Further clean-up the refs subsystem to stop relying on
the_repository, and instead use the repository associated to the
ref_store object.
* ps/refs-without-the-repository-updates:
refs/packed: remove references to `the_hash_algo`
refs/files: remove references to `the_hash_algo`
refs/files: use correct repository
refs: remove `dwim_log()`
refs: drop `git_default_branch_name()`
refs: pass repo when peeling objects
refs: move object peeling into "object.c"
refs: pass ref store when detecting dangling symrefs
refs: convert iteration over replace refs to accept ref store
refs: retrieve worktree ref stores via associated repository
refs: refactor `resolve_gitlink_ref()` to accept a repository
refs: pass repo when retrieving submodule ref store
refs: track ref stores via strmap
refs: implement releasing ref storages
refs: rename `init_db` callback to avoid confusion
refs: adjust names for `init` and `init_db` callbacks
Code clean-up to make the reftable iterator closer to be reusable.
* ps/reftable-reusable-iterator:
reftable/merged: adapt interface to allow reuse of iterators
reftable/stack: provide convenience functions to create iterators
reftable/reader: adapt interface to allow reuse of iterators
reftable/generic: adapt interface to allow reuse of iterators
reftable/generic: move seeking of records into the iterator
reftable/merged: simplify indices for subiterators
reftable/merged: split up initialization and seeking of records
reftable/reader: set up the reader when initializing table iterator
reftable/reader: inline `reader_seek_internal()`
reftable/reader: separate concerns of table iter and reftable reader
reftable/reader: unify indexed and linear seeking
reftable/reader: avoid copying index iterator
reftable/block: use `size_t` to track restart point index
The knobs to tweak how reftable files are written have been made
available as configuration variables.
* ps/reftable-write-options:
refs/reftable: allow configuring geometric factor
reftable: make the compaction factor configurable
refs/reftable: allow disabling writing the object index
refs/reftable: allow configuring restart interval
reftable: use `uint16_t` to track restart interval
refs/reftable: allow configuring block size
reftable/dump: support dumping a table's block structure
reftable/writer: improve error when passed an invalid block size
reftable/writer: drop static variable used to initialize strbuf
reftable: pass opts as constant pointer
reftable: consistently refer to `reftable_write_options` as `opts`
Terminology to call various ref-like things are getting
straightened out.
* ps/pseudo-ref-terminology:
refs: refuse to write pseudorefs
ref-filter: properly distinuish pseudo and root refs
refs: pseudorefs are no refs
refs: classify HEAD as a root ref
refs: do not check ref existence in `is_root_ref()`
refs: rename `is_special_ref()` to `is_pseudo_ref()`
refs: rename `is_pseudoref()` to `is_root_ref()`
Documentation/glossary: define root refs as refs
Documentation/glossary: clarify limitations of pseudorefs
Documentation/glossary: redefine pseudorefs as special refs
Updates to symbolic refs can now be made as a part of ref
transaction.
* kn/ref-transaction-symref:
refs: remove `create_symref` and associated dead code
refs: rename `refs_create_symref()` to `refs_update_symref()`
refs: use transaction in `refs_create_symref()`
refs: add support for transactional symref updates
refs: move `original_update_refname` to 'refs.c'
refs: support symrefs in 'reference-transaction' hook
files-backend: extract out `create_symref_lock()`
refs: accept symref values in `ref_transaction_update()`
Both `peel_object()` and `peel_iterated_oid()` implicitly rely on
`the_repository` to look up objects. Despite the fact that we want to
get rid of `the_repository`, it also leads to some restrictions in our
ref iterators when trying to retrieve the peeled value for a repository
other than `the_repository`.
Refactor these functions such that both take a repository as argument
and remove the now-unnecessary restrictions.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ref storages are typically only initialized once for `the_repository`
and then never released. Until now we got away with that without causing
memory leaks because `the_repository` stays reachable, and because the
ref backend is reachable via `the_repository` its memory basically never
leaks.
