Postgresql Postgres 9.6.17和JDBC 42.2.1如何将连接模式切换到'；扩展的'；

我有一个Postgres9.6.17DBMS和一个简单的Java独立程序（没有Spring），它连接到DBMS并发出查询。根据Postgres文档，查询可以在“简单模式”或“扩展模式”（解析和查询重写一次完成）下执行，但绑定会重复进行

我有一个简单的表

customer（cust\u id integer，first\u name varchar（100），last\u name varchar（100））

。我正在执行的代码如下所示：

Properties props = new Properties();
....//typical properties such as user, password, database etc
props.setProperty("preferQueryMode", "extendedForPrepared");
Connection con = DriverManager.getConnection(url, props);
PreparedStatement st = con.prepareStatement("select * from ecommerce.customer where cust_id = ?");
st.setInt(1, 22);
ResultSet rs = st.executeQuery();    

我希望这将在JDBC客户机和DBMS后端之间产生一个“扩展查询模式”协议。但它始终产生一种“简单查询模式”交互。我通过为postgres驱动程序启用JDBC日志来验证这一点。我还研究了JDBC驱动程序中

Query

接口的实现，我能找到的只有以下3种实现：

Properties props = new Properties();
....//typical properties such as user, password, database etc
props.setProperty("preferQueryMode", "extendedForPrepared");
Connection con = DriverManager.getConnection(url, props);
PreparedStatement st = con.prepareStatement("select * from ecommerce.customer where cust_id = ?");
st.setInt(1, 22);
ResultSet rs = st.executeQuery();    

BatchedQuery

CompositeQuery

SimpleQuery

尽管名称为

CompositeQuery

，它所做的只是将涉及多个语句的查询拆分为

SimpleQuery

对象列表

---

所以我的问题是，我该怎么做才能让我的连接使用扩展模式的协议

默认情况下，Postgres JDBC驱动程序仅在准备好的语句使用5次后才开始使用服务器端语句。从：

prepareThreshold=int

在切换到使用服务器端准备语句之前，确定所需的PreparedStatement执行次数。默认值为5，这意味着在同一PreparedStatement对象的第五次执行时开始使用服务器端准备的语句。有关服务器端准备语句的更多信息，请参阅“服务器准备语句”一节

但这种属性是可以改变的

这是我测试的程序：

Properties props = new Properties();
props.setProperty("user", "test");
props.setProperty("password", "test");
props.setProperty("loggerLevel", "TRACE");
props.setProperty("prepareThreshold", "1");
try (Connection con = DriverManager.getConnection("jdbc:postgresql:test", props);
     PreparedStatement stat = con.prepareStatement("select * from app_user where username = ?"))
{
    for (String username : List.of("user1", "user2", "user3"))
    {
        stat.setString(1, username);
        try (ResultSet rs = stat.executeQuery())
        {
            if (rs.next())
                System.out.println("User " + username + " has ID: " + rs.getString(1));
        }
    }
}

---

当

prepareThreshold

设置为

1

时，日志显示：

Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@33065d67, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendParse
FINEST:  FE=> Parse(stmt=S_1,query="select * from app_user where username = $1",oids={1043})
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user1'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendDescribePortal
FINEST:  FE=> Describe(portal=null)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)
...
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@35dab4eb, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user2'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)
...
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@2d901eb0, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user3'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)

Feb 18, 2020 2:06:19 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@33065d67, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:19 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user1'")
...
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@28261e8e, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user2'")
...
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@d737b89, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user3'")

其中有3个单独的语句解析和绑定。然而，在5次查询之后，它们应该开始被重用

---

关于“简单”与“扩展”的查询模式，看起来日志总是打印出“简单执行”，但区别在于真正的简单模式参数不会绑定在准备语句中，而是整个查询将作为文本发送。在此示例中，如果

preferQueryMode

属性设置为

simple

，则日志显示：

Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@33065d67, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendParse
FINEST:  FE=> Parse(stmt=S_1,query="select * from app_user where username = $1",oids={1043})
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user1'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendDescribePortal
FINEST:  FE=> Describe(portal=null)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)
...
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@35dab4eb, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user2'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)
...
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@2d901eb0, maxRows=0, fetchSize=0, flags=16
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendBind
FINEST:  FE=> Bind(stmt=S_1,portal=null,$1=<'user3'>)
Feb 18, 2020 1:56:59 PM org.postgresql.core.v3.QueryExecutorImpl sendExecute
FINEST:  FE=> Execute(portal=null,limit=0)

Feb 18, 2020 2:06:19 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@33065d67, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:19 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user1'")
...
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@28261e8e, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user2'")
...
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl execute
FINEST:   simple execute, handler=org.postgresql.jdbc.PgStatement$StatementResultHandler@d737b89, maxRows=0, fetchSize=0, flags=1,041
Feb 18, 2020 2:06:20 PM org.postgresql.core.v3.QueryExecutorImpl sendSimpleQuery
FINEST:  FE=> SimpleQuery(query="select * from app_user where username = 'user3'")

请注意这与默认值之间的差异-没有参数，“user1”、“user2”和“user3”值与每个查询一起内联发送

---

我认为您真正需要的是立即重用服务器端语句并重新绑定参数。在这种情况下，将

prepareThreshold

设置为

1

将完成此工作