MySQL内核分析之setFetchSize特性

1、处理流程：
2、标记位
单批次返回时，如果数据集合很大，就需要多次返回，中间采用标记位 SERVER_MORE_RESULTS_EXISTS

从命令COM_STMT_EXECUTE切换到COM_STMT_FETCH需要设置标记位：SERVER_STATUS_CURSOR_EXISTS

fetch命令字，最后一批次数据发送，需要设置标记位：SERVER_STATUS_LAST_ROW_SENT

3、验证代码：

package com.sql;
 
import java.sql.*;
 
public class ConnMySQLMain {
 
    public static void main(String[] args) throws SQLException {
        // TODO Auto-generated method stub
        System.out.println("Hello Java");
        testReadTimeout();
    }
    public static void testReadTimeout() throws SQLException { 
        System.out.println(DriverManager.getDrivers());
        Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:15307/kundb1?" +
                "continueBatchOnError=false" +
                "&useServerPrepStmts=true&alwaysSendSetIsolation=false&useLocalSessionState=true&" +
                "zeroDateTimeBehavior=CONVERT_TO_NULL&serverTimezone=UTC&useCursorFetch=true", "vt_app", "123");
        //https://jdbc.postgresql.org/documentation/head/query.html
        connection.setAutoCommit(false); //NOTE 为了设置fetchSize,必须设置为false
  
        String sql = "select * from Persons order by PersonID;";
        PreparedStatement pstmt;
        try { 
            // 决定的 Prepared类型，后面自己编程BinaryResult
            pstmt = (PreparedStatement)connection.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
           // pstmt.setFetchSize(Integer.MIN_VALUE); //setFetchSize支持后, pstmt.setFetchSize(15);
            pstmt.setFetchSize(15);  //<-------此处
            System.out.println("ps.getQueryTimeout():" + pstmt.getQueryTimeout());
            System.out.println("ps.getFetchSize():" + pstmt.getFetchSize());
            System.out.println("ps.getFetchDirection():" + pstmt.getFetchDirection());
            System.out.println("ps.getMaxFieldSize():" + pstmt.getMaxFieldSize());
  
            ResultSet rs = pstmt.executeQuery();
  
            System.out.println("============================");
            while (rs.next()) {
                System.out.print(rs.getObject(1) + " --- "+rs.getObject(2) + " ---  "+rs.getObject(3) + "  ----  "+rs.getObject(4) + " ---  "+rs.getObject(5));
                System.out.println("");
            }
            System.out.println("============================");
            rs.close();
            pstmt.close();
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //close resources
        }
    }
}