Do checkpoints flush all data from shared buffers ?

[Fabrice Franquenk <Fabrice.Franquenk@xxxxxxxx>]

Hello,
  I was wondering if each checkpoint would flush all transactions from 
the shared buffers or if there could be some left at the end of the 
checkpoint ?
Because i was trying to lower I/Os of the disks, i got the checkpoint 
timeout lowered to 150 seconds so i get twice the number the checkpoint. 
I was hoping it would reduce the number of  I/Os on the disks because 
there would be less data to write in datafiles...

Thanks in advance for your help

regards,
           Fabrice Franquenk