25.5.1 ndbd — NDB Cluster 数据节点守护进程
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 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.
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.
-
Command-Line Format --bind-address=name
Type String Default Value Causes ndbd to bind to a specific network interface (host name or IP address). This option has no default value.
-
Command-Line Format --character-sets-dir=path
Directory containing character sets.
-
Command-Line Format --connect-delay=#
Deprecated Yes Type Numeric Default Value 5
Minimum Value 0
Maximum Value 3600
Determines the time to wait between attempts to contact a management server when starting (the number of attempts is controlled by the
--connect-retries
option). The default is 5 seconds.This option is deprecated, and is subject to removal in a future release of NDB Cluster. Use
--connect-retry-delay
instead. -
Command-Line Format --connect-retries=#
Type Numeric Default Value 12
Minimum Value -1
Maximum Value 65535
Set the number of times to retry a connection before giving up; 0 means 1 attempt only (and no retries). The default is 12 attempts. The time to wait between attempts is controlled by the
--connect-retry-delay
option.It is also possible to set this option to -1, in which case, the data node process continues indefinitely to try to connect.
-
Command-Line Format --connect-retry-delay=#
Type Numeric Default Value 5
Minimum Value 0
Maximum Value 4294967295
Determines the time to wait between attempts to contact a management server when starting (the time between attempts is controlled by the
--connect-retries
option). The default is 5 seconds.This option takes the place of the
--connect-delay
option, which is now deprecated and subject to removal in a future release of NDB Cluster.The short form
-r
for this option is also deprecated, and thus subject to removal. Use the long form instead. -
Command-Line Format --connect-string=connection_string
Type String Default Value [none]
Same as
--ndb-connectstring
. -
Command-Line Format --core-file
Write core file on error; used in debugging.
-
--daemon
,-d
Command-Line Format --daemon
Instructs ndbd or ndbmtd to execute as a daemon process. This is the default behavior.
--nodaemon
can be used to prevent the process from running as a daemon.This option has no effect when running ndbd or ndbmtd on Windows platforms.
-
Command-Line Format --defaults-extra-file=path
Type String Default Value [none]
Read given file after global files are read.
-
Command-Line Format --defaults-file=path
Type String Default Value [none]
Read default options from given file only.
-
Command-Line Format --defaults-group-suffix=string
Type String Default Value [none]
Also read groups with concat(group, suffix).
-
Command-Line Format --filesystem-password=password
Pass the filesystem encryption and decryption password to the data node process using
stdin
,tty
, or themy.cnf
file.Requires
EncryptedFileSystem = 1
.For more information, see Section 25.6.14, “File System Encryption for NDB Cluster”.
-
--filesystem-password-from-stdin
Command-Line Format --filesystem-password-from-stdin={TRUE|FALSE}
Pass the filesystem encryption and decryption password to the data node process from
stdin
(only).Requires
EncryptedFileSystem = 1
.For more information, see Section 25.6.14, “File System Encryption for NDB Cluster”.
-
Command-Line Format --foreground
Causes ndbd or ndbmtd to execute as a foreground process, primarily for debugging purposes. This option implies the
--nodaemon
option.This option has no effect when running ndbd or ndbmtd on Windows platforms.
-
Command-Line Format --help
Display help text and exit.
-
Command-Line Format --initial
Instructs ndbd to perform an initial start. An initial start erases any files created for recovery purposes by earlier instances of ndbd. It also re-creates recovery log files. On some operating systems, this process can take a substantial amount of time.
The option also causes the removal of all data files associated with Disk Data tablespaces and undo log files associated with log file groups that existed previously on this data node (see Section 25.6.11, “NDB Cluster Disk Data Tables”).
An
--initial
start is to be used only when starting the ndbd process under very special circumstances; this is because this option causes all files to be removed from the NDB Cluster file system and all redo log files to be re-created. These circumstances are listed here:-
When performing a software upgrade which has changed the contents of any files.
-
When restarting the node with a new version of ndbd.
-
As a measure of last resort when for some reason the node restart or system restart repeatedly fails. In this case, be aware that this node can no longer be used to restore data due to the destruction of the data files.
WarningTo avoid the possibility of eventual data loss, it is recommended that you not use the
--initial
option together withStopOnError = 0
. Instead, setStopOnError
to 0 inconfig.ini
only after the cluster has been started, then restart the data nodes normally—that is, without the--initial
option. See the description of theStopOnError
parameter for a detailed explanation of this issue. (Bug #24945638)Use of this option prevents the
StartPartialTimeout
andStartPartitionedTimeout
configuration parameters from having any effect.ImportantThis option does not affect backup files that have already been created by the affected node.
