Solution : https://service.sap.com/sap/support/notes/866725 (SAP Service marketplace login required)
Key words : 
db2/db6 jdbc driver issue, fully materialized lob data objects, fully materialize lob data, disable data source property, locator-based lob implementation, bootstrap jvm heap size, engine bootstrap log files, max heap size, engine log files, <instance_dir>/work directory
Related Notes : 
       
| 1160166 | DB6: Add. Information - SAP Enhancement Package Installer | 
| 922454 | Add. info. on upgrading to SAP SCM 5.0 SR1 Java | 
| 918921 | Add. info. on upgrading to SAP ERP Java Components 6.0 SR1 | 
| 918849 | Add. info. on upgrading to SAP CRM Java Comp. 5.0 SR1 | 
| 913972 | Add. info. on upgrading to SAP NW 7.0 SR1 Java | 
| 836198 | Add. info. on upgrading to SAP NW 7.0 Java | 
| 819876 | DB6: Additional info about upgrade (based) on SAP NW AS 7.0 | 
| 784568 | DB6: fullyMaterializeLobData=false |