Due to scalability issues, Shawn Pearce has originally proposed a new
"reftable" format more than six years ago [1]. Initially, this new
format was implemented in JGit with promising results. Around two years
ago, we have then added the "reftable" library to the Git codebase via
a4bbd13be3 (Merge branch 'hn/reftable', 2021-12-15). With this we have
landed all the low-level code to read and write reftables. Notably
missing though was the integration of this low-level code into the Git
code base in the form of a new ref backend that ties all of this
together.
This gap is now finally closed by introducing a new "reftable" backend
into the Git codebase. This new backend promises to bring some notable
improvements to Git repositories:
- It becomes possible to do truly atomic writes where either all refs
are committed to disk or none are. This was not possible with the
"files" backend because ref updates were split across multiple loose
files.
- The disk space required to store many refs is reduced, both compared
to loose refs and packed-refs. This is enabled both by the reftable
format being a binary format, which is more compact, and by prefix
compression.
- We can ignore filesystem-specific behaviour as ref names are not
encoded via paths anymore. This means there is no need to handle
case sensitivity on Windows systems or Unicode precomposition on
macOS.
- There is no need to rewrite the complete refdb anymore every time a
ref is being deleted like it was the case for packed-refs. This
means that ref deletions are now constant time instead of scaling
linearly with the number of refs.
- We can ignore file/directory conflicts so that it becomes possible
to store both "refs/heads/foo" and "refs/heads/foo/bar".
- Due to this property we can retain reflogs for deleted refs. We have
previously been deleting reflogs together with their refs to avoid
file/directory conflicts, which is not necessary anymore.
- We can properly enumerate all refs. With the "files" backend it is
not easily possible to distinguish between refs and non-refs because
they may live side by side in the gitdir.
Not all of these improvements are realized with the current "reftable"
backend implementation. At this point, the new backend is supposed to be
a drop-in replacement for the "files" backend that is used by basically
all Git repositories nowadays. It strives for 1:1 compatibility, which
means that a user can expect the same behaviour regardless of whether
they use the "reftable" backend or the "files" backend for most of the
part.
Most notably, this means we artificially limit the capabilities of the
"reftable" backend to match the limits of the "files" backend. It is not
possible to create refs that would end up with file/directory conflicts,
we do not retain reflogs, we perform stricter-than-necessary checks.
This is done intentionally due to two main reasons:
- It makes it significantly easier to land the "reftable" backend as
tests behave the same. It would be tough to argue for each and every
single test that doesn't pass with the "reftable" backend.
- It ensures compatibility between repositories that use the "files"
backend and repositories that use the "reftable" backend. Like this,
hosters can migrate their repositories to use the "reftable" backend
without causing issues for clients that use the "files" backend in
their clones.
It is expected that these artificial limitations may eventually go away
in the long term.
Performance-wise things very much depend on the actual workload. The
following benchmarks compare the "files" and "reftable" backends in the
current version:
- Creating N refs in separate transactions shows that the "files"
backend is ~50% faster. This is not surprising given that creating a
ref only requires us to create a single loose ref. The "reftable"
backend will also perform auto compaction on updates. In real-world
workloads we would likely also want to perform pack loose refs,
which would likely change the picture.
Benchmark 1: update-ref: create refs sequentially (refformat = files, refcount = 1)
Time (mean ± σ): 2.1 ms ± 0.3 ms [User: 0.6 ms, System: 1.7 ms]
Range (min … max): 1.8 ms … 4.3 ms 133 runs
Benchmark 2: update-ref: create refs sequentially (refformat = reftable, refcount = 1)
Time (mean ± σ): 2.7 ms ± 0.1 ms [User: 0.6 ms, System: 2.2 ms]
Range (min … max): 2.4 ms … 2.9 ms 132 runs
Benchmark 3: update-ref: create refs sequentially (refformat = files, refcount = 1000)
Time (mean ± σ): 1.975 s ± 0.006 s [User: 0.437 s, System: 1.535 s]
Range (min … max): 1.969 s … 1.980 s 3 runs
Benchmark 4: update-ref: create refs sequentially (refformat = reftable, refcount = 1000)
Time (mean ± σ): 2.611 s ± 0.013 s [User: 0.782 s, System: 1.825 s]
Range (min … max): 2.597 s … 2.622 s 3 runs
Benchmark 5: update-ref: create refs sequentially (refformat = files, refcount = 100000)
Time (mean ± σ): 198.442 s ± 0.241 s [User: 43.051 s, System: 155.250 s]
Range (min … max): 198.189 s … 198.670 s 3 runs
Benchmark 6: update-ref: create refs sequentially (refformat = reftable, refcount = 100000)
Time (mean ± σ): 294.509 s ± 4.269 s [User: 104.046 s, System: 190.326 s]
Range (min … max): 290.223 s … 298.761 s 3 runs
- Creating N refs in a single transaction shows that the "files"
backend is significantly slower once we start to write many refs.
