"git commit-graph write" learned to limit the number of bloom
filters that are computed from scratch with the --max-new-filters
option.
* tb/bloom-improvements:
commit-graph: introduce 'commitGraph.maxNewFilters'
builtin/commit-graph.c: introduce '--max-new-filters=<n>'
commit-graph: rename 'split_commit_graph_opts'
bloom: encode out-of-bounds filters as non-empty
bloom/diff: properly short-circuit on max_changes
bloom: use provided 'struct bloom_filter_settings'
bloom: split 'get_bloom_filter()' in two
commit-graph.c: store maximum changed paths
commit-graph: respect 'commitGraph.readChangedPaths'
t/helper/test-read-graph.c: prepare repo settings
commit-graph: pass a 'struct repository *' in more places
t4216: use an '&&'-chain
commit-graph: introduce 'get_bloom_filter_settings()'
"git receive-pack" that accepts requests by "git push" learned to
outsource most of the ref updates to the new "proc-receive" hook.
* jx/proc-receive-hook:
doc: add documentation for the proc-receive hook
transport: parse report options for tracking refs
t5411: test updates of remote-tracking branches
receive-pack: new config receive.procReceiveRefs
doc: add document for capability report-status-v2
New capability "report-status-v2" for git-push
receive-pack: feed report options to post-receive
receive-pack: add new proc-receive hook
t5411: add basic test cases for proc-receive hook
transport: not report a non-head push as a branch
When a changed-path Bloom filter has either zero, or more than a
certain number (commonly 512) of entries, the commit-graph machinery
encodes it as "missing". More specifically, it sets the indices adjacent
in the BIDX chunk as equal to each other to indicate a "length 0"
filter; that is, that the filter occupies zero bytes on disk.
This has heretofore been fine, since the commit-graph machinery has no
need to care about these filters with too few or too many changed paths.
Both cases act like no filter has been generated at all, and so there is
no need to store them.
In a subsequent commit, however, the commit-graph machinery will learn
to only compute Bloom filters for some commits in the current
commit-graph layer. This is a change from the current implementation
which computes Bloom filters for all commits that are in the layer being
written. Critically for this patch, only computing some of the Bloom
filters means adding a third state for length 0 Bloom filters: zero
entries, too many entries, or "hasn't been computed".
It will be important for that future patch to distinguish between "not
representable" (i.e., zero or too-many changed paths), and "hasn't been
computed". In particular, we don't want to waste time recomputing
filters that have already been computed.
To that end, change how we store Bloom filters in the "computed but not
representable" category:
- Bloom filters with no entries are stored as a single byte with all
bits low (i.e., all queries to that Bloom filter will return
"definitely not")
- Bloom filters with too many entries are stored as a single byte with
all bits set high (i.e., all queries to that Bloom filter will
return "maybe").
These rules are sufficient to not incur a behavior change by changing
the on-disk representation of these two classes. Likewise, no
specification changes are necessary for the commit-graph format, either:
- Filters that were previously empty will be recomputed and stored
according to the new rules, and
- old clients reading filters generated by new clients will interpret
the filters correctly and be none the wiser to how they were
generated.
Clients will invoke the Bloom machinery in more cases than before, but
this can be addressed by returning a NULL filter when all bits are set
high. This can be addressed in a future patch.
Note that this does increase the size of on-disk commit-graphs, but far
less than other proposals. In particular, this is generally more
efficient than storing a bitmap for which commits haven't computed their
Bloom filters. Storing a bitmap incurs a penalty of one bit per commit,
whereas storing explicit filters as above incurs a penalty of one byte
per too-large or empty commit.
In practice, these boundary commits likely occupy a small proportion of
the overall number of commits, and so the size penalty is likely smaller
than storing a bitmap for all commits.
