Sybase DC38133-01-0902-01 Running the Message Agent, Message Agent batch and continuous modes

Chapter 10. SQL Remote Administration

Running the Message Agent

The SQL Remote Message Agent is a key component in SQL Remote replication. The Message Agent handles both the sending and receiving of messages. It carries out the following functions:

♦ It processes incoming messages, and applies them in the proper order to

	the database.
	♦ It scans the transaction log or stable queue at each publisher database,
	and translates the log entries into messages for subscribers.
	♦ It parcels the log entries up into messages no larger than a fixed
	maximum size (50,000 bytes by default), and sends them to subscribers.
	♦ It maintains the message tracking information in the system tables, and
	manages the guaranteed transmission mechanism.
Executable names	On Windows operating systems, the Message Agent for Adaptive Server
	Enterprise is named ssremote.exe, and the Message Agent for Adaptive
	Server Anywhere is named dbremote.exe. On UNIX operating systems, the
	names are ssremote and dbremote, respectively.
	☞ The Message Agent for Adaptive Server Enterprise uses a stable queue
	to hold transactions until they are no longer needed. For more information
	on the stable queue, see “How the Message Agent for Adaptive Server
	Enterprise works” on page 264 .

Message Agent batch and continuous modes

The Message Agent can be run in one of two modes:

♦Batch mode In batch mode, the Message Agent starts, receives and sends all messages that can be received and sent, and then shuts down.

Batch mode is useful at occasionally-connected remote sites, where messages can only be exchanged with the consolidated database when the connection is made: for example, when the remote site dials up to the main network.

♦Continuous mode In continuous mode, the Message Agent periodically sends messages, at times specified in the properties of each remote user. When it is not sending messages, it receives messages as they arrive.

Continuous mode is useful at consolidated sites, where messages may be coming in and going out at any time, to spread out the workload and to ensure prompt replication.

223