Re: BUG #15396: initdb emits wrong comment for range for effective_io_concurrency

James Robinson <james(at)jlr-photo(dot)com> writes:
>> On Sep 23, 2018, at 2:27 PM, Sergei Kornilov <sk(at)zsrv(dot)org> wrote:
>> effective_io_concurrency can not be set is your system does not support USE_POSIX_FADVISE. In this case only allowed value for effective_io_concurrency is zero.
>> As far i know mac os does not support posix_fadvise.

> Possibilities of augmenting either the initdb template comments according to if USE_POSIX_FADVISE or not, or perhaps the runtime error (probably harder).

I don't think trying to cram something about this into
postgresql.conf.sample is advisable. Those end-of-line comments need to
be *short*. Plus, you'd almost certainly confuse people as to whether the
info was applicable to them or not. Perhaps a better idea is to rejigger
things so that the bad news is delivered by check_effective_io_concurrency
rather than changing the hard limits of the GUC. Then it'd be possible
to include an errdetail that only zero is supported on platforms that
lack posix_fadvise.

regards, tom lane