Sybase DC38133-01-0902-01 manual Who gets what?

Who gets what?

	Each time a row in a table is inserted, deleted, or updated, a message has to
	be sent to those subscribed to the row. In addition, an update may cause the
	subscription expression to change, so that the statement is sent to some
	subscribers as a delete, some as an update, and some as an insert.
	☞ For details of what statements get sent to which subscribers, see “How
	statements are replicated” on page 78 . For details on subscriptions, see the
	following two chapters.
	This section describes how SQL Remote sends the right operations to the
	right recipients.
	The task of determining who gets what is divided between the database
	server and the Message Agent. The engine handles those aspects that are to
	do with publications, while the Message Agent handles aspects to do with
	subscriptions.
Adaptive Server	Adaptive Server Anywhere evaluates the subscription expression for each
Anywhere actions	update made to a table that is part of a publication. It adds the value of the
	expression to the log, both before and after the update.
	Not the subscriber list
	Adaptive Server Enterprise does not evaluate or enter into the log a list of
	subscribers. The subscription expression (a property of the publication) is
	evaluated and entered. All handling of subscribers is left to the Message
	Agent.
	For a table that is part of more than one publication, the subscription
	expression is evaluated before and after the update for each publication.
	The addition of information to the log can affect performance in the
	following cases:
	♦ Expensive expressions When a subscription expression is expensive
	to evaluate, it can affect performance.
	♦ Many publications When a table belongs to many publications, many
	expressions must be evaluated. In contrast, the number of subscriptions is
	irrelevant.
	♦ Many-valued expressions Some expressions are many-valued. This
	can lead to much additional in formation in the transaction log, with a
	corresponding effect on performance.
Adaptive Server	In a SQL Remote for Adaptive Server Enterprise publication, the
Enterprise actions	subscription expression must be a column. The subscription column

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