Track current transaction isolation level so that we can reset it only when necessary (as it often requires a round trip to the server).

src/main/java/com/zaxxer/hikari/HikariPool.java

@@ -325,20 +325,19 @@ public final class HikariPool implements HikariPoolMBean
             try
             {
                 Connection connection = dataSource.getConnection();
-                IHikariConnectionProxy proxyConnection = (IHikariConnectionProxy) ProxyFactory.getProxyConnection(this, connection);
+                
-
+                connection.setAutoCommit(isAutoCommit);
                 if (transactionIsolation < 0)
                 {
                     transactionIsolation = connection.getTransactionIsolation();
                 }
-                
+                else
-                boolean alive = isConnectionAlive(proxyConnection, configuration.getConnectionTimeout());
-                if (!alive)
                 {
-                    // This will be caught below...
+                    connection.setTransactionIsolation(transactionIsolation);
-                    throw new RuntimeException("Connection not alive, retry.");
                 }
 
+                IHikariConnectionProxy proxyConnection = (IHikariConnectionProxy) ProxyFactory.getProxyConnection(this, connection, transactionIsolation);
+
                 String initSql = configuration.getConnectionInitSql();
                 if (initSql != null && initSql.length() > 0)
                 {

src/main/java/com/zaxxer/hikari/proxy/ConnectionProxy.java

@@ -46,6 +46,7 @@ public abstract class ConnectionProxy implements IHikariConnectionProxy
     private boolean isClosed;
     private boolean forceClose;
     private boolean isTransactionIsolationDirty;
+    private int currentIsolationLevel;
     
     private final long creationTime;
     private volatile long lastAccess;
@@ -64,14 +65,14 @@ public abstract class ConnectionProxy implements IHikariConnectionProxy
         SQL_ERRORS.add("01002");  // SQL92 disconnect error
     }
 
-    protected ConnectionProxy(HikariPool pool, Connection connection)
+    protected ConnectionProxy(HikariPool pool, Connection connection, int defaultIsolationLevel)
     {
         this.parentPool = pool;
         this.delegate = connection;
+        this.currentIsolationLevel = defaultIsolationLevel;
 
         creationTime = lastAccess = System.currentTimeMillis();
         openStatements = new FastStatementList();
-        isTransactionIsolationDirty = true;
     }
     
     public final void unregisterStatement(Object statement)
@@ -418,7 +419,8 @@ public abstract class ConnectionProxy implements IHikariConnectionProxy
         try
         {
             delegate.setTransactionIsolation(level);
-            isTransactionIsolationDirty = true;
+            isTransactionIsolationDirty |= (currentIsolationLevel == level);
+            currentIsolationLevel = level;
         }
         catch (SQLException e)
         {

src/main/java/com/zaxxer/hikari/proxy/ProxyFactory.java

@@ -31,7 +31,7 @@ import com.zaxxer.hikari.HikariPool;
  */
 public final class ProxyFactory
 {
-    public static Connection getProxyConnection(HikariPool pool, Connection connection)
+    public static Connection getProxyConnection(HikariPool pool, Connection connection, int defaultIsolationLevel)
     {
         // Body is injected by JavassistProxyFactory
         return null;