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15.6. Management of MySQL Cluster

Managing a MySQL Cluster involves a number of tasks, the first of which is to configure and start MySQL Cluster. This is covered in Section 15.3, “MySQL Cluster Configuration”, and Section 15.5, “Process Management in MySQL Cluster”.

The following sections cover the management of a running MySQL Cluster.

There are essentially two methods of actively managing a running MySQL Cluster. The first of these is through the use of commands entered into the management client whereby cluster status can be checked, log levels changed, backups started and stopped, and nodes stopped and started. The second method involves studying the contents of the cluster log ndb_node_id_cluster.log; this is usually found in the management server's DataDir directory, but this location can be overridden using the LogDestination option — see Section 15.3.4.4, “Defining the Management Server”, for details. (Recall that node_id represents the unique identifier of the node whose activity is being logged.) The cluster log contains event reports generated by ndbd. It is also possible to send cluster log entries to a Unix system log.

In addition, some aspects of the cluster's operation can be monitored from an SQL node using the SHOW ENGINE NDB STATUS statement. See Section 13.5.4.9, “SHOW ENGINE Syntax”, for more information.

15.6.1. Summary of MySQL Cluster Start Phases

This section provides a simplified outline of the steps involved when MySQL Cluster data nodes are started. More complete information can be found in MySQL Cluster Start Phases.

These phases are the same as those reported in the output from the node_id STATUS command in the management client. (See Section 15.6.2, “Commands in the MySQL Cluster Management Client”, for more information about this command.)

Start types.  There are several different startup types and modes, as shown here:

  • Initial Start.  The cluster starts with a clean filesystem on all data nodes. This occurs either when the cluster started for the very first time, or when it is restarted using the --initial option.

    Note

    Disk Data files are not removed when restarting a node using --initial.

  • System Restart.  The cluster starts and reads data stored in the data nodes. This occurs when the cluster has been shut down after having been in use, when it is desired for the cluster to resume operations from the point where it left off.

  • Node Restart.  This is the online restart of a cluster node while the cluster itself is running.

  • Initial Node Restart.  This is the same as a node restart, except that the node is reinitialized and started with a clean filesystem.

Setup and initialization (Phase -1).  Prior to startup, each data node (ndbd process) must be initialized. Initialization consists of the following steps:

  1. Obtain a node ID

  2. Fetch configuration data

  3. Allocate ports to be used for inter-node communications

  4. Allocate memory according to settings obtained from the configuration file

When a data node or SQL node first connects to the management node, it reserves a cluster node ID. To make sure that no other node allocates the same node ID, this ID is retained until the node has managed to connect to the cluster and at least one ndbd reports that this node is connected. This retention of the node ID is guarded by the connection between the node in question and ndb_mgmd.

Normally, in the event of a problem with the node, the node disconnects from the management server, the socket used for the connection is closed, and the reserved node ID is freed. However, if a node is disconnected abruptly — for example, due to a hardware failure in one of the cluster hosts, or because of network issues — the normal closing of the socket by the operating system may not take place. In this case, the node ID continues to be reserved and not released until a TCP timeout occurs 10 or so minutes later.

To take care of this problem, you can use PURGE STALE SESSIONS. Running this statement forces all reserved node IDs to be checked; any that are not being used by nodes actually connected to the cluster are then freed.

Beginning with MySQL 5.1.11, timeout handling of node ID assignments is implemented. This performs the ID usage checks automatically after approximately 20 seconds, so that PURGE STALE SESSIONS should no longer be necessary in a normal Cluster start.

After each data node has been initialized, the cluster startup process can proceed. The stages which the cluster goes through during this process are listed here:

  • Phase 0.  The NDBFS and NDBCNTR blocks start (see NDB Kernel Blocks). The cluster filesystem is cleared, if the cluster was started with the --initial option.

  • Phase 1.  In this stage, all remaining NDB kernel blocks are started. Cluster connections are set up, inter-block communications are established, and Cluster heartbeats are started. In the case of a node restart, API node connections are also checked.

    Note

    When one or more nodes hang in Phase 1 while the remaining node or nodes hang in Phase 2, this often indicates network problems. One possible cause of such issues is one or more cluster hosts having multiple network interfaces. Another common source of problems causing this condition is the blocking of TCP/IP ports needed for communications between cluster nodes. In the latter case, this is often due to a misconfigured firewall.

  • Phase 2.  The NDBCNTR kernel block checks the states of all existing nodes. The master node is chosen, and the cluster schema file is initialized.

