Solution : https://service.sap.com/sap/support/notes/121058 (SAP Service marketplace login required)
Key words : 
instance profile parameter           dbs/inf/first_rows_off=true, rows additional key words first_rows, respective instance profile parameter, environment variable           informix_fr_off=true, control panel -> system -> environment, 1i patch level >= 113            4, 0b patch level >= 150            4, 5a patch level >= 32            4, symptom poor performance, environment parameter
Related Notes : 
       
| 152378 | Informix Dynamic Server versions 7.30.[UFT]C7XB |