From: "Abhradeep Chakraborty via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Taylor Blau <me@ttaylorr.com>,
Kaartic Sivaraam <kaartic.sivaraam@gmail.com>,
Derrick Stolee <derrickstolee@github.com>,
Junio C Hamano <gitster@pobox.com>,
Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Subject: [PATCH v3 0/3] bitmap-format.txt: fix some formatting issues and include checksum info
Date: Fri, 10 Jun 2022 10:54:38 +0000 [thread overview]
Message-ID: <pull.1246.v3.git.1654858481.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.1246.v2.git.1654623814.gitgitgadget@gmail.com>
There are some issues in the bitmap-format html page. For example, some
nested lists are shown as top-level lists (e.g. [1]- Here
BITMAP_OPT_FULL_DAG (0x1) and BITMAP_OPT_HASH_CACHE (0x4) are shown as
top-level list). There is also a need of adding info about trailing checksum
in the docs.
Changes since v2: The last two commits are updated to address the
suggestions. These changes are -
* previously omitted blank lines are re-added. In the updated commit, use
of <pre> blocks are decreased. Description lists and + are used instead
to add more than one paragraphs under lists. Readability of the source
text might decrease due to the use of +. But other documentation files
(e.g. git-add.txt) also use it to connect two paragraphs. So, I hope this
is acceptable.
* Information about trailing checksum is updated (as suggested by Taylor)
Changes since v1:
* a new commit addressing bitmap-format.txt html page generation is added
* Remove extra indentation from the previous change
* elaborate more about the trailing checksum (as suggested by Kaartic)
initial version:
* first commit fixes some formatting issues
* information about trailing checksum in the bitmap file is added in the
bitmap-format doc.
[1] https://git-scm.com/docs/bitmap-format#_on_disk_format
Abhradeep Chakraborty (3):
bitmap-format.txt: feed the file to asciidoc to generate html
bitmap-format.txt: fix some formatting issues
bitmap-format.txt: add information for trailing checksum
Documentation/Makefile | 1 +
Documentation/technical/bitmap-format.txt | 113 ++++++++++++----------
2 files changed, 63 insertions(+), 51 deletions(-)
base-commit: 2668e3608e47494f2f10ef2b6e69f08a84816bcb
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1246%2FAbhra303%2Ffix-doc-formatting-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1246/Abhra303/fix-doc-formatting-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1246
Range-diff vs v2:
1: a1b9bd9af90 = 1: a1b9bd9af90 bitmap-format.txt: feed the file to asciidoc to generate html
2: cb919513c14 ! 2: c74b9a52c2a bitmap-format.txt: fix some formatting issues
@@ Commit message
format.txt` is broken. This is mainly because `-` is used for nested
lists (which is not allowed in asciidoc) instead of `*`.
- Fix these and also reformat it (e.g. removing some blank lines) for
- better readability of the html page.
+ Fix these and also reformat it for better readability of the html page.
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cac
- - A header appears at the beginning:
+ * A header appears at the beginning:
- 4-byte signature: {'B', 'I', 'T', 'M'}
+- 4-byte signature: {'B', 'I', 'T', 'M'}
++ 4-byte signature: :: {'B', 'I', 'T', 'M'}
++
++ 2-byte version number (network byte order): ::
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+- 2-byte version number (network byte order)
+ The current implementation only supports version 1
of the bitmap index (the same one as JGit).
- 2-byte flags (network byte order)
--
+- 2-byte flags (network byte order)
++ 2-byte flags (network byte order): ::
+
The following flags are supported:
--
- - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
+
+- - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
++ ** {empty}
++ BITMAP_OPT_FULL_DAG (0x1) REQUIRED: :::
++
This flag must always be present. It implies that the
bitmap index has been generated for a packfile or
+ multi-pack index (MIDX) with full closure (i.e. where
@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
- requirement for the bitmap index format, also present in
JGit, that greatly reduces the complexity of the
implementation.
--
- - BITMAP_OPT_HASH_CACHE (0x4)
+
+- - BITMAP_OPT_HASH_CACHE (0x4)
++ ** {empty}
++ BITMAP_OPT_HASH_CACHE (0x4): :::
++
If present, the end of the bitmap file contains
`N` 32-bit name-hash values, one per object in the
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+ pack/MIDX. The format and meaning of the name-hash is
described below.
- 4-byte entry count (network byte order)
+- 4-byte entry count (network byte order)
-
++ 4-byte entry count (network byte order): ::
The total count of entries (bitmapped commits) in this bitmap index.
