Enumerating refs in the packed-refs file, while excluding refs that
match certain patterns, has been optimized.
* tb/refs-exclusion-and-packed-refs:
ls-refs.c: avoid enumerating hidden refs where possible
upload-pack.c: avoid enumerating hidden refs where possible
builtin/receive-pack.c: avoid enumerating hidden references
refs.h: implement `hidden_refs_to_excludes()`
refs.h: let `for_each_namespaced_ref()` take excluded patterns
revision.h: store hidden refs in a `strvec`
refs/packed-backend.c: add trace2 counters for jump list
refs/packed-backend.c: implement jump lists to avoid excluded pattern(s)
refs/packed-backend.c: refactor `find_reference_location()`
refs: plumb `exclude_patterns` argument throughout
builtin/for-each-ref.c: add `--exclude` option
ref-filter.c: parameterize match functions over patterns
ref-filter: add `ref_filter_clear()`
ref-filter: clear reachable list pointers after freeing
ref-filter.h: provide `REF_FILTER_INIT`
refs.c: rename `ref_filter`
The previous commit added low-level tests to ensure that the packed-refs
iterator did not enumerate excluded sections of the refspace.
However, there was no guarantee that these sections weren't being
visited, only that they were being suppressed from the output. To harden
these tests, add a trace2 counter which tracks the number of regions
skipped by the packed-refs iterator, and assert on its value.
Suggested-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When iterating through the `packed-refs` file in order to answer a query
like:
$ git for-each-ref --exclude=refs/__hidden__
it would be useful to avoid walking over all of the entries in
`refs/__hidden__/*` when possible, since we know that the ref-filter
code is going to throw them away anyways.
In certain circumstances, doing so is possible. The algorithm for doing
so is as follows:
- For each excluded pattern, find the first record that matches it,
and the first record that *doesn't* match it (i.e. the location
you'd next want to consider when excluding that pattern).
- Sort the set of excluded regions from the previous step in ascending
order of the first location within the `packed-refs` file that
matches.
- Clean up the results from the previous step: discard empty regions,
and combine adjacent regions. The set of regions which remains is
referred to as the "jump list", and never contains any references
which should be included in the result set.
Then when iterating through the `packed-refs` file, if `iter->pos` is
ever contained in one of the regions from the previous steps, advance
`iter->pos` past the end of that region, and continue enumeration.
Note that we only perform this optimization when none of the excluded
pattern(s) have special meta-characters in them. For a pattern like
"refs/foo[ac]", the excluded regions ("refs/fooa", "refs/fooc", and
everything underneath them) are not connected. A future implementation
that handles this case may split the character class (pretending as if
two patterns were excluded: "refs/fooa", and "refs/fooc").
There are a few other gotchas worth considering. First, note that the
jump list is sorted, so once we jump past a region, we can avoid
considering it (or any regions preceding it) again. The member
`jump_pos` is used to track the first next-possible region to jump
through.
Second, note that the jump list is best-effort, since we do not handle
loose references, and because of the meta-character issue above. The
jump list may not skip past all references which won't appear in the
results, but will never skip over a reference which does appear in the
result set.
In repositories with a large number of hidden references, the speed-up
can be significant. Tests here are done with a copy of linux.git with a
reference "refs/pull/N" pointing at every commit, as in:
$ git rev-list HEAD | awk '{ print "create refs/pull/" NR " " $0 }' |
git update-ref --stdin
$ git pack-refs --all
, it is significantly faster to have `for-each-ref` jump over the
excluded references, as opposed to filtering them out after the fact:
$ hyperfine \
'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"' \
'git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"' \
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"'
Benchmark 1: git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"
Time (mean ± σ): 798.1 ms ± 3.3 ms [User: 687.6 ms, System: 146.4 ms]
Range (min … max): 794.5 ms … 805.5 ms 10 runs
Benchmark 2: git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"
Time (mean ± σ): 98.9 ms ± 1.4 ms [User: 93.1 ms, System: 5.7 ms]
Range (min … max): 97.0 ms … 104.0 ms 29 runs
Benchmark 3: git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 0.7 ms, System: 3.8 ms]
Range (min … max): 4.1 ms … 5.8 ms 524 runs
Summary
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"' ran
21.87 ± 1.05 times faster than 'git.prev for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"'
176.52 ± 8.19 times faster than 'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"'
(Comparing stock git and this patch isn't quite fair, since an earlier
commit in this series adds a naive implementation of the `--exclude`
option. `git.prev` is built from the previous commit and includes this
naive implementation).
