1) if you have more than 1GB RAM, you can user 25% of memory for shared_buffers...
2) if you get error like «MSD FATAL: could not create shared memory segment: Invalid argument» when you try to change shared_buffers size in postgresql.conf
shared_buffers = 1024MB // default was 24Mb
you should increase the size of kernel shared memory
sysctl -w kernel.shmmax=1610612736 // (1.5Gb)
and try to start postgresql.