HOWTO distribute user privileges in a MySQL Cluster.

This text is a short description how to distribute MySQL
privilege tables to all connected MySQL servers belonging to
a MySQL Cluster. This enables adding and removing users to
the system as well as defining grants for various privileges
in a more or less transparent manner. Flushing of grants
might be needed to make changes visible on already opened
connections.

The procedure is based on moving the privilege tables from local
storage (MyISAM) to distributed storage (ndbcluster). To
simplify the procedure a number of store procedures have been
defined to more or less automate the procedure.
The procedures can be created by running the script ndb_dist_priv.sql
(which you find in storage/ndb/tools/ or share/mysql/ depending
on your distribution of the mysql files) through "mysql"
Example:
"mysql <connect-options> --user root < storage/ndb/tool/ndb_dist_priv.sql"

IMPORTANT: Prior to performing the actual distribution it is recommended
to backup the current privilege tables, using for example mysqldump:
"mysqldump <connect-options> --user root mysql user db tables_priv columns_priv procs_priv"

The actual procedure can be initiated by running the stored procedure
mysql_cluster_move_privilege_tables once on any connected MySQL server:
"call mysql.mysql_cluster_move_privileges();"

NOTE: This procedure will create two sets of backups of the privilege tables
as well, one local and one distributed. These are used to revert the tables
if anything goes wrong during the distribution process.

To verify that the procedure was successful one can do the following query:
"select mysql.mysql_cluster_privileges_are_distributed();"
which should return 1 if procedure was successful.

NOTE: If a MySQL server is disconnected from the cluster while the privilege
tables are being moved the local privilege tables will need to be dropped and
refreshed when the MySQL server has reconnected:
use mysql;
select mysql_cluster_privileges_are_distributed();
0
drop table if exists user db tables_priv columns_priv procs_priv;
show tables;
select mysql_cluster_privileges_are_distributed();
1

In case cluster being restarted with resetting of all tables (--inital)
the privilege tables will be lost after the they have been moved. If no
MySQL server is available to revert the tables (either from the local backup
tables or from a mysqldump file). If a new MYSQL server needs to be connected
to the cluster to perform restoring the privilege tables it will need to be
started with the flag --skip-grant-tables. After the local tables have been
restored they can be distributed again by again calling:
"call mysql.mysql_cluster_move_privileges();"
After that the MySQL server should be restarted without the --skip-grant-tables
flag.

Once privilige tables have been stored in ndb they will be part of
ndb backups. However, if one want to restore these tables from a backup
one has to give an new option flag --restore-privilege-tables to ndb_restore.

Known limitations:
All changes to privilege tables are automatically distributed when the
privilege tables have been moved to ndb. However, since privilege data
is cached per connection, a remote change will not be vissible until one
do a:
"flush privileges;"

If for some reason want to revert distribution of privilege tables back
to local tables this has to be done on each mysqld by running:
"call mysql.mysql_cluster_restore_local_privileges();"