Performance Problem

I have an IBM rs6000 (4x166 processors) and 1.5 G Ram running Informix 7.24. The problem is that unless I cripple Informix using the SHMTOTAL directive in the onconfig (set to 700M) the system goes so slow that no one can use it, which also results in AIX reporting fork failures due to insufficient memory. If I let Informix do its own thing and set SHMTOTAL to zero (unlimited) Informix appears to allocate far more memory than it needs to, all stats appear normal. In addition if I up the BUFFERS to a point where the Informix instance uses for than 500M of memory I also get the same problem. If anyone has come across this problem I would love to hear from you. Regards Callum callum@stasis.f9.co.uk