Automatic session cleanup process with TTL (Time-To-Live) support.

This GenServer runs in the background and periodically cleans up expired session processes based on their last activity time. This prevents memory leaks from abandoned sessions and ensures efficient resource utilization.

How It Works

Cleanup Strategy

• Runs cleanup tasks every 60 seconds (@cleanup_interval)
• Checks all active session processes for expiration
• Terminates sessions that have exceeded their TTL
• Emits telemetry events for monitoring cleanup operations

TTL Calculation

Each session process tracks its last activity timestamp. The cleanup process:

1. Gets the configured TTL from Phoenix.SessionProcess.Config.session_ttl()
2. Calculates the expiration threshold (current_time - TTL)
3. Compares each session's last activity against the threshold
4. Terminates sessions that have been inactive longer than TTL

Configuration

The cleanup process respects the TTL configuration:

config :phoenix_session_process,
  session_ttl: :timer.hours(2)  # Sessions expire after 2 hours

Performance Considerations

Memory Efficiency

• Prevents memory accumulation from abandoned sessions
• Releases resources back to the system
• Maintains optimal memory usage patterns

Performance Impact

• Cleanup runs in the background without blocking requests
• Uses efficient registry operations for session discovery
• Minimal impact on active session performance

Scalability

• Handles thousands of concurrent sessions efficiently
• Cleanup time scales linearly with active session count
• Can be tuned for different deployment scales

Telemetry

The cleanup process emits several telemetry events:

• [:phoenix, :session_process, :cleanup] - Cleanup cycle completed
• [:phoenix, :session_process, :cleanup_error] - Cleanup operation failed
• [:phoenix, :session_process, :session_expired] - Individual session expired

Monitoring

You can monitor cleanup performance through telemetry events. See the Telemetry section above for available events.

Example handler setup is documented in the telemetry module.

Error Handling

• Session process termination failures are logged but don't stop cleanup
• Registry lookup errors are handled gracefully
• Continuous operation ensures consistent cleanup performance

Integration

This process is automatically started by the top-level supervisor and requires no manual intervention or configuration beyond setting the desired TTL.