This is about to change though because of the upcoming migration logic,
which will create a secondary ref storage. In that case, we will either
have to release the old or new ref storage to avoid leaks.
Implement a new `release` callback and expose it via a new
`ref_storage_release()` function.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reference backends have two callbacks `init` and `init_db`. The
similarity of these two callbacks has repeatedly confused me whenever I
was looking at them, where I always had to look up which of them does
what.
Rename the `init_db` callback to `create_on_disk`, which should
hopefully be clearer.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Root refs are those refs that live in the root of the ref hierarchy.
Our old and venerable "HEAD" reference falls into this category, but we
don't yet classify it as such in `is_root_ref()`.
Adapt the function to also treat "HEAD" as a root ref. This change is
safe to do for all current callers:
- `ref_kind_from_refname()` already handles "HEAD" explicitly before
calling `is_root_ref()`.
- The "files" and "reftable" backends explicitly call both
`is_root_ref()` and `is_headref()` together.
This also aligns behaviour or `is_root_ref()` and `is_headref()` such
that we stop checking for ref existence. This changes semantics for our
backends:
- In the reftable backend we already know that the ref must exist
because `is_headref()` is called as part of the ref iterator. The
existence check is thus redundant, and the change is safe to do.
- In the files backend we use it when populating root refs, where we
would skip adding the "HEAD" file if it was not possible to resolve
it. The new behaviour is to instead mark "HEAD" as broken, which
will cause us to emit warnings in various places.
As there are no callers of `is_headref()` left afer the refactoring, we
can absorb it completely into `is_root_ref()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Before this patch series, root refs except for "HEAD" and our special
refs were classified as pseudorefs. Furthermore, our terminology
clarified that pseudorefs must not be symbolic refs. This restriction
is enforced in `is_root_ref()`, which explicitly checks that a supposed
root ref resolves to an object ID without recursing.
This has been extremely confusing right from the start because (in old
terminology) a ref name may sometimes be a pseudoref and sometimes not
depending on whether it is a symbolic or regular ref. This behaviour
does not seem reasonable at all and I very much doubt that it results in
anything sane.
Last but not least, the current behaviour can actually lead to a
segfault when calling `is_root_ref()` with a reference that either does
not exist or that is a symbolic ref because we never initialized `oid`,
but then read it via `is_null_oid()`.
We have now changed terminology to clarify that pseudorefs are really
only "MERGE_HEAD" and "FETCH_HEAD", whereas all the other refs that live
in the root of the ref hierarchy are just plain refs. Thus, we do not
need to check whether the ref is symbolic or not. In fact, we can now
avoid looking up the ref completely as the name is sufficient for us to
figure out whether something would be a root ref or not.
This change of course changes semantics for our callers. As there are
only three of them we can assess each of them individually:
- "ref-filter.c:ref_kind_from_refname()" uses it to classify refs.
It's clear that the intent is to classify based on the ref name,
only.
- "refs/reftable_backend.c:reftable_ref_iterator_advance()" uses it to
filter root refs. Again, using existence checks is pointless here as
the iterator has just surfaced the ref, so we know it does exist.
- "refs/files_backend.c:add_pseudoref_and_head_entries()" uses it to
determine whether it should add a ref to the root directory of its
iterator. This had the effect that we skipped over any files that
are either a symbolic ref, or which are not a ref at all.
The new behaviour is to include symbolic refs know, which aligns us
with the adapted terminology. Furthermore, files which look like
root refs but aren't are now mark those as "broken". As broken refs
are not surfaced by our tooling, this should not lead to a change in
user-visible behaviour, but may cause us to emit warnings. This
feels like the right thing to do as we would otherwise just silently
ignore corrupted root refs completely.
So in all cases the existence check was either superfluous, not in line
with the adapted terminology or masked potential issues. This commit
thus changes the behaviour as proposed and drops the existence check
altogether.
