The Download Type tab lets you decide how the rows downloaded to the remote database are chosen. The tab shows the following information for the selected table:
Download Type Choose one of the following download types from the dropdown list.
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.
The following options are only available if Timestamp is chosen for the download type.
Timestamp column name Specify the name of the column to be used to track the last time each row was changed.
Use timestamp columns in consolidated table Select this option to add a TIMESTAMP column to the consolidated table if the TIMESTAMP column does not already exist.
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.
Use shadow table to hold timestamp column Select this option to create a shadow table for the synchronized consolidated database table. The shadow table contains the TIMESTAMP column used to keep track of when each row was last modified. Shadow tables are created with the same owner as the base table.
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