>> Then, how about semaphores? When I just do configure, PostgreSQL
>> seems to use SysV semaphores. But POSIX semaphore implementation
is
>> prepared in src/backend/port/posix_sema.c. Why isn't it used by
>> default? Does it have any problem?
>>
>
> Either way, Essentially, no one is running out of shared memory due
> to semaphores.
> In this case, semaphore usage is unrelated to shared memory
> shortages.
Yes, of course, shared memory is not related to semaphores.
> Also, on many platforms the posix_sema's code is used.
Really? When I run 'configure' without any parameter on Red Hat
Enterprise Linux 4.0 (kernel 2.6.x), PostgreSQL uses SysV semaphores.
I confirmed that by seeing the result of 'ipcs -u'. What platforms is
POSIX sema used by PostgreSQL by default?