Add a test that verifies that this does not change user-visible
behaviour. Namely, we still don't want to show broken refs to the user
by default in git-for-each-ref(1). What this does allow though is for
internal callers to surface dangling root refs when they pass in the
`DO_FOR_EACH_INCLUDE_BROKEN` flag.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Rename `is_pseudoref()` to `is_root_ref()` to adapt to the newly defined
terminology in our gitglossary(7).
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There exist a bunch of call sites in the reftable backend that want to
create iterators for a reftable stack. This is rather convoluted right
now, where you always have to go via the merged table. And it is about
to become even more convoluted when we split up iterator initialization
and seeking in the next commit.
Introduce convenience functions that allow the caller to create an
iterator from a reftable stack directly without going through the merged
table. Adapt callers accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Allow configuring the geometric factor used by the auto-compaction
algorithm whenever a new table is appended to the stack of tables.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Besides the expected "ref" and "log" records, the reftable library also
writes "obj" records. These are basically a reverse mapping of object
IDs to their respective ref records so that it becomes efficient to
figure out which references point to a specific object. The motivation
for this data structure is the "uploadpack.allowTipSHA1InWant" config,
which allows a client to fetch any object by its hash that has a ref
pointing to it.
This reverse index is not used by Git at all though, and the expectation
is that most hosters nowadays use "uploadpack.allowAnySHA1InWant". It
may thus be preferable for many users to disable writing these optional
object indices altogether to safe some precious disk space.
Add a new config "reftable.indexObjects" that allows the user to disable
the object index altogether.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a new option `reftable.restartInterval` that allows the user to
control the restart interval when writing reftable records used by the
reftable library.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a new option `reftable.blockSize` that allows the user to control
the block size used by the reftable library.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We sometimes pass the refatble write options as value and sometimes as a
pointer. This is quite confusing and makes the reader wonder whether the
options get modified sometimes.
In fact, `reftable_new_writer()` does cause the caller-provided options
to get updated when some values aren't set up. This is quite unexpected,
but didn't cause any harm until now.
Adapt the code so that we do not modify the caller-provided values
anymore. While at it, refactor the code to code to consistently pass the
options as a constant pointer to clarify that the caller-provided opts
will not ever get modified.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Code to write out reftable has seen some optimization and
simplification.
* ps/reftable-write-optim:
reftable/block: reuse compressed array
reftable/block: reuse zstream when writing log blocks
reftable/writer: reset `last_key` instead of releasing it
reftable/writer: unify releasing memory
reftable/writer: refactorings for `writer_flush_nonempty_block()`
reftable/writer: refactorings for `writer_add_record()`
refs/reftable: don't recompute committer ident
reftable: remove name checks
refs/reftable: skip duplicate name checks
refs/reftable: perform explicit D/F check when writing symrefs
refs/reftable: fix D/F conflict error message on ref copy
In the previous commits, we converted `refs_create_symref()` to utilize
transactions to perform symref updates. Earlier `refs_create_symref()`
used `create_symref()` to do the same.
We can now remove `create_symref()` and any code associated with it
which is no longer used. We remove `create_symref()` code from all the
reference backends and also remove it entirely from the `ref_storage_be`
struct.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reference backends currently support transactional reference
updates. While this is exposed to users via 'git-update-ref' and its
'--stdin' mode, it is also used internally within various commands.
However, we do not support transactional updates of symrefs. This commit
adds support for symrefs in both the 'files' and the 'reftable' backend.
Here, we add and use `ref_update_has_null_new_value()`, a helper
function which is used to check if there is a new_value in a reference
update. The new value could either be a symref target `new_target` or a
OID `new_oid`.
We also add another common function `ref_update_check_old_target` which
will be used to check if the update's old_target corresponds to a
reference's current target.
