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


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