
   my_pthread_setspecific_ptr(RPL_MASTER_INFO, mi);
 
+  /* Load the set of seen GTIDs, if we did not already. */
+  if (rpl_load_gtid_slave_state(thd))
+  {
+    mi->report(ERROR_LEVEL, thd->stmt_da->sql_errno(), 
+                "Unable to load replication GTID slave state from mysql.%s: %s",
+                rpl_gtid_slave_state_table_name.str, thd->stmt_da->message());
+    goto err;
+  }
+
+
   if (RUN_HOOK(binlog_relay_io, thread_start, (thd, mi)))
   {
     mi->report(ERROR_LEVEL, ER_SLAVE_FATAL_ERROR,