The progress offset is an integer value that indicates the point in time up to which all operations for the subscription have been uploaded and acknowledged. The dbmlsync utility uses the offset to decide what data to upload. On the remote database, the offset is stored in the progress column of the SYS.ISYSSYNC system table. On the consolidated database, the offset is stored in the progress column of the ml_subscription table.

For each remote, the remote and consolidated databases maintain an offset for every subscription. When a MobiLink user synchronizes, the offsets are confirmed for all subscriptions that are associated with the MobiLink user, even if they are not being synchronized at the time. This is required because more than one publication can contain the same data. The only exception is that dbmlsync does not check the progress offset of a subscription until it has attempted an upload.

If there is any disagreement between the remote and consolidated database offsets, the default behavior is to update the offsets on the remote database with values from the consolidated database and then send a new upload based on those offsets. In most cases, this default is appropriate. For example, it is generally appropriate when the consolidated database is restored from backup and the remote transaction log is intact, or when an upload is successful but communication failure prevented an upload acknowledgement from being sent.

Most progress offset mismatches are resolved automatically using the consolidated progress values. In the rare case that you must intervene to fix a problem with progress offsets, you can use the dbmlsync -r option.

For more information, see -r option.

First synchronization always works

The first time you attempt to synchronize a newly created subscription, the progress offsets for the subscription are not checked against those on the consolidated database. This feature allows a remote database to be recreated and synchronized without having to delete its state information, which is maintained in the consolidated database.

The dbmlsync utility detects a first synchronization when the columns in the remote database system table SYS.ISYSSYNC are as follows: the value for the progress column is the same as the value for the created column, and the value for the log_sent column is null.

However, when you synchronize two or more subscriptions in the same upload, and one of the subscriptions is not synchronizing for the first time, then progress offsets are checked for all subscriptions being synchronized, including the ones that are being synchronized for the first time. For example, if you specify the dbmlsync -n option with two publications (-n pub1,pub2), and pub1 has synchronized before but pub2 has not, then the progress offsets of both subscriptions are checked against the consolidated database values.

For more information, see:

• ISYSSYNC system table
• ml_subscription
• Transaction log files