This option also has no effect on recovery of data by a data node that is just starting (or restarting) from data nodes that are already running (unless they also were started with
--initial
, as part of an initial restart). This recovery of data occurs automatically, and requires no user intervention in an NDB Cluster that is running normally.It is permissible to use this option when starting the cluster for the very first time (that is, before any data node files have been created); however, it is not necessary to do so.
-
-
Command-Line Format --initial-start
This option is used when performing a partial initial start of the cluster. Each node should be started with this option, as well as
--nowait-nodes
.Suppose that you have a 4-node cluster whose data nodes have the IDs 2, 3, 4, and 5, and you wish to perform a partial initial start using only nodes 2, 4, and 5—that is, omitting node 3:
$> ndbd --ndb-nodeid=2 --nowait-nodes=3 --initial-start $> ndbd --ndb-nodeid=4 --nowait-nodes=3 --initial-start $> ndbd --ndb-nodeid=5 --nowait-nodes=3 --initial-start
When using this option, you must also specify the node ID for the data node being started with the
--ndb-nodeid
option.ImportantDo not confuse this option with the
--nowait-nodes
option for ndb_mgmd, which can be used to enable a cluster configured with multiple management servers to be started without all management servers being online. -
Command-Line Format --install[=name]
Platform Specific Windows Type String Default Value ndbd
Causes ndbd to be installed as a Windows service. Optionally, you can specify a name for the service; if not set, the service name defaults to
ndbd
. Although it is preferable to specify other ndbd program options in amy.ini
ormy.cnf
configuration file, it is possible to use together with--install
. However, in such cases, the--install
option must be specified first, before any other options are given, for the Windows service installation to succeed.It is generally not advisable to use this option together with the
--initial
option, since this causes the data node file system to be wiped and rebuilt every time the service is stopped and started. Extreme care should also be taken if you intend to use any of the other ndbd options that affect the starting of data nodes—including--initial-start
,--nostart
, and--nowait-nodes
—together with--install
, and you should make absolutely certain you fully understand and allow for any possible consequences of doing so.The
--install
option has no effect on non-Windows platforms. -
Command-Line Format --logbuffer-size=#
Type Integer Default Value 32768
Minimum Value 2048
Maximum Value 4294967295
Sets the size of the data node log buffer. When debugging with high amounts of extra logging, it is possible for the log buffer to run out of space if there are too many log messages, in which case some log messages can be lost. This should not occur during normal operations.
-
Command-Line Format --login-path=path
Type String Default Value [none]
Read given path from login file.
-
Command-Line Format --no-login-paths
Skips reading options from the login path file.
-
Command-Line Format --ndb-connectstring=connection_string
Type String Default Value [none]
Set connection string for connecting to ndb_mgmd. Syntax:
[nodeid=
. Overrides entries inid
;][host=]hostname
[:port
]NDB_CONNECTSTRING
andmy.cnf
. -
Command-Line Format --ndb-mgmd-host=connection_string
Type String Default Value [none]
Same as
--ndb-connectstring
. -
Command-Line Format --ndb-mgm-tls=level
Type Enumeration Default Value relaxed
Valid Values relaxed
strict
Sets the level of TLS support required to connect to the management server; one of
relaxed
orstrict
.relaxed
(the default) means that a TLS connection is attempted, but success is not required;strict
means that TLS is required to connect. -
Command-Line Format --ndb-nodeid=#
Type Integer Default Value [none]
Set node ID for this node, overriding any ID set by --ndb-connectstring.
-
--ndb-optimized-node-selection
Command-Line Format --ndb-optimized-node-selection
Enable optimizations for selection of nodes for transactions. Enabled by default; use
--skip-ndb-optimized-node-selection
to disable. -
Command-Line Format --ndb-tls-search-path=list
Type Path name Default Value (Unix) $HOME/ndb-tls
Default Value (Windows) $HOMEDIR/ndb-tls
Specify a list of directories to search for a CA file. On Unix platforms, the directory names are separated by colons (
:
); on Windows systems, the semicolon character (;
) is used as the separator. A directory reference may be relative or absolute; it may contain one or more environment variables, each denoted by a prefixed dollar sign ($
), and expanded prior to use.Searching begins with the leftmost named directory and proceeds from left to right until a file is found. An empty string denotes an empty search path, which causes all searches to fail. A string consisting of a single dot (
.