The "reftable" backend only needs to update two files, whereas the
"files" backend needs to write one file per ref.
Benchmark 1: update-ref: create many refs (refformat = files, refcount = 1)
Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.4 ms, System: 1.4 ms]
Range (min … max): 1.8 ms … 2.6 ms 151 runs
Benchmark 2: update-ref: create many refs (refformat = reftable, refcount = 1)
Time (mean ± σ): 2.5 ms ± 0.1 ms [User: 0.7 ms, System: 1.7 ms]
Range (min … max): 2.4 ms … 3.4 ms 148 runs
Benchmark 3: update-ref: create many refs (refformat = files, refcount = 1000)
Time (mean ± σ): 152.5 ms ± 5.2 ms [User: 19.1 ms, System: 133.1 ms]
Range (min … max): 148.5 ms … 167.8 ms 15 runs
Benchmark 4: update-ref: create many refs (refformat = reftable, refcount = 1000)
Time (mean ± σ): 58.0 ms ± 2.5 ms [User: 28.4 ms, System: 29.4 ms]
Range (min … max): 56.3 ms … 72.9 ms 40 runs
Benchmark 5: update-ref: create many refs (refformat = files, refcount = 1000000)
Time (mean ± σ): 152.752 s ± 0.710 s [User: 20.315 s, System: 131.310 s]
Range (min … max): 152.165 s … 153.542 s 3 runs
Benchmark 6: update-ref: create many refs (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 51.912 s ± 0.127 s [User: 26.483 s, System: 25.424 s]
Range (min … max): 51.769 s … 52.012 s 3 runs
- Deleting a ref in a fully-packed repository shows that the "files"
backend scales with the number of refs. The "reftable" backend has
constant-time deletions.
Benchmark 1: update-ref: delete ref (refformat = files, refcount = 1)
Time (mean ± σ): 1.7 ms ± 0.1 ms [User: 0.4 ms, System: 1.2 ms]
Range (min … max): 1.6 ms … 2.1 ms 316 runs
Benchmark 2: update-ref: delete ref (refformat = reftable, refcount = 1)
Time (mean ± σ): 1.8 ms ± 0.1 ms [User: 0.4 ms, System: 1.3 ms]
Range (min … max): 1.7 ms … 2.1 ms 294 runs
Benchmark 3: update-ref: delete ref (refformat = files, refcount = 1000)
Time (mean ± σ): 2.0 ms ± 0.1 ms [User: 0.5 ms, System: 1.4 ms]
Range (min … max): 1.9 ms … 2.5 ms 287 runs
Benchmark 4: update-ref: delete ref (refformat = reftable, refcount = 1000)
Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.5 ms, System: 1.3 ms]
Range (min … max): 1.8 ms … 2.1 ms 217 runs
Benchmark 5: update-ref: delete ref (refformat = files, refcount = 1000000)
Time (mean ± σ): 229.8 ms ± 7.9 ms [User: 182.6 ms, System: 46.8 ms]
Range (min … max): 224.6 ms … 245.2 ms 6 runs
Benchmark 6: update-ref: delete ref (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 2.0 ms ± 0.0 ms [User: 0.6 ms, System: 1.3 ms]
Range (min … max): 2.0 ms … 2.1 ms 3 runs
- Listing all refs shows no significant advantage for either of the
backends. The "files" backend is a bit faster, but not by a
significant margin. When repositories are not packed the "reftable"
backend outperforms the "files" backend because the "reftable"
backend performs auto-compaction.
