Users may want to specify a minimum batch size for their needs. This is only
a minimum: the path-walk API provides a list of OIDs that correspond to the
same path, and thus it is optimal to allow delta compression across those
objects in a single server request.
We could consider limiting the request to have a maximum batch size in the
future. For now, we let the path-walk API batches determine the
boundaries.
To get a feeling for the value of specifying the --min-batch-size parameter,
I tested a number of open source repositories available on GitHub. The
procedure was generally:
1. git clone --filter=blob:none <url>
2. git backfill
Checking the number of packfiles and the size of the .git/objects/pack
directory helps to identify the effects of different batch sizes.
For the Git repository, we get these results:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|-------|
| (Initial clone) | 2 | 119 MB | |
| 25K | 8 | 290 MB | 24s |
| 50K | 5 | 290 MB | 24s |
| 100K | 4 | 290 MB | 29s |
Other than the packfile counts decreasing as we need fewer batches, the
size and time required is not changing much for this small example.
For the nodejs/node repository, we see these results:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|--------|
| (Initial clone) | 2 | 330 MB | |
| 25K | 19 | 1,222 MB | 1m 22s |
| 50K | 11 | 1,221 MB | 1m 24s |
| 100K | 7 | 1,223 MB | 1m 40s |
| 250K | 4 | 1,224 MB | 2m 23s |
| 500K | 3 | 1,216 MB | 4m 38s |
Here, we don't have much difference in the size of the repo, though the
500K batch size results in a few MB gained. That comes at a cost of a
much longer time. This extra time is due to server-side delta
compression happening as the on-disk deltas don't appear to be reusable
all the time. But for smaller batch sizes, the server is able to find
reasonable deltas partly because we are asking for objects that appear
in the same region of the directory tree and include all versions of a
file at a specific path.
To contrast this example, I tested the microsoft/fluentui repo, which
has been known to have inefficient packing due to name hash collisions.
These results are found before GitHub had the opportunity to repack the
server with more advanced name hash versions:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|--------|
| (Initial clone) | 2 | 105 MB | |
| 5K | 53 | 348 MB | 2m 26s |
| 10K | 28 | 365 MB | 2m 22s |
| 15K | 19 | 407 MB | 2m 21s |
| 20K | 15 | 393 MB | 2m 28s |
| 25K | 13 | 417 MB | 2m 06s |
| 50K | 8 | 509 MB | 1m 34s |
| 100K | 5 | 535 MB | 1m 56s |
| 250K | 4 | 698 MB | 1m 33s |
| 500K | 3 | 696 MB | 1m 42s |
Here, a larger variety of batch sizes were chosen because of the great
variation in results. By asking the server to download small batches
corresponding to fewer paths at a time, the server is able to provide
better compression for these batches than it would for a regular clone.
A typical full clone for this repository would require 738 MB.
This example justifies the choice to batch requests by path name,
leading to improved communication with a server that is not optimally
packed.
Finally, the same experiment for the Linux repository had these results:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|---------|
| (Initial clone) | 2 | 2,153 MB | |
| 25K | 63 | 6,380 MB | 14m 08s |
| 50K | 58 | 6,126 MB | 15m 11s |
| 100K | 30 | 6,135 MB | 18m 11s |
| 250K | 14 | 6,146 MB | 18m 22s |
| 500K | 8 | 6,143 MB | 33m 29s |
Even in this example, where the default name hash algorithm leads to
decent compression of the Linux kernel repository, there is value for
selecting a smaller batch size, to a limit. The 25K batch size has the
fastest time, but uses 250 MB more than the 50K batch size. The 500K
batch size took much more time due to server compression time and thus
we should avoid large batch sizes like this.
Based on these experiments, a batch size of 50,000 was chosen as the
default value.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The default behavior of 'git backfill' is to fetch all missing blobs that
are reachable from HEAD. Document and test this behavior.
The implementation is a very simple use of the path-walk API, initializing
the revision walk at HEAD to start the path-walk from all commits reachable
from HEAD. Ignore the object arrays that correspond to tree entries,
assuming that they are all present already.
The path-walk API provides lists of objects in batches according to a
common path, but that list could be very small. We want to balance the
number of requests to the server with the ability to have the process
interrupted with minimal repeated work to catch up in the next run.