  • Phase 3.  The DBLQH and DBTC kernel blocks set up communications between them. The startup type is determined; if this is a restart, the DBDIH block obtains permission to perform the restart.

  • Phase 4.  For an initial start or initial node restart, the redo log files are created. The number of these files is equal to NoOfFragmentLogFiles.

    For a system restart:

    • Read schema or schemas.

    • Read data from the local checkpoint.

    • Apply all redo information until the latest restorable global checkpoint has been reached.

    For a node restart, find the tail of the redo log.

  • Phase 5.  Most of the database-related portion of a data node start is perfomed during this phase. For an initial start or system restart, a local checkpoint is executed, followed by a global checkpoint. Periodic checks of memory usage begin during this phase, and any required node takeovers are performed.

  • Phase 6.  In this phase, node groups are defined and set up.

  • Phase 7.  The arbitrator node is selected and begins to function. The next backup ID is set, as is the backup disk write speed. Nodes reaching this start phase are marked as Started. It is now possible for API nodes (including SQL nodes) to connect to the cluster. connect.

  • Phase 8.  If this is a system restart, all indexes are rebuilt (by DBDIH).

  • Phase 9.  The node internal startup variables are reset.

  • Phase 100 (OBSOLETE).  Formerly, it was at this point during a node restart or initial node restart that API nodes could connect to the node and begin to receive events. Currently, this phase is empty.

  • Phase 101.  At this point in a node restart or initial node restart, event delivery is handed over to the node joining the cluster. The newly-joined node takes over responsibility for delivering its primary data to subscribers. This phase is also referred to as SUMA handover phase.

After this process is completed for an initial start or system restart, transaction handling is enabled. For a node restart or initial node restart, completion of the startup process means that the node may now act as a transaction coordinator.

15.6.2. Commands in the MySQL Cluster Management Client

In addition to the central configuration file, a cluster may also be controlled through a command-line interface available through the management client ndb_mgm. This is the primary administrative interface to a running cluster.

Commands for the event logs are given in Section 15.6.3, “Event Reports Generated in MySQL Cluster”; commands for creating backups and restoring from backup are provided in Section 15.7, “On-line Backup of MySQL Cluster”.

The management client has the following basic commands. In the listing that follows, node_id denotes either a database node ID or the keyword ALL, which indicates that the command should be applied to all of the cluster's data nodes.

  • HELP

    Displays information on all available commands.

  • SHOW

    Displays information on the cluster's status.

    Note: In a cluster where multiple management nodes are in use, this command displays information only for data nodes that are actually connected to the current management server.

  • node_id START

    Brings online the data node identified by node_id (or all data nodes).

    Beginning with MySQL 5.0.19, this command can also be used to individual management nodes online. Note: ALL START continues to affect data nodes only.

    Important: To use this command to bring a data node online, the data node must have been started using ndbd --nostart or ndbd -n.

  • node_id STOP

    Stops the data node identified by node_id (or all data nodes).

    Beginning with MySQL 5.0.19, this command can also be used to stop individual management nodes. Note: ALL STOP continues to affect data nodes only.

    A node affected by this command disconnects from the cluster, and its associated ndbd or ndb_mgmd process terminates.

  • node_id RESTART [-n] [-i] [-a]

    Restarts the data node identified by node_id (or all data nodes).

    Using the -i option with RESTART causes the data node to perform an initial restart; that is, the node's filesystem is deleted and recreated. The effect is the same as that obtained from stopping the data node process and then starting it again using ndbd --initial from the system shell.

    Using the -n option causes the data node process to be restarted, but the data node is not actually brought online until the appropriate START command is issued. The effect of this option is the same as that obtained from stopping the data node and then starting it again using ndbd --nostart or ndbd -n from the system shell.

    Using the -a causes all current transactions relying on this node to be aborted. No GCP check is done when the node rejoins the cluster.

  • node_id STATUS

    Displays status information for the data node identified by node_id (or for all data nodes).

  • ENTER SINGLE USER MODE node_id

    Enters single user mode, whereby only the MySQL server identified by the node ID node_id is allowed to access the database.

    Important: Do not attempt to have data nodes join the cluster while it is running in single user mode. Doing so can cause subsequent multiple node failures. Beginning with MySQL 5.1.12, it is no longer possible to add nodes while in single user mode. (See Bug#20395 for more information.)