Benchmark 1: show-ref: print all refs (refformat = files, refcount = 1, packed = true)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.0 ms 1729 runs
Benchmark 2: show-ref: print all refs (refformat = reftable, refcount = 1, packed = true)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 1.8 ms 1816 runs
Benchmark 3: show-ref: print all refs (refformat = files, refcount = 1000, packed = true)
Time (mean ± σ): 4.3 ms ± 0.1 ms [User: 0.9 ms, System: 3.3 ms]
Range (min … max): 4.1 ms … 4.6 ms 645 runs
Benchmark 4: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = true)
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.0 ms, System: 3.3 ms]
Range (min … max): 4.2 ms … 5.9 ms 643 runs
Benchmark 5: show-ref: print all refs (refformat = files, refcount = 1000000, packed = true)
Time (mean ± σ): 2.537 s ± 0.034 s [User: 0.488 s, System: 2.048 s]
Range (min … max): 2.511 s … 2.627 s 10 runs
Benchmark 6: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = true)
Time (mean ± σ): 2.712 s ± 0.017 s [User: 0.653 s, System: 2.059 s]
Range (min … max): 2.692 s … 2.752 s 10 runs
Benchmark 7: show-ref: print all refs (refformat = files, refcount = 1, packed = false)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 1.9 ms 1834 runs
Benchmark 8: show-ref: print all refs (refformat = reftable, refcount = 1, packed = false)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 2.0 ms 1840 runs
Benchmark 9: show-ref: print all refs (refformat = files, refcount = 1000, packed = false)
Time (mean ± σ): 13.8 ms ± 0.2 ms [User: 2.8 ms, System: 10.8 ms]
Range (min … max): 13.3 ms … 14.5 ms 208 runs
Benchmark 10: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = false)
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.2 ms, System: 3.3 ms]
Range (min … max): 4.3 ms … 6.2 ms 624 runs
Benchmark 11: show-ref: print all refs (refformat = files, refcount = 1000000, packed = false)
Time (mean ± σ): 12.127 s ± 0.129 s [User: 2.675 s, System: 9.451 s]
Range (min … max): 11.965 s … 12.370 s 10 runs
Benchmark 12: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = false)
Time (mean ± σ): 2.799 s ± 0.022 s [User: 0.735 s, System: 2.063 s]
Range (min … max): 2.769 s … 2.836 s 10 runs
- Printing a single ref shows no real difference between the "files"
and "reftable" backends.
Benchmark 1: show-ref: print single ref (refformat = files, refcount = 1)
Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.4 ms, System: 1.0 ms]
Range (min … max): 1.4 ms … 1.8 ms 1779 runs
Benchmark 2: show-ref: print single ref (refformat = reftable, refcount = 1)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 2.5 ms 1753 runs
Benchmark 3: show-ref: print single ref (refformat = files, refcount = 1000)
Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.3 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 1.9 ms 1840 runs
Benchmark 4: show-ref: print single ref (refformat = reftable, refcount = 1000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.0 ms 1831 runs
Benchmark 5: show-ref: print single ref (refformat = files, refcount = 1000000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.1 ms 1848 runs
Benchmark 6: show-ref: print single ref (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.1 ms 1762 runs
So overall, performance depends on the usecases. Except for many
sequential writes the "reftable" backend is roughly on par or
significantly faster than the "files" backend though. Given that the
"files" backend has received 18 years of optimizations by now this can
be seen as a win. Furthermore, we can expect that the "reftable" backend
will grow faster over time when attention turns more towards
optimizations.
The complete test suite passes, except for those tests explicitly marked
to require the REFFILES prerequisite. Some tests in t0610 are marked as
failing because they depend on still-in-flight bug fixes. Tests can be
run with the new backend by setting the GIT_TEST_DEFAULT_REF_FORMAT
environment variable to "reftable".
There is a single known conceptual incompatibility with the dumb HTTP
transport. As "info/refs" SHOULD NOT contain the HEAD reference, and
because the "HEAD" file is not valid anymore, it is impossible for the
remote client to figure out the default branch without changing the
protocol. This shortcoming needs to be handled in a subsequent patch
series.
As the reftable library has already been introduced a while ago, this
commit message will not go into the details of how exactly the on-disk
format works. Please refer to our preexisting technical documentation at
Documentation/technical/reftable for this.
[1]: https://public-inbox.org/git/CAJo=hJtyof=HRy=2sLP0ng0uZ4=S-DpZ5dR1aF+VHVETKG20OQ@mail.gmail.com/
Original-idea-by: Shawn Pearce <spearce@spearce.org>
Based-on-patch-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a new "extensions.refStorage" extension that allows us to
specify the ref storage format used by a repository. For now, the only
supported format is the "files" format, but this list will likely soon
be extended to also support the upcoming "reftable" format.
There have been discussions on the Git mailing list in the past around
how exactly this extension should look like. One alternative [1] that
was discussed was whether it would make sense to model the extension in
such a way that backends are arbitrarily stackable. This would allow for
a combined value of e.g. "loose,packed-refs" or "loose,reftable", which
indicates that new refs would be written via "loose" files backend and
compressed into "packed-refs" or "reftable" backends, respectively.
It is arguable though whether this flexibility and the complexity that
it brings with it is really required for now. It is not foreseeable that
there will be a proliferation of backends in the near-term future, and
the current set of existing formats and formats which are on the horizon
can easily be configured with the much simpler proposal where we have a
single value, only.
