git.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jeff King <peff@peff.net>
To: ZheNing Hu <adlternative@gmail.com>
Cc: Git List <git@vger.kernel.org>
Subject: Re: [PATCH 1/2] ref-filter: hacky "streaming" mode
Date: Sun, 5 Sep 2021 09:04:05 -0400	[thread overview]
Message-ID: <YTTARcEvpXWSDfYW@coredump.intra.peff.net> (raw)
In-Reply-To: <CAOLTT8Tka0nxHb3G9yb-fs8ue7RaPCUVSKi5PM+GY+rMjFRnog@mail.gmail.com>

On Sun, Sep 05, 2021 at 04:20:02PM +0800, ZheNing Hu wrote:

> But here is a terrible fact: we did not use ref_array_sort() for sorting here.
> So in fact, for_each_fullref_in() does the sorting work () for us by
> default sort (%(refname)),
> This may be due to the file system or some implementation of ref_iterator.
> But this limit the application of this optimization when we use other
> atoms to sort.

Right. This technique does not help at all if you use --sort. I do think
it's reasonable to rely on the sorted output of the for_each_ref()
functions; other parts of Git likely do as well, so I think we'd try
pretty hard to maintain that (and no, it's not a filesystem thing; we do
make sure to sort it ourselves; see the calls to sort_ref_dir()).

> > +       /*
> > +        * the %(symref) placeholder is broken with pretty_print_ref(),
> > +        * which our streaming code uses. I suspect this is a sign of breakage
> > +        * in other callers like verify_tag(), which should be fixed. But for
> > +        * now just disable streaming.
> > +        *
> > +        * Note that this implies we've parsed the format already with
> > +        * verify_ref_format().
> > +        */
> > +       if (need_symref)
> > +               return;
> > +
> 
> I haven’t taken a closer look at why pretty_print_ref() does not
> support %(symref),
> we can skip it first.

I think it's just because pretty_print_ref() does not take a "flag"
parameter for the caller. So it never sees that REF_ISSYMREF is set.

There aren't many callers of that function, so I think nobody ever
really noticed. But you can see the bug like this:

  git init repo
  cd repo
  
  git commit --allow-empty -m foo
  git tag -s -m bar annotated &&
  git symbolic-ref refs/tags/symref refs/tags/annotated
  
  # this is ok; ref-filter handles the flags
  git tag --list --format='list: %(refname) %(symref)'
  
  # not ok; we do not tell the formatter about the flags, so it does
  # not notice that "symref" is a symref
  git tag --verify --format='verify: %(refname) %(symref)' annotated symref

I notice that the --verify output also shows the short refname, which
makes me wonder if %(symref) would have other bugs there (because it
has to re-resolve the ref to come up with the symref destination).

> Unfortunately, this optimization may not be helpful for git cat-file --batch,
> see [1], batch_object_write() directly constructs a ref_array_item and call
> format_ref_array_item() to grab data, It does not use ref_array. So it also
> does not have this malloc() | free() overhead.

Right. It would only be helped by the "quick" formats in the second
patch (and by skipping the malloc/free of the individual
ref_array_items).

-Peff

  reply	other threads:[~2021-09-05 13:04 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-04 12:40 [hacky PATCH 0/2] speeding up trivial for-each-ref invocations Jeff King
2021-09-04 12:41 ` [PATCH 1/2] ref-filter: hacky "streaming" mode Jeff King
2021-09-05  8:20   ` ZheNing Hu
2021-09-05 13:04     ` Jeff King [this message]
2021-09-07  5:28       ` ZheNing Hu
2021-09-07 18:01         ` Jeff King
2021-09-09 14:45           ` ZheNing Hu
2021-09-10 14:26             ` Jeff King
2021-09-15 12:27               ` ZheNing Hu
2021-09-15 14:23                 ` ZheNing Hu
2021-09-16 21:45                   ` Jeff King
2021-09-20  7:42                     ` ZheNing Hu
2021-09-16 21:31                 ` Jeff King
2021-09-05 13:15     ` Jeff King
2021-09-07  5:42       ` ZheNing Hu
2021-09-04 12:42 ` [PATCH 2/2] ref-filter: implement "quick" formats Jeff King
2021-09-05  8:20   ` ZheNing Hu
2021-09-05 13:07     ` Jeff King
2021-09-06 13:34       ` ZheNing Hu
2021-09-07 20:06       ` Junio C Hamano
2021-09-05  8:19 ` [hacky PATCH 0/2] speeding up trivial for-each-ref invocations ZheNing Hu
2021-09-05 12:49   ` Jeff King
2021-09-06 13:30     ` ZheNing Hu
2021-09-07 17:28       ` Jeff King
2021-09-09 13:20         ` ZheNing Hu
2021-09-06  6:54 ` Patrick Steinhardt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YTTARcEvpXWSDfYW@coredump.intra.peff.net \
    --to=peff@peff.net \
    --cc=adlternative@gmail.com \
    --cc=git@vger.kernel.org \
    --subject='Re: [PATCH 1/2] ref-filter: hacky "streaming" mode' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).