Based on some experiments (detailed in the next change) a minimum batch
size of 50,000 is selected for the default.
This batch size is a _minimum_. As the path-walk API emits lists of blob
IDs, they are collected into a list of objects for a request to the
server. When that list is at least the minimum batch size, then the
request is sent to the server for the new objects. However, the list of
blob IDs from the path-walk API could be much longer than the batch
size. At this moment, it is unclear if there is a benefit to split the
list when there are too many objects at the same path.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In anticipation of implementing 'git backfill', populate the necessary files
with the boilerplate of a new builtin. Mark the builtin as experimental at
this time, allowing breaking changes in the near future, if necessary.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* master: (446 commits)
The seventh batch
The sixth batch
The fifth batch
The fourth batch
refs/reftable: fix uninitialized memory access of `max_index`
remote: announce removal of "branches/" and "remotes/"
The third batch
hash.h: drop unsafe_ function variants
csum-file: introduce hashfile_checkpoint_init()
t/helper/test-hash.c: use unsafe_hash_algo()
csum-file.c: use unsafe_hash_algo()
hash.h: introduce `unsafe_hash_algo()`
csum-file.c: extract algop from hashfile_checksum_valid()
csum-file: store the hash algorithm as a struct field
t/helper/test-tool: implement sha1-unsafe helper
trace2: prevent segfault on config collection with valueless true
refs: fix creation of reflog entries for symrefs
ci: wire up Visual Studio build with Meson
ci: raise error when Meson generates warnings
meson: fix compilation with Visual Studio
...
More build fixes and enhancements on meson based build procedure.
* ps/build-meson-fixes:
ci: wire up Visual Studio build with Meson
ci: raise error when Meson generates warnings
meson: fix compilation with Visual Studio
meson: make the CSPRNG backend configurable
meson: wire up fuzzers
meson: wire up generation of distribution archive
meson: wire up development environments
meson: fix dependencies for generated headers
meson: populate project version via GIT-VERSION-GEN
GIT-VERSION-GEN: allow running without input and output files
GIT-VERSION-GEN: simplify computing the dirty marker
Following the procedure we established to introduce breaking
changes for Git 3.0, allow an early opt-in for removing support of
$GIT_DIR/branches/ and $GIT_DIR/remotes/ directories to configure
remotes.
* ps/3.0-remote-deprecation:
remote: announce removal of "branches/" and "remotes/"
builtin/pack-redundant: remove subcommand with breaking changes
ci: repurpose "linux-gcc" job for deprecations
ci: merge linux-gcc-default into linux-gcc
Makefile: wire up build option for deprecated features
Code clean-up for code paths around combined diff.
* jk/combine-diff-cleanup:
tree-diff: make list tail-passing more explicit
tree-diff: simplify emit_path() list management
tree-diff: use the name "tail" to refer to list tail
tree-diff: drop list-tail argument to diff_tree_paths()
combine-diff: drop public declaration of combine_diff_path_size()
tree-diff: inline path_appendnew()
tree-diff: pass whole path string to path_appendnew()
tree-diff: drop path_appendnew() alloc optimization
run_diff_files(): de-mystify the size of combine_diff_path struct
diff: add a comment about combine_diff_path.parent.path
combine-diff: use pointer for parent paths
tree-diff: clear parent array in path_appendnew()
combine-diff: add combine_diff_path_new()
run_diff_files(): delay allocation of combine_diff_path
The API around choosing to use unsafe variant of SHA-1
implementation has been updated in an attempt to make it harder to
abuse.
* tb/unsafe-hash-cleanup:
hash.h: drop unsafe_ function variants
csum-file: introduce hashfile_checkpoint_init()
t/helper/test-hash.c: use unsafe_hash_algo()
csum-file.c: use unsafe_hash_algo()
hash.h: introduce `unsafe_hash_algo()`
csum-file.c: extract algop from hashfile_checksum_valid()
csum-file: store the hash algorithm as a struct field
t/helper/test-tool: implement sha1-unsafe helper
Doc and short-help text for "show-index" has been clarified to
stress that the command reads its data from the standard input.
* jc/show-index-h-update:
show-index: the short help should say the command reads from its input
The "git refs migrate" command did not migrate the reflog for
refs/stash, which is the contents of the stashes, which has been
corrected.