  • EXIT SINGLE USER MODE

    Exits single user mode, allowing all SQL nodes (that is, all running mysqld processes) to access the database.

  • QUIT, EXIT

    Terminates the management client.

    This command does not affect any nodes connected to the cluster.

  • SHUTDOWN

    Shuts down all cluster data nodes and management nodes. To exit the management client after this has been done, use EXIT or QUIT.

    This command does not shut down any SQL nodes or API nodes that are connected to the cluster.

15.6.3. Event Reports Generated in MySQL Cluster

In this section, we discuss the types of event logs provided by MySQL Cluster, and the types of events that are logged.

MySQL Cluster provides two types of event log:

  • The cluster log, which includes events generated by all cluster nodes. The cluster log is the log recommended for most uses because it provides logging information for an entire cluster in a single location.

    By default, the cluster log is saved to a file named ndb_node_id_cluster.log, (where node_id is the node ID of the management server) in the same directory where the ndb_mgm binary resides.

    Cluster logging information can also be sent to stdout or a syslog facility in addition to or instead of being saved to a file, as determined by the values set for the DataDir and LogDestination configuration parameters. See Section 15.3.4.4, “Defining the Management Server”, for more information about these parameters.

  • Node logs are local to each node.

    Output generated by node event logging is written to the file ndb_node_id_out.log (where node_id is the node's node ID) in the node's DataDir. Node event logs are generated for both management nodes and data nodes.

    Node logs are intended to be used only during application development, or for debugging application code.

Both types of event logs can be set to log different subsets of events.

Each reportable event can be distinguished according to three different criteria:

  • Category: This can be any one of the following values: STARTUP, SHUTDOWN, STATISTICS, CHECKPOINT, NODERESTART, CONNECTION, ERROR, or INFO.

  • Priority: This is represented by one of the numbers from 1 to 15 inclusive, where 1 indicates “most important” and 15 “least important.

  • Severity Level: This can be any one of the following values: ALERT, CRITICAL, ERROR, WARNING, INFO, or DEBUG.

Both the cluster log and the node log can be filtered on these properties.

The format used in the cluster log is as shown here:

2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 1: Data usage is 2%(60 32K pages of total 2560)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 1: Index usage is 1%(24 8K pages of total 2336)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 1: Resource 0 min: 0 max: 639 curr: 0
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 2: Data usage is 2%(76 32K pages of total 2560)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 2: Index usage is 1%(24 8K pages of total 2336)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 2: Resource 0 min: 0 max: 639 curr: 0
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 3: Data usage is 2%(58 32K pages of total 2560)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 3: Index usage is 1%(25 8K pages of total 2336)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 3: Resource 0 min: 0 max: 639 curr: 0
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 4: Data usage is 2%(74 32K pages of total 2560)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 4: Index usage is 1%(25 8K pages of total 2336)
2007-01-26 19:35:55 [MgmSrvr] INFO     -- Node 4: Resource 0 min: 0 max: 639 curr: 0
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 4: Node 9 Connected
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 1: Node 9 Connected
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 1: Node 9: API version 5.1.15
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 2: Node 9 Connected
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 2: Node 9: API version 5.1.15
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 3: Node 9 Connected
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 3: Node 9: API version 5.1.15
2007-01-26 19:39:42 [MgmSrvr] INFO     -- Node 4: Node 9: API version 5.1.15
2007-01-26 19:59:22 [MgmSrvr] ALERT    -- Node 2: Node 7 Disconnected
2007-01-26 19:59:22 [MgmSrvr] ALERT    -- Node 2: Node 7 Disconnected

Each line in the cluster log contains the following information:

  • A timestamp in YYYY-MM-DD HH:MM:SS format.

  • The type of node which is performing the logging. In the cluster log, this is always [MgmSrvr].

  • The severity of the event.

  • The ID of the node reporting the event.

  • A description of the event. The most common types of events to appear in the log are connections and disconnections between different nodes in the cluster, and when checkpoints occur. In some cases, the description may contain status information.

15.6.3.1. Logging Management Commands

The following management commands are related to the cluster log:

  • CLUSTERLOG ON

    Turns the cluster log on.

  • CLUSTERLOG OFF

    Turns the cluster log off.

  • CLUSTERLOG INFO

    Provides information about cluster log settings.

  • node_id CLUSTERLOG category=threshold

    Logs category events with priority less than or equal to threshold in the cluster log.

  • CLUSTERLOG FILTER severity_level

    Toggles cluster logging of events of the specified severity_level.

