Channel attributes for MQSC keywords (M)

An alphabetical list of the channel attributes for MQSC keywords, starting with the letter M.

MAXINST (Maximum instances)

This attribute specifies the maximum number of simultaneous instances of a server-connection channel or AMQP channel that can be started.

Maximum instances of server-connection channel connections

For a server-connection channel, this attribute specifies the maximum number of simultaneous instances of a server-connection channel that can be started.

This attribute can be set from zero through 999 999 999. A value of zero indicates that no client connections are allowed on this channel. The default value is 999 999 999.

If the value is reduced so that it is less than the number of instances of the server-connection channel that are currently running, then the running channels are not affected. However, new instances are not able to start until sufficient existing ones have ceased to run.

Maximum instances of AMQP channel connections

For an AMQP channel, this attribute specifies the maximum number of simultaneous instances of an AMQP channel that can be started.

This attribute can be set from zero through 999 999 999. A value of zero indicates that no client connections are allowed on this channel. The default value is 999 999 999.

If a client attempts to connect, and the number of connected clients has reached MAXINST, the channel closes the connection with a close frame. The close frame contains the following message: 
amqp:resource-limit-exceeded

If a client connects with an ID that is already connected (that is, it performs a client-takeover), the takeover will succeed regardless of whether the number of connected clients has reached MAXINST.

See Server-connection channel limits for additional information.

MAXINSTC (Maximum instances per client)

This attribute specifies the maximum number of simultaneous instances of a server-connection channel that can be started from a single client.

This attribute can be set from zero through 999 999 999. A value of zero indicates that no client connections are allowed on this channel. The default value is 999 999 999.

If the value is reduced so that it is less than the number of instances of the server-connection channel that are currently running from individual clients, then the running channels are not affected. However, new instances from those clients are not able to start until sufficient existing ones have ceased to run.

This attribute is valid only for server-connection channels.

See Server-connection channel limits for additional information.

MAXMSGL (Maximum message length)

This attribute specifies the maximum length of a message that can be transmitted on the channel.

[UNIX, Linux, Windows, IBM i]On Multiplatforms, specify a value greater than or equal to zero, and less than or equal to the maximum message length for the queue manager. See the MAXMSGL parameter of the ALTER QMGR command in ALTER QMGR for more information.

[z/OS]On IBM® MQ for z/OS®, specify a value greater than or equal to zero, and less than or equal to 104 857 600 bytes (that is, 100 MB).

Because various implementations of IBM MQ systems exist on different platforms, the size available for message processing might be limited in some applications. This number must reflect a size that your system can handle without stress. When a channel starts, the lower of the two numbers at each end of the channel is taken.
Note: You can use a maximum message size of 0 for the channel, which is taken to mean that the size is to be set to the local queue manager maximum value.

By adding the digital signature and key to the message, Advanced Message Security increases the length of the message.

This attribute is valid for all channel types.

MCANAME (Message channel agent name)

This attribute is reserved, if specified must be set only to blanks and has a maximum length is 20 characters.

MCATYPE (Message channel agent type)

This attribute can specify the message channel agent as a process or a thread.

Advantages of running as a process include:
  • Isolation for each channel providing greater integrity
  • Job authority specific for each channel
  • Control over job scheduling
Advantages of threads include:
  • Much reduced use of storage
  • Easier configuration by typing on the command line
  • Faster execution - it is quicker to start a thread than to instruct the operating system to start a process
Note: For channel types of sender, server, and requester, the default is process. For channel types of cluster-sender and cluster-receiver, the default is thread. These defaults can change during your installation.

If you specify process on the channel definition, a RUNMQCHL process is started. If you specify thread, the MCA runs on a thread of the AMQRMPPA process, or of the RUNMQCHI process if MQNOREMPOOL is specified. On the machine that receives the inbound allocates, the MCA runs as a thread if you use RUNMQLSR. It runs as a process if you use inetd.

[z/OS]On IBM MQ for z/OS, this attribute is supported only for channels with a channel type of cluster-receiver.

[UNIX, Linux, Windows, IBM i]On other platforms, this attribute is valid for channel types of:
  • Sender
  • Server
  • Requester
  • Cluster sender
  • Cluster receiver

MCAUSER (Message channel agent user identifier)

This attribute is the user identifier (a string) to be used by the MCA for authorization to access IBM MQ resources.
Note: An alternative way of providing a user ID for a channel to run under is to use channel authentication records. With channel authentication records, different connections can use the same channel while using different credentials. If both MCAUSER on the channel is set and channel authentication records are used to apply to the same channel, the channel authentication records take precedence. The MCAUSER on the channel definition is only used if the channel authentication record uses USERSRC(CHANNEL).

