Re: error context for vacuum to include block number

On Wed, 25 Mar 2020 at 14:08, Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
>
> On Wed, Mar 25, 2020 at 10:22:21AM +0530, Amit Kapila wrote:
> > On Wed, Mar 25, 2020 at 10:05 AM Masahiko Sawada
> > <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> > >
> > > On Wed, 25 Mar 2020 at 12:44, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > On Tue, Mar 24, 2020 at 7:51 PM Masahiko Sawada
> > > > <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> > > > >
> > > > >
> > > > > I got the point. But if we set the error context before that, I think
> > > > > we need to change the error context message. The error context message
> > > > > of heap truncation phase is "while truncating relation \"%s.%s\" to %u
> > > > > blocks", but cbarg->blkno will be the number of blocks of the current
> > > > > relation.
> > > > >
> > > > > case VACUUM_ERRCB_PHASE_TRUNCATE:
> > > > > if (BlockNumberIsValid(cbarg->blkno))
> > > > > errcontext("while truncating relation \"%s.%s\" to %u blocks",
> > > > > cbarg->relnamespace, cbarg->relname, cbarg->blkno);
> > > > > break;
> > > > >
> > > >
> > > > Do you mean to say that actually we are just prefetching or reading
> > > > the pages in count_nondeletable_pages() but the message doesn't have
> > > > any such indication? If not that, what problem do you see with the
> > > > message? What is your suggestion?
> > >
> > > I meant that with the patch, suppose that the table has 100 blocks and
> > > we're truncating it to 50 blocks in RelationTruncate(), the error
> > > context message will be "while truncating relation "aaa.bbb" to 100
> > > blocks", which is not correct. I think it should be "while truncating
> > > relation "aaa.bbb" to 50 blocks". We can know the relation can be
> > > truncated to 50 blocks by the result of count_nondeletable_pages(). So
> > > if we update the arguments before it we will use the number of blocks
> > > of relation before truncation.
> > >
> >
> > Won't the latest patch by Justin will fix this as he has updated the
> > block count after count_nondeletable_pages? Apart from that, I feel
>
> The issue is if the error happens *during* count_nondeletable_pages().
> We don't want it to say "truncating relation to 100 blocks".

Right.

>
> > the first call to update_vacuum_error_cbarg in lazy_truncate_heap
> > should have input parameter as vacrelstats->nonempty_pages instead of
> > new_rel_pages to indicate the remaining pages after truncation?
>
> Yea, I think that addresses the issue.

+1

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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