What must happen for global transactions to be executed across multiple databases?

For global transactions to be executed across multiple databases, the databases must be configured with a distributed system. This setup is essential because global transactions involve coordinating multiple resource managers (like different databases) to ensure that a transaction is executed as a single, atomic operation across all participants.

In a distributed system configuration, mechanisms like two-phase commit protocol can be utilized. This approach allows the system to manage and ensure data consistency across all databases involved in the transaction. It helps in coordinating the commitment of the transaction so that either all databases commit the transaction or none do, thus maintaining data integrity.

This principle is crucial for applications that require transactions spanning different systems or databases, and without this configuration, executing global transactions effectively would be impossible.