To facilitate record referencing and synchronization between Sales Cloud and an external database, the best practice is to use a custom External ID field. This field can be mapped directly to the unique record ID from the source database. External ID fields in Salesforce are specifically designed for integrating with external systems, allowing efficient data cross-referencing and deduplication.

Using a custom External ID field ensures that the migrated records maintain a unique identifier that matches the original source, simplifying future synchronization and data management tasks. This setup is especially useful when dealing with large volumes of data, as in the case of Cloud Kicks, which has migrated 70 million records. This method is preferable over a standard External ID, as it offers flexibility in defining the exact field and data type to meet Cloud Kicks ' specific requirements.