User's Manual

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.
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