Timestamp   Data is downloaded only if it changed since the last download. When using timestamp-based downloads, the consolidated table must have a TIMESTAMP column to track when changes are made to rows. This can be done by adding a column to the consolidated database table or by creating a shadow table.

Shadow tables are created with the same owner as the base table. A shadow table is a separate table that contains the primary key columns of the table being synchronized along with a timestamp that indicates the last time the row was changed.

When you choose Timestamp, the necessary objects are generated for you when you deploy the model. See Implementing timestamp-based downloads.

Snapshot   All data in the consolidated table is downloaded in every synchronization, even if it has already been downloaded. See Snapshot synchronization

Custom   Write your own download logic to select the rows to be downloaded. If you choose this option, you must write the download_cursor and download_delete_cursor scripts. You can do this on the Events tab. See download_cursor scripts and download_delete_cursor scripts.

Use a column default instead of a trigger   Select this option to use a column default instead of a trigger to update the value in the timestamp column.

Column defaults are not available on all consolidated databases. When they are available, they provide better performance than using triggers. However, using triggers makes it more difficult to accidentally update the timestamp column.