This section discusses how to perform a rolling restart of an NDB 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.
Configuration change. To make a change in the cluster's configuration, such as adding an SQL node to the cluster, or setting a configuration parameter to a new value.
NDB Cluster software upgrade or downgrade. To upgrade the cluster to a newer version of the NDB Cluster software (or to downgrade it to an older version).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 NDB Cluster).
Change on node host. To make changes in the hardware or operating system on which one or more NDB 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) with the
--initialoption, which forces the data node to clear its file system and to reload all NDB Cluster data and metadata from the other data nodes.Create a backup using the ndb_mgm client
BACKUPcommand prior to performing the restart. Following the upgrade, restore the node or nodes using ndb_restore.See Section 18.5.3, “Online Backup of NDB Cluster”, and Section 18.4.20, “ndb_restore — Restore an NDB Cluster Backup”, for more information.
Use mysqldump to create a backup prior to the upgrade; afterward, restore the dump using
LOAD DATA INFILE.
Resource Recovery.
To free memory previously allocated to a table by successive
INSERT and
DELETE operations, for re-use by
other NDB Cluster tables.
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. (See Rolling restarts with multiple management servers.)
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
client STOP command, then
started again from a system shell by invoking the
ndbd or ndb_mgmd executable
as appropriate. On Windows, you can also use the system
NET START and NET STOP
commands or the Windows Service Manager to start and stop nodes
which have been installed as Windows services (see
Section 18.2.3.4, “Installing NDB Cluster Processes as Windows Services”).
Restart indicates that the
process may be restarted using the ndb_mgm
management client RESTART
command (see Section 18.5.2, “Commands in the NDB Cluster Management Client”).
NDB Cluster supports a flexible order for upgrading nodes. When upgrading an NDB Cluster, 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 NDB Cluster releases is neither intended nor supported for continuous, 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.
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 NDB Cluster in general.)
See also Bug #48528 and Bug #49163.
It is not possible for any API node to perform schema operations (such as data definition statements) during a node restart.
Rolling restarts with multiple management servers. When performing a rolling restart of an NDB Cluster with multiple management nodes, you should keep in mind that ndb_mgmd 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 NDB Cluster ndb_mgmd processes.
Update all
config.inifiles.Start a single ndb_mgmd with
--reload,--initial, or both options as desired.If you started the first ndb_mgmd with the
--initialoption, you must also start any remaining ndb_mgmd processes using--initial.Regardless of any other options used when starting the first ndb_mgmd, you should not start any remaining ndb_mgmd processes after the first one using
--reload.Complete the rolling restarts of the data nodes and API nodes as normal.
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 18.5.10.18, “The ndbinfo nodes Table”.