Manual sync allows you to manually initiate the synchronization process when needed, typically by a user or an administrator. Since Appian won't be making updates to the source database table, there's no need for frequent or automatic synchronization. Instead, you can trigger the synchronization as necessary, which provides greater control over the process and doesn't require automatic, periodic synchronization like the other options (Hourly Sync, Daily Sync, and Immediate Sync).

If data sync is enabled, Appian will Sync all of your source data once each day at the specified time - this is the default configuration in appian. Manual configuration is not a correct answer at all

that's an awful logic by nyxxx. my record need to be in sync with hourly changes that happen in source db. how should i do it?

The most appropriate data sync option in this situation would be B. Manual Sync, since Appian cannot write updates to the source database table and therefore, it would not make sense to schedule a regular automatic sync. Instead, the sync should be initiated manually by an authorized user when necessary.