Now transactional updates (verify, create, delete, update) can be used
for:
- regular refs
- symbolic refs
- conversion of regular to symbolic refs and vice versa
This also allows us to expose this to users via new commands in
'git-update-ref' in the future.
Note that a dangling symref update does not record a new reflog entry,
which is unchanged before and after this commit.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The files backend and the reftable backend implement
`original_update_refname` to obtain the original refname of the update.
Move it out to 'refs.c' and only expose it internally to the refs
library. This will be used in an upcoming commit to also introduce
another common functionality for the two backends.
We also rename the function to `ref_update_original_update_refname` to
keep it consistent with the upcoming other 'ref_update_*' functions
that'll be introduced.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The function `ref_transaction_update()` obtains ref information and
flags to create a `ref_update` and add them to the transaction at hand.
To extend symref support in transactions, we need to also accept the
old and new ref targets and process it. This commit adds the required
parameters to the function and modifies all call sites.
The two parameters added are `new_target` and `old_target`. The
`new_target` is used to denote what the reference should point to when
the transaction is applied. Some functions allow this parameter to be
NULL, meaning that the reference is not changed.
The `old_target` denotes the value the reference must have before the
update. Some functions allow this parameter to be NULL, meaning that the
old value of the reference is not checked.
We also update the internal function `ref_transaction_add_update()`
similarly to take the two new parameters.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git pack-refs" learned the "--auto" option, which is a useful
addition to be triggered from "git gc --auto".
Acked-by: Karthik Nayak <karthik.188@gmail.com>
cf. <CAOLa=ZRAEA7rSUoYL0h-2qfEELdbPHbeGpgBJRqesyhHi9Q6WQ@mail.gmail.com>
* ps/pack-refs-auto:
builtin/gc: pack refs when using `git maintenance run --auto`
builtin/gc: forward git-gc(1)'s `--auto` flag when packing refs
t6500: extract objects with "17" prefix
builtin/gc: move `struct maintenance_run_opts`
builtin/pack-refs: introduce new "--auto" flag
builtin/pack-refs: release allocated memory
refs/reftable: expose auto compaction via new flag
refs: remove `PACK_REFS_ALL` flag
refs: move `struct pack_refs_opts` to where it's used
t/helper: drop pack-refs wrapper
refs/reftable: print errors on compaction failure
reftable/stack: gracefully handle failed auto-compaction due to locks
reftable/stack: use error codes when locking fails during compaction
reftable/error: discern locked/outdated errors
reftable/stack: fix error handling in `reftable_stack_init_addition()`
In order to write reflog entries we need to compute the committer's
identity as it gets encoded in the log record itself. The reftable
backend does this via `git_committer_info()` and `split_ident_line()` in
`fill_reftable_log_record()`, which use the Git config as well as
environment variables to figure out the identity.
While most callers would only call `fill_reftable_log_record()` once or
twice, `write_transaction_table()` will call it as many times as there
are queued ref updates. This can be quite a waste of effort when writing
many refs with reflog entries in a single transaction.
Refactor the code to pre-compute the committer information. This results
in a small speedup when writing 100000 refs in a single transaction:
Benchmark 1: update-ref: create many refs (HEAD~)
Time (mean ± σ): 2.895 s ± 0.020 s [User: 1.516 s, System: 1.374 s]
Range (min … max): 2.868 s … 2.983 s 100 runs
Benchmark 2: update-ref: create many refs (HEAD)
Time (mean ± σ): 2.845 s ± 0.017 s [User: 1.461 s, System: 1.379 s]
Range (min … max): 2.803 s … 2.913 s 100 runs
Summary
update-ref: create many refs (HEAD) ran
1.02 ± 0.01 times faster than update-ref: create many refs (HEAD~)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the preceding commit we have disabled name checks in the "reftable"
backend. These checks were responsible for verifying multiple things
when writing records to the reftable stack:
- Detecting file/directory conflicts. Starting with the preceding
commits this is now handled by the reftable backend itself via
`refs_verify_refname_available()`.
