Alex Pilosov <alex@pilosoft.com> writes:
> I'd suggest you do this: add a global backend_shmid_offset in ipc.c,
> initialized to current default, and an option to postgres to put a value
> there.
Don't waste your time. This issue is gone in current sources. See
IpcMemoryCreate and IpcSemaphoreCreate in src/backend/storage/ipc/ipc.c.
regards, tom lane