Re: why do hash index builds use smgrextend() for new splitpoint pages

On Sat, Feb 26, 2022 at 3:01 AM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> Since _hash_alloc_buckets() WAL-logs the last page of the
> splitpoint, is it safe to skip the smgrimmedsync()? What if the last
> page of the splitpoint doesn't end up having any tuples added to it
> during the index build and the redo pointer is moved past the WAL for
> this page and then later there is a crash sometime before this page
> makes it to permanent storage. Does it matter that this page is lost? If
> not, then why bother WAL-logging it?
>

I think we don't care if the page is lost before we update the
meta-page in the caller because we will try to reallocate in that
case. But we do care after meta page update (having the updated
information about this extension via different masks) in which case we
won't lose this last page because it would have registered the sync
request for it via sgmrextend before meta page update.

--
With Regards,
Amit Kapila.