See, for example, these relative proportions of such boundary commits
(collected by SZEDER Gábor):
| Percentage of | commit-graph | |
| commits modifying | file size | |
├────────┬──────────────┼───────────────────┤ pct. |
| 0 path | >= 512 paths | before | after | change |
┌────────────────┼────────┼──────────────┼─────────┼─────────┼───────────┤
| android-base | 13.20% | 0.13% | 37.468M | 37.534M | +0.1741 % |
| cmssw | 0.15% | 0.23% | 17.118M | 17.119M | +0.0091 % |
| cpython | 3.07% | 0.01% | 7.967M | 7.971M | +0.0423 % |
| elasticsearch | 0.70% | 1.00% | 8.833M | 8.835M | +0.0128 % |
| gcc | 0.00% | 0.08% | 16.073M | 16.074M | +0.0030 % |
| gecko-dev | 0.14% | 0.64% | 59.868M | 59.874M | +0.0105 % |
| git | 0.11% | 0.02% | 3.895M | 3.895M | +0.0020 % |
| glibc | 0.02% | 0.10% | 3.555M | 3.555M | +0.0021 % |
| go | 0.00% | 0.07% | 3.186M | 3.186M | +0.0018 % |
| homebrew-cask | 0.40% | 0.02% | 7.035M | 7.035M | +0.0065 % |
| homebrew-core | 0.01% | 0.01% | 11.611M | 11.611M | +0.0002 % |
| jdk | 0.26% | 5.64% | 5.537M | 5.540M | +0.0590 % |
| linux | 0.01% | 0.51% | 63.735M | 63.740M | +0.0073 % |
| llvm-project | 0.12% | 0.03% | 25.515M | 25.516M | +0.0050 % |
| rails | 0.10% | 0.10% | 6.252M | 6.252M | +0.0027 % |
| rust | 0.07% | 0.17% | 9.364M | 9.364M | +0.0033 % |
| tensorflow | 0.09% | 1.02% | 7.009M | 7.010M | +0.0158 % |
| webkit | 0.05% | 0.31% | 17.405M | 17.406M | +0.0047 % |
(where the above increase is determined by computing a non-split
commit-graph before and after this patch).
Given that these projects are all "large" by commit count, the storage
cost by writing these filters explicitly is negligible. In the most
extreme example, android-base (which has 494,848 commits at the time of
writing) would have its commit-graph increase by a modest 68.4 KB.
Finally, a test to exercise filters which contain too many changed path
entries will be introduced in a subsequent patch.
Suggested-by: SZEDER Gábor <szeder.dev@gmail.com>
Suggested-by: Jakub Narębski <jnareb@gmail.com>
Helped-by: Derrick Stolee <dstolee@microsoft.com>
Helped-by: SZEDER Gábor <szeder.dev@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The correct value from commit-graph.c:
#define GRAPH_PARENT_NONE 0x70000000
Signed-off-by: Conor Davis <git@conor.fastmail.fm>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Updates to on-demand fetching code in lazily cloned repositories.
* jt/lazy-fetch:
fetch: no FETCH_HEAD display if --no-write-fetch-head
fetch-pack: remove no_dependents code
promisor-remote: lazy-fetch objects in subprocess
fetch-pack: do not lazy-fetch during ref iteration
fetch: only populate existing_refs if needed
fetch: avoid reading submodule config until needed
fetch: allow refspecs specified through stdin
negotiator/noop: add noop fetch negotiator
Add ABNF notation for capability 'report-status-v2' which extends
capability 'report-status' by adding additional option lines.
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
midx and commit-graph files now use the byte defined in their file
format specification for identifying the hash function used for
object names.
* ds/sha256-leftover-bits:
multi-pack-index: use hash version byte
commit-graph: use the "hash version" byte
t/README: document GIT_TEST_DEFAULT_HASH
Further update of docs to adjust to the recent SHA-256 work.
* ma/sha-256-docs:
shallow.txt: document SHA-256 shallow format
protocol-capabilities.txt: clarify "allow-x-sha1-in-want" re SHA-256
index-format.txt: document SHA-256 index format
http-protocol.txt: document SHA-256 "want"/"have" format
Further update of docs to adjust to the recent SHA-256 work.