Furthermore, if we ever see that we indeed want to gain the ability to
arbitrarily stack the ref formats, then we can adapt the current
extension rather easily. Given that Git clients will refuse any unknown
value for the "extensions.refStorage" extension they would also know to
ignore a stacked "loose,packed-refs" in the future.
So let's stick with the easy proposal for the time being and wire up the
extension.
[1]: <pull.1408.git.1667846164.gitgitgadget@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Process to add some form of low-level unit tests has started.
* js/doc-unit-tests:
ci: run unit tests in CI
unit tests: add TAP unit test framework
unit tests: add a project plan document
In our current testing environment, we spend a significant amount of
effort crafting end-to-end tests for error conditions that could easily
be captured by unit tests (or we simply forgo some hard-to-setup and
rare error conditions). Describe what we hope to accomplish by
implementing unit tests, and explain some open questions and milestones.
Discuss desired features for test frameworks/harnesses, and provide a
comparison of several different frameworks. Finally, document our
rationale for implementing a custom framework.
Co-authored-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Header files cleanup.
* en/header-split-cache-h-part-3: (28 commits)
fsmonitor-ll.h: split this header out of fsmonitor.h
hash-ll, hashmap: move oidhash() to hash-ll
object-store-ll.h: split this header out of object-store.h
khash: name the structs that khash declares
merge-ll: rename from ll-merge
git-compat-util.h: remove unneccessary include of wildmatch.h
builtin.h: remove unneccessary includes
list-objects-filter-options.h: remove unneccessary include
diff.h: remove unnecessary include of oidset.h
repository: remove unnecessary include of path.h
log-tree: replace include of revision.h with simple forward declaration
cache.h: remove this no-longer-used header
read-cache*.h: move declarations for read-cache.c functions from cache.h
repository.h: move declaration of the_index from cache.h
merge.h: move declarations for merge.c from cache.h
diff.h: move declaration for global in diff.c from cache.h
preload-index.h: move declarations for preload-index.c from elsewhere
sparse-index.h: move declarations for sparse-index.c from cache.h
name-hash.h: move declarations for name-hash.c from cache.h
run-command.h: move declarations for run-command.c from cache.h
...
A long term (but rather minor) pet-peeve of mine was the name
ll-merge.[ch]. I thought it made it harder to realize what stuff was
related to merging when I was working on the merge machinery and trying
to improve it.
Further, back in d1cbe1e6d8 ("hash-ll.h: split out of hash.h to remove
dependency on repository.h", 2023-04-22), we have split the portions of
hash.h that do not depend upon repository.h into a "hash-ll.h" (due to
the recommendation to use "ll" for "low-level" in its name[1], but which
I used as a suffix precisely because of my distaste for "ll-merge").
When we discussed adding additional "*-ll.h" files, a request was made
that we use "ll" consistently as either a prefix or a suffix. Since it
is already in use as both a prefix and a suffix, the only way to do so
is to rename some files.
Besides my distaste for the ll-merge.[ch] name, let me also note that
the files
ll-fsmonitor.h, ll-hash.h, ll-merge.h, ll-object-store.h, ll-read-cache.h
would have essentially nothing to do with each other and make no sense
to group. But giving them the common "ll-" prefix would group them. Using
"-ll" as a suffix thus seems just much more logical to me. Rename
ll-merge.[ch] to merge-ll.[ch] to achieve this consistency, and to
ensure we get a more logical grouping of files.
[1] https://lore.kernel.org/git/kl6lsfcu1g8w.fsf@chooglen-macbookpro.roam.corp.google.com/
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
These were found with an automated CLI tool [1]. Only the
"Documentation" subfolder (and not source code files) was considered
because the docs are user-facing.
[1]: https://crates.io/crates/typos-cli
Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bundle-URI subsystem adds support for creation-token heuristics
to help incremental fetches.
* ds/bundle-uri-5:
bundle-uri: test missing bundles with heuristic
bundle-uri: store fetch.bundleCreationToken
fetch: fetch from an external bundle URI
bundle-uri: drop bundle.flag from design doc
clone: set fetch.bundleURI if appropriate
bundle-uri: download in creationToken order
bundle-uri: parse bundle.<id>.creationToken values
bundle-uri: parse bundle.heuristic=creationToken
t5558: add tests for creationToken heuristic
bundle: verify using check_connected()
bundle: test unbundling with incomplete history
The Implementation Plan section lists a 'bundle.flag' option that is not
documented anywhere else. What is documented elsewhere in the document
and implemented by previous changes is the 'bundle.heuristic' config
key. For now, a heuristic is required to indicate that a bundle list is
organized for use during 'git fetch', and it is also sufficient for all
existing designs.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Three hyphens are rendered verbatim in documentation, so "--" has to be
used to produce a dash. Fix asciidoc output for dashes. This is
similar to previous commits f0b922473e (Documentation: render special
characters correctly, 2021-07-29) and de82095a95 (doc
hash-function-transition: fix asciidoc output, 2021-02-05).
Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remotes are considered "promisor" if extensions.partialClone and some
other configuration variables are set. The casing for this in
Documentation/technical/repository-version.txt is not proper and may
cause confusion. This change corrects this casing.
Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
The glossary entries for "commit-graph file" and "reachability
bitmap" have been added.
* po/glossary-around-traversal:
glossary: add reachability bitmap description
glossary: add "commit graph" description
doc: use 'object database' not ODB or abbreviation
doc: use "commit-graph" hyphenation consistently
Once upon a time, Matheus wrote some patches to make
git grep [--cached | <REVISION>] ...
restrict its output to the sparsity specification when working in a
sparse checkout[1]. That effort got derailed by two things:
(1) The --sparse-index work just beginning which we wanted to avoid
creating conflicts for
(2) Never deciding on flag and config names and planned high level
behavior for all commands.
More recently, Shaoxuan implemented a more limited form of Matheus'
patches that only affected --cached, using a different flag name,
but also changing the default behavior in line with what Matheus did.
This again highlighted the fact that we never decided on command line
flag names, config option names, and the big picture path forward.
The --sparse-index work has been mostly complete (or at least released
into production even if some small edges remain) for quite some time
now. We have also had several discussions on flag and config names,
though we never came to solid conclusions. Stolee once upon a time
suggested putting all these into some document in
Documentation/technical[3], which Victoria recently also requested[4].
I'm behind the times, but here's a patch attempting to finally do that.
[1] https://lore.kernel.org/git/5f3f7ac77039d41d1692ceae4b0c5df3bb45b74a.1612901326.git.matheus.bernardino@usp.br/
(See his second link in that email in particular)
[2] https://lore.kernel.org/git/20220908001854.206789-2-shaoxuan.yuan02@gmail.com/
[3] https://lore.kernel.org/git/CABPp-BHwNoVnooqDFPAsZxBT9aR5Dwk5D9sDRCvYSb8akxAJgA@mail.gmail.com/
(Scroll to the very end for the final few paragraphs)
[4] https://lore.kernel.org/git/cafcedba-96a2-cb85-d593-ef47c8c8397c@github.com/
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
The abbreviation 'ODB' is used in the technical documentation
sections for commit-graph and parallel-checkout, along with an
'odb' option in `git-pack-redundant`, without expansion.
Use 'object database' in full, in those entries. The text has not
been reflowed to keep the changes minimal.
While in the glossary for `object` terms, add the common`oid`
abbreviation to its entry.
Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Note, historical release notes have not been updated.
Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Add global counters mechanism to Trace2.
The Trace2 counters mechanism adds the ability to create a set of
global counter variables and an API to increment them efficiently.
Counters can optionally report per-thread usage in addition to the sum
across all threads.
Counter events are emitted to the Trace2 logs when a thread exits and
at process exit.
Counters are an alternative to `data` and `data_json` events.
Counters are useful when you want to measure something across the life
of the process, when you don't want per-measurement events for
performance reasons, when the data does not fit conveniently within a
region, or when your control flow does not easily let you write the
final total. For example, you might use this to report the number of
calls to unzip() or the number of de-delta steps during a checkout.
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add stopwatch timer mechanism to Trace2.
Timers are an alternative to Trace2 Regions. Regions are useful for
measuring the time spent in various computation phases, such as the
time to read the index, time to scan for unstaged files, time to scan
for untracked files, and etc.
However, regions are not appropriate in all places. For example,
during a checkout, it would be very inefficient to use regions to
measure the total time spent inflating objects from the ODB from
across the entire lifetime of the process; a per-unzip() region would
flood the output and significantly slow the command; and some form of
post-processing would be requried to compute the time spent in unzip().
Timers can be used to measure a series of timer intervals and emit
a single summary event (at thread and/or process exit).
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Eliminate the mostly obsolete `Public API` sub-section from the
`Trace2 API` section in the documentation. Strengthen the referral
to `trace2.h`.
Most of the technical information in this sub-section was moved to
`trace2.h` in 6c51cb525d (trace2: move doc to trace2.h, 2019-11-17) to
be adjacent to the function prototypes. The remaining text wasn't
that useful by itself.