This authorization includes (if PUT authority is DEF) putting the message to the destination queue for receiver or requester channels.

On IBM MQ for Windows, the user identifier can be domain-qualified by using the format, user@domain, where the domain must be either the Windows systems domain of the local system, or a trusted domain.

If this attribute is blank, the MCA uses its default user identifier. For more information, see DEFINE CHANNEL.

This attribute is valid for channel types of:
  • Receiver
  • Requester
  • Server connection
  • Cluster receiver

MODENAME (LU 6.2 mode name)

This attribute is for use with LU 6.2 connections. It gives extra definition for the session characteristics of the connection when a communication session allocation is performed.

When using side information for SNA communications, the mode name is defined in the CPI-C Communications Side Object or APPC side information, and this attribute must be left blank; otherwise, it must be set to the SNA mode name.

The name must be one to eight alphanumeric characters long.

This attribute is valid only for channel types of:
  • Sender
  • Server
  • Requester
  • Client connection
  • Cluster sender
  • Cluster receiver

MONCHL (Monitoring)

This attribute controls the collection of online Monitoring data.

Possible values are:
QMGR
The collection of Online Monitoring Data is inherited from the setting of the MONCHL attribute in the queue manager object. This value is the default value.
OFF
Online Monitoring Data collection for this channel is disabled.
LOW
A low ratio of data collection with a minimal effect on performance. However, the monitoring results shown might not be up to date.
MEDIUM
A moderate ratio of data collection with limited effect on the performance of the system.
HIGH
A high ratio of data collection with the possibility of an effect on performance. However, the monitoring results shown are the most current.
This attribute is valid for channel types of:
  • Sender
  • Server
  • Receiver
  • Requester
  • Server connection
  • Cluster sender
  • Cluster receiver
For more information about monitoring data, see Displaying queue and channel monitoring data.

MRDATA (Message-retry exit user data)

his attribute specifies data passed to the channel message-retry exit when it is called.

This attribute is valid for channel types of:
  • Receiver
  • Requester
  • Cluster receiver

MREXIT (Message-retry exit name)

This attribute specifies the name of the user exit program to be run by the message-retry user exit.

Leave blank if no message-retry exit program is in effect.

The format and maximum length of the name depend on the platform, as for RCVEXIT (Receive exit name). However, you can specify only one message-retry exit.

This attribute is valid for channel types of:
  • Receiver
  • Requester
  • Cluster receiver

MRRTY (Message retry count)

This attribute specifies the number of times the channel tries to redeliver the message.

This attribute controls the action of the MCA only if the message-retry exit name is blank. If the exit name is not blank, the value of MRRTY is passed to the exit, but the number of attempts made (if any) is controlled by the exit, and not by this attribute.

The value must be in the range 0 - 999 999 999. A value of zero means that no additional attempts are made. The default is 10.

This attribute is valid for channel types of:
  • Receiver
  • Requester
  • Cluster receiver

MRTMR (Message retry interval)

This attribute specifies the minimum interval of time in milliseconds that must pass before the channel can retry the MQPUT operation.

This attribute controls the action of the MCA only if the message-retry exit name is blank. If the exit name is not blank, the value of MRTMR is passed to the exit for use by the exit, but the retry interval is controlled by the exit, and not by this attribute.

The value must be in the range 0 - 999 999 999. A value of zero means that the retry is performed as soon as possible (if the value of MRRTY is greater than zero). The default is 1000.

This attribute is valid for the following channel types:
  • Receiver
  • Requester
  • Cluster receiver

MSGDATA (Message exit user data)

This attribute specifies user data that is passed to the channel message exits.

You can run a sequence of message exits. The limitations on the user data length and an example of how to specify MSGDATA for more than one exit are as shown for RCVDATA. See RCVDATA (Receive exit user data).

This attribute is valid for channel types of:
  • Sender
  • Server
  • Receiver
  • Requester
  • Cluster sender
  • Cluster receiver

MSGEXIT (Message exit name)

This attribute specifies the name of the user exit program to be run by the channel message exit.

This attribute can be a list of names of programs that are to be run in succession. Leave blank, if no channel message exit is in effect.

The format and maximum length of this attribute depend on the platform, as for RCVEXIT (Receive exit name).

This attribute is valid for channel types of:
  • Sender
  • Server
  • Receiver
  • Requester
  • Cluster sender
  • Cluster receiver