Re: display offset along with block number in vacuum errors

On Wed, Jul 29, 2020 at 12:35:17AM +0530, Mahendra Singh Thalor wrote:
> Apart from these, I fixed comments given by Sawada and Michael in the
> latest patch. Attaching v2 patch for review.

Thanks.

lazy_check_needs_freeze iterates over blocks and this patch changes it to
update vacrelstats. I think it should do what
lazy_{vacuum/cleanup}_heap/page/index do and call update_vacuum_error_info() at
its beginning (even though only the offset is changed), and then
restore_vacuum_error_info() at its end (to "revert back" to the item number it
started with).

The same is true of heap_page_is_all_visible(), except it's only called by
lazy_vacuum_page(), which already calls restore_vacuum_error_info() a few lines
later.

As for the message:

+ if (OffsetNumberIsValid(errinfo->offnum))
+ errcontext("while scanning block %u and offset %u of relation \"%s.%s\"",
+ errinfo->blkno, errinfo->offnum, errinfo->relnamespace, errinfo->relname);
+ else
+ errcontext("while scanning block %u of relation \"%s.%s\"",
+ errinfo->blkno, errinfo->relnamespace, errinfo->relname);

I think that may be confusing. A DBA should know what a "block" is, but
"offset" sounds like a byte offset, rather than an item number. Here's what
I'd written. Maybe it should say "offset number".

+ errcontext("while vacuuming block %u of relation \"%s.%s\", item offset %u",

--
Justin