What is a Connection in JDBC?

Question

What is a Connection Object in JDBC ? How is this Connection maintained(I mean is it a Network connection) ? Are they TCP/IP Connections ? Why is it a costly operation to create a Connection every time ? Why do these connections become stale after sometime and I need to refresh the Pool ? Why can't I use one connection to execute multiple queries ?

Answer 1

These connections are TCP/IP connections. To not have to overhead of creating every time a new connection there are connection pools that expand and shrink dynamically. You can use one connection for multiple queries. I think you mean that you release it to the pool. If you do that you might get back the same connection from the pool. In this case it just doesn't matter if you do one or multiple queries

The cost of a connection is to connect which takes some time. ANd the database prepares some stuff like sessions, etc for every connection. That would have to be done every time. Connections become stale through multiple reasons. The most prominent is a firewall in between. Connection problems could lead to connection resetting or there could be simple timeouts

Answer 2

To add to the other answers:

Yes, you can reuse the same connection for multiple queries. This is even advisable, as creating a new connection is quite expensive.

You can even execute multiple queries concurrently. You just have to use a new java.sql.Statement/PreparedStatement instance for every query. Statements are what JDBC uses to keep track of ongoing queries, so each parallel query needs its own Statement. You can and should reuse Statements for consecutive queries, though.