Re: [PATCH v3 2/4] pack-refs: teach --exclude option to exclude refs from being packed

> On Thu, May 11, 2023 at 06:10:32PM +0000, John Cai via GitGitGadget wrote:
>> From: John Cai <johncai86@gmail.com>
>>
>> At GitLab, we have a system that creates ephemeral internal refs that
>> don't live long before getting deleted. Having an option to exclude
>> certain refs from a packed-refs file allows these internal references to
>> be deleted much more efficiently.
>>
>> Add an --exclude option to the pack-refs builtin, and use the ref
>> exclusions API to exclude certain refs from being packed into the final
>> packed-refs file
>>
>> Signed-off-by: John Cai <johncai86@gmail.com>
>> ---
>>  Documentation/git-pack-refs.txt | 12 +++++++++++-
>>  builtin/pack-refs.c             | 20 ++++++++++++++++----
>>  refs.c                          |  4 ++--
>>  refs.h                          |  7 ++++++-
>>  refs/debug.c                    |  4 ++--
>>  refs/files-backend.c            | 16 ++++++++++------
>>  refs/packed-backend.c           |  2 +-
>>  refs/refs-internal.h            |  3 ++-
>>  revision.h                      |  2 +-
>>  t/helper/test-ref-store.c       |  3 ++-
>>  t/t3210-pack-refs.sh            | 16 ++++++++++++++++
>>  11 files changed, 69 insertions(+), 20 deletions(-)
>>
>> diff --git a/Documentation/git-pack-refs.txt b/Documentation/git-pack-refs.txt
>> index e011e5fead3..c0f7426e519 100644
>> --- a/Documentation/git-pack-refs.txt
>> +++ b/Documentation/git-pack-refs.txt
>> @@ -8,7 +8,7 @@ git-pack-refs - Pack heads and tags for efficient repository access
>>  SYNOPSIS
>>  --------
>>  [verse]
>> -'git pack-refs' [--all] [--no-prune]
>> +'git pack-refs' [--all] [--no-prune] [--exclude <pattern>]
>>
>>  DESCRIPTION
>>  -----------
>> @@ -60,6 +60,16 @@ interests.
>>  The command usually removes loose refs under `$GIT_DIR/refs`
>>  hierarchy after packing them.  This option tells it not to.
>>
>> +--exclude <pattern>::
>> +
>> +Do not pack refs matching the given `glob(7)` pattern. Repetitions of this option
>> +accumulate exclusion patterns. Use `--no-exclude` to clear and reset the list of
>> +patterns. If a ref is already packed, including it with `--exclude` will not
>> +unpack it.
>> +
>> +When used with `--all`, it will use the difference between the set of all refs,
>> +and what is provided to `--exclude`.
>> +
>
> I think this last paragraph could be simplified, though feel free to
> discard my suggestion if you think it makes things less clear.
>
>   When used with `--all`, pack only loose refs which do not match any of
>   the provided `--exclude` patterns.

>
>>  int cmd_pack_refs(int argc, const char **argv, const char *prefix)
>>  {
>>  	unsigned int flags = PACK_REFS_PRUNE;
>> +	static struct ref_exclusions excludes = REF_EXCLUSIONS_INIT;
>> +	struct pack_refs_opts pack_refs_opts = {.exclusions = &excludes, .flags = flags};
>> +	static struct string_list option_excluded_refs = STRING_LIST_INIT_NODUP;
>> +	struct string_list_item *item;
>
> Since this list does not appear to be sensitive to its order, have you
> considered using the strvec API instead of the string_list one?

>
>> diff --git a/refs.c b/refs.c
>> index d2a98e1c21f..881a0da65cf 100644
>> --- a/refs.c
>> +++ b/refs.c
>> @@ -2132,9 +2132,9 @@ void base_ref_store_init(struct ref_store *refs, struct repository *repo,
>>  }
>>
>>  /* backend functions */
>> -int refs_pack_refs(struct ref_store *refs, unsigned int flags)
>> +int refs_pack_refs(struct ref_store *refs, struct pack_refs_opts *opts)
>>  {
>> -	return refs->be->pack_refs(refs, flags);
>> +	return refs->be->pack_refs(refs, opts);
>>  }
>>
>>  int peel_iterated_oid(const struct object_id *base, struct object_id *peeled)
>> diff --git a/refs.h b/refs.h
>> index 123cfa44244..46020bd335c 100644
>> --- a/refs.h
>> +++ b/refs.h
>> @@ -63,6 +63,11 @@ struct worktree;
>>  #define RESOLVE_REF_NO_RECURSE 0x02
>>  #define RESOLVE_REF_ALLOW_BAD_NAME 0x04
>>
>> +struct pack_refs_opts {
>> +	unsigned int flags;
>> +	struct ref_exclusions *exclusions;
>
> I think this would be OK to include directly in the struct instead of
> via a pointer, but either is fine.
>
>> @@ -1175,15 +1176,18 @@ static void prune_refs(struct files_ref_store *refs, struct ref_to_prune **refs_
>>   */
>>  static int should_pack_ref(const char *refname,
>>  			   const struct object_id *oid, unsigned int ref_flags,
>> -			   unsigned int pack_flags)
>> +			   struct pack_refs_opts *opts)
>>  {
>>  	/* Do not pack per-worktree refs: */
>>  	if (parse_worktree_ref(refname, NULL, NULL, NULL) !=
>>  	    REF_WORKTREE_SHARED)
>>  		return 0;
>>
>> +	if (opts->exclusions && ref_excluded(opts->exclusions, refname))
>> +		return 0;
>
> Looks good, here is where we throw out refs that we don't want. I wonder
> if ref_excluded() does the right thing with a zero-initialized argument
> (i.e. that it behaves as if nothing matches).

>
> I wonder if it's possible to skip over certain loose references by
> avoiding traversal into the sub-directories for simple prefixes. That
> may be a premature optimization, though, so I don't think you
> necessarily need to worry about it in this round.
>
>> +test_expect_success 'test excluded refs are not packed' '
>> +	git branch dont_pack1 &&
>> +	git branch dont_pack2 &&
>> +	git branch pack_this &&
>> +	git pack-refs --all --exclude "refs/heads/dont_pack*" &&
>> +	test -f .git/refs/heads/dont_pack1 &&
>> +	test -f .git/refs/heads/dont_pack2 &&
>> +	! test -f ./git/refs/heads/pack_this'
>> +
>> +test_expect_success 'test --no-exclude refs clears excluded refs' '
>> +	git branch dont_pack3 &&
>> +	git branch dont_pack4 &&
>> +	git pack-refs --all --exclude "refs/heads/dont_pack*" --no-exclude &&
>> +	! test -f .git/refs/heads/dont_pack3 &&
>> +	! test -f .git/refs/heads/dont_pack4'
>
> Tests look good. The trailing quote is a little odd to be placed on the
> last line of the test instead of off on its own, but I suppose that is
> imitating existing style, which is OK.