misc. sql/slave.cc & co. refactor

* `sql/mysqld.cc`: init `master-retry-count` with `master_retry_count`
* `get_master_version_and_clock()` de-duplicate label using fall-through
* `io_slave_killed()` & `check_io_slave_killed()`:
  * reüse the result from the level lower
  * add distinguishing docs
* `try_to_reconnect()`: extract `'` from `if`-`else`
* `handle_slave_io()`: Both `while`s have the same condition;
  looks like the outer `while` can simply be an `if`.
* `connect_to_master()`:
  * assume `mysql_errno()` is not 0 on connection error
  * utilize 0’s falsiness in the loop
  * remove kill check around error reporting –
    other kill checks don’t even use this result
  * extend docs

mysql-test/include/check-testcase.inc

@@ -163,4 +163,3 @@ if (`SELECT COUNT(*)=1 FROM INFORMATION_SCHEMA.PLUGINS WHERE PLUGIN_NAME = 'wsre
 }
 
 --enable_query_log
-

sql/mysqld.cc

@@ -780,7 +780,7 @@ File_parser_dummy_hook file_parser_dummy_hook;
 
 /* replication parameters, if master_host is not NULL, we are a slave */
 uint report_port= 0;
-ulong master_retry_count=0;
+ulong master_retry_count=100000;
 char *master_info_file;
 char *relay_log_info_file, *report_user, *report_password, *report_host;
 char *opt_relay_logname = 0, *opt_relaylog_index_name=0;
@@ -6820,7 +6820,7 @@ struct my_option my_long_options[]=
   {"master-retry-count", 0,
    "The number of tries the slave will make to connect to the master before giving up",
    &master_retry_count, &master_retry_count, 0, GET_ULONG,
-   REQUIRED_ARG, 100000, 0, 0, 0, 0, 0},
+   REQUIRED_ARG, static_cast<longlong>(master_retry_count), 0, 0, 0, 0, 0},
 #ifdef HAVE_REPLICATION
   {"init-rpl-role", 0, "Set the replication role",
    &rpl_status, &rpl_status, &rpl_role_typelib,

sql/slave.cc

@@ -1293,14 +1293,15 @@ void end_slave()
   DBUG_VOID_RETURN;
 }
 
+/** @return whether the replica's Master_info is marked as killed */
 static bool io_slave_killed(Master_info* mi)
 {
   DBUG_ENTER("io_slave_killed");
-
   DBUG_ASSERT(mi->slave_running); // tracking buffer overrun
-  if (mi->abort_slave || mi->io_thd->killed)
+  bool is_io_slave_killed= mi->abort_slave || mi->io_thd->killed;
+  if (is_io_slave_killed)
     DBUG_PRINT("info", ("killed"));
-  DBUG_RETURN(mi->abort_slave || mi->io_thd->killed);
+  DBUG_RETURN(is_io_slave_killed);
 }
 
 /**
@@ -2585,10 +2586,6 @@ when it try to get the value of TIME_ZONE global variable from master.";
   DBUG_RETURN(0);
 
 network_err:
-  if (master_res)
-    mysql_free_result(master_res);
-  DBUG_RETURN(2);
-
 slave_killed_err:
   if (master_res)
     mysql_free_result(master_res);
@@ -4361,15 +4358,13 @@ on this slave.\
 }
 
 
+/** Return io_slave_killed(); if it's `true`, also log the given `info`. */
 static bool check_io_slave_killed(Master_info *mi, const char *info)
 {
-  if (io_slave_killed(mi))
-  {
-    if (info && global_system_variables.log_warnings)
-      sql_print_information("%s", info);
-    return TRUE;
-  }
-  return FALSE;
+  bool is_io_slave_killed= io_slave_killed(mi);
+  if (is_io_slave_killed && info && global_system_variables.log_warnings)
+    sql_print_information("%s", info);
+  return is_io_slave_killed;
 }
 
 /**
@@ -4416,11 +4411,10 @@ static int try_to_reconnect(THD *thd, MYSQL *mysql, Master_info *mi,
     {
       tmp.append(STRING_WITH_LEN("; GTID position '"));
       mi->gtid_current_pos.append_to_string(&tmp);
-      if (mi->events_queued_since_last_gtid == 0)
-        tmp.append(STRING_WITH_LEN("'"));
-      else
+      tmp.append('\'');
+      if (mi->events_queued_since_last_gtid)
       {
-        tmp.append(STRING_WITH_LEN("', GTID event skip "));
+        tmp.append(STRING_WITH_LEN(", GTID event skip "));
         tmp.append_ulonglong((ulonglong)mi->events_queued_since_last_gtid);
       }
     }
@@ -4664,7 +4658,7 @@ pthread_handler_t handle_slave_io(void *arg)
 
   DBUG_PRINT("info",("Starting reading binary log from master"));
   thd->set_command(COM_SLAVE_IO);
-  while (!io_slave_killed(mi))
+  if (!io_slave_killed(mi))
   {
     const uchar *event_buf;
 
@@ -6917,20 +6911,20 @@ static int safe_connect(THD* thd, MYSQL* mysql, Master_info* mi)
 }
 
 
-/*
-  SYNPOSIS
-    connect_to_master()
-
-  IMPLEMENTATION
-    Try to connect until successful or slave killed or we have retried
-    mi->retry_count times
+/**
+  @brief Re/connect to the primary
+  @details
+    After preparations, this repeatedly calls the low-level connection function
+    up to mi->retry_count times until success or when the replica's killed.
+    Logs describe either config mistakes or generic connection statuses.
+  @param reconnect whether this is a reconnection or a new first-time connection
+  @return errno: 1 if error or 0 if successful
 */
-
 static int connect_to_master(THD* thd, MYSQL* mysql, Master_info* mi,
                              bool reconnect, bool suppress_warnings)
 {
   int slave_was_killed;
-  int last_errno= -2;                           // impossible error
+  unsigned int last_errno= 0; // initialize with not-error
   mi->connects_tried= 0; // reset retry counter
   my_bool my_true= 1;
   DBUG_ENTER("connect_to_master");
@@ -6991,13 +6985,13 @@ static int connect_to_master(THD* thd, MYSQL* mysql, Master_info* mi,
                "terminated.");
     DBUG_RETURN(1);
   }
-  while (!(slave_was_killed = io_slave_killed(mi)) &&
-         (reconnect ? mysql_reconnect(mysql) != 0 :
-          mysql_real_connect(mysql, mi->host, mi->user, mi->password, 0,
-                             mi->port, 0, client_flag) == 0))
+  while (!(slave_was_killed= io_slave_killed(mi)) &&
+         (reconnect ? mysql_reconnect(mysql) :
+          !mysql_real_connect(mysql, mi->host, mi->user, mi->password, 0,
+                              mi->port, 0, client_flag)))
   {
     /* Don't repeat last error */
-    if ((int)mysql_errno(mysql) != last_errno && !io_slave_killed(mi))
+    if (mysql_errno(mysql) != last_errno)
     {
       last_errno=mysql_errno(mysql);
       suppress_warnings= 0;