FileHandler vs DatabaseHandler for CodeIgniter 4 Session Persistence

When deploying a CodeIgniter 4 application across a load-balanced cluster, session persistence depends on the chosen driver in Config\Session. The framework provides distinct behaviors for local and shared storage.

Storage Trade-offs

• FileHandler: Writes session data to a local writable directory. This minimizes database overhead and offers high performance for single-server setups.
• DatabaseHandler: Stores session records in a centralized table, allowing any server node in the cluster to retrieve the user state.

The decision involves balancing the I/O speed of the local filesystem against the network latency and query overhead of a shared database. Using the file driver in a multi-node environment without a shared network filesystem leads to session fragmentation.

Which driver is most sustainable for high-traffic environments where horizontal scaling is required? Under what specific load conditions does the database overhead outweigh the benefits of session persistence?