Using the jump list is fairly straightforward (see the changes to
`refs/packed-backend.c::next_record()`), but constructing the list is
not. To ensure that the construction is correct, add a new suite of
tests in t1419 covering various corner cases (overlapping regions,
partially overlapping regions, adjacent regions, etc.).
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The function `find_reference_location()` is used to perform a
binary search-like function over the contents of a repository's
`$GIT_DIR/packed-refs` file.
The search it implements is unlike a standard binary search in that the
records it searches over are not of a fixed width, so the comparison
must locate the end of a record before comparing it.
Extract the core routine of `find_reference_location()` in order to
implement a function in the following patch which will find the first
location in the `packed-refs` file that *doesn't* match the given
pattern.
The behavior of `find_reference_location()` is unchanged.
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The subsequent patch will want to access an optional `excluded_patterns`
array within `refs/packed-backend.c` that will cull out certain
references matching any of the given patterns on a best-effort basis.
To do so, the refs subsystem needs to be updated to pass this value
across a number of different locations.
Prepare for a future patch by introducing this plumbing now, passing
NULLs at top-level APIs in order to make that patch less noisy and more
easily readable.
Signed-off-by: Taylor Blau <me@ttaylorr.co>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This also made it clear that several .c files that depended upon path.h
were missing a #include for it; add the missing includes while at it.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since this header showed up in some places besides just #include
statements, update/clean-up/remove those other places as well.
Note that compat/fsmonitor/fsm-path-utils-darwin.c previously got
away with violating the rule that all files must start with an include
of git-compat-util.h (or a short-list of alternate headers that happen
to include it first). This change exposed the violation and caused it
to stop building correctly; fix it by having it include
git-compat-util.h first, as per policy.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
These functions do not depend upon struct cache_entry or struct
index_state in any way, and it seems more logical to break them out into
this file, especially since statinfo.h already has the struct stat_data
declaration.
Diff best viewed with `--color-moved`.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git pack-refs" learns "--include" and "--exclude" to tweak the ref
hierarchy to be packed using pattern matching.
* jc/pack-ref-exclude-include:
pack-refs: teach pack-refs --include option
pack-refs: teach --exclude option to exclude refs from being packed
docs: clarify git-pack-refs --all will pack all refs
Allow users to be more selective over which refs to pack by adding an
--include option to git-pack-refs.
The existing options allow some measure of selectivity. By default
git-pack-refs packs all tags. --all can be used to include all refs,
and the previous commit added the ability to exclude certain refs with
--exclude.
While these knobs give the user some selection over which refs to pack,
it could be useful to give more control. For instance, a repository may
have a set of branches that are rarely updated and would benefit from
being packed. --include would allow the user to easily include a set of
branches to be packed while leaving everything else unpacked.
Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
At GitLab, we have a system that creates ephemeral internal refs that
don't live long before getting deleted. Having an option to exclude
certain refs from a packed-refs file allows these internal references to
be deleted much more efficiently.
Add an --exclude option to the pack-refs builtin, and use the ref
exclusions API to exclude certain refs from being packed into the final
packed-refs file
Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
More header clean-up.
