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ndbmtd

NAME

ndbmtd - the MySQL Cluster storage engine node process (multi-threaded version)

SYNOPSIS

ndbmtd options

DESCRIPTION

ndbmtd

is a multi-threaded version of ndbd, the process that is used to handle all the data in tables using the NDBCLUSTER storage engine. ndbmtd is intended for use on host computers having multiple CPU cores. Except where otherwise noted, ndbmtd functions in the same way as ndbd; therefore, in this section, we concentrate on the ways in which ndbmtd differs from ndbd, and you should consult ndbd(8), for additional information about running MySQL Cluster data nodes that apply to both the single-threaded and multi-threaded versions of the data node process.

Command-line options and configuration parameters used with ndbd also apply to ndbmtd. For more information about these options and parameters, see Section 6.2.1, "Command Options for ndbd and ndbmtd", and Section 3.4.6, "Defining MySQL Cluster Data Nodes", respectively.

ndbmtd is also file system-compatible with ndbd. In other words, a data node running ndbd can be stopped, the binary replaced with ndbmtd, and then restarted without any loss of data. (However, when doing this, you must make sure that MaxNoOfExecutionThreads is set to an apppriate value before restarting the node if you wish for ndbmtd to run in multi-threaded fashion.) Similarly, an ndbmtd binary can be replaced with ndbd simply by stopping the node and then starting ndbd in place of the multi-threaded binary. It is not necessary when switching between the two to start the data node binary using --initial.

Using ndbmtd differs from using ndbd in two key respects:

1.

You must set an appropriate value for the MaxNoOfExecutionThreads configuration parameter in the config.ini file. If you do not do so, ndbmtd runs in single-threaded mode --- that is, it behaves like ndbd.

2.

Trace files are generated by critical errors in ndbmtd processes in a somewhat different fashion from how these are generated by ndbd failures.

These differences are discussed in more detail in the next few paragraphs.

Number of execution threads. The MaxNoOfExecutionThreads configuration parameter is used to determine the number of execution threads spawned by ndbmtd. Although this parameter is set in [ndbd] or [ndbd default] sections of the config.ini file, it is exclusive to ndbmtd and does not apply to ndbd.

This parameter takes an integer value from 2 to 8 inclusive. Generally, you should set this to the number of CPU cores on the data node host, as shown in the following table:

Number of Cores	Recommended MaxNoOfExecutionThreads Value
2	2
4	4
8 or more	8

It is possible to set this parameter to other values, but these are automatically rounded as follows:

config.ini Value	Value Used
3	2
5 or 6	4
7	8

Setting this parameter outside the permitted range of values causes the management server to abort on startup with the error Error line number: Illegal value value for parameter MaxNoOfExecutionThreads.

Note

In MySQL Cluster NDB 6.4.0, it is not possible to set MaxNoOfExecutionThreads to 2. You can safely use the value 3 instead (it is treated as 2 internally). This issue is resolved in MySQL Cluster NDB 6.4.1.

Like ndbd, ndbmtd generates a set of log files which are placed in the directory specified by DataDir in the config.ini configuration file. Except for trace files, these are generated in the same way and have the same names as those generated by ndbd.

In the event of a critical error, ndbmtd generates trace files describing what happened just prior to the error' occurrence. These files, which can be found in the data node's DataDir, are useful for analysis of problems by the MySQL Cluster Development and Support teams. One trace file is generated for each ndbmtd thread. The names of these files follow the pattern ndb_node_id_trace.log.trace_id_tthread_id, where node_id is the data node's unique node ID in the cluster, trace_id is a trace sequence number, and thread_id is the thread ID. For example, in the event of the failure of an ndbmtd process running as a MySQL Cluster data node having the node ID 3 and with MaxNoOfExecutionThreads equal to 4, four trace files are generated in the data node's data directory; if the is the first time this node has failed, then these files are named ndb_3_trace.log.1_t1, ndb_3_trace.log.1_t2, ndb_3_trace.log.1_t3, and ndb_3_trace.log.1_t4. Internally, these trace files follow the same format as ndbd trace files.

The ndbd exit codes and messages that are generated when a data node process shuts down prematurely are also used by ndbmtd. See [1]ndbd Error Messages, for a listing of these.

Note

It is possible to use ndbd and ndbmtd concurrently on different data nodes in the same MySQL Cluster. However, such configurations have not been tested extensively; thus, we cannot not recommend doing so in a production setting at this time.

COPYRIGHT

Copyright 2007-2008 MySQL AB, 2009 Sun Microsystems, Inc.

This documentation is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License.

This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see http://www.gnu.org/licenses/.

REFERENCES

1. ndbd Error Messages

http://dev.mysql.com/doc/ndbapi/en/ndbd-error-messages.html

SEE ALSO

For more information, please refer to the MySQL Reference Manual, which may already be installed locally and which is also available online at http://dev.mysql.com/doc/.

AUTHOR

MySQL AB (http://www.mysql.com/).