) indicates that the search path limited to the current working directory.If no search path is supplied, the compiled-in default value is used. This value depends on the platform used: On Windows, this is
\ndb-tls
; on other platforms (including Linux), it is$HOME/ndb-tls
. This can be overridden by compiling NDB Cluster using-DWITH_NDB_TLS_SEARCH_PATH
. -
Command-Line Format --nodaemon
Prevents ndbd or ndbmtd from executing as a daemon process. This option overrides the
--daemon
option. This is useful for redirecting output to the screen when debugging the binary.The default behavior for ndbd and ndbmtd on Windows is to run in the foreground, making this option unnecessary on Windows platforms, where it has no effect.
-
Command-Line Format --no-defaults
Do not read default options from any option file other than login file.
-
--nostart
,-n
Command-Line Format --nostart
Instructs ndbd not to start automatically. When this option is used, ndbd connects to the management server, obtains configuration data from it, and initializes communication objects. However, it does not actually start the execution engine until specifically requested to do so by the management server. This can be accomplished by issuing the proper
START
command in the management client (see Section 25.6.1, “Commands in the NDB Cluster Management Client”). -
--nowait-nodes=
node_id_1
[,node_id_2
[, ...]]Command-Line Format --nowait-nodes=list
Type String Default Value This option takes a list of data nodes for which the cluster does not wait, prior to starting.
This can be used to start the cluster in a partitioned state. For example, to start the cluster with only half of the data nodes (nodes 2, 3, 4, and 5) running in a 4-node cluster, you can start each ndbd process with
--nowait-nodes=3,5
. In this case, the cluster starts as soon as nodes 2 and 4 connect, and does not waitStartPartitionedTimeout
milliseconds for nodes 3 and 5 to connect as it would otherwise.If you wanted to start up the same cluster as in the previous example without one ndbd (say, for example, that the host machine for node 3 has suffered a hardware failure) then start nodes 2, 4, and 5 with
--nowait-nodes=3
. Then the cluster starts as soon as nodes 2, 4, and 5 connect, and does not wait for node 3 to start. -
Command-Line Format --print-defaults
Print program argument list and exit.
-
Command-Line Format --remove[=name]
Platform Specific Windows Type String Default Value ndbd
Causes an ndbd process that was previously installed as a Windows service to be removed. Optionally, you can specify a name for the service to be uninstalled; if not set, the service name defaults to
ndbd
.The
--remove
option has no effect on non-Windows platforms. -
Command-Line Format --usage
Display help text and exit; same as --help.
-
--verbose
,-v
Causes extra debug output to be written to the node log.
You can also use
NODELOG DEBUG ON
andNODELOG DEBUG OFF
to enable and disable this extra logging while the data node is running. -
Command-Line Format --version
Display version information and exit.
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
.
-
ndb_
is a file containing records of all crashes which the referenced ndbd process has encountered. Each record in this file contains a brief error string and a reference to a trace file for this crash. A typical entry in this file might appear as shown here:node_id
_error.logDate/Time: Saturday 30 July 2004 - 00:20:01 Type of error: error Message: Internal program error (failed ndbrequire) Fault ID: 2341 Problem data: DbtupFixAlloc.cpp Object of reference: DBTUP (Line: 173) ProgramName: NDB Kernel ProcessID: 14909 TraceFile: ndb_2_trace.log.2 ***EOM***
Listings of possible ndbd exit codes and messages generated when a data node process shuts down prematurely can be found in Data Node Error Messages.
ImportantThe last entry in the error log file is not necessarily the newest one (nor is it likely to be). Entries in the error log are not listed in chronological order; rather, they correspond to the order of the trace files as determined in the
ndb_
file (see below). Error log entries are thus overwritten in a cyclical and not sequential fashion.node_id
_trace.log.next -
ndb_
is a trace file describing exactly what happened just before the error occurred. This information is useful for analysis by the NDB Cluster development team.node_id
_trace.log.trace_id
It is possible to configure the number of these trace files that are created before old files are overwritten.
trace_id
is a number which is incremented for each successive trace file. -
ndb_
is the file that keeps track of the next trace file number to be assigned.node_id
_trace.log.next -
ndb_
is a file containing any data output by the ndbd process. This file is created only if ndbd is started as a daemon, which is the default behavior.node_id
_out.log -
ndb_
is a file containing the process ID of the ndbd process when started as a daemon. It also functions as a lock file to avoid the starting of nodes with the same identifier.node_id
.pid -
ndb_
is a file used only in debug versions of ndbd, where it is possible to trace all incoming, outgoing, and internal messages with their data in the ndbd process.node_id
_signal.log
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”.