Java.HikariCP.Explain the role of keepaliveTime and when to use it

Answer:
🔹 What is keepaliveTime?
The keepaliveTime setting in HikariCP specifies how often idle connections should be proactively pinged (validated) to keep them alive.

If a connection sits idle longer than keepaliveTime, HikariCP will run a lightweight validation (using isValid() or your connectionTestQuery) on it.

🔹 Why is it important?
Some databases, proxies, or firewalls (e.g., AWS RDS, load balancers) may silently close idle connections after a period of inactivity (e.g., 5 or 10 minutes).

• When this happens, your app could get stale or broken connections from the pool, resulting in errors like Connection reset or SocketException on first use.
• By proactively sending keepalive pings, HikariCP prevents idle connections from becoming stale, ensuring your app always receives a valid, ready-to-use connection.

🔹 When should you use it?

• If you know your database, proxy, or network infrastructure has short idle connection timeouts (e.g., AWS ALB closes idle connections after 5 minutes).
• When you observe intermittent Communications link failure or Connection reset errors on the first query after a period of inactivity.
• Best practice is to set keepaliveTime shorter than the known idle timeout of your DB/network.

🔹 Example configuration:

spring.datasource.hikari.keepalive-time=300000  # 5 minutes in milliseconds

✅ Key point:
Unlike idleTimeout, which closes idle connections, keepaliveTime keeps them alive by periodically validating them — helping avoid unexpected connection errors.