`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 https://github.com/brettwooldridge/HikariCP/blob/0a6ccdb334b2ecde25ae090034669d534736a0de/src/main/java/com/zaxxer/hikari/pool/ProxyConnection.java#L126-L129

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.

https://github.com/brettwooldridge/HikariCP/blob/0a6ccdb334b2ecde25ae090034669d534736a0de/src/main/java/com/zaxxer/hikari/pool/ProxyConnection.java#L419-L424