* en/header-split-cache-h-part-2: (22 commits)
reftable: ensure git-compat-util.h is the first (indirect) include
diff.h: reduce unnecessary includes
object-store.h: reduce unnecessary includes
commit.h: reduce unnecessary includes
fsmonitor: reduce includes of cache.h
cache.h: remove unnecessary headers
treewide: remove cache.h inclusion due to previous changes
cache,tree: move basic name compare functions from read-cache to tree
cache,tree: move cmp_cache_name_compare from tree.[ch] to read-cache.c
hash-ll.h: split out of hash.h to remove dependency on repository.h
tree-diff.c: move S_DIFFTREE_IFXMIN_NEQ define from cache.h
dir.h: move DTYPE defines from cache.h
versioncmp.h: move declarations for versioncmp.c functions from cache.h
ws.h: move declarations for ws.c functions from cache.h
match-trees.h: move declarations for match-trees.c functions from cache.h
pkt-line.h: move declarations for pkt-line.c functions from cache.h
base85.h: move declarations for base85.c functions from cache.h
copy.h: move declarations for copy.c functions from cache.h
server-info.h: move declarations for server-info.c functions from cache.h
packfile.h: move pack_window and pack_entry from cache.h
...
Mark strtok() and strtok_r() to be banned.
* tb/ban-strtok:
banned.h: mark `strtok()` and `strtok_r()` as banned
t/helper/test-json-writer.c: avoid using `strtok()`
t/helper/test-oidmap.c: avoid using `strtok()`
t/helper/test-hashmap.c: avoid using `strtok()`
string-list: introduce `string_list_setlen()`
string-list: multi-delimiter `string_list_split_in_place()`
Enhance `string_list_split_in_place()` to accept multiple characters as
delimiters instead of a single character.
Instead of using `strchr(2)` to locate the first occurrence of the given
delimiter character, `string_list_split_in_place_multi()` uses
`strcspn(2)` to move past the initial segment of characters comprised of
any characters in the delimiting set.
When only a single delimiting character is provided, `strpbrk(2)` (which
is implemented with `strcspn(2)`) has equivalent performance to
`strchr(2)`. Modern `strcspn(2)` implementations treat an empty
delimiter or the singleton delimiter as a special case and fall back to
calling strchrnul(). Both glibc[1] and musl[2] implement `strcspn(2)`
this way.
This change is one step to removing `strtok(2)` from the tree. Note that
`string_list_split_in_place()` is not a strict replacement for
`strtok()`, since it will happily turn sequential delimiter characters
into empty entries in the resulting string_list. For example:
string_list_split_in_place(&xs, "foo:;:bar:;:baz", ":;", -1)
would yield a string list of:
["foo", "", "", "bar", "", "", "baz"]
Callers that wish to emulate the behavior of strtok(2) more directly
should call `string_list_remove_empty_items()` after splitting.
To avoid regressions for the new multi-character delimter cases, update
t0063 in this patch as well.
[1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=string/strcspn.c;hb=glibc-2.37#l35
[2]: https://git.musl-libc.org/cgit/musl/tree/src/string/strcspn.c?h=v1.2.3#n11
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
hash.h depends upon and includes repository.h, due to the definition and
use of the_hash_algo (defined as the_repository->hash_algo). However,
most headers trying to include hash.h are only interested in the layout
of the structs like object_id. Move the parts of hash.h that do not
depend upon repository.h into a new file hash-ll.h (the "low level"
parts of hash.h), and adjust other files to use this new header where
the convenience inline functions aren't needed.
