Sybase SQL Remote DC38133-01-0902-01 User Manual
Chapter 8. SQL Remote Design for Adaptive Server Enterprise
Managing conflicts
An UPDATE conflict occurs when the following sequence of events takes
place:
place:
1. User 1 updates a row at remote site 1.
2. User 2 updates the same row at remote site 2.
3. The update from User 1 is replicated to the consolidated database.
4. The update from User 2 is replicated to the consolidated database.
When the SQL Remote Message Agent replicates UPDATE statements, it
does so as a separate UPDATE for each row. Also, the message contains the
old row values for comparison. When the update from user 2 arrives at the
consolidated database, the values in the row are not those recorded in the
message.
does so as a separate UPDATE for each row. Also, the message contains the
old row values for comparison. When the update from user 2 arrives at the
consolidated database, the values in the row are not those recorded in the
message.
UPDATE SalesRep
SET Dept=104
WHERE ID = 3
SET Dept=104
WHERE ID = 3
UPDATE SalesRep
SET Dept=103
WHERE ID = 3
SET Dept=103
WHERE ID = 3
First UPDATE
succeeds
succeeds
Second UPDATE
overwrites the
first
overwrites the
first
ID
Rep
Ann
2
1
Marc
Dept
101
101
3
Shih
102>103
ID
Rep
Ann
2
1
Marc
Dept
101
101
3
Shih
102>104
ID
Rep
Ann
2
1
Marc
Dept
101
101
3
Shih
104
Default conflict resolution
By default, the UPDATE still proceeds, so that the User 2 update (the last to
reach the consolidated database) becomes the value in the consolidated
database, and is replicated to all other databases subscribed to that row. In
general, the default method of conflict resolution is that the most recent
operation (in this case that from User 2) succeeds, and no report is made of
the conflict. The update from User 1 is lost.
reach the consolidated database) becomes the value in the consolidated
database, and is replicated to all other databases subscribed to that row. In
general, the default method of conflict resolution is that the most recent
operation (in this case that from User 2) succeeds, and no report is made of
the conflict. The update from User 1 is lost.
SQL Remote also allows custom conflict resolution, using a stored procedure
to resolve conflicts in a way that makes sense for the data being changed.
to resolve conflicts in a way that makes sense for the data being changed.
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