From: Duy Nguyen <pclouds@gmail.com>
Date: Fri, 25 Oct 2013 01:16:18 GMT
Subject: Re: [PATCH 09/19] documentation: add documentation for the bitmap format
Message-ID: <CACsJy8DFisnZZiPOWjktuMC2J289AYGtgefZob=4YFAJAxBc6w@mail.gmail.com>
In-Reply-To: <20131024180347.GI24180@sigill.intra.peff.net>

On Fri, Oct 25, 2013 at 1:03 AM, Jeff King <peff@peff.net> wrote:
> diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt
> new file mode 100644
> index 0000000..c686dd1
> --- /dev/null
> +++ b/Documentation/technical/bitmap-format.txt
> @@ -0,0 +1,131 @@
> +GIT bitmap v1 format
> +====================
> +
> +       - A header appears at the beginning:
> +
> +               4-byte signature: {'B', 'I', 'T', 'M'}
> +
> +               2-byte version number (network byte order)
> +                       The current implementation only supports version 1
> +                       of the bitmap index (the same one as JGit).

I suppose this means if I want to extend pack bitmaps to be used on
shallow clones, I need to step version to 2 before adding the shallow
points in .bitmap file as there's no chance of modifying v1 anymore,
correct?

> +
> +               2-byte flags (network byte order)
> +
> +                       The following flags are supported:
> +
> +                       - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
> +                       This flag must always be present. It implies that the bitmap
> +                       index has been generated for a packfile with full closure
> +                       (i.e. where every single object in the packfile can find
> +                        its parent links inside the same packfile). This is a
> +                       requirement for the bitmap index format, also present in JGit,
> +                       that greatly reduces the complexity of the implementation.
> +
> +               4-byte entry count (network byte order)
> +
> +                       The total count of entries (bitmapped commits) in this bitmap index.
> +
> +               20-byte checksum
> +
> +                       The SHA1 checksum of the pack this bitmap index belongs to.
> +
-- 
Duy