- 20-byte checksum
+- 20-byte checksum
-
++ 20-byte checksum: ::
The SHA1 checksum of the pack/MIDX this bitmap index
belongs to.
- - 4 EWAH bitmaps that act as type indexes
-+ * 4 EWAH bitmaps that act as type indexes
-
- Type indexes are serialized after the hash cache in the shape
- of four EWAH bitmaps stored consecutively (see Appendix A for
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
-
- There is a bitmap for each Git object type, stored in the following
- order:
-
- - Commits
- - Trees
- - Blobs
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
- in a full set (all bits set), and the AND of all 4 bitmaps will
- result in an empty bitmap (no bits set).
-
+- Type indexes are serialized after the hash cache in the shape
+- of four EWAH bitmaps stored consecutively (see Appendix A for
+- the serialization format of an EWAH bitmap).
+-
+- There is a bitmap for each Git object type, stored in the following
+- order:
+-
+- - Commits
+- - Trees
+- - Blobs
+- - Tags
+-
+- In each bitmap, the `n`th bit is set to true if the `n`th object
+- in the packfile or multi-pack index is of that type.
+-
+- The obvious consequence is that the OR of all 4 bitmaps will result
+- in a full set (all bits set), and the AND of all 4 bitmaps will
+- result in an empty bitmap (no bits set).
+-
- - N entries with compressed bitmaps, one for each indexed commit
-+ * N entries with compressed bitmaps, one for each indexed commit
-
- Where `N` is the total amount of entries in this bitmap index.
- Each entry contains the following:
-
+-
+- Where `N` is the total amount of entries in this bitmap index.
+- Each entry contains the following:
+-
- - 4-byte object position (network byte order)
-+ ** 4-byte object position (network byte order)
++ * 4 EWAH bitmaps that act as type indexes
+++
++Type indexes are serialized after the hash cache in the shape
++of four EWAH bitmaps stored consecutively (see Appendix A for
++the serialization format of an EWAH bitmap).
+++
++There is a bitmap for each Git object type, stored in the following
++order:
+++
++ - Commits
++ - Trees
++ - Blobs
++ - Tags
++
+++
++In each bitmap, the `n`th bit is set to true if the `n`th object
++in the packfile or multi-pack index is of that type.
++
++ The obvious consequence is that the OR of all 4 bitmaps will result
++ in a full set (all bits set), and the AND of all 4 bitmaps will
++ result in an empty bitmap (no bits set).
++
++ * N entries with compressed bitmaps, one for each indexed commit
+++
++Where `N` is the total amount of entries in this bitmap index.
++Each entry contains the following:
++
++ ** {empty}
++ 4-byte object position (network byte order): ::
The position **in the index for the packfile or
multi-pack index** where the bitmap for this commit is
found.
- - 1-byte XOR-offset
-+ ** 1-byte XOR-offset
++ ** {empty}
++ 1-byte XOR-offset: ::
The xor offset used to compress this bitmap. For an entry
in position `x`, a XOR offset of `y` means that the actual
bitmap representing this commit is composed by XORing the
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
- with **previous** bitmaps, not bitmaps that will come afterwards
- in the index.
-
+ bitmap for this entry with the bitmap in entry `x-y` (i.e.
+ the bitmap `y` entries before this one).
+-
+- Note that this compression can be recursive. In order to
+- XOR this entry with a previous one, the previous entry needs
+- to be decompressed first, and so on.
+-
+- The hard-limit for this offset is 160 (an entry can only be
+- xor'ed against one of the 160 entries preceding it). This
+- number is always positive, and hence entries are always xor'ed
+- with **previous** bitmaps, not bitmaps that will come afterwards
+- in the index.
+-
- - 1-byte flags for this bitmap
-+ ** 1-byte flags for this bitmap
+++
++NOTE: This compression can be recursive. In order to
++XOR this entry with a previous one, the previous entry needs
++to be decompressed first, and so on.
+++
++The hard-limit for this offset is 160 (an entry can only be
++xor'ed against one of the 160 entries preceding it). This
++number is always positive, and hence entries are always xor'ed
++with **previous** bitmaps, not bitmaps that will come afterwards
++in the index.
++
++ ** {empty}
++ 1-byte flags for this bitmap: ::
At the moment the only available flag is `0x1`, which hints
that this bitmap can be re-used when rebuilding bitmap indexes
for the repository.
