HikariProxyConnection directly calls delegate.getTransactionIsolation(), causing a network call every time.

[tacascer]

Version: Hibernate 5.1

What

HikariProxyConnection.getTransactionIsolation() causes a network call everytime due to invoking delegate.getTransactionIsolation()

The method for HikariProxyConnection says:

public int getTransactionIsolation() throws SQLException {
  try {
    return super.delegate.getTransactionIsolation();
  } catch (SQLException var2) {
     throw this.checkException(var2);
  }

This causes a call to the underlying Connection.getTransactionIsolation(), which is usually a network call to the database.

Curiously, in ProxyConnection there is a similarly named method

HikariCP/src/main/java/com/zaxxer/hikari/pool/ProxyConnection.java

Lines 126 to 129 in 0a6ccdb

	final int getTransactionIsolationState()
	{
	return transactionIsolation;
	}

Which returns the cached transaction isolation level stored by Hikari.

Why is this a problem

Example: In Spring, there is a check to see if the isolation level of the transaction matches that of the connection.
https://github.com/spring-projects/spring-framework/blob/8137cc95669690f3e4055d6ccf484e98a07b6703/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/DataSourceUtils.java#L208-L218

Thank you for your valuable time and attention!

[quaff]

Which returns the cached transaction isolation level stored by Hikari.

The cached transaction isolation only available if Connection::setTransactionIsolation called, I think it could be improved here, but the network call cannot be avoided if Connection::setTransactionIsolation not called first.

HikariCP/src/main/java/com/zaxxer/hikari/pool/ProxyConnection.java

Lines 419 to 424 in 0a6ccdb

	public void setTransactionIsolation(int level) throws SQLException
	{
	delegate.setTransactionIsolation(level);
	transactionIsolation = level;
	dirtyBits |= DIRTY_BIT_ISOLATION;
	}