Furthermore, the text would need a bit of overhaul to add routines
that do not immediately generate a message, such as stopwatch timers.
So it seemed simpler to just get rid of it.
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reduce or eliminate use of the term "TLS" in the Trace2 code.
The term "TLS" has two popular meanings: "thread-local storage" and
"transport layer security". In the Trace2 source, the term is associated
with the former. There was concern on the mailing list about it refering
to the latter.
Update the source and documentation to eliminate the use of the "TLS" term
or replace it with the phrase "thread-local storage" to reduce ambiguity.
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Two documentation issues exist in the technical docs for the bundle URI
feature.
First, there is an extraneous "the" across a linebreak, making the
nonsensical phrase "the bundle the list" which should just be "the
bundle list".
Secondly, the asciidoc update treats the string "`have`s" as starting a
"<code>" block, but the second tick is interpreted as an apostrophe
instead of a closing "</code>" tag. This causes entire sentences to be
formatted as code until the next one comes along. Simply adding a space
here does not work properly as the rendered HTML keeps that space.
Instead, restructure the sentence slightly to avoid using a plural,
allowing the HTML to render correctly.
Reported-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Used GNU "aspell check <filename>" to review various technical
documentation files with the default aspell dictionary. Ignored
false-positives between american and british english.
Signed-off-by: Jacob Stopak <jacob@initialcommit.io>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Hoist the remainder of "scalar" out of contrib/ to the main part of
the codebase.
* vd/scalar-to-main:
Documentation/technical: include Scalar technical doc
t/perf: add 'GIT_PERF_USE_SCALAR' run option
t/perf: add Scalar performance tests
scalar-clone: add test coverage
scalar: add to 'git help -a' command list
scalar: implement the `help` subcommand
git help: special-case `scalar`
scalar: include in standard Git build & installation
scalar: fix command documentation section header
In f6d25d7878 (api docs: document that BUG() emits a trace2 error event,
2021-04-13), a link to the plain text version of api-trace2 was added in
`technical/api-error-handling.txt`.
All of our other `link:`s point to the html versions. Do the same here.
Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some links were broken in the recent move of various technical docs
c0f6dd49f1 (Merge branch 'ab/tech-docs-to-help', 2022-08-14).
Fix them.
Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Inspired by 24966cd982 ("doc: fix repeated words", 08-09-2019),
I ran "egrep -R "\<([a-zA-Z]+)\> \<\1\>" ./Documentation/*" to
find current cases of repeated words such as "the the" that were
quite clearly typos.
There were many false positives reported, such as "really really"
or valid uses of "that that" which I left alone.
Signed-off-by: Jacob Stopak <jacob@initialcommit.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The pack bitmap file gained a bitmap-lookup table to speed up
locating the necessary bitmap for a given commit.
* ac/bitmap-lookup-table:
pack-bitmap-write: drop unused pack_idx_entry parameters
bitmap-lookup-table: add performance tests for lookup table
pack-bitmap: prepare to read lookup table extension
pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests
pack-bitmap-write.c: write lookup table extension
bitmap: move `get commit positions` code to `bitmap_writer_finish`
Documentation/technical: describe bitmap lookup table extension
Include 'Documentation/technical/scalar.txt' alongside the other HTML
technical docs when installing them.
Now that the document is intended as a widely-accessible reference, remove
the internal work-in-progress roadmap from the document. Those details
should no longer be needed to guide Scalar's development and, if they were
left, they could fall out-of-date and be misleading to readers.
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce the "subcommand" mode to parse-options API and update the
command line parser of Git commands with subcommands.
* sg/parse-options-subcommand: (23 commits)
remote: run "remote rm" argv through parse_options()
maintenance: add parse-options boilerplate for subcommands
pass subcommand "prefix" arguments to parse_options()
builtin/worktree.c: let parse-options parse subcommands
builtin/stash.c: let parse-options parse subcommands
builtin/sparse-checkout.c: let parse-options parse subcommands
builtin/remote.c: let parse-options parse subcommands
builtin/reflog.c: let parse-options parse subcommands
builtin/notes.c: let parse-options parse subcommands
builtin/multi-pack-index.c: let parse-options parse subcommands
builtin/hook.c: let parse-options parse subcommands
builtin/gc.c: let parse-options parse 'git maintenance's subcommands
builtin/commit-graph.c: let parse-options parse subcommands
builtin/bundle.c: let parse-options parse subcommands
parse-options: add support for parsing subcommands
parse-options: drop leading space from '--git-completion-helper' output
parse-options: clarify the limitations of PARSE_OPT_NODASH
parse-options: PARSE_OPT_KEEP_UNKNOWN only applies to --options
api-parse-options.txt: fix description of OPT_CMDMODE
t0040-parse-options: test parse_options() with various 'parse_opt_flags'
...
