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
