Solution : https://service.sap.com/sap/support/notes/711245 (SAP Service marketplace login required)
Key words : 
-time update task viaits volatile tables support, db2 works onthe problem resolution, workaroundsto address db2 optimizer inefficiencies, suggest creating jobs similar, cases db2/390 catalog statistics, abap export/import table, significantly enhance db2 optimization, mentionedvolatile tables support, db2 support channels, special sap tables
Related Notes : 
       
| 712019 | |
| 132424 | DB2-z/OS: Optimizing access to the TRFC Tables | 
| 116698 | DB2/390: Optimizing Access to Tables VBHDR, VBMOD, VBDATA | 
| 113008 | DB2/390: Maintaining Catalog Statistics | 
| 83335 | DB2/390: Deadlocks, bad performance on cluster tables |