But its limited to the value of SHMMAX with which the kernel was compiled. SHMMAX is defined in shmparam.h.

However, if I read the docs correct, this value is the per-segment limit, not the grand total. The number of segments is capped by SHMALL. So if your DB can be taught to allocate more than one segment you can avoid recompiling.

It seems not all architectures store SHMMAX in shmparam.h. For i386, they are defined in linux/shm.h instead. I didn't have all the kernel sources handy earlier. Sorry for the wild goose chase.

But the documentation does seem to conflict. shm.h gives the impression that SHMMAX is a default which can be adjusted through sysctl; the kernel docs claim its the max. segment size.