This allows hash.h and object.h to be fairly small, minimal headers. It
also exposes a lot of hidden dependencies on both path.h (which was
brought in by repository.h) and repository.h (which was previously
implicitly brought in by object.h), so also adjust other files to be
more explicit about what they depend upon.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We had a handful of headers including cache.h that didn't need to
anymore. Drop those includes and replace them with includes of
smaller files, or forward declarations. However, note that two .c
files now need to directly include cache.h, though they should have
been including it all along given they are directly using structs
defined in it.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
cache.h's nature of a dumping ground of includes prevented it from
being included in some compat/ files, forcing us into a workaround
of having a double forward declaration of the read_in_full() function
(see commit 14086b0a13 ("compat/pread.c: Add a forward declaration to
fix a warning", 2007-11-17)). Now that we have moved functions like
read_in_full() from cache.h to wrapper.h, and wrapper.h isn't littered
with unrelated and scary #defines, get rid of the extra forward
declaration and just have compat/pread.c include wrapper.h.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A number of files were apparently including cache.h solely to get
gettext.h. By making those files explicitly include gettext.h, we can
already drop the include of cache.h in these files. On top of that,
there were some files using cache.h that didn't need to for any reason.
Remove these unnecessary includes.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Dozens of files made use of gettext functions, without explicitly
including gettext.h. This made it more difficult to find which files
could remove a dependence on cache.h. Make C files explicitly include
gettext.h if they are using it.
However, while compat/fsmonitor/fsm-ipc-darwin.c should also gain an
include of gettext.h, it was left out to avoid conflicting with an
in-flight topic.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ever since a64215b6cd ("object.h: stop depending on cache.h; make
cache.h depend on object.h", 2023-02-24), we have a few headers that
could have replaced their include of cache.h with an include of
object.h. Make that change now.
Some C files had to start including cache.h after this change (or some
smaller header it had brought in), because the C files were depending
on things from cache.h but were only formerly implicitly getting
cache.h through one of these headers being modified in this patch.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
These functions were all defined in a separate ident.c already, so
create ident.h and move the declarations into that file.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This allows us to replace includes of cache.h with includes of the much
smaller alloc.h in many places. It does mean that we also need to add
includes of alloc.h in a number of C files.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We had several header files include cache.h unnecessarily. Remove
those. These have all been verified via both ensuring that
gcc -E $HEADER | grep '"cache.h"'
found no hits and that
cat >temp.c <<EOF &&
#include "git-compat-util.h"
#include "$HEADER"
int main() {}
EOF
gcc -c temp.c
successfully compiles without warnings.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We had several C files ignoring the rule to include one of the
appropriate headers first; fix that.
While at it, the rule in Documentation/CodingGuidelines about which
header to include has also fallen out of sync, so update the wording to
mention other allowed headers.
Unfortunately, C files in reftable/ don't actually follow the previous
or updated rule. If you follow the #include chain in its C files,
reftable/system.h _tends_ to be first (i.e. record.c first includes
record.h, which first includes basics.h, which first includees
system.h), but not always (e.g. publicbasics.c includes another header
first that does not include system.h). However, I'm going to punt on
making actual changes to the C files in reftable/ since I do not want to
risk bringing it out-of-sync with any version being used externally.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Fix the sequence to fsync $GIT_DIR/packed-refs file that forgot to
flush its output to the disk..
* ps/fsync-refs-fix:
refs: fix corruption by not correctly syncing packed-refs to disk
At GitLab we have recently received a report where a repository was left
with a corrupted `packed-refs` file after the node hard-crashed even
though `core.fsync=reference` was set. This is something that in theory
should not happen if we correctly did the atomic-rename dance to:
1. Write the data into a temporary file.
2. Synchronize the temporary file to disk.
3. Rename the temporary file into place.
So if we crash in the middle of writing the `packed-refs` file we should
only ever see either the old or the new state of the file.
And while we do the dance when writing the `packed-refs` file, there is
indeed one gotcha: we use a `FILE *` stream to write the temporary file,
but don't flush it before synchronizing it to disk. As a consequence any
data that is still buffered will not get synchronized and a crash of the
machine may cause corruption.
Fix this bug by flushing the file stream before we fsync.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The logic to handle worktree refs (worktrees/NAME/REF and
main-worktree/REF) existed in two places:
* ref_type() in refs.c
* parse_worktree_ref() in worktree.c
Collapse this logic together in one function parse_worktree_ref():
this avoids having to cross-check the result of parse_worktree_ref()
and ref_type().
