Re: Free WAL caches on switching segments

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Tom Lane wrote:
> >> Depending on OS features we have never depended on before is a *huge*
> >> ongoing maintenance cost, and I have not seen an argument that I think
> >> justifies this one.
>
> > I disagree. It is a localized change and seems like a win, and it uses
> > a standard POSIX feature, rather than an OS-specific one.
>
> It's still gonna need a configure test and so on. "POSIX" does not mean
> "exists everywhere". Moreover, the submitter has not even proven that
> the code works (or even builds, much less does anything useful) on the
> platforms it's supposedly for.

The submitter believes the C macro test is sufficient:

I think we can use _POSIX_ADVISORY_INFO to test if posix_fadvise exists.
Also, I added the check on whether WAL archiving is enabled, because
archivers might use the caches to read the WAL segment.

I assume if it follows the POSIX spec it will work on all platforms that
support this feature.

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