* bc/sha-256-doc-updates:
docs: fix step in transition plan
docs: document SHA-256 pack and indices
Teach Git to lazy-fetch missing objects in a subprocess instead of doing
it in-process. This allows any fatal errors that occur during the fetch
to be isolated and converted into an error return value, instead of
causing the current command being run to terminate.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to the commit-graph format, the multi-pack-index format has a
byte in the header intended to track the hash version used to write the
file. This allows one to interpret the hash length without having the
context of the repository config specifying the hash length. This was
not modified as part of the SHA-256 work because the hash length was
automatically up-shifted due to that config.
Since we have this byte available, we can make the file formats more
obviously incompatible instead of relying on other context from the
repository.
Add a new oid_version() method in midx.c similar to the one in
commit-graph.c. This is specifically made separate from that
implementation to avoid artificially linking the formats.
The test impact requires a few more things than the corresponding change
in the commit-graph format. Specifically, 'test-tool read-midx' was not
writing anything about this header value to output. Since the value
available in 'struct multi_pack_index' is hash_len instead of a version
value, we output "20" or "32" instead of "1" or "2".
Since we want a user to not have their Git commands fail if their
multi-pack-index has the incorrect hash version compared to the
repository's hash version, we relax the die() to an error() in
load_multi_pack_index(). This has some effect on 'git multi-pack-index
verify' as we need to check that a failed parse of a file that exists is
actually a verify error. For that test that checks the hash version
matches, we change the corrupted byte from "2" to "3" to ensure the test
fails for both hash algorithms.
Helped-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The commit-graph format reserved a byte among the header of the file to
store a "hash version". During the SHA-256 work, this was not modified
because file formats are not necessarily intended to work across hash
versions. If a repository has SHA-256 as its hash algorithm, it
automatically up-shifts the lengths of object names in all necessary
formats.
However, since we have this byte available for adjusting the version, we
can make the file formats more obviously incompatible instead of relying
on other context from the repository.
Update the oid_version() method in commit-graph.c to add a new value, 2,
for sha-256. This automatically writes the new value in a SHA-256
repository _and_ verifies the value is correct. This is a breaking
change relative to the current 'master' branch since 092b677 (Merge
branch 'bc/sha-256-cvs-svn-updates', 2020-08-13) but it is not breaking
relative to any released version of Git.
The test impact is relatively minor: the output of 'test-tool
read-graph' lists the header information, so those instances of '1' need
to be replaced with a variable determined by GIT_TEST_DEFAULT_HASH. A
more careful test is added that specifically creates a repository of
each type then swaps the commit-graph files. The important value here is
that the "git log" command succeeds while writing a message to stderr.
Helped-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to recent commits, document that we list object names rather
than SHA-1s.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Two of our capabilities contain "sha1" in their names, but that's
historical. Clarify that object names are still to be given using
whatever object format has been negotiated using the "object-format"
capability.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Document that in SHA-1 repositories, we use SHA-1 and in SHA-256
repositories, we use SHA-256, then replace all other uses of "SHA-1"
with something more neutral. Avoid referring to "160-bit" hash values.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Document that rather than always naming objects using SHA-1, we should
use whatever has been negotiated using the object-format capability.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
One of the required steps for the objectFormat extension is to implement
the loose object index. However, without support for
compatObjectFormat, we don't even know if the loose object index is
needed, so it makes sense to move that step to the compatObjectFormat
section. Do so.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have SHA-256 support for packs and indices, let's document
that in SHA-256 repositories, we use SHA-256 instead of SHA-1 for object
names and checksums. Instead of duplicating this information throughout
the document, let's just document that in SHA-1 repositories, we use
SHA-1 for these purposes, and in SHA-256 repositories, we use SHA-256.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the merge diagram, some whitespace is missing which
makes it a bit confusing, fix that.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The final leg of SHA-256 transition.
* bc/sha-256-part-3: (39 commits)
t: remove test_oid_init in tests
docs: add documentation for extensions.objectFormat
ci: run tests with SHA-256
t: make SHA1 prerequisite depend on default hash
t: allow testing different hash algorithms via environment
t: add test_oid option to select hash algorithm
repository: enable SHA-256 support by default
setup: add support for reading extensions.objectformat
bundle: add new version for use with SHA-256
builtin/verify-pack: implement an --object-format option
http-fetch: set up git directory before parsing pack hashes
t0410: mark test with SHA1 prerequisite
t5308: make test work with SHA-256
t9700: make hash size independent
t9500: ensure that algorithm info is preserved in config
t9350: make hash size independent
t9301: make hash size independent
t9300: use $ZERO_OID instead of hard-coded object ID
t9300: abstract away SHA-1-specific constants
t8011: make hash size independent
...
