Transactions and batch processing

Querying a PostgreSQL Database in Java

Miller Trujillo

Staff Software Engineer

What's the problem?

Transaction: a safety net for database operations
All operations succeed or fail together

Bank transfer transaction example

The ACID properties

Atomicity: operations complete or none apply
Consistency: database stays valid
Isolation: prevents operations from interfering with each other
Durability: completed transactions persist permanently

ACID properties

By default, JDBC runs in auto-commit mode 🔄

Transaction control in JDBC

Connection conn = DriverManager.getConnection(DB_URL, USERNAME, PASSWORD)
conn.setAutoCommit(false);

try (...) {
    // Execute your SQL statements here

    conn.commit();

} catch (SQLException e) {
  conn.rollback();
}

Bank transfer example

// Reduce the sender's balance
String withdrawSQL = "UPDATE accounts SET balance = balance - ?
  WHERE account_id = ? AND balance >= ?";

// Increase the recipient's balance
String depositSQL = "UPDATE accounts SET balance = balance + ?
  WHERE account_id = ?";

UPDATE - modifies existing rows in a table
SET - specifies which columns to change

Bank transfer example

try (Connection conn = DriverManager.getConnection(DB_URL, USERNAME, PASSWORD)) {

  conn.setAutoCommit(false);

  try {
    try (PreparedStatement withdrawStmt = conn.prepareStatement(withdrawSQL);
         PreparedStatement depositStmt = conn.prepareStatement(depositSQL)) {
      // Set parameters and execute both statements...
    }

    conn.commit();

  } catch (SQLException e) {
    conn.rollback(); 
  }
}

Batch processing

Groups multiple operations together

Screenshot 2025-12-03 at 10.40.25.png

Batch processing example

PreparedStatement pstmt = conn.prepareStatement("INSERT INTO transfers
   (sender_id, recipient_id, amount) VALUES (?, ?, ?)")

for (Object[] transfer : transfers) {
  pstmt.setInt(1, (Integer) transfer[0]);
  pstmt.setInt(2, (Integer) transfer[1]); 
  pstmt.setInt(3, (Integer) transfer[2]);

  pstmt.addBatch(); // Queue for later
}

int[] results = pstmt.executeBatch(); // Send all at once

Let's practice!

Querying a PostgreSQL Database in Java