Chapter 6. Principles of SQL Remote Design

contains either a single value or a comma-separated list of values.

Not the subscriber list

Adaptive Server Enterprise does not enter into the log a list of subscribers.

The column value is entered. All handling of subscribers is left to the

Message Agent.

When a table is marked for replication using sp_add_remote_table (which calls sp_setreplicate), Adaptive Server Enterprise places an entire before image of the row in the transaction log for deletes, and entire after image for inserts, and both images for updates. This means that the before and after values of the subscription column are available.

Message Agent actions The Message Agent reads the evaluated subscription expressions or subscription column entries from the transaction log, and matches the before and after values against the subscription value for each subscriber to the publication. In this way, the Message Agent can send the correct operations to each subscriber.

While large numbers of subscribers do not have any impact on server performance, they can impact Message Agent performance. Both the work in matching subscription values against large numbers of subscription values, and the work in sending the messages, can be demanding.

87

Page 105
Image 105
Sybase DC38133-01-0902-01 manual Principles of SQL Remote Design