✅ When you close a connection in your code, does the connection return to the pool?
Answer:
Yes — that’s exactly how connection pooling works.
🔹 How it works in HikariCP (and other connection pools):
- When you call
connection.close()on aConnectionobject you obtained from the pool, the connection isn’t actually closed at the database level. - Instead, HikariCP intercepts the close() call through a proxy object, marks the connection as idle, and returns it to the pool so it can be reused for the next request.
🔹 Why it’s important:
- Because physically closing and reopening database connections is expensive (slow), the pool keeps the connection alive and simply gives it to other threads when needed.
- This reuse of connections is what makes connection pools performant and scalable.
🔹 What happens if you don’t call close()?
- The connection stays marked as active in the pool, and never becomes available to other threads → over time, this can exhaust the pool, leading to timeouts or errors.
✅ Key takeaway:
Always close your connections in a finally block (or use try-with-resources) to ensure they return to the pool — you’re not shutting down the connection, you’re giving it back for reuse.