The argv_array API is useful for not just managing argv but any
"vector" (NULL-terminated array) of strings, and has seen adoption
to a certain degree. It has been renamed to "strvec" to reduce the
barrier to adoption.
* jk/strvec:
strvec: rename struct fields
strvec: drop argv_array compatibility layer
strvec: update documention to avoid argv_array
strvec: fix indentation in renamed calls
strvec: convert remaining callers away from argv_array name
strvec: convert more callers away from argv_array name
strvec: convert builtin/ callers away from argv_array name
quote: rename sq_dequote_to_argv_array to mention strvec
strvec: rename files from argv-array to strvec
argv-array: rename to strvec
argv-array: use size_t for count and alloc
The changed-path Bloom filter is improved using ideas from an
independent implementation.
* sg/commit-graph-cleanups:
commit-graph: simplify write_commit_graph_file() #2
commit-graph: simplify write_commit_graph_file() #1
commit-graph: simplify parse_commit_graph() #2
commit-graph: simplify parse_commit_graph() #1
commit-graph: clean up #includes
diff.h: drop diff_tree_oid() & friends' return value
commit-slab: add a function to deep free entries on the slab
commit-graph-format.txt: all multi-byte numbers are in network byte order
commit-graph: fix parsing the Chunk Lookup table
tree-walk.c: don't match submodule entries for 'submod/anything'
Currently we detect the hash algorithm in use by the length of the
object ID. This is inelegant and prevents us from using a different
hash algorithm that is also 256 bits in length.
Since we cannot extend the v2 format in a backward-compatible way, let's
add a v3 format, which is identical, except for the addition of
capabilities, which are prefixed by an at sign. We add "object-format"
as the only capability and reject unknown capabilities, since we do not
have a network connection and therefore cannot negotiate with the other
side.
For compatibility, default to the v2 format for SHA-1 and require v3
for SHA-256.
In t5510, always use format v3 so we can be sure we produce consistent
results across hash algorithms. Since head -n N lists the top N lines
instead of the Nth line, let's run our output through sed to normalize
it and compare it against a fixed value, which will make sure we get
exactly what we're expecting.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There were a few mentions of argv_array in a non-code file which didn't
get picked up in the previous commits (note that even comments in code
files were already covered because of the mechanical conversion via
perl).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
SHA-256 migration work continues.
* bc/sha-256-part-2: (44 commits)
remote-testgit: adapt for object-format
bundle: detect hash algorithm when reading refs
t5300: pass --object-format to git index-pack
t5704: send object-format capability with SHA-256
t5703: use object-format serve option
t5702: offer an object-format capability in the test
t/helper: initialize the repository for test-sha1-array
remote-curl: avoid truncating refs with ls-remote
t1050: pass algorithm to index-pack when outside repo
builtin/index-pack: add option to specify hash algorithm
remote-curl: detect algorithm for dumb HTTP by size
builtin/ls-remote: initialize repository based on fetch
t5500: make hash independent
serve: advertise object-format capability for protocol v2
connect: parse v2 refs with correct hash algorithm
connect: pass full packet reader when parsing v2 refs
Documentation/technical: document object-format for protocol v2
t1302: expect repo format version 1 for SHA-256
builtin/show-index: provide options to determine hash algo
t5302: modernize test formatting
...
The "fetch/clone" protocol has been updated to allow the server to
instruct the clients to grab pre-packaged packfile(s) in addition
to the packed object data coming over the wire.
* jt/cdn-offload:
upload-pack: fix a sparse '0 as NULL pointer' warning
upload-pack: send part of packfile response as uri
fetch-pack: support more than one pack lockfile
upload-pack: refactor reading of pack-objects out
Documentation: add Packfile URIs design doc
Documentation: order protocol v2 sections
http-fetch: support fetching packfiles by URL
http-fetch: refactor into function
http: refactor finish_http_pack_request()
http: use --stdin when indexing dumb HTTP pack
Preliminary clean-ups around refs API, plus file format
specification documentation for the reftable backend.