- Validating refnames. This is handled by `check_refname_format()` in
the generic ref transacton layer.
The code in the reftable library is thus not used anymore and likely to
bitrot over time. Remove it.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All the callback functions which write refs in the reftable backend
perform D/F conflict checks via `refs_verify_refname_available()`. But
in reality we perform these D/F conflict checks a second time in the
reftable library via `stack_check_addition()`.
Interestingly, the code in the reftable library is inferior compared to
the generic function:
- It is slower than `refs_verify_refname_available()`, even though
this can probably be optimized.
- It does not provide a proper error message to the caller, and thus
all the user would see is a generic "file/directory conflict"
message.
Disable the D/F conflict checks in the reftable library by setting the
`skip_name_check` write option. This results in a non-negligible speedup
when writing many refs. The following benchmark writes 100k refs in a
single transaction:
Benchmark 1: update-ref: create many refs (HEAD~)
Time (mean ± σ): 3.241 s ± 0.040 s [User: 1.854 s, System: 1.381 s]
Range (min … max): 3.185 s … 3.454 s 100 runs
Benchmark 2: update-ref: create many refs (HEAD)
Time (mean ± σ): 2.878 s ± 0.024 s [User: 1.506 s, System: 1.367 s]
Range (min … max): 2.838 s … 2.960 s 100 runs
Summary
update-ref: create many refs (HEAD~) ran
1.13 ± 0.02 times faster than update-ref: create many refs (HEAD)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We already perform explicit D/F checks in all reftable callbacks which
write refs, except when writing symrefs. For one this leads to an error
message which isn't perfectly actionable because we only tell the user
that there was a D/F conflict, but not which refs conflicted with each
other. But second, once all ref updating callbacks explicitly check for
D/F conflicts, we can disable the D/F checks in the reftable library
itself and thus avoid some duplicated efforts.
Refactor the code that writes symref tables to explicitly call into
`refs_verify_refname_available()` when writing symrefs.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `write_copy_table()` function is shared between the reftable
implementations for renaming and copying refs. The only difference
between those two cases is that the rename will also delete the old
reference, whereas copying won't.
This has resulted in a bug though where we don't properly verify refname
availability. When calling `refs_verify_refname_available()`, we always
add the old ref name to the list of refs to be skipped when computing
availability, which indicates that the name would be available even if
it already exists at the current point in time. This is only the right
thing to do for renames though, not for copies.
The consequence of this bug is quite harmless because the reftable
backend has its own checks for D/F conflicts further down in the call
stack, and thus we refuse the update regardless of the bug. But all the
user gets in this case is an uninformative message that copying the ref
has failed, without any further details.
Fix the bug and only add the old name to the skip-list in case we rename
the ref. Consequently, this error case will now be handled by
`refs_verify_refname_available()`, which knows to provide a proper error
message.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In future tests it will be neccesary to create repositories with a set
number of tables. To make this easier, introduce the
`GIT_TEST_REFTABLE_AUTOCOMPACTION` environment variable that, when set
to false, disables autocompaction of reftables.
Signed-off-by: Justin Tobler <jltobler@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* ps/pack-refs-auto:
builtin/gc: pack refs when using `git maintenance run --auto`
builtin/gc: forward git-gc(1)'s `--auto` flag when packing refs
t6500: extract objects with "17" prefix
builtin/gc: move `struct maintenance_run_opts`
builtin/pack-refs: introduce new "--auto" flag
builtin/pack-refs: release allocated memory
refs/reftable: expose auto compaction via new flag
refs: remove `PACK_REFS_ALL` flag
refs: move `struct pack_refs_opts` to where it's used
t/helper: drop pack-refs wrapper
refs/reftable: print errors on compaction failure
reftable/stack: gracefully handle failed auto-compaction due to locks
reftable/stack: use error codes when locking fails during compaction
reftable/error: discern locked/outdated errors
reftable/stack: fix error handling in `reftable_stack_init_addition()`
Under normal circumstances, the "reftable" backend will automatically
perform compaction after appending to the stack. It is thus not
necessary and may even be considered wasteful to run git-pack-refs(1) in
"reftable"-backed repositories as it will cause the backend to compact
all tables into a single one. We do exactly that though when running
`git maintenance run --auto` or `git gc --auto`, which gets spawned by
Git after running some specific commands.
