MDEV-13563 lock DDL for mariabackup in 10.2

Implement lock-ddl-per-table option that locks tables before it
is copied to backup, and helds the lock until backup finished

The "DDL-lock" itself is implemented as "SELECT * from <table> LIMIT 0",
inside a transaction, and "COMMIT" of this transaction is the DDL-unlock.

extra/mariabackup/backup_mysql.cc

@@ -117,6 +117,7 @@ xb_mysql_connect()
 		mysql_options(connection, MYSQL_PLUGIN_DIR, xb_plugin_dir);
 	}
 	mysql_options(connection, MYSQL_OPT_PROTOCOL, &opt_protocol);
+	mysql_options(connection,MYSQL_SET_CHARSET_NAME, "utf8");
 
 	msg_ts("Connecting to MySQL server host: %s, user: %s, password: %s, "
 	       "port: %s, socket: %s\n", opt_host ? opt_host : "localhost",
@@ -1629,3 +1630,96 @@ backup_cleanup()
 		mysql_close(mysql_connection);
 	}
 }
+
+
+static pthread_mutex_t mdl_lock_con_mutex;
+static MYSQL *mdl_con = NULL;
+
+void
+mdl_lock_init()
+{
+  pthread_mutex_init(&mdl_lock_con_mutex, NULL);
+  mdl_con = xb_mysql_connect();
+  if (mdl_con)
+  {
+    xb_mysql_query(mdl_con, "BEGIN", false, true);
+  }
+}
+
+#ifndef DBUF_OFF
+/* Test  that table is really locked, if lock_ddl_per_table is set.
+   The test is executed in DBUG_EXECUTE_IF block inside mdl_lock_table().
+*/
+static void check_mdl_lock_works(const char *table_name)
+{
+  MYSQL *test_con=  xb_mysql_connect();
+  char *query;
+  xb_a(asprintf(&query,
+    "SET STATEMENT max_statement_time=1 FOR ALTER TABLE %s"
+    " ADD COLUMN mdl_lock_column int", table_name));
+  int err = mysql_query(test_con, query);
+  DBUG_ASSERT(err);
+  int err_no = mysql_errno(test_con);
+  DBUG_ASSERT(err_no == ER_STATEMENT_TIMEOUT);
+  mysql_close(test_con);
+}
+#endif
+
+extern void
+dict_fs2utf8(const char*, char*, size_t, char*, size_t);
+
+void
+mdl_lock_table(ulint space_id)
+{
+  char *query;
+
+  pthread_mutex_lock(&mdl_lock_con_mutex);
+
+  xb_a(asprintf(&query,
+    "SELECT NAME FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES "
+    "WHERE SPACE = %llu AND NAME LIKE '%%/%%'", (ulonglong)space_id));
+
+  xb_mysql_query(mdl_con, query, true, true);
+
+  MYSQL_RES *mysql_result = xb_mysql_query(mdl_con, query, true);
+
+  MYSQL_ROW row;
+  while ((row = mysql_fetch_row(mysql_result))) {
+    char full_table_name[2*FN_REFLEN +2];
+    char db_utf8[FN_REFLEN];
+    char table_utf8[FN_REFLEN];
+
+    dict_fs2utf8(row[0], db_utf8, sizeof(db_utf8),table_utf8,sizeof(table_utf8));
+    snprintf(full_table_name,sizeof(full_table_name),"`%s`.`%s`",db_utf8,table_utf8);
+
+    char *lock_query;
+
+    msg_ts("Locking MDL for %s\n", full_table_name);
+
+    xb_a(asprintf(&lock_query,
+    "SELECT * FROM %s LIMIT 0",
+    full_table_name));
+
+    xb_mysql_query(mdl_con, lock_query, false, false);
+
+    free(lock_query);
+
+    DBUG_EXECUTE_IF("check_mdl_lock_works",
+      check_mdl_lock_works(full_table_name););
+  }
+
+ mysql_free_result(mysql_result);
+ free(query);
+ pthread_mutex_unlock(&mdl_lock_con_mutex);
+}
+
+
+void
+mdl_unlock_all()
+{
+  msg_ts("Unlocking MDL for all tables");
+  xb_mysql_query(mdl_con, "COMMIT", false, true);
+  mysql_close(mdl_con);
+  pthread_mutex_destroy(&mdl_lock_con_mutex);
+}
+

extra/mariabackup/xtrabackup.cc

@@ -296,6 +296,8 @@ my_bool opt_noversioncheck = FALSE;
 my_bool opt_no_backup_locks = FALSE;
 my_bool opt_decompress = FALSE;
 