"scalar" now enables built-in fsmonitor on enlisted repositories,
when able.
* vd/scalar-enables-fsmonitor:
scalar: update technical doc roadmap with FSMonitor support
scalar unregister: stop FSMonitor daemon
scalar: enable built-in FSMonitor on `register`
scalar: move config setting logic into its own function
scalar-delete: do not 'die()' in 'delete_enlistment()'
scalar-[un]register: clearly indicate source of error
scalar-unregister: handle error codes greater than 0
scalar: constrain enlistment search
When reading bitmap file, Git loads each and every bitmap one by one
even if all the bitmaps are not required. A "bitmap lookup table"
extension to the bitmap format can reduce the overhead of loading
bitmaps which stores a list of bitmapped commit id pos (in the midx
or pack, along with their offset and xor offset. This way Git can
load only the necessary bitmaps without loading the previous bitmaps.
Older versions of Git ignore the lookup table extension and don't
throw any kind of warning or error while parsing the bitmap file.
Add some information for the new "bitmap lookup table" extension in the
bitmap-format documentation.
Mentored-by: Taylor Blau <me@ttaylorr.com>
Co-Mentored-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Co-Authored-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "diagnose" feature to create a zip archive for diagnostic
material has been lifted from "scalar" and made into a feature of
"git bugreport".
* vd/scalar-generalize-diagnose:
scalar: update technical doc roadmap
scalar-diagnose: use 'git diagnose --mode=all'
builtin/bugreport.c: create '--diagnose' option
builtin/diagnose.c: add '--mode' option
builtin/diagnose.c: create 'git diagnose' builtin
diagnose.c: add option to configure archive contents
scalar-diagnose: move functionality to common location
scalar-diagnose: move 'get_disk_info()' to 'compat/'
scalar-diagnose: add directory to archiver more gently
scalar-diagnose: avoid 32-bit overflow of size_t
scalar-diagnose: use "$GIT_UNZIP" in test
Several Git commands have subcommands to implement mutually exclusive
"operation modes", and they usually parse their subcommand argument
with a bunch of if-else if statements.
Teach parse-options to handle subcommands as well, which will result
in shorter and simpler code with consistent error handling and error
messages on unknown or missing subcommand, and it will also make
possible for our Bash completion script to handle subcommands
programmatically.
The approach is guided by the following observations:
- Most subcommands [1] are implemented in dedicated functions, and
most of those functions [2] either have a signature matching the
'int cmd_foo(int argc, const char **argc, const char *prefix)'
signature of builtin commands or can be trivially converted to
that signature, because they miss only that last prefix parameter
or have no parameters at all.
- Subcommand arguments only have long form, and they have no double
dash prefix, no negated form, and no description, and they don't
take any arguments, and can't be abbreviated.
- There must be exactly one subcommand among the arguments, or zero
if the command has a default operation mode.
- All arguments following the subcommand are considered to be
arguments of the subcommand, and, conversely, arguments meant for
the subcommand may not preceed the subcommand.
So in the end subcommand declaration and parsing would look something
like this:
parse_opt_subcommand_fn *fn = NULL;
struct option builtin_commit_graph_options[] = {
OPT_STRING(0, "object-dir", &opts.obj_dir, N_("dir"),
N_("the object directory to store the graph")),
OPT_SUBCOMMAND("verify", &fn, graph_verify),
OPT_SUBCOMMAND("write", &fn, graph_write),
OPT_END(),
};
argc = parse_options(argc, argv, prefix, options,
builtin_commit_graph_usage, 0);
return fn(argc, argv, prefix);
Here each OPT_SUBCOMMAND specifies the name of the subcommand and the
function implementing it, and the address of the same 'fn' subcommand
function pointer. parse_options() then processes the arguments until
it finds the first argument matching one of the subcommands, sets 'fn'
to the function associated with that subcommand, and returns, leaving
the rest of the arguments unprocessed. If none of the listed
subcommands is found among the arguments, parse_options() will show
usage and abort.
If a command has a default operation mode, 'fn' should be initialized
to the function implementing that mode, and parse_options() should be
invoked with the PARSE_OPT_SUBCOMMAND_OPTIONAL flag. In this case
parse_options() won't error out when not finding any subcommands, but
will return leaving 'fn' unchanged. Note that if that default
operation mode has any --options, then the PARSE_OPT_KEEP_UNKNOWN_OPT
flag is necessary as well (otherwise parse_options() would error out
upon seeing the unknown option meant to the default operation mode).
