Date: Sat, 29 Mar 2025 06:41:43 -0700
From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	Robert Haas <robertmhaas@gmail.com>,
	Jakub Wartak <jakub.wartak@enterprisedb.com>,
	Jelte Fennema-Nio <postgres@jeltef.nl>,
	Antonin Houska <ah@cybertec.at>
Subject: Re: AIO v2.5
Message-ID: <20250329134143.ca.nmisch@google.com>
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On Fri, Mar 28, 2025 at 11:35:23PM -0400, Andres Freund wrote:
> The number of combinations is annoyingly large. It's e.g. plausible to use
> ignore_checksum_failure=on and zero_damaged_pages=on at the same time for
> recovery.

That's intricate indeed.

> But I finally got to a point where the code ends up readable, without undue
> duplication.  It would, leaving some nasty hack aside, require a
> errhint_internal() - but I can't imagine a reason against introducing that,
> given we have it for the errmsg and errhint.

Introducing that is fine.

> Here's the relevant code:
> 
> 	/*
> 	 * Treat a read that had both zeroed buffers *and* ignored checksums as a
> 	 * special case, it's too irregular to be emitted the same way as the other
> 	 * cases.
> 	 */
> 	if (zeroed_any && ignored_any)
> 	{
> 		Assert(zeroed_any && ignored_any);
> 		Assert(nblocks > 1);	/* same block can't be both zeroed and ignored */
> 		Assert(result.status != PGAIO_RS_ERROR);
> 		affected_count = zeroed_or_error_count;
> 
> 		ereport(elevel,
> 				errcode(ERRCODE_DATA_CORRUPTED),
> 				errmsg("zeroing %u pages and ignoring %u checksum failures among blocks %u..%u of relation %s",
> 					   affected_count, checkfail_count, first, last, rpath.str),

Translation stumbles on this one, because each of the first two %u are
plural-sensitive.  I'd do one of:

- Call ereport() twice, once for zeroed pages and once for ignored checksums.
  Since elevel <= ERROR here, that doesn't lose the second call.

- s/pages/page(s)/ like msgid "There are %d other session(s) and %d prepared
  transaction(s) using the database."

- Something more like the style of VACUUM VERBOSE, e.g. "INTRO_TEXT: %u
  zeroed, %u checksums ignored".  I've not written INTRO_TEXT, and this
  doesn't really resolve pluralization.  Probably don't use this option.

> 				affected_count > 1 ?
> 				errdetail("Block %u held first zeroed page.",
> 						  first + first_off) : 0,
> 				errhint("See server log for details about the other %u invalid blocks.",
> 						affected_count + checkfail_count - 1));
> 		return;
> 	}
> 
> 	/*
> 	 * The other messages are highly repetitive. To avoid duplicating a long
> 	 * and complicated ereport(), gather the translated format strings
> 	 * separately and then do one common ereport.
> 	 */
> 	if (result.status == PGAIO_RS_ERROR)
> 	{
> 		Assert(!zeroed_any);	/* can't have invalid pages when zeroing them */
> 		affected_count = zeroed_or_error_count;
> 		msg_one = _("invalid page in block %u of relation %s");
> 		msg_mult = _("%u invalid pages among blocks %u..%u of relation %s");
> 		det_mult = _("Block %u held first invalid page.");
> 		hint_mult = _("See server log for the other %u invalid blocks.");

For each hint_mult, we would usually use ngettext() instead of _().  (Would be
errhint_plural() if not separated from its ereport().)  Alternatively,
s/blocks/block(s)/ is fine.

> 	}
> 	else if (zeroed_any && !ignored_any)
> 	{
> 		affected_count = zeroed_or_error_count;
> 		msg_one = _("invalid page in block %u of relation %s; zeroing out page");
> 		msg_mult = _("zeroing out %u invalid pages among blocks %u..%u of relation %s");
> 		det_mult = _("Block %u held first zeroed page.");
> 		hint_mult = _("See server log for the other %u zeroed blocks.");
> 	}
> 	else if (!zeroed_any && ignored_any)
> 	{
> 		affected_count = checkfail_count;
> 		msg_one = _("ignoring checksum failure in block %u of relation %s");
> 		msg_mult = _("ignoring %u checksum failures among blocks %u..%u of relation %s");
> 		det_mult = _("Block %u held first ignored page.");
> 		hint_mult = _("See server log for the other %u ignored blocks.");
> 	}
> 	else
> 		pg_unreachable();
> 
> 	ereport(elevel,
> 			errcode(ERRCODE_DATA_CORRUPTED),
> 			affected_count == 1 ?
> 			errmsg_internal(msg_one, first + first_off, rpath.str) :
> 			errmsg_internal(msg_mult, affected_count, first, last, rpath.str),
> 			affected_count > 1 ? errdetail_internal(det_mult, first + first_off) : 0,
> 			affected_count > 1 ? errhint_internal(hint_mult, affected_count - 1) : 0);
> 
> Does that approach make sense?

Yes.

> What do you think about using
>   "zeroing invalid page in block %u of relation %s"
> instead of
>   "invalid page in block %u of relation %s; zeroing out page"

I like the replacement.  It moves the important part to the front, and it's
shorter.

> I thought about instead translating "ignoring", "ignored", "zeroing",
> "zeroed", etc separately, but I have doubts about how well that would actually
> translate.

Agreed, I wouldn't have high hopes for that.  An approach like that would
probably need messages that separate the independently-translated part
grammatically, e.g.:

  /* last %s is translation of "ignore" or "zero-fill" */
  "invalid page in block %u of relation %s; resolved by method \"%s\""

(Again, I'm not recommending that.)