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ndbmtd is a multithreaded 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
Section 22.4.1, “ndbd — The NDB Cluster Data Node Daemon”, for additional
information about running NDB Cluster data nodes that apply to
both the single-threaded and multithreaded 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 22.4.1, “ndbd — The NDB Cluster Data Node Daemon”, and Section 22.3.3.6, “Defining NDB 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 multithreaded
fashion.) Similarly, an ndbmtd binary can be
replaced with ndbd simply by stopping the
node and then starting ndbd in place of the
multithreaded 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:
Because ndbmtd runs by default in single-threaded mode (that is, it behaves like ndbd), you must configure it to use multiple threads. This can be done by setting an appropriate value in the
config.ini
file for theMaxNoOfExecutionThreads
configuration parameter or theThreadConfig
configuration parameter. UsingMaxNoOfExecutionThreads
is simpler, butThreadConfig
offers more flexibility. For more information about these configuration parameters and their use, see Multi-Threading Configuration Parameters (ndbmtd).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.
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 NDB Cluster Development and Support
teams. One trace file is generated for each
ndbmtd thread. The names of these files have
the following pattern:
ndb_node_id_trace.log.trace_id_tthread_id,
In this pattern, node_id
stands for
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 an NDB 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 Data Node Error Messages, for a listing of these.
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