Dumping the contents of the log using the dmpmqlog command

How to use the dmpmqlog command to dump the contents of the queue manager log.

Use the dmpmqlog command to dump the contents of the queue manager log. By default all active log records are dumped, that is, the command starts dumping from the head of the log (usually the start of the last completed checkpoint).

• Start dumping from the base of the log. The base of the log is the first log record in the log file that contains the head of the log. The amount of additional data dumped in this case depends on where the head of the log is positioned in the log file. If it is near the start of the log file, only a small amount of additional data is dumped. If the head is near the end of the log file, significantly more data is dumped.
• Specify the start position of the dump as an individual log record. Each log record is identified by a unique log sequence number (LSN). In the case of circular logging, this starting log record cannot be before the base of the log; this restriction does not apply to linear logs. We might need to reinstate inactive log files before running the command. We must specify a valid LSN, taken from previous dmpmqlog output, as the start position.

  For example, with linear logging we can specify the nextlsn from your last dmpmqlog output. The nextlsn appears in Log File Header and indicates the LSN of the next log record to be written. Use this as a start position to format all log records written since the last time the log was dumped.

• For linear logs only, we can instruct dmpmqlog to start formatting log records from any given log file extent. In this case, dmpmqlog expects to find this log file, and each successive one, in the same directory as the active log files. This option does not apply to circular logs, where dmpmqlog cannot access log records prior to the base of the log.

The output from the dmpmqlog command is the Log File Header and a series of formatted log records. The queue manager uses several log records to record changes to its data.

Some of the information that is formatted is only of use internally. The following list includes the most useful log records:

Log File Header

Each log has a single log file header, which is always the first thing formatted by the dmpmqlog command. It contains the following fields:

	logactive	The number of primary log extents.
	loginactive	The number of secondary log extents.
	logsize	The number of 4 KB pages per extent.
	baselsn	The first LSN in the log extent containing the head of the log.
	nextlsn	The LSN of the next log record to be written.
	headlsn	The LSN of the log record at the head of the log.
	tailsn	The LSN identifying the tail position of the log.
	hflag1	Whether the log is CIRCULAR or LOG RETAIN (linear).
	HeadExtentID	The log extent containing the head of the log.

Log Record Header

Each log record within the log has a fixed header containing the following information:

	LSN	The log sequence number.
	LogRecdType	The type of the log record.
	XTranid	The transaction identifier associated with this log record (if any). A TranType of MQI indicates an IBM MQ -only transaction. A TranType of XA is involved with other resource managers. Updates involved within the same unit of work have the same XTranid.
	QueueName	The queue associated with this log record (if any).
	Qid	The unique internal identifier for the queue.
	PrevLSN	The LSN of the previous log record within the same transaction (if any).

Start Queue Manager

This logs that the queue manager has started.

	StartDate	The date that the queue manager started.
	StartTime	The time that the queue manager started.

Stop Queue Manager

This logs that the queue manager has stopped.

	StopDate	The date that the queue manager stopped.
	StopTime	The time that the queue manager stopped.
	ForceFlag	The type of shutdown used.

Start Checkpoint

This denotes the start of a queue manager checkpoint.

End Checkpoint

This denotes the end of a queue manager checkpoint.

ChkPtLSN

The LSN of the log record that started this checkpoint.

Put Message

This logs a persistent message put to a queue. If the message was put under sync point, the log record header contains a non-null XTranid. The remainder of the record contains:

	MapIndex	An identifier for the message on the queue. It can be used to match the corresponding MQGET that was used to get this message from the queue. In this case a subsequent Get Message log record can be found containing the same QueueName and MapIndex. At this point the MapIndex identifier can be reused for a subsequent put message to that queue.
	Data	Contained in the hex dump for this log record is various internal data, followed by a representation of the Message Descriptor (eyecatcher MD) and then the message data itself.

Put Part

Persistent messages that are too large for a single log record are logged as multiple Put Part log records followed by a single Put Message record. If there are Put Part records, then the PrevLSN field will chain the Put Part records and the final Put Message record together.

Data

Continues the message data where the previous log record left off.

Get Message

Only gets of persistent messages are logged. If the message was got under sync point, the log record header contains a non-null XTranid. The remainder of the record contains:

	MapIndex	Identifies the message that was retrieved from the queue. The most recent Put Message log record containing the same QueueName and MapIndex identifies the message that was retrieved.
	QPriority	The priority of the message retrieved from the queue.

Start Transaction

Indicates the start of a new transaction. A TranType of MQI indicates an IBM MQ-only transaction. A TranType of XA indicates one that involves other resource managers. All updates made by this transaction will have the same XTranid.

Prepare Transaction

Indicates that the queue manager is prepared to commit the updates associated with the specified XTranid. This log record is written as part of a two-phase commit involving other resource managers.

Commit Transaction

Indicates that the queue manager has committed all updates made by a transaction.

Roll back Transaction

This denotes the queue manager's intention to roll back a transaction.

End Transaction

This denotes the end of a rolled-back transaction.

Transaction Table

This record is written during sync point. It records the state of each transaction that has made persistent updates. For each transaction the following information is recorded:

	XTranid	The transaction identifier.
	FirstLSN	The LSN of the first log record associated with the transaction.
	LastLSN	The LSN of the last log record associated with the transaction.

Transaction Participants

This log record is written by the XA Transaction Manager component of the queue manager. It records the external resource managers that are participating in transactions. For each participant the following is recorded:

	RMName	The name of the resource manager.
	RMID	The resource manager identifier. This is also logged in subsequent Transaction Prepared log records that record global transactions in which the resource manager is participating.
	SwitchFile	The switch load file for this resource manager.
	XAOpenString	The XA open string for this resource manager.
	XACloseString	The XA close string for this resource manager.

Transaction Prepared

This log record is written by the XA Transaction Manager component of the queue manager. It indicates that the specified global transaction has been successfully prepared. Each of the participating resource managers will be instructed to commit. The RMID of each prepared resource manager is recorded in the log record. If the queue manager itself is participating in the transaction a Participant Entry with an RMID of zero will be present.

Transaction Forget

This log record is written by the XA Transaction Manager component of the queue manager. It follows the Transaction Prepared log record when the commit decision has been delivered to each participant.

Purge Queue

This logs the fact that all messages on a queue have been purged, for example, using the MQSC command CLEAR QUEUE.

Queue Attributes

This logs the initialization or change of the attributes of a queue.

Create Object

This logs the creation of an IBM MQ object.

	ObjName	The name of the object that was created.
	UserId	The user ID performing the creation.

Delete Object

This logs the deletion of an IBM MQ object.

ObjName

The name of the object that was deleted.

Parent topic: Logging: Making sure that messages are not lost