Follower Read

In Java, to enable Follower Read, define a FollowerReadHelper class.

public enum FollowReadMode {
    LEADER("leader"),
    FOLLOWER("follower"),
    LEADER_AND_FOLLOWER("leader-and-follower");

    private final String mode;

    FollowReadMode(String mode) {
        this.mode = mode;
    }

    public String getMode() {
        return mode;
    }
}

public class FollowerReadHelper {

    public static void setSessionReplicaRead(Connection conn, FollowReadMode mode) throws SQLException {
        if (mode == null) mode = FollowReadMode.LEADER;
        PreparedStatement stmt = conn.prepareStatement(
            "SET @@tidb_replica_read = ?;"
        );
        stmt.setString(1, mode.getMode());
        stmt.execute();
    }

    public static void setGlobalReplicaRead(Connection conn, FollowReadMode mode) throws SQLException {
        if (mode == null) mode = FollowReadMode.LEADER;
        PreparedStatement stmt = conn.prepareStatement(
            "SET GLOBAL @@tidb_replica_read = ?;"
        );
        stmt.setString(1, mode.getMode());
        stmt.execute();
    }

}

When reading data from the Follower node, use the setSessionReplicaRead(conn, FollowReadMode.LEADER_AND_FOLLOWER) method to enable the Follower Read feature, which can balance the load between the Leader node and the Follower node in the current session. When the connection is disconnected, it will be restored to the original mode.

public static class AuthorDAO {

    // Omit initialization of instance variables...

    public void getAuthorsByFollowerRead() throws SQLException {
        try (Connection conn = ds.getConnection()) {
            // Enable the follower read feature.
            FollowerReadHelper.setSessionReplicaRead(conn, FollowReadMode.LEADER_AND_FOLLOWER);

            // Read the authors list for 100000 times.
            Random random = new Random();
            for (int i = 0; i < 100000; i++) {
                Integer birthYear = 1920 + random.nextInt(100);
                List<Author> authors = this.getAuthorsByBirthYear(birthYear);
                System.out.println(authors.size());
            }
        }
    }

    public List<Author> getAuthorsByBirthYear(Integer birthYear) throws SQLException {
        List<Author> authors = new ArrayList<>();
        try (Connection conn = ds.getConnection()) {
            PreparedStatement stmt = conn.prepareStatement("SELECT id, name FROM authors WHERE birth_year = ?");
            stmt.setInt(1, birthYear);
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                Author author = new Author();
                author.setId( rs.getLong("id"));
                author.setName(rs.getString("name"));
                authors.add(author);
            }
        }
        return authors;
    }
}