User's Manual

Chapter 10. SQL Remote Administration
Setting a very small interval may have some detrimental impact on overall
system throughput, for the following reasons:
♦ Each poll of the mail server (if you are using e-mail) places a load on
your message system. Too-frequent polling may affect your message
system and produce no benefits.
♦ If you do not modify the Message Agent patience before it assumes that
an out of sequence message is lost, and requests it be sent again, you can
flood your system with resend requests.
In general, you should not use a very small polling interval unless you have a
specific reason for requiring a very quick response time for messages.
Setting larger intervals may provide a better overall throughput of messages
in your system, at the cost of waiting somewhat longer for each message to
be applied. In many SQL Remote installations, optimizing turnaround time
is not the primary concern.
Requesting resends
If, when the Message Agent polls for incoming messages, one message is
missing from a sequence, the Message Agent does not immediately request
that the message be resent. Instead, it has a default patience of one poll.
If the next message expected is number 6 and message 7 is found, the
Message Agent takes no action until the next poll. Then, if no new message
for that user is found, it issues a resend request.
You can change the number of polls for which the Message Agent waits
before sending a request using the -rp option. This option is often used in
conjunction with the -rd option that sets the polling interval.
For example, if you have a very small polling interval, and a message system
that does not preserver the order in which messages arrive, it may be very
common for out-of-sync messages to arrive only after two or three polls
have been completed. In such a case, you should instruct the Message Agent
to be more patient before sending a resend request, by increasing the -rp
value. If you do not do this, a large number of unnecessary resend requests
may be sent.
Example
Suppose there are two remote users, named user1 and user2, and suppose
the Message Agent command line is as follows:
dbremote -rd 30s -rp 3
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