This section discusses how to perform a rolling restart of a MySQL Cluster installation, so called because it involves stopping and starting (or restarting) each node in turn, so that the cluster itself remains operational. This is often done as part of a rolling upgrade or rolling downgrade, where high availability of the cluster is mandatory and no downtime of the cluster as a whole is permissible. Where we refer to upgrades, the information provided here also generally applies to downgrades as well.
There are a number of reasons why a rolling restart might be desirable. These are described in the next few paragraphs.
MySQL Cluster software upgrade or downgrade. To upgrade the cluster to a newer version of the MySQL Cluster software (or to downgrade it to an older version). This is usually referred to as a “rolling upgrade” (or “rolling downgrade”, when reverting to an older version of MySQL Cluster).
Change on node host. To make changes in the hardware or operating system on which one or more MySQL Cluster node processes are running.
System reset (cluster reset). To reset the cluster because it has reached an undesirable state. In such cases it is often desirable to reload the data and metadata of one or more data nodes. This can be done in any of three ways:
Start each data node process (ndbd, or
possibly ndbmtd in MySQL Cluster NDB 7.0
and later) with the
option, which forces the data node to clear its file system
and to reload all MySQL Cluster data and metadata from the
other data nodes.
See Section 17.5.3, “Online Backup of MySQL Cluster”, and Section 17.4.18, “ndb_restore — Restore a MySQL Cluster Backup”, for more information.
The process for performing a rolling restart may be generalized as follows:
Stop all cluster management nodes (ndb_mgmd processes), reconfigure them, then restart them.
(If there are multiple management servers and you are using MySQL Cluster NDB 7.0.8 or later, see Rolling restarts with multiple management servers (MySQL Cluster NDB 7.0.8 and later).)
Stop, reconfigure, then restart each cluster data node (ndbd process) in turn.
Stop, reconfigure, then restart each cluster SQL node (mysqld process) in turn.
The specifics for implementing a given rolling upgrade depend upon the changes being made. A more detailed view of the process is presented here:
In the previous diagram, the Stop
and Start steps indicate that the
process must be stopped completely using a shell command (such as
kill on most Unix systems) or the management
STOP command, then started again from a
system shell by invoking the ndbd or
ndb_mgmd executable as appropriate. On Windows
(MySQL Cluster NDB 7.1.3 and later), you can also use the system
NET START and
commands or the Windows Service Manager to start and stop nodes
which have been installed as Windows services (see
Section 126.96.36.199, “Installing MySQL Cluster Processes as Windows Services”).
Restart indicates that the
process may be restarted using the ndb_mgm
RESTART command (see
Section 17.5.2, “Commands in the MySQL Cluster Management Client”).
Prior to MySQL Cluster NDB 6.3.29 and MySQL Cluster NDB 7.0.10. When performing an upgrade or downgrade of the cluster software, you must upgrade or downgrade the management nodes first, then the data nodes, and finally the SQL nodes. Doing so in any other order may leave the cluster in an unusable state.
MySQL Cluster NDB 6.3.29 and later; MySQL Cluster NDB 7.0.10 and later. MySQL Cluster supports a more flexible order for upgrading the cluster nodes. When upgrading a cluster running MySQL Cluster NDB 6.3.29 or later, or a cluster that is running MySQL Cluster NDB 7.0.10 or later, you may upgrade API nodes (including SQL nodes) before upgrading the management nodes, data nodes, or both. In other words, you are permitted to upgrade the API and SQL nodes in any order. This is subject to the following provisions:
This functionality is intended for use as part of an online upgrade only. A mix of node binaries from different MySQL Cluster releases is neither intended nor supported for constant, long-term use in a production setting.
All management nodes must be upgraded before any data nodes are upgraded. This remains true regardless of the order in which you upgrade the cluster's API and SQL nodes.
For MySQL Cluster NDB 6.3, the ability to upgrade API nodes in
any order relative to upgrading management nodes and data
nodes is supported only for MySQL Cluster NDB 6.3.29 and
later; for MySQL Cluster NDB 7.0, it supported only for MySQL
Cluster NDB 7.0.10 and later. This means that, if you are
upgrading from a MySQL Cluster NDB 6.3 release to a MySQL
Cluster NDB 7.0 release, the “old”
NDB engine version must be 6.3.29
or later, and the “new”
NDB engine version must be 7.0.10
When upgrading the cluster from a MySQL Cluster NDB 6.3 release to a MySQL Cluster NDB 7.0 release: Once you have started upgrading the API nodes, you should not perform DDL operations until all management nodes and data nodes have been upgraded. DML operations should be unaffected, and can continue while the upgrade is in progress.
However, it is possible to perform DDL from an “old” (NDB 6.3 version) API node as long as the master data node is also running the “old” version of MySQL Cluster. You should keep in mind that a data node restart could result in the master node running a “new” (NDB 7.0 version) binary while one or more data nodes are still using the “old” (NDB 6.3) version; in this situation, no DDL can be performed from any API node, because the master data node is no longer using an NDB 6.3 binary, but the cluster still contains nodes which are not yet using NDB 7.0. For this reason, we recommend that you avoid performing DDL at any time while the upgrade is in progress.
Features specific to the “new” version must not be used until all management nodes and data nodes have been upgraded.
This also applies to any MySQL Server version change that may apply, in addition to the NDB engine version change, so do not forget to take this into account when planning the upgrade. (This is true for online upgrades of MySQL Cluster in general.)
See also Bug #48528 and Bug #49163.
Rolling restarts with multiple management servers (MySQL Cluster NDB 7.0.8 and later). A change in MySQL Cluster NDB 7.0.8 in the way in which management nodes obtain configuration data makes it necessary to alter the procedure previously outlined, when performing a rolling restart of a MySQL Cluster with multiple management nodes. (Previously, a management node checked only its own configuration cache, but in MySQL Cluster NDB 7.0.8 and later, ndb_mgmd also checks to see if any other management node is running, and, if so, tries to use that node's configuration data.) To keep this from occurring, and to force ndb_mgmd to reread its configuration file, perform the following steps:
Stop all MySQL Cluster ndb_mgmd processes.
Complete the rolling restarts of the data nodes and API nodes as normal.
See also Bug #45495 and Bug #46488.
MySQL Cluster NDB 7.0.24 and later; MySQL Cluster NDB 7.1.13 and later.
When performing a rolling restart to update the cluster's
configuration, you can use the
config_generation column of the
ndbinfo.nodes table to keep
track of which data nodes have been successfully restarted with
the new configuration. See
Section 188.8.131.52, “The
ndbinfo nodes Table”.