17.4.1 ndbd — The MySQL Cluster Data Node Daemon

ndbd is the process that is used to handle all the data in tables using the NDB Cluster storage engine. This is the process that empowers a data node to accomplish distributed transaction handling, node recovery, checkpointing to disk, online backup, and related tasks.

In a MySQL 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.

The following table includes command options specific to the MySQL Cluster data node program ndbd. Additional descriptions follow the table. For options common to most MySQL Cluster programs (including ndbd), see Section 17.4.20, “Options Common to MySQL Cluster Programs — Options Common to MySQL Cluster Programs”.

Table 17.26  This table describes command-line options for the ndbd program

Format Description Added or Removed

--initial

Perform initial start of ndbd, including cleaning the file system. Consult the documentation before using this option

All MySQL 5.0 based releases

--nostart,

-n

Don't start ndbd immediately; ndbd waits for command to start from ndb_mgmd

All MySQL 5.0 based releases

--daemon,

-d

Start ndbd as daemon (default); override with --nodaemon

All MySQL 5.0 based releases

--nodaemon

Do not start ndbd as daemon; provided for testing purposes

All MySQL 5.0 based releases

--foreground

Run ndbd in foreground, provided for debugging purposes (implies --nodaemon)

All MySQL 5.0 based releases

--nowait-nodes=list

Do not wait for these data nodes to start (takes comma-separated list of node IDs). Also requires --ndb-nodeid to be used.

ADDED: 5.0.21

--initial-start

Perform partial initial start (requires --nowait-nodes)

ADDED: 5.0.21

--bind-address=name

Local bind address

ADDED: 5.0.29


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 the node's unique identifier. Note that node_id 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.

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

See Section 17.3.2.2, “MySQL Cluster Connection Strings”, for additional information about this issue. Section 17.4.1, “ndbd — The MySQL Cluster Data Node Daemon”, describes other options for ndbd.

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 5.0 in a production setting. See Section 17.1.5, “Known Limitations of MySQL Cluster”.