The following table describes the default setting (for all data nodes) of the cluster log category threshold. If an event has a priority with a value lower than or equal to the priority threshold, it is reported in the cluster log.

Note that events are reported per data node, and that the threshold can be set to different values on different nodes.

CategoryDefault threshold (All data nodes)
STARTUP7
SHUTDOWN7
STATISTICS7
CHECKPOINT7
NODERESTART7
CONNECTION7
ERROR15
INFO7

The STATISTICS category can provide a great deal of useful data. See Section 15.6.3.3, “Using CLUSTERLOG STATISTICS, for more information.

Thresholds are used to filter events within each category. For example, a STARTUP event with a priority of 3 is not logged unless the threshold for STARTUP is changed to 3 or lower. Only events with priority 3 or lower are sent if the threshold is 3.

The following table shows the event severity levels. (Note: These correspond to Unix syslog levels, except for LOG_EMERG and LOG_NOTICE, which are not used or mapped.)

1ALERTA condition that should be corrected immediately, such as a corrupted system database
2CRITICALCritical conditions, such as device errors or insufficient resources
3ERRORConditions that should be corrected, such as configuration errors
4WARNINGConditions that are not errors, but that might require special handling
5INFOInformational messages
6DEBUGDebugging messages used for NDB Cluster development

Event severity levels can be turned on or off (using CLUSTERLOG FILTER — see above). If a severity level is turned on, then all events with a priority less than or equal to the category thresholds are logged. If the severity level is turned off then no events belonging to that severity level are logged.

15.6.3.2. Log Events

An event report reported in the event logs has the following format:

datetime [string] severity -- message

For example:

09:19:30 2005-07-24 [NDB] INFO -- Node 4 Start phase 4 completed

This section discusses all reportable events, ordered by category and severity level within each category.

In the event descriptions, GCP and LCP mean “Global Checkpoint” and “Local Checkpoint,” respectively.

CONNECTION Events

These events are associated with connections between Cluster nodes.

EventPrioritySeverity LevelDescription
data nodes connected8INFOData nodes connected
data nodes disconnected8INFOData nodes disconnected
Communication closed8INFOSQL node or data node connection closed
Communication opened8INFOSQL node or data node connection opened

CHECKPOINT Events

The logging messages shown here are associated with checkpoints.

EventPrioritySeverity LevelDescription
LCP stopped in calc keep GCI0ALERTLCP stopped
Local checkpoint fragment completed11INFOLCP on a fragment has been completed
Global checkpoint completed10INFOGCP finished
Global checkpoint started9INFOStart of GCP: REDO log is written to disk
Local checkpoint completed8INFOLCP completed normally
Local checkpoint started7INFOStart of LCP: data written to disk
Report undo log blocked7INFOUNDO logging blocked; buffer near overflow

STARTUP Events

The following events are generated in response to the startup of a node or of the cluster and of its success or failure. They also provide information relating to the progress of the startup process, including information concerning logging activities.

EventPrioritySeverity LevelDescription
Internal start signal received STTORRY15INFOBlocks received after completion of restart
Undo records executed15INFO 
New REDO log started10INFOGCI keep X, newest restorable GCI Y
New log started10INFOLog part X, start MB Y, stop MB Z
Node has been refused for inclusion in the cluster8INFONode cannot be included in cluster due to misconfiguration, inability to establish communication, or other problem
data node neighbors8INFOShows neighboring data nodes
data node start phase X completed4INFOA data node start phase has been completed
Node has been successfully included into the cluster3INFODisplays the node, managing node, and dynamic ID
data node start phases initiated1INFONDB Cluster nodes starting
data node all start phases completed1INFONDB Cluster nodes started
data node shutdown initiated1INFOShutdown of data node has commenced
data node shutdown aborted1INFOUnable to shut down data node normally

NODERESTART Events

The following events are generated when restarting a node and relate to the success or failure of the node restart process.

