diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/GetTableDetails.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/GetTableDetails.java
index 02ec87f..91eda20 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/GetTableDetails.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/GetTableDetails.java
@@ -88,7 +88,7 @@ public class GetTableDetails extends StandardLocalExternalAlgorithm {
 			List<String> Info = retrieveInfo();
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// get table's details
 
@@ -97,9 +97,6 @@ public class GetTableDetails extends StandardLocalExternalAlgorithm {
 
 			map = getDetails();
 
-			// close the connection
-			sf.close();
-
 		} catch (HibernateException h) {
 
 			AnalysisLogger.getLogger().debug(
@@ -146,11 +143,8 @@ public class GetTableDetails extends StandardLocalExternalAlgorithm {
 			throw e4;
 
 		} finally {
-
-			if (sf!=null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
-
+			// close the connection
+			mgt.closeConnection();
 		}
 
 	}
@@ -188,7 +182,7 @@ public class GetTableDetails extends StandardLocalExternalAlgorithm {
 	}
 
 	// create the database's connection
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -200,15 +194,12 @@ public class GetTableDetails extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
 		AnalysisLogger.getLogger().debug(
 				"In GetTableDetails->database " + DatabaseName + ": connected");
-
-		return sf;
-
 	}
 
 	// Method that recover the info useful for the connection
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListSchemas.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListSchemas.java
index 439ddc8..3ab6410 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListSchemas.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListSchemas.java
@@ -82,7 +82,7 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 			List<String> Info = retrieveInfo();
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// get the schema's list
 
@@ -112,8 +112,6 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 
 			}
 
-			sf.close();
-
 		} catch (HibernateException h) {
 
 			AnalysisLogger.getLogger().debug(
@@ -163,13 +161,9 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 			throw e4;
 
 		} finally {
-
-			if (sf != null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
-
+			// close the connection
+			mgt.closeConnection();
 		}
-
 	}
 
 	@Override
@@ -223,13 +217,11 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 
 		}
 
-		finally {
-
-			if (sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
-
-		}
+//		finally {
+//			if (sf.isClosed() == false) {
+//				mgt.closeConnection();
+//			}
+//		}
 
 		return listSchemas;
 
@@ -418,7 +410,7 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 	}
 
 	// method that allows to create the connection
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -430,7 +422,7 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
@@ -439,9 +431,6 @@ public class ListSchemas extends StandardLocalExternalAlgorithm {
 		// AnalysisLogger.getLogger().debug("In ListSchemas->database "+DatabaseName+": connected");
 
 		// }
-
-		return sf;
-
 	}
 
 	private void normalizeDBInfo(DBResource resource) throws Exception {
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListTables.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListTables.java
index 99c0908..cc46fd6 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListTables.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/ListTables.java
@@ -83,7 +83,7 @@ public class ListTables extends StandardLocalExternalAlgorithm {
 			List<String> Info = retrieveInfo();
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// get the table' list
 
@@ -154,9 +154,6 @@ public class ListTables extends StandardLocalExternalAlgorithm {
 				}
 			}
 
-			// close the connection
-			sf.close();
-
 		} catch (HibernateException h) {
 
 			AnalysisLogger.getLogger().debug(
@@ -203,13 +200,9 @@ public class ListTables extends StandardLocalExternalAlgorithm {
 			throw e4;
 
 		} finally {
-
-			if (sf != null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
-
+			// close the connection
+			mgt.closeConnection();
 		}
-
 	}
 
 	@Override
@@ -408,7 +401,7 @@ public class ListTables extends StandardLocalExternalAlgorithm {
 
 	}
 
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -420,15 +413,12 @@ public class ListTables extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
 		AnalysisLogger.getLogger().debug(
 				"In ListTables->database " + DatabaseName + ": connected");
-
-		return sf;
-
 	}
 
 	private void normalizeDBInfo(DBResource resource) throws Exception {
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/RandomSampleOnTable.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/RandomSampleOnTable.java
index eae9e44..c229ace 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/RandomSampleOnTable.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/RandomSampleOnTable.java
@@ -101,13 +101,11 @@ public class RandomSampleOnTable extends StandardLocalExternalAlgorithm {
 			}
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// smart sample operation on table
 			map = randomSampleOnTable();
-
-			// close the connection
-			sf.close();
+			
 		} catch (HibernateException h) {
 			AnalysisLogger.getLogger().debug(
 					"In RandomSmartSampleOnTable-> ERROR " + h.getMessage());
@@ -148,9 +146,7 @@ public class RandomSampleOnTable extends StandardLocalExternalAlgorithm {
 
 		} finally {
 			// close the connection
-			if (sf != null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
+			mgt.closeConnection();
 		}
 	}
 
@@ -314,7 +310,7 @@ public class RandomSampleOnTable extends StandardLocalExternalAlgorithm {
 	}
 
 	// create the database's connection
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -326,7 +322,7 @@ public class RandomSampleOnTable extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
@@ -334,8 +330,6 @@ public class RandomSampleOnTable extends StandardLocalExternalAlgorithm {
 				"In RandomSampleOnTable->database " + DatabaseName
 						+ ": connected");
 
