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SQL Anywhere 12.0.0 » SQL Remote » Managing SQL Remote systems » Improving SQL Remote performance


Sending message tasks

The SQL Remote Message Agent (dbremote) performs the following tasks to send messages:

  • Scanning the publisher transaction log   The SQL Remote Message Agent (dbremote) scans the transaction log of the publisher database and translates the transaction log entries into messages for subscribers. The maximum message length, as defined by the -l option, must be the same on all databases in the system.

    For large transactions, the SQL Remote Message Agent (dbremote) creates multi-part messages. These messages each contain a sequence number that keeps track of their place in the transaction. The SQL Remote Message Agent (dbremote) on the subscriber database uses the sequence number to ensure that the messages are applied in the correct order and that no message is lost.

  • Sending messages to the remote databases   The SQL Remote Message Agent (dbremote) sends messages at times specified by the send frequency properties of each remote user. See Adjusting the send delay.

    The SQL Remote Message Agent (dbremote) sends messages earlier if its cache memory exceeds the set value. The SQL Remote Message Agent (dbremote) stores its messages in cache memory. When the cache memory being used exceeds the specified value, messages are sent. See Adjusting throughput by caching sent messages.

  • Processing resend requests from remote databases   When a user requests that a message be resent, the SQL Remote Message Agent (dbremote) on the publisher database interrupts the regular message sending process to process the resend request.

    You control the urgency with which these resend requests are processed with the -ru option. See Adjusting how quickly resent requests are processed.

  • Sending confirmations to the publisher database   Once a message has been received and applied at the subscribed database, confirmation is sent back to the publisher. See Understanding the Guaranteed Message Delivery System.