EventPrioritySeverity LevelDescription
Node failure phase completed8ALERTReports completion of node failure phases
Node has failed, node state was X8ALERTReports that a node has failed
Report arbitrator results2ALERTThere are eight different possible results for arbitration attempts:
  • Arbitration check failed — less than 1/2 nodes left

  • Arbitration check succeeded — node group majority

  • Arbitration check failed — missing node group

  • Network partitioning — arbitration required

  • Arbitration succeeded — affirmative response from node X

  • Arbitration failed - negative response from node X

  • Network partitioning - no arbitrator available

  • Network partitioning - no arbitrator configured

Completed copying a fragment10INFO 
Completed copying of dictionary information8INFO 
Completed copying distribution information8INFO 
Starting to copy fragments8INFO 
Completed copying all fragments8INFO 
GCP takeover started7INFO 
GCP takeover completed7INFO 
LCP takeover started7INFO 
LCP takeover completed (state = X)7INFO 
Report whether an arbitrator is found or not6INFOThere are seven different possible outcomes when seeking an arbitrator:
  • Management server restarts arbitration thread [state=X]

  • Prepare arbitrator node X [ticket=Y]

  • Receive arbitrator node X [ticket=Y]

  • Started arbitrator node X [ticket=Y]

  • Lost arbitrator node X - process failure [state=Y]

  • Lost arbitrator node X - process exit [state=Y]

  • Lost arbitrator node X <error msg> [state=Y]

STATISTICS Events

The following events are of a statistical nature. They provide information such as numbers of transactions and other operations, amount of data sent or received by individual nodes, and memory usage.

EventPrioritySeverity LevelDescription
Report job scheduling statistics9INFOMean internal job scheduling statistics
Sent number of bytes9INFOMean number of bytes sent to node X
Received # of bytes9INFOMean number of bytes received from node X
Report transaction statistics8INFONumbers of: transactions, commits, reads, simple reads, writes, concurrent operations, attribute information, and aborts
Report operations8INFONumber of operations
Report table create7INFO 
Memory usage5INFOData and index memory usage (80%, 90%, and 100%)

ERROR Events

These events relate to Cluster errors and warnings. The presence of one or more of these generally indicates that a major malfunction or failure has occurred.

EventPrioritySeverityDescription
Dead due to missed heartbeat8ALERTNode X declared “dead” due to missed heartbeat
Transporter errors2ERROR 
Transporter warnings8WARNING 
Missed heartbeats8WARNINGNode X missed heartbeat #Y
General warning events2WARNING 

INFO Events

These events provide general information about the state of the cluster and activities associated with Cluster maintenance, such as logging and heartbeat transmission.

EventPrioritySeverityDescription
Sent heartbeat12INFOHeartbeat sent to node X
Create log bytes11INFOLog part, log file, MB
General information events2INFO 

15.6.3.3. Using CLUSTERLOG STATISTICS

The NDB management client's CLUSTERLOG STATISTICS command can provide a number of useful statistics in its output. The following statistics are reported by the transaction coordinator:

StatisticDescription (Number of...)
Trans. CountTransactions attempted with this node as coordinator
Commit CountTransactions committed with this node as coordinator
Read CountPrimary key reads (all)
Simple Read CountPrimary key reads reading the latest committed value
Write CountPrimary key writes (includes all INSERT, UPDATE, and DELETE operations)
AttrInfoCountData words used to describe all reads and writes received
Concurrent OperationsAll concurrent operations ongoing at the moment the report is taken
Abort CountTransactions with this node as coordinator that were aborted
ScansScans (all)
Range ScansIndex scans

The ndbd process has a scheduler that runs in an infinite loop. During each loop scheduler performs the following tasks:

  1. Read any incoming messages from sockets into a job buffer.

  2. Check whether there are any timed messages to be executed; if so, put these into the job buffer as well.

  3. Execute (in a loop) any messages in the job buffer.

  4. Send any distributed messages that were generated by executing the messages in the job buffer.

  5. Wait for any new incoming messages.

The number of loops executed in the third step is reported as the Mean Loop Counter. This statistic increases in size as the utilisation of the TCP/IP buffer improves. You can use this to monitor performance as you add new processes to the cluster.

The Mean send size and Mean receive size statistics allow you to gauge the efficiency of writes and reads (respectively) between nodes. These values are given in bytes. Higher values mean a lower cost per byte sent or received; the maximum is 64k.

To cause all cluster log statistics to be logged, you can use the following command in the NDB management client:

ndb_mgm> ALL CLUSTERLOG STATISTICS=15

Note: Setting the threshold for STATISTICS to 15 causes the cluster log to become very verbose, and to gow quite rapidly in size, in direct proportion to the number of cluster nodes and the amount of activity on the cluster.

15.6.4. Single User Mode

Single user mode allows the database administrator to restrict access to the database system to a single API node, such as a MySQL server (SQL node) or an instance of ndb_restore. When entering single user mode, connections to all other API nodes are closed gracefully and all running transactions are aborted. No new transactions are permitted to start.