Some thoughts about the implementation:
- The same pointer to 'fn' must be specified as 'value' for each
OPT_SUBCOMMAND, because there can be only one set of mutually
exclusive subcommands; parse_options() will BUG() otherwise.
There are other ways to tell parse_options() where to put the
function associated with the subcommand given on the command line,
but I didn't like them:
- Change parse_options()'s signature by adding a pointer to
subcommand function to be set to the function associated with
the given subcommand, affecting all callsites, even those that
don't have subcommands.
- Introduce a specific parse_options_and_subcommand() variant
with that extra funcion parameter.
- I decided against automatically calling the subcommand function
from within parse_options(), because:
- There are commands that have to perform additional actions
after option parsing but before calling the function
implementing the specified subcommand.
- The return code of the subcommand is usually the return code
of the git command, but preserving the return code of the
automatically called subcommand function would have made the
API awkward.
- Also add a OPT_SUBCOMMAND_F() variant to allow specifying an
option flag: we have two subcommands that are purposefully
excluded from completion ('git remote rm' and 'git stash save'),
so they'll have to be specified with the PARSE_OPT_NOCOMPLETE
flag.
- Some of the 'parse_opt_flags' don't make sense with subcommands,
and using them is probably just an oversight or misunderstanding.
Therefore parse_options() will BUG() when invoked with any of the
following flags while the options array contains at least one
OPT_SUBCOMMAND:
- PARSE_OPT_KEEP_DASHDASH: parse_options() stops parsing
arguments when encountering a "--" argument, so it doesn't
make sense to expect and keep one before a subcommand, because
it would prevent the parsing of the subcommand.
However, this flag is allowed in combination with the
PARSE_OPT_SUBCOMMAND_OPTIONAL flag, because the double dash
might be meaningful for the command's default operation mode,
e.g. to disambiguate refs and pathspecs.
- PARSE_OPT_STOP_AT_NON_OPTION: As its name suggests, this flag
tells parse_options() to stop as soon as it encouners a
non-option argument, but subcommands are by definition not
options... so how could they be parsed, then?!
- PARSE_OPT_KEEP_UNKNOWN: This flag can be used to collect any
unknown --options and then pass them to a different command or
subsystem. Surely if a command has subcommands, then this
functionality should rather be delegated to one of those
subcommands, and not performed by the command itself.
However, this flag is allowed in combination with the
PARSE_OPT_SUBCOMMAND_OPTIONAL flag, making possible to pass
--options to the default operation mode.
- If the command with subcommands has a default operation mode, then
all arguments to the command must preceed the arguments of the
subcommand.
AFAICT we don't have any commands where this makes a difference,
because in those commands either only the command accepts any
arguments ('notes' and 'remote'), or only the default subcommand
('reflog' and 'stash'), but never both.
- The 'argv' array passed to subcommand functions currently starts
with the name of the subcommand. Keep this behavior. AFAICT no
subcommand functions depend on the actual content of 'argv[0]',
but the parse_options() call handling their options expects that
the options start at argv[1].
- To support handling subcommands programmatically in our Bash
completion script, 'git cmd --git-completion-helper' will now list
both subcommands and regular --options, if any. This means that
the completion script will have to separate subcommands (i.e.
words without a double dash prefix) from --options on its own, but
that's rather easy to do, and it's not much work either, because
the number of subcommands a command might have is rather low, and
those commands accept only a single --option or none at all. An
alternative would be to introduce a separate option that lists
only subcommands, but then the completion script would need not
one but two git invocations and command substitutions for commands
with subcommands.
Note that this change doesn't affect the behavior of our Bash
completion script, because when completing the --option of a
command with subcommands, e.g. for 'git notes --<TAB>', then all
subcommands will be filtered out anyway, as none of them will
match the word to be completed starting with that double dash
prefix.
[1] Except 'git rerere', because many of its subcommands are
implemented in the bodies of the if-else if statements parsing the
command's subcommand argument.
[2] Except 'credential', 'credential-store' and 'fsmonitor--daemon',
because some of the functions implementing their subcommands take
special parameters.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The description of 'PARSE_OPT_KEEP_UNKNOWN' starts with "Keep unknown
arguments instead of erroring out". This is a bit misleading, as this
flag only applies to unknown --options, while non-option arguments are
kept even without this flag.
Update the description to clarify this, and rename the flag to
PARSE_OPTIONS_KEEP_UNKNOWN_OPT to make this obvious just by looking at
the flag name.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
