Re: confusing checkpoint_flush_after / bgwriter_flush_after

Hello Tomas,

> #checkpoint_flush_after = 0 # 0 disables,
> # default is 256kB on linux, 0 otherwise

> I find this pretty confusing, because for all other GUCs in the file, the
> commented-out value is the default one. In this case that would mean "0",
> disabling the flushing.
>
> But in practice we use platform-dependent defaults - 256/512K on Linux, 0
> otherwise. There are other GUCs where the default is platform-specific, but
> none of them suggests "disabled" is the default state.
>
> While the 9.6 cat is out of the bag, I think we can fix this quite easily -
> use "-1" to specify the default value should be used, and use that in the
> sample file. This won't break any user configuration.

Although I understand the issue, I'm not sure about -1 as a special value
to mean the default.

> If that's considered not acceptable, perhaps we should at least improve the
> comments, so make this clearer.

Yep, what about not putting a value and inverting/adapting the comments,
maybe something like:

#checkpoint_flush_after = ... # default is 256kB on linux, 0 otherwise
# where 0 disables flushing

--
Fabien.