Introduce enum ref_worktree_type, which is slightly different from
enum ref_type. The latter is a misleading name (one would think that
'ref_type' would have the symref option).
Instead, enum ref_worktree_type only makes explicit how a refname
relates to a worktree. From this point of view, HEAD and
refs/bisect/abc are the same: they specify the current worktree
implicitly.
The files-backend must avoid packing refs/bisect/* and friends into
packed-refs, so expose is_per_worktree_ref() separately.
Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As reported in [1] the "UNUSED(var)" macro introduced in
2174b8c75d (Merge branch 'jk/unused-annotation' into next,
2022-08-24) breaks coccinelle's parsing of our sources in files where
it occurs.
Let's instead partially go with the approach suggested in [2] of
making this not take an argument. As noted in [1] "coccinelle" will
ignore such tokens in argument lists that it doesn't know about, and
it's less of a surprise to syntax highlighters.
This undoes the "help us notice when a parameter marked as unused is
actually use" part of 9b24034754 (git-compat-util: add UNUSED macro,
2022-08-19), a subsequent commit will further tweak the macro to
implement a replacement for that functionality.
1. https://lore.kernel.org/git/220825.86ilmg4mil.gmgdl@evledraar.gmail.com/
2. https://lore.kernel.org/git/220819.868rnk54ju.gmgdl@evledraar.gmail.com/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The refs code uses various polymorphic types (e.g., loose vs packed
ref_stores, abstracted iterators). Not every virtual function or
callback needs all of its parameters. Let's mark the unused ones to
quiet -Wunused-parameter.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Functions used with for_each_ref(), etc, need to conform to the
each_ref_fn interface. But most of them don't need every parameter;
let's annotate the unused ones to quiet -Wunused-parameter.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce and apply coccinelle rule to discourage an explicit
comparison between a pointer and NULL, and applies the clean-up to
the maintenance track.
* ep/maint-equals-null-cocci:
tree-wide: apply equals-null.cocci
tree-wide: apply equals-null.cocci
contrib/coccinnelle: add equals-null.cocci
Code clean-up.
* ab/refs-various-fixes:
refs debug: add a wrapper for "read_symbolic_ref"
packed-backend: remove stub BUG(...) functions
misc *.c: use designated initializers for struct assignments
refs: use designated initializers for "struct ref_iterator_vtable"
refs: use designated initializers for "struct ref_storage_be"
Updates to refs traditionally weren't fsync'ed, but we can
configure using core.fsync variable to do so.
* ps/fsync-refs:
core.fsync: new option to harden references
In cd475b3b03 (refs: add ability for backends to special-case reading
of symbolic refs, 2022-03-01) when the "read_symbolic_ref" callback
was added we'd fall back on "refs_read_raw_ref" if there wasn't any
backend implementation of "read_symbolic_ref".
As discussed in the preceding commit this would only happen if we were
running the "debug" backend, e.g. in the "setup for ref completion"
test in t9902-completion.sh with:
GIT_TRACE_REFS=1 git fetch --no-tags other
Let's improve the trace output, but and also eliminate the
now-redundant refs_read_raw_ref() fallback case. As noted in the
preceding commit the "packed" backend will never call
refs_read_symbolic_ref() (nor is it ever going to). For any future
backend such as reftable it's OK to ask that they either implement
this (or a wrapper) themselves.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove the stub BUG(...) functions previously used by the "struct
ref_storage_be refs_be_packed" backend.
We never call any functions in the packed backend by using it as a
"normal" primary ref store, instead we'll always initialize a "files"
backend ref-store.
It will then via the "packed_ref_store" member of "struct
files_ref_store" call selected functions in the "packed" backend, and
we'll in addition call others via wrappers in refs.c.
