Re: prevent immature WAL streaming

Hi,

On 2021-09-01 11:34:34 +0900, Fujii Masao wrote:
> On 2021/09/01 0:53, Andres Freund wrote:
> > Of course, we need to be careful to not weaken WAL validity checking too
> > much. How about the following:
> >
> > If we're "aborting" a continued record, we set XLP_FIRST_IS_ABORTED_PARTIAL on
> > the page at which we do so (i.e. the page after the valid end of the WAL).
>
> When do you expect that XLP_FIRST_IS_ABORTED_PARTIAL is set? It's set
> when recovery finds a a partially-flushed segment-spanning record?
> But maybe we cannot do that (i.e., cannot overwrite the page) because
> the page that the flag is set in might have already been archived. No?

I was imagining that XLP_FIRST_IS_ABORTED_PARTIAL would be set in the "tail
end" of a partial record. I.e. if there's a partial record starting in the
successfully archived segment A, but the end of the record, in B, has not been
written to disk before a crash, we'd set XLP_FIRST_IS_ABORTED_PARTIAL at the
end of the valid data in B. Which could not have been archived yet, or we'd
not have a partial record. So we should never need to set the flag on an
already archived page.

Greetings,

Andres Freund