MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4

25.5.1 ndbd — The NDB Cluster Data Node Daemon

The ndbd binary provides the single-threaded version of the process that is used to handle all the data in tables employing the NDBCLUSTER storage engine. This data node process enables a data node to accomplish distributed transaction handling, node recovery, checkpointing to disk, online backup, and related tasks. In NDB 8.4.1 and later, when started, ndbd logs a warning similar to that shown here:

2024-05-28 13:32:16 [ndbd] WARNING  -- Running ndbd with a single thread of
signal execution.  For multi-threaded signal execution run the ndbmtd binary.

ndbmtd is the multi-threaded version of this binary.

In an NDB Cluster, a set of ndbd processes cooperate in handling data. These processes can execute on the same computer (host) or on different computers. The correspondences between data nodes and Cluster hosts is completely configurable.

Options that can be used with ndbd are shown in the following table. Additional descriptions follow the table.

Note

All of these options also apply to the multithreaded version of this program (ndbmtd) and you may substitute ndbmtd for ndbd wherever the latter occurs in this section.

ndbd generates a set of log files which are placed in the directory specified by DataDir in the config.ini configuration file.

These log files are listed below. node_id is and represents the node's unique identifier. For example, ndb_2_error.log is the error log generated by the data node whose node ID is 2.

It is recommended not to use a directory mounted through NFS because in some environments this can cause problems whereby the lock on the .pid file remains in effect even after the process has terminated.

To start ndbd, it may also be necessary to specify the host name of the management server and the port on which it is listening. Optionally, one may also specify the node ID that the process is to use.

$> ndbd --connect-string="nodeid=2;host=ndb_mgmd.mysql.com:1186"

See Section 25.4.3.3, “NDB Cluster Connection Strings”, for additional information about this issue. For more information about data node configuration parameters, see Section 25.4.3.6, “Defining NDB Cluster Data Nodes”.

When ndbd starts, it actually initiates two processes. The first of these is called the angel process; its only job is to discover when the execution process has been completed, and then to restart the ndbd process if it is configured to do so. Thus, if you attempt to kill ndbd using the Unix kill command, it is necessary to kill both processes, beginning with the angel process. The preferred method of terminating an ndbd process is to use the management client and stop the process from there.

The execution process uses one thread for reading, writing, and scanning data, as well as all other activities. This thread is implemented asynchronously so that it can easily handle thousands of concurrent actions. In addition, a watch-dog thread supervises the execution thread to make sure that it does not hang in an endless loop. A pool of threads handles file I/O, with each thread able to handle one open file. Threads can also be used for transporter connections by the transporters in the ndbd process. In a multi-processor system performing a large number of operations (including updates), the ndbd process can consume up to 2 CPUs if permitted to do so.

For a machine with many CPUs it is possible to use several ndbd processes which belong to different node groups; however, such a configuration is still considered experimental and is not supported for MySQL 8.4 in a production setting. See Section 25.2.7, “Known Limitations of NDB Cluster”.