Chapter 10. SQL Remote Administration
Settinga very small interval may have some detrimental impact on overall
systemthroughput, for the following reasons:
Eachpoll of the mail server (if you are using e-mail) places a load on
yourmessage system. Too-frequentpolling may affect your message
systemand produce no benefits.
Ifyou do not modify the Message Agent patience before it assumes that
anout of sequence message is lost, and requests it be sent again, you can
floodyour system with resend requests.
Ingeneral, you should not use a very small polling interval unless you have a
specificreason for requiring a very quick response time for messages.
Settinglarger intervals may provide a better overall throughput of messages
inyour system, at the cost of waiting somewhat longer for each message to
beapplied. Inmany SQL Remote installations, optimizing turnaround time
isnot the primary concern.
Requesting resends
If,when the Message Agent polls for incoming messages, one message is
missingfrom a sequence, the Message Agent does not immediately request
thatthe message be resent. Instead,it has a default patience of one poll.
Ifthe next message expected is number 6 and message 7 is found, the
MessageAgent takes no action until the next poll. Then,if no new message
forthat user is found, it issues a resend request.
Youcan change the number of polls for which the Message Agent waits
beforesending a request using the -rp option. Thisoption is often used in
conjunctionwith the -rd option that sets the polling interval.
Forexample, if you have a very small polling interval, and a message system
thatdoes not preserver the order in which messages arrive, it may be very
commonfor out-of-sync messages to arrive only after two or three polls
havebeen completed. Insuch a case, you should instruct the Message Agent
tobe 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
maybe sent.
Example
Supposethere are two remote users, named user1 and user2, and suppose
theMessage Agent command line is as follows:
dbremote -rd 30s -rp 3
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