Once the cluster has entered single user mode, only the designated API node is granted access to the database.

You can use the ALL STATUS command to see when the cluster has entered single user mode.

Example:

ndb_mgm> ENTER SINGLE USER MODE 5

After this command has executed and the cluster has entered single user mode, the API node whose node ID is 5 becomes the cluster's only permitted user.

The node specified in the preceding command must be an API node; attempting to specify any other type of node will be rejected.

Note: When the preceding commmand is invoked, all transactions running on the designated node are aborted, the connection is closed, and the server must be restarted.

The command EXIT SINGLE USER MODE changes the state of the cluster's data nodes from single user mode to normal mode. API nodes — such as MySQL Servers — waiting for a connection (that is, waiting for the cluster to become ready and available), are again permitted to connect. The API node denoted as the single-user node continues to run (if still connected) during and after the state change.

Example:

ndb_mgm> EXIT SINGLE USER MODE

There are two recommended ways to handle a node failure when running in single user mode:

  • Method 1:

    1. Finish all single user mode transactions

    2. Issue the EXIT SINGLE USER MODE command

    3. Restart the cluster's data nodes

  • Method 2:

    Restart database nodes prior to entering single user mode.

15.6.5. Quick Reference: MySQL Cluster SQL Statements

This section discusses several SQL statements that can prove useful in managing and monitoring a MySQL server that is connected to a MySQL Cluster, and in some cases provide information about the cluster itself.

  • SHOW ENGINE NDB STATUS, SHOW ENGINE NDBCLUSTER STATUS

    The output of this statement contains information about the server's connection to the cluster, creation and usage of MySQL Cluster objects, and binary logging for MySQL Cluster replication.

    See Section 13.5.4.9, “SHOW ENGINE Syntax”, for a usage example and more detailed information.

  • SHOW ENGINES [LIKE 'NDB%']

    This statement can be used to determine whether or not clustering support is enabled in the MySQL server, and if so, whether it is active.

    See Section 13.5.4.10, “SHOW ENGINES Syntax”, for more detailed information.

  • SHOW VARIABLES LIKE 'NDB%'

    This statement provides a list of most server system variables relating to the NDB storage engine, and their values, as shown here:

    mysql> SHOW VARIABLES LIKE 'NDB%';
    +-------------------------------------+-------+
    | Variable_name                       | Value |
    +-------------------------------------+-------+
    | ndb_autoincrement_prefetch_sz       | 32    |
    | ndb_cache_check_time                | 0     |
    | ndb_extra_logging                   | 0     |
    | ndb_force_send                      | ON    |
    | ndb_index_stat_cache_entries        | 32    |
    | ndb_index_stat_enable               | OFF   |
    | ndb_index_stat_update_freq          | 20    |
    | ndb_report_thresh_binlog_epoch_slip | 3     |
    | ndb_report_thresh_binlog_mem_usage  | 10    |
    | ndb_use_copying_alter_table         | OFF   |
    | ndb_use_exact_count                 | ON    |
    | ndb_use_transactions                | ON    |
    +-------------------------------------+-------+

    See Section 5.2.3, “System Variables”, for more information.

  • SHOW STATUS LIKE 'NDB%'

    This statement shows at a glance whether or not the MySQL server is acting as a cluster SQL node, and if so, it provides the MySQL server's cluster node ID, the hostname and port for the cluster management server to which it is connected, and the number of data nodes in the cluster, as shown here:

    mysql> SHOW STATUS LIKE 'NDB%';
    +--------------------------+---------------+
    | Variable_name            | Value         |
    +--------------------------+---------------+
    | Ndb_cluster_node_id      | 10            |
    | Ndb_config_from_host     | 192.168.0.103 |
    | Ndb_config_from_port     | 1186          |
    | Ndb_number_of_data_nodes | 4             |
    +--------------------------+---------------+

    If the MySQL server was built with clustering support, but it is not connected to a cluster, all rows in the output of this statement contain a zero or an empty string:

    mysql> SHOW STATUS LIKE 'NDB%';
    +--------------------------+-------+
    | Variable_name            | Value |
    +--------------------------+-------+
    | Ndb_cluster_node_id      | 0     |
    | Ndb_config_from_host     |       |
    | Ndb_config_from_port     | 0     |
    | Ndb_number_of_data_nodes | 0     |
    +--------------------------+-------+

    See also Section 13.5.4.23, “SHOW STATUS Syntax”.

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