MDEV-39880 Reïmplement MDEV-37146 to include MDEV-39519

MDEV-39519 added MySQL 8 compatibility to `mariadb-dump --dump-slave`
by attempting `SHOW REPLICA STATUS` first and then `SHOW SLAVE STATUS`.
This conflicted with MDEV-37146, where `mariadb-dump --dump-slave`
queries either `SELECT … FROM information_schema.SLAVE_STATUS`
or `SHOW ALL SLAVES STATUS` depending on the server version.

This commit merges MDEV-37146 and MDEV-39519:
* Use MDEV-39519’s strategy based on syntax error handling.
* Use MDEV-37146’s preference order:
  1. `SELECT … FROM information_schema.SLAVE_STATUS`
  2. `SHOW ALL SLAVES STATUS`
  3. `SHOW REPLICA STATUS` (for MySQL compatibility _only_)
* Send `STOP`/`START REPLICA SQL_THREAD FOR CHANNEL '…'`
  commands for both MariaDB (est. 10.7) and MySQL.
* Refactor column indices to variables set when a query succeeds.
* Partially revert MDEV-37146’s removal of `--dump-slave`’s support for
  pre-GTID & pre-multi-source, but tailored for MySQL compatibility;
  coverage for MariaDB pre-10.0 is not fully restored.

Author: ParadoxV5

client/mysqldump.cc

@@ -176,17 +176,20 @@ static uint opt_use_gtid;
 static uint my_end_arg;
 static char * opt_mysql_unix_port=0;
 static int   first_error=0;
-/**
-  `true` for 11.6 or above servers, `false` otherwise.
-  @deprecated This and its `false` branches are to be removed after 11.4's EOL.
-*/
 static bool have_info_schema_slave_status;
 static DYNAMIC_STRING extended_row;
 static DYNAMIC_STRING dynamic_where;
 static MYSQL_RES *get_table_name_result= NULL;
 static MEM_ROOT glob_root;
 static MYSQL_RES *routine_res, *routine_list_res, *slave_status_res= NULL;
 
+static struct
+{
+  ptrdiff_t connection_name, slave_sql_running,
+            master_host, master_port,
+            relay_master_log_file, exec_master_log_pos;
+} slave_status_indices;
+
 
 #include <sslopt-vars.h>
 FILE *md_result_file= 0;
@@ -6499,23 +6502,48 @@ static int do_stop_slave_sql(MYSQL *mysql_con)
   // do_stop_slave_sql() should only be called once
   DBUG_ASSERT(!slave_status_res);
 
-  if (mysql_query_with_error_report(mysql_con, &slave_status_res,
-    have_info_schema_slave_status ?
+  // 11.6 and above
+  switch (mysql_query_with_error_report(mysql_con, &slave_status_res,
       "SELECT Connection_name FROM information_schema.SLAVE_STATUS"
       // If the slave's SQL thread is not running, we don't stop (or start) it.
-      " WHERE Slave_SQL_Running <> 'No'" :
-      "SHOW ALL SLAVES STATUS"
-  ))
-    return(1);
+      " WHERE Slave_SQL_Running <> 'No'", true
+  )) {
+  default:
+    return 1;
+  case 0:
+    have_info_schema_slave_status= true;
+    break;
+  case -1:
+    have_info_schema_slave_status= false;
+    // Between 10.0 and 11.5 inclusive
+    switch (mysql_query_with_error_report(mysql_con, &slave_status_res,
+      "SHOW ALL SLAVES STATUS", true
+    )) {
+    default:
+      return 1;
+    case 0:
+      slave_status_indices= {0, 13, 3, 5, 11, 23};
+      break;
+    case -1:
+      // MySQL 8.0.22 and above
+      if (mysql_query_with_error_report(mysql_con, &slave_status_res,
+      "SHOW REPLICA STATUS"
+      ))
+        return 1;
+      slave_status_indices= {55, 11, 1, 3, 9, 21};
+    }
+  }
+
   // Loop over all slaves
   while ((row= mysql_fetch_row(slave_status_res)))
   {
     if ((have_info_schema_slave_status ||
-        strcmp(row[/* Slave_SQL_Running */ 13], "No")))
+        strcmp(row[slave_status_indices.slave_sql_running], "No")))
     {
-      char query[25 + NAME_CHAR_LEN]; // sizeof(snprintf)
-        snprintf(query, sizeof(query), "STOP SLAVE '%.*s' SQL_THREAD",
-          NAME_CHAR_LEN, row[/* Connection_name */ 0]);
+      char query[37 + NAME_CHAR_LEN]; // sizeof(snprintf)
+        snprintf(query, sizeof(query),
+          "STOP SLAVE SQL_THREAD FOR CHANNEL '%.*s'",
+          NAME_CHAR_LEN, row[slave_status_indices.connection_name]);
       if (mysql_query_with_error_report(mysql_con, nullptr, query))
         return 1;
     }
@@ -6541,7 +6569,7 @@ static int add_slave_statements(void)
   return(0);
 }
 
