What is the recommended solution to avoid time-out errors when migrating order lines?

Utilizing an External ID from source orders is a highly effective solution to mitigate time-out errors during the migration of order lines. External IDs provide a unique identifier from an external system that can be used to link Salesforce records with records in other databases. This facilitates a more efficient data import process, particularly when dealing with large volumes of data.

By using External IDs, Salesforce can perform upserts, which means it can either insert new records or update existing ones based on the presence of the External ID. This method is generally faster than traditional inserts and helps in reducing the likelihood of time-out errors, especially when multiple order lines are being processed in bulk.

In contrast, other available strategies might not sufficiently address performance challenges or could complicate the migration process. For instance, querying only indexed ID field values could limit the scope of the data being accessed, while leveraging Batch Apex would add complexity to the process. Similarly, employing a sequence of numbers might not provide a reliable link to external data, thus making it less effective than using External IDs.