LargeScan.java

package com.yugabyte.sample.apps;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.PreparedStatement;
import java.sql.Array;
import java.util.ArrayList;

public class LargeScan {

    public static void main(String[] args) throws ClassNotFoundException, SQLException, InterruptedException {
        Class.forName("org.postgresql.Driver");
        try {
            // String host = "localhost";
            String host = "172.151.24.185";

            String connect_string = "jdbc:postgresql://" + host + ":5433/yugabyte";

            // We'll use this connection to do the long-running scan.
            Connection scan_conn = DriverManager.getConnection(connect_string, "yugabyte", "yugabyte");

            System.out.println("Connected to the PostgreSQL server successfully.");

            // By default, the driver collects all results for the query at once. The JDBC driver provides
            // a means of basing a ResultSet on a database cursor and only fetching a small number of rows.
            // But to use this feature, the Connection must not be in autocommit mode.
            //
            // See documentation here https://jdbc.postgresql.org/documentation/head/query.html#query-with-cursor
            scan_conn.setAutoCommit(false);

            Statement stmt = scan_conn.createStatement();
            stmt.executeUpdate("BEGIN");

            Statement selectStmt = scan_conn.createStatement();
            selectStmt.setFetchSize(100);
            ResultSet rs = selectStmt.executeQuery("select id, ename, age, city from users");
            int rows = 0;
            while (rs.next()) {
                rows++;
                // Print every 10K rows; this is just some debug logging.
                if ((rows % 10000) == 0) {
                    System.out.println("Query returned: "+
                                       "ename=" + rs.getString(2) +
                                       ", age=" + rs.getString(3) +
                                       ", city=" + rs.getString(4));
                }
            }

            rs.close();
            System.out.println("Rows = " + rows);
            System.out.println("Closing cursor");
            scan_conn.close();

        } catch (SQLException e) {
            System.err.println("Error: " + e.getMessage());
        }
    }
}