25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded) (original) (raw)

25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)

ndbmtd is a multithreaded version ofndbd, the process that is used to handle all the data in tables using theNDBCLUSTER storage engine.ndbmtd is intended for use on host computers having multiple CPU cores. Except where otherwise noted,ndbmtd functions in the same way asndbd; therefore, in this section, we concentrate on the ways in which ndbmtd differs from ndbd, and you should consultSection 25.5.1, “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 withndbd also apply to ndbmtd. For more information about these options and parameters, seeSection 25.5.1, “ndbd — The NDB Cluster Data Node Daemon”, andSection 25.4.3.6, “Defining NDB Cluster Data Nodes”, respectively.

ndbmtd is also file system-compatible withndbd. In other words, a data node runningndbd can be stopped, the binary replaced withndbmtd, and then restarted without any loss of data. (However, when doing this, you must make sure thatMaxNoOfExecutionThreads is set to an appropriate 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 usingndbd in two key respects:

  1. Because ndbmtd runs by default in single-threaded mode (that is, it behaves likendbd), 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, seeMulti-Threading Configuration Parameters (ndbmtd).
  2. Trace files are generated by critical errors inndbmtd processes in a somewhat different fashion from how these are generated byndbd 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'sDataDir, are useful for analysis of problems by the NDB Cluster Development and Support teams. One trace file is generated for eachndbmtd thread. The names of these files have the following pattern:

ndb_node_id_trace.log.trace_id_tthread_id,

In this pattern, nodeid stands for the data node's unique node ID in the cluster,traceid is a trace sequence number, and threadid is the thread ID. For example, in the event of the failure of anndbmtd process running as an NDB Cluster data node having the node ID 3 and withMaxNoOfExecutionThreads 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 namedndb_3_trace.log.1_t1,ndb_3_trace.log.1_t2,ndb_3_trace.log.1_t3, andndb_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. SeeData Node Error Messages, for a listing of these.

Note

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