Redundant "Reset stmt" before "Execute" when setting useServerPrepStmts and cachePrepStmts to true in MySQL Connector/J

Question

I'm using MySQL Connector/J (version 8.0.28) as the driver on client side. Following is part of my code for test purpose:

PreparedStatement ps = null;
String url = "jdbc:mysql://10.86.49.16:3306/test?useServerPrepStmts=true&cachePrepStmts=true";
...
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, user, password);
String sql = "select * from test where id=?";
for (int i = 1; i <= 3; i++) {
    ps = conn.prepareStatement(sql);
    ps.setInt(1, i);
    ps.execute();
    ps.close();
}

When setting "useServerPrepStmts=true" alone, my general log looks like this:

6 Prepare   select * from test where id=?
6 Execute   select * from test where id=1
6 Close stmt
6 Prepare   select * from test where id=?
6 Execute   select * from test where id=2
6 Close stmt
6 Prepare   select * from test where id=?
6 Execute   select * from test where id=3
6 Close stmt

However after enabling "cachePrepStmts" together, the log becomes:

7 Prepare   select * from test where id=?
7 Execute   select * from test where id=1
7 Reset stmt
7 Execute   select * from test where id=2
7 Reset stmt
7 Execute   select * from test where id=3

Looks like the prepared statement cache does take effect but there're unexpected "Reset stmt" which cause extra round-trips. I've checked the source code of MySQL Connector/J and found a strange logic executed when closing the prepared statement. It will always set longParameterSwitchDetected to true in my case!

com.mysql.cj.ServerPreparedQuery#clearParameters

/**
 * @param clearServerParameters
 *            flag indicating whether we need an additional clean up
 */
public void clearParameters(boolean clearServerParameters) {
    boolean hadLongData = false;
    if (this.queryBindings != null) {
        hadLongData = this.queryBindings.clearBindValues();
        this.queryBindings.setLongParameterSwitchDetected(clearServerParameters && hadLongData ? false : true);
    }
    ...
}

Then when next "Execute" comes, it will check this flag and decide whether to send "Reset stmt" or not as shown below:

com.mysql.cj.ServerPreparedQuery#prepareExecutePacket

public NativePacketPayload prepareExecutePacket() {
    ServerPreparedQueryBindValue[] parameterBindings = this.que
    if (this.queryBindings.isLongParameterSwitchDetected()) {
        ...
        // Okay, we've got all "newly"-bound streams, so reset server-side state to clear out previous bindings
        serverResetStatement();
    }
    ...
}

I've tried to set this longParameterSwitchDetected manually to false in debug mode and the statement executed successfully without sending the "Reset stmt". So here're my questions:

1. Are there any configurations for removing this "Reset stmt"?
2. What's the exact meaning/logic of this "longParameterSwitchDetected"?

Answer 1

This turns out to be a code bug in MySQL Connector/J after reaching out to the authors. I've already reported the bug to the community. See https://bugs.mysql.com/bug.php?id=107107