Re: AIO v2.5 - Mailing list pgsql-hackers

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.)