3: 2171d31fb2b ! 3: b971558e1cb bitmap-format.txt: add information for trailing checksum
@@ Commit message
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
## Documentation/technical/bitmap-format.txt ##
-@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+@@ Documentation/technical/bitmap-format.txt: in the index.
** The compressed bitmap itself, see Appendix A.
-+ * TRAILER:
-+
-+ Index checksum of the above contents. It is a 20-byte SHA1 checksum.
++ * {empty}
++ TRAILER: ::
++ Trailing checksum of the preceding contents.
+
== Appendix A: Serialization format for an EWAH bitmap
--
gitgitgadget
next prev parent reply other threads:[~2022-06-10 10:57 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-02 13:52 [PATCH 0/2] bitmap-format.txt: fix some formatting issues and include checksum info Abhradeep Chakraborty via GitGitGadget
2022-06-02 13:52 ` [PATCH 1/2] bitmap-format.txt: fix some formatting issues Abhradeep Chakraborty via GitGitGadget
2022-06-06 15:55 ` Junio C Hamano
2022-06-07 10:25 ` Abhradeep Chakraborty
2022-06-02 13:52 ` [PATCH 2/2] bitmap-format.txt: add information for trailing checksum Abhradeep Chakraborty via GitGitGadget
2022-06-07 17:43 ` [PATCH v2 0/3] bitmap-format.txt: fix some formatting issues and include checksum info Abhradeep Chakraborty via GitGitGadget
2022-06-07 17:43 ` [PATCH v2 1/3] bitmap-format.txt: feed the file to asciidoc to generate html Abhradeep Chakraborty via GitGitGadget
2022-06-07 18:39 ` Junio C Hamano
2022-06-08 15:02 ` Abhradeep Chakraborty
2022-06-07 20:21 ` Taylor Blau
2022-06-07 17:43 ` [PATCH v2 2/3] bitmap-format.txt: fix some formatting issues Abhradeep Chakraborty via GitGitGadget
2022-06-07 20:51 ` Taylor Blau
2022-06-07 22:02 ` Junio C Hamano
2022-06-08 16:06 ` Abhradeep Chakraborty
2022-06-08 15:40 ` Abhradeep Chakraborty
2022-06-07 17:43 ` [PATCH v2 3/3] bitmap-format.txt: add information for trailing checksum Abhradeep Chakraborty via GitGitGadget
2022-06-07 20:56 ` Taylor Blau
2022-06-08 16:15 ` Abhradeep Chakraborty
2022-06-07 18:28 ` [PATCH v2 0/3] bitmap-format.txt: fix some formatting issues and include checksum info Junio C Hamano
2022-06-07 20:58 ` Taylor Blau
2022-06-07 21:00 ` Junio C Hamano
2022-06-08 17:12 ` Abhradeep Chakraborty
2022-06-10 10:54 ` Abhradeep Chakraborty via GitGitGadget [this message]
2022-06-10 10:54 ` [PATCH v3 1/3] bitmap-format.txt: feed the file to asciidoc to generate html Abhradeep Chakraborty via GitGitGadget
2022-06-10 10:54 ` [PATCH v3 2/3] bitmap-format.txt: fix some formatting issues Abhradeep Chakraborty via GitGitGadget
2022-06-15 2:27 ` Taylor Blau
2022-06-15 14:28 ` Abhradeep Chakraborty
2022-06-10 10:54 ` [PATCH v3 3/3] bitmap-format.txt: add information for trailing checksum Abhradeep Chakraborty via GitGitGadget
2022-06-10 17:01 ` [PATCH v3 0/3] bitmap-format.txt: fix some formatting issues and include checksum info Junio C Hamano
2022-06-15 2:28 ` Taylor Blau
2022-06-15 22:41 ` Junio C Hamano
2022-06-16 5:03 ` [PATCH v4 " Abhradeep Chakraborty via GitGitGadget
2022-06-16 5:03 ` [PATCH v4 1/3] bitmap-format.txt: feed the file to asciidoc to generate html Abhradeep Chakraborty via GitGitGadget
2022-06-16 5:03 ` [PATCH v4 2/3] bitmap-format.txt: fix some formatting issues Abhradeep Chakraborty via GitGitGadget
2022-06-16 5:03 ` [PATCH v4 3/3] bitmap-format.txt: add information for trailing checksum Abhradeep Chakraborty via GitGitGadget
2022-06-16 18:53 ` [PATCH v4 0/3] bitmap-format.txt: fix some formatting issues and include checksum info Junio C Hamano
2022-06-16 21:18 ` Taylor Blau
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