-static int do_show_slave_status(MYSQL *mysql_con,
+static int do_show_slave_status(MYSQL *mysql_con, int have_mariadb_gtid,
                                 int use_gtid, char *set_gtid_pos,
                                 size_t set_gtid_pos_size)
 {
@@ -6551,7 +6579,6 @@ static int do_show_slave_status(MYSQL *mysql_con,
     (opt_slave_data == MYSQL_OPT_SLAVE_DATA_COMMENTED_SQL) ? "-- " : "";
   const char *gtid_comment_prefix= (use_gtid ? comment_prefix : "-- ");
   const char *nogtid_comment_prefix= (!use_gtid ? comment_prefix : "-- ");
-  char gtid_pos[MAX_GTID_LENGTH];
 
   if (have_info_schema_slave_status)
   {
@@ -6566,6 +6593,7 @@ static int do_show_slave_status(MYSQL *mysql_con,
       mysql_free_result(slave);
       return 1;
     }
+    slave_status_indices= {0, /* unused */ 3, 1, 2, 3, 4};
   }
   else
   {
@@ -6574,13 +6602,18 @@ static int do_show_slave_status(MYSQL *mysql_con,
     slave= slave_status_res;
   }
 
-  if (get_gtid_pos(gtid_pos, false))
+  if (have_mariadb_gtid)
   {
-    mysql_free_result(slave);
-    return 1;
+    char gtid_pos[MAX_GTID_LENGTH];
+    if (get_gtid_pos(gtid_pos, false))
+    {
+      if (have_info_schema_slave_status)
+        mysql_free_result(slave);
+      return 1;
+    }
+    snprintf(set_gtid_pos, set_gtid_pos_size,
+             fmt_gtid_pos, gtid_comment_prefix, gtid_pos);
   }
-  snprintf(set_gtid_pos, set_gtid_pos_size,
-           fmt_gtid_pos, gtid_comment_prefix, gtid_pos);
 
   print_comment(md_result_file, 0,
     "\n-- The following is the replication SQL position "
@@ -6603,16 +6636,18 @@ static int do_show_slave_status(MYSQL *mysql_con,
     if (use_gtid)
       fprintf(md_result_file,
         "%sCHANGE MASTER '%.*s' TO MASTER_USE_GTID=slave_pos;\n",
-        gtid_comment_prefix, NAME_CHAR_LEN, row[/* Connection_name */ 0]);
+        gtid_comment_prefix,
+        NAME_CHAR_LEN, row[slave_status_indices.connection_name]);
     fprintf(md_result_file, "%sCHANGE MASTER '%.*s' TO ",
-      nogtid_comment_prefix, NAME_CHAR_LEN, row[/* Connection_name */ 0]);
+      nogtid_comment_prefix,
+      NAME_CHAR_LEN, row[slave_status_indices.connection_name]);
     if (opt_include_master_host_port)
       fprintf(md_result_file, "MASTER_HOST='%s', MASTER_PORT=%s, ",
-        row[have_info_schema_slave_status ? 1 : /* Master_Host */ 3],
-        row[have_info_schema_slave_status ? 2 : /* Master_Port */ 5]);
+        row[slave_status_indices.master_host],
+        row[slave_status_indices.master_port]);
     fprintf(md_result_file, "MASTER_LOG_FILE='%s', MASTER_LOG_POS=%s;\n",
-      row[have_info_schema_slave_status ? 3 : /* Relay_Master_Log_File */ 11],
-      row[have_info_schema_slave_status ? 4 : /*  Exec_Master_Log_Pos  */ 23]);
+      row[slave_status_indices.relay_master_log_file],
+      row[slave_status_indices.exec_master_log_pos  ]);
     check_io(md_result_file);
   }
 
@@ -6641,12 +6676,12 @@ static int do_start_slave_sql(MYSQL *mysql_con)
   */
   while ((row= mysql_fetch_row(slave_status_res)))
   {
-    char query[26 + NAME_CHAR_LEN]; // sizeof(snprintf)
+    char query[38 + NAME_CHAR_LEN]; // sizeof(snprintf)
     snprintf(query, sizeof(query),
-                   "START SLAVE '%.*s' SQL_THREAD",
-            NAME_CHAR_LEN, row[/* Connection_name */ 0]);
+      "START SLAVE SQL_THREAD FOR CHANNEL '%.*s'",
+      NAME_CHAR_LEN, row[slave_status_indices.connection_name]);
     if ((have_info_schema_slave_status ||
-         strcmp(row[/* Slave_SQL_Running */ 13], "No")
+         strcmp(row[slave_status_indices.slave_sql_running], "No")
         ) && mysql_query_with_error_report(mysql_con, nullptr, query))
     {
       fprintf(stderr, "%s: Error: Unable to start slave '%s'\n",
@@ -7675,12 +7710,7 @@ int main(int argc, char **argv)
     init_connection_pool(opt_parallel);
 
   /* Check if the server support multi source */
-  unsigned long server_version= mysql_get_server_version(mysql);
-  if (server_version >= 100000)
-  {
-    have_info_schema_slave_status= server_version >= 110600;
-    have_mariadb_gtid= 1;
-  }
+  have_mariadb_gtid= mysql_get_server_version(mysql) >= 100000;
 
   if (opt_slave_data && do_stop_slave_sql(mysql))
     goto err;
@@ -7747,6 +7777,7 @@ int main(int argc, char **argv)
                                                sizeof(master_set_gtid_pos)))
     goto err;
   if (opt_slave_data && do_show_slave_status(mysql,
+                                             have_mariadb_gtid,
                                              opt_use_gtid,
                                              slave_set_gtid_pos,
                                              sizeof(slave_set_gtid_pos)))