+my_bool opt_lock_ddl_per_table = FALSE;
+
 static const char *binlog_info_values[] = {"off", "lockless", "on", "auto",
 					   NullS};
 static TYPELIB binlog_info_typelib = {array_elements(binlog_info_values)-1, "",
@@ -537,7 +539,8 @@ enum options_xtrabackup
 
   OPT_XTRA_TABLES_EXCLUDE,
   OPT_XTRA_DATABASES_EXCLUDE,
-  OPT_PROTOCOL
+  OPT_PROTOCOL,
+  OPT_LOCK_DDL_PER_TABLE
 };
 
 struct my_option xb_client_options[] =
@@ -1072,6 +1075,11 @@ struct my_option xb_server_options[] =
    (G_PTR*) &xb_open_files_limit, (G_PTR*) &xb_open_files_limit, 0, GET_ULONG,
    REQUIRED_ARG, 0, 0, UINT_MAX, 0, 1, 0},
 
+  {"lock-ddl-per-table", OPT_LOCK_DDL_PER_TABLE, "Lock DDL for each table "
+   "before xtrabackup starts to copy it and until the backup is completed.",
+   (uchar*) &opt_lock_ddl_per_table, (uchar*) &opt_lock_ddl_per_table, 0,
+   GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
+
   { 0, 0, 0, 0, 0, 0, GET_NO_ARG, NO_ARG, 0, 0, 0, 0, 0, 0}
 };
 
@@ -2205,6 +2213,10 @@ xtrabackup_copy_datafile(fil_node_t* node, uint thread_n)
 		return(FALSE);
 	}
 
+	if (opt_lock_ddl_per_table) {
+		mdl_lock_table(node->space->id);
+	}
+
 	if (!changed_page_bitmap) {
 		read_filter = &rf_pass_through;
 	}
@@ -3552,6 +3564,10 @@ xtrabackup_backup_func()
 		    "or RENAME TABLE during the backup, inconsistent backup will be "
 		    "produced.\n");
 
+	if (opt_lock_ddl_per_table) {
+		mdl_lock_init();
+	}
+
 	/* initialize components */
         if(innodb_init_param()) {
 fail:
@@ -3930,6 +3946,10 @@ xtrabackup_backup_func()
 		goto fail;
 	}
 
+	if (opt_lock_ddl_per_table) {
+		mdl_unlock_all();
+	}
+
 	xtrabackup_destroy_datasinks();
 
 	msg("xtrabackup: Redo log (from LSN " LSN_PF " to " LSN_PF

extra/mariabackup/xtrabackup.h

@@ -193,4 +193,8 @@ xb_get_one_option(int optid,
 const char*
 xb_get_copy_action(const char *dflt = "Copying");
 
+void mdl_lock_init();
+void mdl_lock_table(ulint space_id);
+void mdl_unlock_all();
+
 #endif /* XB_XTRABACKUP_H */

mysql-test/suite/mariabackup/lock_ddl_per_table.result

@@ -0,0 +1,4 @@
+CREATE TABLE t(i INT) ENGINE INNODB;
+INSERT INTO t VALUES(1);
+# xtrabackup backup
+DROP TABLE t;

mysql-test/suite/mariabackup/lock_ddl_per_table.test

@@ -0,0 +1,12 @@
+--source include/have_debug.inc
+
+CREATE TABLE t(i INT) ENGINE INNODB;
+INSERT INTO t VALUES(1);
+echo # xtrabackup backup;
+let $targetdir=$MYSQLTEST_VARDIR/tmp/backup;
+
+--disable_result_log
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --target-dir=$targetdir --lock-ddl-per-table=1 --dbug=+d,check_mdl_lock_works;
+--enable_result_log
+DROP TABLE t;
+rmdir $targetdir;

mysql-test/suite/mariabackup/suite.opt

@@ -1 +1 @@
---innodb --loose-changed_page_bitmaps --innodb-file-format=Barracuda
+--innodb --loose-changed_page_bitmaps --innodb-file-format=Barracuda --innodb-sys-tables