* hn/refs-cleanup:
reftable: define version 2 of the spec to accomodate SHA256
reftable: clarify how empty tables should be written
reftable: file format documentation
refs: improve documentation for ref iterator
t: use update-ref and show-ref to reading/writing refs
refs.h: clarify reflog iteration order
The current C Git implementation expects Git servers to follow a
specific order of sections when transmitting protocol v2 responses, but
this is not explicit in the documentation. Make the order explicit.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Version appends a hash ID to the file header, making it slightly larger.
This commit also changes "SHA-1" into "object ID" in many places.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The format allows for some ambiguity, as a lone footer also starts
with a valid file header. However, the current JGit code will barf on
this. This commit codifies this behavior into the standard.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Shawn Pearce explains:
Some repositories contain a lot of references (e.g. android at 866k,
rails at 31k). The reftable format provides:
- Near constant time lookup for any single reference, even when the
repository is cold and not in process or kernel cache.
- Near constant time verification if a SHA-1 is referred to by at least
one reference (for allow-tip-sha1-in-want).
- Efficient lookup of an entire namespace, such as `refs/tags/`.
- Support atomic push `O(size_of_update)` operations.
- Combine reflog storage with ref storage.
This file format spec was originally written in July, 2017 by Shawn
Pearce. Some refinements since then were made by Shawn and by Han-Wen
Nienhuys based on experiences implementing and experimenting with the
format. (All of this was in the context of our work at Google and
Google is happy to contribute the result to the Git project.)
Imported from JGit[1]'s current version (c217d33ff,
"Documentation/technical/reftable: improve repo layout", 2020-02-04)
of Documentation/technical/reftable.md and converted to asciidoc by
running
pandoc -t asciidoc -f markdown reftable.md >reftable.txt
using pandoc 2.2.1. The result required the following additional
minor changes:
- removed the [TOC] directive to add a table of contents, since
asciidoc does not support it
- replaced git-scm.com/docs links with linkgit: directives that link
to other pages within Git's documentation
[1] https://eclipse.googlesource.com/jgit/jgit
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
On-the-wire protocol v2 easily falls into a deadlock between the
remote-curl helper and the fetch-pack process when the server side
prematurely throws an error and disconnects. The communication has
been updated to make it more robust.
* dl/remote-curl-deadlock-fix:
stateless-connect: send response end packet
pkt-line: define PACKET_READ_RESPONSE_END
remote-curl: error on incomplete packet
pkt-line: extern packet_length()
transport: extract common fetch_pack() call
remote-curl: remove label indentation
remote-curl: fix typo
The commit-graph format specifies that "All 4-byte numbers are in
network order", but the commit-graph contains 8-byte integers as well
(file offsets in the Chunk Lookup table), and their byte order is
unspecified.
Clarify that all multi-byte integers are in network byte order.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Document the object-format extension for protocol v2.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Currently, remote-curl acts as a proxy and blindly forwards packets
between an HTTP server and fetch-pack. In the case of a stateless RPC
connection where the connection is terminated before the transaction is
complete, remote-curl will blindly forward the packets before waiting on
more input from fetch-pack. Meanwhile, fetch-pack will read the
transaction and continue reading, expecting more input to continue the
transaction. This results in a deadlock between the two processes.
This can be seen in the following command which does not terminate:
$ git -c protocol.version=2 clone https://github.com/git/git.git --shallow-since=20151012
Cloning into 'git'...
whereas the v1 version does terminate as expected:
$ git -c protocol.version=1 clone https://github.com/git/git.git --shallow-since=20151012
Cloning into 'git'...
fatal: the remote end hung up unexpectedly
Instead of blindly forwarding packets, make remote-curl insert a
response end packet after proxying the responses from the remote server
when using stateless_connect(). On the RPC client side, ensure that each
response ends as described.
