Re: Show various offset arrays for heap WAL records

On Sun, Apr 9, 2023 at 5:12 PM Peter Geoghegan <pg@bowt.ie> wrote:
> I noticed that the nbtree VACUUM and DELETE record types have their
> update/xl_btree_update arrays output incorrectly. We cannot use the
> generic array_desc() approach with xl_btree_update elements, because
> they're variable-width elements. The problem is that array_desc() only deals
> with fixed-width elements.

I pushed this fix just now, though without the updates to the
guidelines (or only minimal updates).

A remaining problem with arrays appears in "infobits" fields for
record types such as LOCK. Here's an example of the problem:

off: 34, xid: 3, flags: 0x00, infobits: [, LOCK_ONLY, EXCL_LOCK ]

Clearly the punctuation from the array is malformed.

A second issue (related to the first) is the name of the key itself,
"infobits". While "infobits" actually seems fine in this particular
example, I don't think that we want to do the same for record types
such as HEAP_UPDATE, since such records require that the description
show information about flags whose underlying field in the WAL record
struct is actually called "old_infobits_set". I think that we should
be outputting "old_infobits: [ ... ] " in the description of
HEAP_UPDATE records, which isn't the case right now.

A third issue is present in the nearby handling of xl_heap_truncate
status flags. It's the same basic array punctuation issue again, so
arguably this is the same issue as the first one.

Attached patch fixes all of these issues, and overhauls the guidelines
in the way originally proposed by the nbtree fix patch (since I didn't
keep that part of the nbtree patch when I pushed it today).

Note that the patch makes many individual (say) HOT_UPDATE records
have descriptions that look like this:

... old_infobits: [], ...

This differs from HEAD, where the output is totally suppressed because
there are no flag bits to show. I think that this behavior is more
logical and consistent overall.

-- 
Peter Geoghegan