The `--auto` mode is typically only executing optimizations as needed.
To do so, we already use several heuristics for the various different
data structures in Git to determine whether to optimize them or not.
We do not use any heuristics for refs though and instead always optimize
them.
Introduce a new `PACK_REFS_AUTO` flag that can be passed to the backend.
When not handled by the backend we will continue to behave the exact
same as we do right now, that is we optimize refs unconditionally. This
is done for the "files" backend for now to retain current behaviour,
even though we may eventually also want to introduce heuristics here.
For the "reftable" backend though we already do have auto-compaction, so
we can easily reuse that logic to implement the new auto-packing flag.
Note that under normal circumstances, this should always end up being a
no-op. After all, we already invoke the code for every single addition
to the stack. But there are special cases where it can still be helpful
to execute the auto-compaction code explicitly:
- Concurrent writers may cause compaction to not run due to locks.
- Callers may decide to disable compaction altogether and then pack
refs at a later point due to various reasons.
- Other implementations of the reftable format may do compaction
differently or even not at all.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When git-pack-refs(1) fails in the reftable backend we end up printing
no error message at all, leaving the caller puzzled as to why compaction
has failed. Fix this.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code to iterate over reflogs in the reftable has been optimized
to reduce memory allocation and deallocation.
Reviewed-by: Josh Steadmon <steadmon@google.com>
cf. <Ze9eX-aaWoVaqsPP@google.com>
* ps/reftable-reflog-iteration-perf:
refs/reftable: track last log record name via strbuf
reftable/record: use scratch buffer when decoding records
reftable/record: reuse message when decoding log records
reftable/record: reuse refnames when decoding log records
reftable/record: avoid copying author info
reftable/record: convert old and new object IDs to arrays
refs/reftable: reload correct stack when creating reflog iter
The code to iterate over refs with the reftable backend has seen
some optimization.
* ps/reftable-iteration-perf-part2:
refs/reftable: precompute prefix length
reftable: allow inlining of a few functions
reftable/record: decode keys in place
reftable/record: reuse refname when copying
reftable/record: reuse refname when decoding
reftable/merged: avoid duplicate pqueue emptiness check
reftable/merged: circumvent pqueue with single subiter
reftable/merged: handle subiter cleanup on close only
reftable/merged: remove unnecessary null check for subiters
reftable/merged: make subiters own their records
reftable/merged: advance subiter on subsequent iteration
reftable/merged: make `merged_iter` structure private
reftable/pq: use `size_t` to track iterator index
Clear the fallout from a fix for 2.44 regression.
* ps/reftable-repo-init-fix:
t0610: remove unused variable assignment
refs/reftable: don't fail empty transactions in repo without HEAD
"git for-each-ref" learned "--include-root-refs" option to show
even the stuff outside the 'refs/' hierarchy.
* kn/for-all-refs:
for-each-ref: add new option to include root refs
ref-filter: rename 'FILTER_REFS_ALL' to 'FILTER_REFS_REGULAR'
refs: introduce `refs_for_each_include_root_refs()`
refs: extract out `loose_fill_ref_dir_regular_file()`
refs: introduce `is_pseudoref()` and `is_headref()`
The reflog iterator enumerates all reflogs known to a ref backend. In
the "reftable" backend there is no way to list all existing reflogs
directly. Instead, we have to iterate through all reflog entries and
discard all those redundant entries for which we have already returned a
reflog entry.
