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Opening a new database connection for every query is slow and resource-heavy. A connection pool keeps a set of reusable connections ready, dramatically improving throughput.

The most popular JVM connection pool is HikariCP. The next.jdbc.connection namespace provides a helper to build a pooled datasource.

Use connection/->pool with the pool class and your db spec. The returned datasource is what you query against.

Once created, pass the pooled datasource directly to jdbc/execute! just like a plain connection. The pool checks a connection out and back automatically.

A pooled datasource is a closeable resource. Close it on shutdown to release all connections.

A transaction groups several statements so they all succeed or all fail together. This guarantees consistency, like transferring money between accounts.

next.jdbc provides with-transaction. Statements inside the body run atomically; if an exception is thrown, everything rolls back.

If any statement throws, the transaction is rolled back automatically and the exception propagates. No partial updates are committed.

You can specify an isolation level to control how concurrent transactions see each other.

• :read-committed
• :repeatable-read
• :serializable

You can force a rollback without throwing by setting the rollback flag on the connection.

In production you create one pooled datasource at startup and wrap critical multi-step writes in with-transaction. This gives both performance and integrity.

Test your transaction knowledge.

You learned to use connection pooling and transactions with next.jdbc.

• Build a pool with connection/->pool and HikariCP
• Wrap atomic writes in with-transaction
• Failures roll back automatically; choose isolation levels for concurrency