Date: Tue, 28 Jul 2020 14:39:19 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Mahendra Singh Thalor <mahi6run@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: display offset along with block number in vacuum errors
Message-ID: <20200728193919.GK20393@telsasoft.com>
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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