Solution : https://service.sap.com/sap/support/notes/955670 (SAP Service marketplace login required)
Key words : 
log by2=> sql error -4008      performing con    [dbds#3 @ 1044] [dbds    1044 ], info <targetdb-hostname>-<targetdb-sid> caution, target database>db password    <user password, database connection sdbtest [dbds#3 @ 1035] [dbds    1035 ], /password combination    [dbds#3 @ 1044] [dbds    1044 ], log by0=> unknown user, \sys\exe\run\dbadaslib, sap dbi interface library, maxdb interfaces               #789086 - precompiler runtime, target database>conn
Related Notes : 
       
| 1037016 | IBM i: MaxDB Client Support for IBM i application server | 
| 822271 | FAQ: SAP MaxDB client software | 
| 822239 | FAQ: SAP MaxDB Interfaces | 
| 789086 | Precompiler Runtime to be used for Extended Kernel | 
| 520647 | External DB connect to a MaxDB database | 
| 323151 | Several DB connections with Native SQL |