Re: 回复： Why is XLOG_FPI_FOR_HINT always need backups?

At Sat, 17 Jul 2021 00:14:34 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
> Thanks for updating the patch! It basically looks good to me.
>
> * Full-page image (FPI) records contain nothing else but a backup
> * block (or multiple backup blocks). Every block reference must
> * include a full-page image - otherwise there would be no point in
> * this record.
>
> The above comment also needs to be updated?

In short, no. In contrast to the third paragraph, the first paragraph
should be thought that it is describing XLOG_FPI. However, actually
it is not super obvious so it's better to make it clearer. Addition to
that, it seems to me (yes, to *me*) somewhat confused between "block
reference", "backup block" and "full-page image". So I'd like to
adjust the paragraph as the following.

> * XLOG_FPI records contain nothing else but one or more block
> * references. Every block reference must include a full-page image
> * regardless of the full_page_writes setting - otherwise there would
> * be no point in this record.

FYI (or, for the record), the first paragraph got to the current shape
by the commit 9155580fd5, where XLOG_FPI was modified to be able to
hold more than one block references.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center