So while these would arguably give us *slightly* more meaningful error
messages we'll NULL the missing members in the initializer anyway, so
we'll reliably get a segfault if we're ever changing the backend and
having it call something it doesn't have.
So there's no need for this verbose boilerplate, and as shown in a
subsequent commit it might even lead to some confusion about the
packed backend being a "real" backend. Let's make it clear that it's
not.
As an aside, this also fixes a warning emitted by SunCC in at least
versions 12.5 and 12.6 of Oracle Developer Studio:
"refs/packed-backend.c", line 1599: warning: Function has no return statement : packed_create_symref
"refs/packed-backend.c", line 1606: warning: Function has no return statement : packed_rename_ref)
"refs/packed-backend.c", line 1613: warning: Function has no return statement : packed_copy_ref
"refs/packed-backend.c", line 1648: warning: Function has no return statement : packed_create_reflog
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change the definition of the three refs backends we currently carry to
use designated initializers.
The "= NULL" assignments being retained here are redundant, and could
be removed, but let's keep them for clarity. All of these backends
define almost all fields, so we're not saving much in terms of line
count by omitting these, but e.g. for "refs_be_debug" it's immediately
apparent that we're omitting "init" when comparing its assignment to
the others.
This is a follow-up to similar work merged in bd4232fac3 (Merge
branch 'ab/struct-init', 2021-07-16), a4b9fb6a5c (Merge branch
'ab/designated-initializers-more', 2021-10-18) and a30321b9ea (Merge
branch 'ab/designated-initializers' into
ab/designated-initializers-more, 2021-09-27).
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing both loose and packed references to disk we first create a
lockfile, write the updated values into that lockfile, and on commit we
rename the file into place. According to filesystem developers, this
behaviour is broken because applications should always sync data to disk
before doing the final rename to ensure data consistency [1][2][3]. If
applications fail to do this correctly, a hard crash of the machine can
easily result in corrupted on-disk data.
This kind of corruption can in fact be easily observed with Git when the
machine hard-resets shortly after writing references to disk. On
machines with ext4, this will likely lead to the "empty files" problem:
the file has been renamed, but its data has not been synced to disk. The
result is that the reference is corrupt, and in the worst case this can
lead to data loss.
Implement a new option to harden references so that users and admins can
avoid this scenario by syncing locked loose and packed references to
disk before we rename them into place.
[1]: https://thunk.org/tytso/blog/2009/03/15/dont-fear-the-fsync/
[2]: https://btrfs.wiki.kernel.org/index.php/FAQ (What are the crash guarantees of overwrite-by-rename)
[3]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/ext4.rst (see auto_da_alloc)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When reading references via `files_read_raw_ref()` we always consult
both the loose reference, and if that wasn't found, we also consult the
packed-refs file. While this makes sense to read a generic reference, it
is wasteful in the case where we only care about symbolic references:
the packed-refs backend does not support them, and thus it cannot ever
return one for us.
Special-case reading of symbolic references for the files backend such
that we always skip asking the packed-refs backend.
We use `refs_read_symbolic_ref()` extensively to determine whether we
need to skip updating local symbolic references during a fetch, which is
why the change results in a significant speedup when doing fetches in
repositories with huge numbers of references. The following benchmark
executes a mirror-fetch in a repository with about 2 million references
via `git fetch --prune --no-write-fetch-head +refs/*:refs/*`:
Benchmark 1: HEAD~
Time (mean ± σ): 68.372 s ± 2.344 s [User: 65.629 s, System: 8.786 s]
Range (min … max): 65.745 s … 70.246 s 3 runs
Benchmark 2: HEAD
Time (mean ± σ): 60.259 s ± 0.343 s [User: 61.019 s, System: 7.245 s]
Range (min … max): 60.003 s … 60.649 s 3 runs
Summary
'HEAD' ran
1.13 ± 0.04 times faster than 'HEAD~'
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
