Re: fd.c: flush data problems on osx

> On 17 Mar 2016, at 20:23, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
>>
>> Also there are no default ifdef inside this function, is there any
>> check that will guarantee that pg_flush_data will not end up with
>> empty body on some platform?
>
> There doesn't need to be - it's purely "advisory", i.e. just an
> optimization.

Ah, okay, then I misinterpret purpose of that function and it shouldn’t be forced to sync.

>
>> One possible solution for that is just fallback to pg_fdatasync in case when offset = nbytes = 0.
>
> Hm, that's a bit heavyweight. I'd rather do an lseek(SEEK_END) to get
> the file size. Could you test that?
>

It looks like OSX mmap raises EINVAL when length isn’t aligned to pagesize while manual says it can be of arbitrary length, so i aligned it.
Also there were call to mmap with PROT_READ | PROT_WRITE, but when called from pre_sync_fname file descriptor is just O_RDONLY, so i changed mmap mode to PROT_READ — seems that PROT_WRITE wasn’t needed anyway.

And all of that reduces number of warnings in order of magnitude but there are still some and I don’t yet understand why are they happening.

>
> Greetings,
>
> Andres Freund
>
>
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---
Stas Kelvich
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Russian Postgres Company