Sybase DC38133-01-0902-01 manual Requesting resends, Example, 231

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 -rpoption. This option is often used in conjunction with the -rdoption 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 -rpvalue. 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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