Re: Map WAL segment files on PMEM as WAL buffers

Hello Matthias,

Thank you for your comment!

> > [ v3-0002-Add-wal_pmem_map-to-GUC.patch ]
> > +extern bool wal_pmem_map;
>
> A lot of the new code in these patches is gated behind this one flag,
> but the flag should never be true on !pmem systems. Could you instead
> replace it with something like the following?
>
> +#ifdef USE_LIBPMEM
> +extern bool wal_pmem_map;
> +#else
> +#define wal_pmem_map false
> +#endif
>
> A good compiler would then eliminate all the dead code from being
> generated on non-pmem builds (instead of the compiler needing to keep
> that code around just in case some extension decides to set
> wal_pmem_map to true on !pmem systems because it has access to that
> variable).

That sounds good. I will introduce it in the next update.

> > [ v3-0004-Map-WAL-segment-files-on-PMEM-as-WAL-buffers.patch ]
> > + if ((uintptr_t) addr & ~PG_DAX_HUGEPAGE_MASK)
> > + elog(WARNING,
> > + "file not mapped on DAX hugepage boundary: path \"%s\" addr %p",
> > + path, addr);
>
> I'm not sure that we should want to log this every time we detect the
> issue; It's likely that once it happens it will happen for the next
> file as well. Maybe add a timeout, or do we generally not deduplicate
> such messages?

Let me give it some thought. I have believed this WARNING is most
unlikely to happen, and is mutually independent from other happenings.
I will try to find a case where the WARNING happens repeatedly; or I
will de-duplicate the messages if it is easier.

Best regards,
Takashi

--
Takashi Menjo <takashi(dot)menjo(at)gmail(dot)com>