This logic is implemented by tracking the last reflog name that we have
emitted to the iterator's user. If the next log record has the same name
we simply skip it until we find another record with a different refname.
This last reflog name is stored in a simple C string, which requires us
to free and reallocate it whenever we need to update the reflog name.
Convert it to use a `struct strbuf` instead, which reduces the number of
allocations. Before:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 1,068,485 allocs, 1,068,363 frees, 281,122,886 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 68,485 allocs, 68,363 frees, 256,234,072 bytes allocated
Note that even after this change we still allocate quite a lot of data,
even though the number of allocations does not scale with the number of
log records anymore. This remainder comes mostly from decompressing the
log blocks, where we decompress each block into newly allocated memory.
This will be addressed at a later point in time.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 7af607c58d (reftable/record: store "val1" hashes as static arrays,
2024-01-03) and b31e3cc620 (reftable/record: store "val2" hashes as
static arrays, 2024-01-03) we have converted ref records to store their
object IDs in a static array. Convert log records to do the same so that
their old and new object IDs are arrays, too.
This change results in two allocations less per log record that we're
iterating over. Before:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 8,068,495 allocs, 8,068,373 frees, 401,011,862 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 6,068,489 allocs, 6,068,367 frees, 361,011,822 bytes allocated
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When creating a new reflog iterator, we first have to reload the stack
that the iterator is being created. This is done so that any concurrent
writes to the stack are reflected. But `reflog_iterator_for_stack()`
always reloads the main stack, which is wrong.
Fix this and reload the correct stack.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* ps/reftable-iteration-perf-part2:
refs/reftable: precompute prefix length
reftable: allow inlining of a few functions
reftable/record: decode keys in place
reftable/record: reuse refname when copying
reftable/record: reuse refname when decoding
reftable/merged: avoid duplicate pqueue emptiness check
reftable/merged: circumvent pqueue with single subiter
reftable/merged: handle subiter cleanup on close only
reftable/merged: remove unnecessary null check for subiters
reftable/merged: make subiters own their records
reftable/merged: advance subiter on subsequent iteration
reftable/merged: make `merged_iter` structure private
reftable/pq: use `size_t` to track iterator index
We're recomputing the prefix length on every iteration of the ref
iterator. Precompute it for another speedup when iterating over 1
million refs:
Benchmark 1: show-ref: single matching ref (revision = HEAD~)
Time (mean ± σ): 100.3 ms ± 3.7 ms [User: 97.3 ms, System: 2.8 ms]
Range (min … max): 97.5 ms … 139.7 ms 1000 runs
Benchmark 2: show-ref: single matching ref (revision = HEAD)
Time (mean ± σ): 95.8 ms ± 3.4 ms [User: 92.9 ms, System: 2.8 ms]
Range (min … max): 93.0 ms … 121.9 ms 1000 runs
Summary
show-ref: single matching ref (revision = HEAD) ran
1.05 ± 0.05 times faster than show-ref: single matching ref (revision = HEAD~)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Under normal circumstances, it shouldn't ever happen that a repository
has no HEAD reference. In fact, git-update-ref(1) would fail any request
to delete the HEAD reference, and a newly initialized repository always
pre-creates it, too.
We have however changed git-clone(1) to partially initialize the
refdb just up to the point where remote helpers can find the
repository. With that change, we are going to run into a situation
where repositories have no refs at all.
Now there is a very particular edge case in this situation: when
preparing an empty ref transacton, we end up returning whatever value
`read_ref_without_reload()` returned to the caller. Under normal
conditions this would be fine: "HEAD" should usually exist, and thus the
function would return `0`. But if "HEAD" doesn't exist, the function
returns a positive value which we end up returning to the caller.
Fix this bug by resetting the return code to `0` and add a test.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The git-for-each-ref(1) command doesn't provide a way to print root refs
i.e pseudorefs and HEAD with the regular "refs/" prefixed refs.