-		return sf;
-
 	}
 
 	// to perform the sample operation on the table randomly
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SampleOnTable.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SampleOnTable.java
index 937ef2d..8c0052e 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SampleOnTable.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SampleOnTable.java
@@ -99,14 +99,11 @@ public class SampleOnTable extends StandardLocalExternalAlgorithm {
 			}
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// sample operation on table
 			map = sampleOnTable();
-
-			// close the connection
-			sf.close();
-
+			
 		} catch (HibernateException h) {
 			AnalysisLogger.getLogger().debug(
 					"In SampleOnTable-> ERROR " + h.getMessage());
@@ -146,9 +143,7 @@ public class SampleOnTable extends StandardLocalExternalAlgorithm {
 
 		} finally {
 			// close the connection
-			if (sf!=null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
+			mgt.closeConnection();
 		}
 	}
 
@@ -314,7 +309,7 @@ public class SampleOnTable extends StandardLocalExternalAlgorithm {
 	}
 
 	// create the database's connection
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -326,14 +321,12 @@ public class SampleOnTable extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
 		AnalysisLogger.getLogger().debug(
 				"In SampleOnTable->database " + DatabaseName + ": connected");
-
-		return sf;
 	}
 
 	// to perform the sample operation on the table
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SmartSampleOnTable.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SmartSampleOnTable.java
index a8513a9..e70f2b2 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SmartSampleOnTable.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SmartSampleOnTable.java
@@ -101,13 +101,11 @@ public class SmartSampleOnTable extends StandardLocalExternalAlgorithm {
 			}
 
 			// create the connection
-			sf = getConnection(Info);
+			getConnection(Info);
 
 			// smart sample operation on table
 			map = smartSampleOnTable();
-
-			// close the connection
-			sf.close();
+		
 		} catch (HibernateException h) {
 			AnalysisLogger.getLogger().debug(
 					"In SmartSampleOnTable-> ERROR " + h.getMessage());
@@ -146,10 +144,7 @@ public class SmartSampleOnTable extends StandardLocalExternalAlgorithm {
 			throw e4;
 
 		} finally {
-			// close the connection
-			if (sf!=null && sf.isClosed() == false) {
-				mgt.closeConnection();
-			}
+			mgt.closeConnection();
 		}
 	}
 
@@ -315,7 +310,7 @@ public class SmartSampleOnTable extends StandardLocalExternalAlgorithm {
 	}
 
 	// create the database's connection
-	private SessionFactory getConnection(List<String> Info) throws IOException {
+	private void getConnection(List<String> Info) throws IOException {
 
 		// create the connection
 		Iterator<String> iterator = Info.iterator();
@@ -327,15 +322,14 @@ public class SmartSampleOnTable extends StandardLocalExternalAlgorithm {
 		String DatabaseURL = iterator.next();
 		String DatabaseName = iterator.next();
 
-		SessionFactory sf = mgt.createConnection(DatabaseUserName,
+		mgt.createConnection(DatabaseUserName,
 				DatabasePassword, DatabaseDriver, DatabaseDialect, DatabaseURL,
 				DatabaseName);
 
 		AnalysisLogger.getLogger().debug(
 				"In SmartSampleOnTable->database " + DatabaseName
 						+ ": connected");
-		return sf;
-	}
+		}
 
 	// to perform the sample operation on the table
 	private LinkedHashMap<String, StatisticalType> smartSampleOnTable()
diff --git a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SubmitQuery.java b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SubmitQuery.java
index 6695145..6e0ded8 100644
--- a/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SubmitQuery.java
+++ b/src/main/java/org/gcube/dataaccess/algorithms/drmalgorithms/SubmitQuery.java
@@ -122,8 +122,8 @@ public class SubmitQuery extends StandardLocalExternalAlgorithm {
 			// submit a query
 			map = submitQuery();
 
-			// close the connection
-			dbconnection.close();
+//			// close the connection
+//			dbconnection.close();
 
 		} catch (HibernateException h) {
 
@@ -181,8 +181,10 @@ public class SubmitQuery extends StandardLocalExternalAlgorithm {
 			throw e4;
 
 		} finally {
-			if (dbconnection!=null && dbconnection.isClosed() == false) {
+			if (dbconnection!=null) {
 				dbconnection.close();
+				AnalysisLogger.getLogger().debug("In SubmitQuery-> Connection closed");
+				dbconnection=null;
 			}
 			//remove the timer if the execution query has already terminated
 			if (stopper!=null){
@@ -295,8 +297,10 @@ public class SubmitQuery extends StandardLocalExternalAlgorithm {
 				
 		AnalysisLogger.getLogger().debug("In SubmitQuery->Shutdown");
 		try{
-		if (dbconnection!=null && dbconnection.isClosed() == false) {
+		if (dbconnection!=null) {
 			dbconnection.close();
+			AnalysisLogger.getLogger().debug("In SubmitQuery-> Connection closed");
+			dbconnection=null;
 		}
 		}catch(Exception e){
 			AnalysisLogger.getLogger().debug("In SubmitQuery->Unable to close connection "+e.getMessage());