Re: error context for vacuum to include block number

On Mon, Feb 17, 2020 at 02:18:11PM +0900, Masahiko Sawada wrote:
> Oops it seems to me that it's better to set error context after
> tupindex = 0. Sorry for my bad.

I take your point but did it differently - see what you think

> And the above comment can be written in a single line as other same comments.

Thanks :)

> Hmm I don't think it's a good idea to have count_nondeletable_pages
> set the error context of PHASE_TRUNCATE.

I think if we don't do it there then we shouldn't bother handling
PHASE_TRUNCATE at all, since that's what's likely to hit filesystem or other
lowlevel errors, before lazy_truncate_heap() hits them.

> Because the patch sets the
> error context during RelationTruncate that actually truncates the heap
> but count_nondeletable_pages doesn't truncate it.

I would say that ReadBuffer called by the prefetch in
count_nondeletable_pages() is called during the course of truncation, the same
as ReadBuffer called during the course of vacuuming can be attributed to
vacuuming.

> I think setting the error context only during RelationTruncate would be a
> good start. We can hear other opinions from other hackers. Some hackers may
> want to set the error context for whole lazy_truncate_heap.

I avoided doing that since it has several "return" statements, each of which
would need to "Pop the error context stack", which is at risk of being
forgotten and left unpopped by anyone who adds or changes flow control.

Also, I just added this to the TRUNCATE case, even though that should never
happen: if (BlockNumberIsValid(cbarg->blkno))...

-- 
Justin