This commit adds a new option "--include-root-refs" to
git-for-each-ref(1). When used this would also print pseudorefs and HEAD
for the current worktree.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reflog iterator tries to resolve the corresponding ref for every
reflog that it is about to yield. Historically, this was done due to
multiple reasons:
- It ensures that the refname is safe because we end up calling
`check_refname_format()`. Also, non-conformant refnames are skipped
altogether.
- The iterator used to yield the resolved object ID as well as its
flags to the callback. This info was never used though, and the
corresponding parameters were dropped in the preceding commit.
- When a ref is corrupt then the reflog is not emitted at all.
We're about to introduce a new `git reflog list` subcommand that will
print all reflogs that the refdb knows about. Skipping over reflogs
whose refs are corrupted would be quite counterproductive in this case
as the user would have no way to learn about reflogs which may still
exist in their repository to help and rescue such a corrupted ref. Thus,
the only remaining reason for why we'd want to resolve the ref is to
verify its refname.
Refactor the code to call `check_refname_format()` directly instead of
trying to resolve the ref. This is significantly more efficient given
that we don't have to hit the object database anymore to list reflogs.
And second, it ensures that we end up showing reflogs of broken refs,
which will help to make the reflog more useful.
Note that this really only impacts the case where the corresponding ref
is corrupt. Reflogs for nonexistent refs would have been returned to the
caller beforehand already as we did not pass `RESOLVE_REF_READING` to
the function, and thus `refs_resolve_ref_unsafe()` would have returned
successfully in that case.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ref and reflog iterators share much of the same underlying code to
iterate over the corresponding entries. This results in some weird code
because the reflog iterator also exposes an object ID as well as a flag
to the callback function. Neither of these fields do refer to the reflog
though -- they refer to the corresponding ref with the same name. This
is quite misleading. In practice at least the object ID cannot really be
implemented in any other way as a reflog does not have a specific object
ID in the first place. This is further stressed by the fact that none of
the callbacks except for our test helper make use of these fields.
Split up the infrastucture so that ref and reflog iterators use separate
callback signatures. This allows us to drop the nonsensical fields from
the reflog iterator.
Note that internally, the backends still use the same shared infra to
iterate over both types. As the backends should never end up being
called directly anyway, this is not much of a problem and thus kept
as-is for simplicity's sake.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the preceding commit we have converted the reflog iterator of the
"files" backend to be ordered, which was the only remaining ref iterator
that wasn't ordered. Refactor the ref iterator infrastructure so that we
always assume iterators to be ordered, thus simplifying the code.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When iterating through reflogs in a worktree we create a merged iterator
that merges reflogs from both refdbs. The resulting refs are ordered so
that instead we first return all worktree reflogs before we return all
common refs.
This is the only remaining case where a ref iterator returns entries in
a non-lexicographic order. The result would look something like the
following (listed with a command we introduce in a subsequent commit):
```
$ git reflog list
HEAD
refs/worktree/per-worktree
refs/heads/main
refs/heads/wt
```
So we first print the per-worktree reflogs in lexicographic order, then
the common reflogs in lexicographic order. This is confusing and not
consistent with how we print per-worktree refs, which are exclusively
sorted lexicographically.
Sort reflogs lexicographically in the same way as we sort normal refs.
As this is already implemented properly by the "reftable" backend via a
separate selection function, we simply pull out that logic and reuse it
for the "files" backend. As logs are properly sorted now, mark the
merged reflog iterator as sorted.
Tests will be added in a subsequent commit.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When copying a ref with the reftable backend we also copy the
corresponding log records. When seeking the first log record that we're
about to copy fails though we directly return from `write_copy_table()`
without doing any cleanup, leaking several allocated data structures.
Fix this by exiting via our common cleanup logic instead.
Reported-by: Jeff King <peff@peff.net> via Coverity
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
Junio C Hamano