A separate control packet is chosen because we need to be able to
differentiate between what the remote server sends and remote-curl's
control packets. By ensuring in the remote-curl code that a server
cannot send response end packets, we prevent a malicious server from
being able to perform a denial of service attack in which they spoof a
response end packet and cause the described deadlock to happen.
Reported-by: Force Charlie <charlieio@outlook.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The first four bytes of the line, the pkt-len, indicates the total
length of the pkt-line in hexadecimal. Fix wrong pkt-len headers of
some pkt-line messages in `http-protocol.txt` and `pack-protocol.txt`.
Reviewed-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Jiuyang Xie <jiuyang.xjy@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Code cleanup and typofixes
* ds/bloom-cleanup:
completion: offer '--(no-)patch' among 'git log' options
bloom: use num_changes not nr for limit detection
bloom: de-duplicate directory entries
Documentation: changed-path Bloom filters use byte words
bloom: parse commit before computing filters
test-bloom: fix usage typo
bloom: fix whitespace around tab length
Document a capability that indicates which hash algorithms are in use by
both sides of a remote connection. Use the term "object-format", since
this is the term used for the repository extension as well.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In Documentation/technical/commit-graph-format.txt, the definition
of the BIDX chunk specifies the length is a number of 8-byte words.
During development we discovered that using 8-byte words in the
Murmur3 hash algorithm causes issues with big-endian versus little-
endian machines. Thus, the hash algorithm was adapted to work on a
byte-by-byte basis. However, this caused a change in the definition
of a "word" in bloom.h. Now, a "word" is a single byte, which allows
filters to be as small as two bytes. These length-two filters are
demonstrated in t0095-bloom.sh, and a larger filter of length 25 is
demonstrated as well.
The original point of using 8-byte words was for alignment reasons.
It also presented opportunities for extremely sparse Bloom filters
when there were a small number of changes at a commit, creating a
very low false-positive rate. However, modifying the format at this
point is unlikely to be a valuable exercise. Also, this use of
single-byte granularity does present opportunities to save space.
It is unclear if 8-byte alignment of the filters would present any
meaningful performance benefits.
Modify the format document to reflect reality.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce an extension to the commit-graph to make it efficient to
check for the paths that were modified at each commit using Bloom
filters.
* gs/commit-graph-path-filter:
bloom: ignore renames when computing changed paths
commit-graph: add GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS test flag
t4216: add end to end tests for git log with Bloom filters
revision.c: add trace2 stats around Bloom filter usage
revision.c: use Bloom filters to speed up path based revision walks
commit-graph: add --changed-paths option to write subcommand
commit-graph: reuse existing Bloom filters during write
commit-graph: write Bloom filters to commit graph file
commit-graph: examine commits by generation number
commit-graph: examine changed-path objects in pack order
commit-graph: compute Bloom filters for changed paths
diff: halt tree-diff early after max_changes
bloom.c: core Bloom filter implementation for changed paths.
bloom.c: introduce core Bloom filter constructs
bloom.c: add the murmur3 hash implementation
commit-graph: define and use MAX_NUM_CHUNKS
Update the technical documentation for commit-graph-format with
the formats for the Bloom filter index (BIDX) and Bloom filter
data (BDAT) chunks. Write the computed Bloom filters information
to the commit graph file using this format.
Helped-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Garima Singh <garima.singh@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Via trace2, Git can already log interesting config parameters (see the
trace2_cmd_list_config() function). However, this can grant an
incomplete picture because many config parameters also allow overrides
via environment variables.
To allow for more complete logs, we add a new trace2_cmd_list_env_vars()
function and supporting implementation, modeled after the pre-existing
config param logging implementation.
Signed-off-by: Josh Steadmon <steadmon@google.com>
Acked-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The description of the multi-pack-index contains a small bug,
if all offsets are < 2^32 then there will be no LOFF chunk,
not only if they're all < 2^31 (since the highest bit is only
needed as the "LOFF-escape" when that's actually needed.)
Correct this, and clarify that in that case only offsets up
to 2^31-1 can be stored in the OOFF chunk.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bundle format was not documented. Describe the format with ABNF and
explain the meaning of each part.
Signed-off-by: Masaya Suzuki <masayasuzuki@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
