From: Junio C Hamano <firstname.lastname@example.org> To: Masaya Suzuki <email@example.com> Cc: Git Mailing List <firstname.lastname@example.org> Subject: Re: [PATCH v3] doc: describe Git bundle format Date: Fri, 07 Feb 2020 17:49:46 -0800 Message-ID: <email@example.com> (raw) In-Reply-To: <CAJB1erVZ5E6FxtD8gJXXpzJjquvksLxpz+h1TzG52Yr9DFmDRQ@mail.gmail.com> (Masaya Suzuki's message of "Fri, 7 Feb 2020 14:21:37 -0800") Masaya Suzuki <firstname.lastname@example.org> writes: > Yes. The reason that I've been trying to check the semantics of the > prerequisites is that I DO recognize that this is possible > format-wise. I'm not sure if this Git implementation can create such > bundles, but format-wise such bundles can be created. Yeah, now I get it. The problem is *not* that v2 format "cannot represent a shallow clone repository", but is that there is nothing that prevents a bundle in v2 format from depending on objects behind (not just at) the shallow boundary, making it impossible for a reader to guarantee that a bundle with prereqs can be used to create an equivalent shallow repository with shallow boundary at the same place as prereqs. IOW, bundle with prereqs in the v2 format allows more objects to be omitted than an equivalent shallow repository omits, because prereqs and shallow cutoff points mean different things. While we are at it, I suspect that with reachability bitmap, a "git fetch" that updates a history up to commit A to a new history up to commit B can omit more objects than what is directly reachable from the commit A. That is, if A's direct child (call it C) is a commit that reverts A, a blob in A's tree won't be in the bundle (because A is a prereq), but the blob at the same path in C is the same blob as the blob at the same path in A's parent (that is what it means for that A's direct child to be a revert of A). In the normal enumeration based on object-walk to decide which objects to send, such a blob in C will be included in the pack, but a reachability bitmap can say "if we assume the reader has A, it must have A^1, so that blob should exist at the reader, hence can be omitted from the transfer even though we are sending commit C."
next prev parent reply other threads:[~2020-02-08 1:49 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-01-30 22:58 [PATCH] " Masaya Suzuki 2020-01-31 13:56 ` Johannes Schindelin 2020-01-31 20:38 ` Junio C Hamano 2020-01-31 21:49 ` Masaya Suzuki 2020-01-31 23:01 ` Junio C Hamano 2020-01-31 23:57 ` Masaya Suzuki 2020-02-04 18:20 ` Junio C Hamano 2020-01-31 22:18 ` [PATCH v2] " Masaya Suzuki 2020-01-31 23:06 ` Junio C Hamano 2020-02-07 20:42 ` [PATCH v3] " Masaya Suzuki 2020-02-07 20:44 ` Masaya Suzuki 2020-02-07 20:59 ` Junio C Hamano 2020-02-07 22:21 ` Masaya Suzuki 2020-02-08 1:49 ` Junio C Hamano [this message] 2020-02-12 22:13 ` Masaya Suzuki 2020-02-12 22:43 ` Junio C Hamano
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