* ps/reflog-migration-with-logall-fix:
refs: fix migration of reflogs respecting "core.logAllRefUpdates"
The trace2 code was not prepared to show a configuration variable
that is set to true using the valueless true syntax, which has been
corrected.
* am/trace2-with-valueless-true:
trace2: prevent segfault on config collection with valueless true
reflog entries for symbolic ref updates were broken, which has been
corrected.
* kn/reflog-symref-fix:
refs: fix creation of reflog entries for symrefs
"git branch --sort=..." and "git for-each-ref --format=... --sort=..."
did not work as expected with some atoms, which has been corrected.
* rs/ref-fitler-used-atoms-value-fix:
ref-filter: remove ref_format_clear()
ref-filter: move is-base tip to used_atom
ref-filter: move ahead-behind bases into used_atom
Doc updates.
* ja/doc-commit-markup-updates:
doc: migrate git-commit manpage secondary files to new format
doc: convert git commit config to new format
doc: make more direct explanations in git commit options
doc: the mode param of -u of git commit is optional
doc: apply new documentation guidelines to git commit
Introduce a new API to visit objects in batches based on a common
path, or by type.
* ds/path-walk-1:
path-walk: drop redundant parse_tree() call
path-walk: reorder object visits
path-walk: mark trees and blobs as UNINTERESTING
path-walk: visit tags and cached objects
path-walk: allow consumer to specify object types
t6601: add helper for testing path-walk API
test-lib-functions: add test_cmp_sorted
path-walk: introduce an object walk by path
The reftable/ library code has been made -Wsign-compare clean.
* ps/reftable-sign-compare:
reftable: address trivial -Wsign-compare warnings
reftable/blocksource: adjust `read_block()` to return `ssize_t`
reftable/blocksource: adjust type of the block length
reftable/block: adjust type of the restart length
reftable/block: adapt header and footer size to return a `size_t`
reftable/basics: adjust `hash_size()` to return `uint32_t`
reftable/basics: adjust `common_prefix_size()` to return `size_t`
reftable/record: handle overflows when decoding varints
reftable/record: drop unused `print` function pointer
meson: stop disabling -Wsign-compare
The "cache" credential back-end did not handle authtype correctly,
which has been corrected.
* mh/credential-cache-authtype-request-fix:
credential-cache: respect authtype capability
It was possible for "git unpack-objects" and "git index-pack" to
make an unaligned access, which has been corrected.
* jk/pack-header-parse-alignment-fix:
index-pack, unpack-objects: use skip_prefix to avoid magic number
index-pack, unpack-objects: use get_be32() for reading pack header
parse_pack_header_option(): avoid unaligned memory writes
packfile: factor out --pack_header argument parsing
bswap.h: squelch potential sparse -Wcast-truncate warnings
The meson-driven build is now aware of "git-subtree" housed in
contrib/subtree hierarchy.
* ps/build-meson-subtree:
meson: wire up the git-subtree(1) command
meson: introduce build option for contrib
contrib/subtree: fix building docs
The code in connect.c has been updated to work around complaints
from -Wsign-compare.
* mh/connect-sign-compare:
connect: address -Wsign-compare warnings
Move a few more unit tests to the clar test framework.
* sk/unit-tests:
t/unit-tests: convert reftable tree test to use clar test framework
t/unit-tests: adapt priority queue test to use clar test framework
t/unit-tests: convert mem-pool test to use clar test framework
t/unit-tests: handle dashes in test suite filenames
The help text from "git $cmd -h" appear on the standard output for
some $cmd and the standard error for others. The built-in commands
have been fixed to show them on the standard output consistently.
* jc/show-usage-help:
builtin: send usage() help text to standard output
oddballs: send usage() help text to standard output
builtins: send usage_with_options() help text to standard output
usage: add show_usage_if_asked()
parse-options: add show_usage_with_options_if_asked()
t0012: optionally check that "-h" output goes to stdout
When migrating reflogs between reference backends, maintaining the
original order of the reflog entries is crucial. To achieve this, an
`index` field is stored within the `ref_update` struct that encodes the
relative order of reflog entries. This field is used by the reftable
backend as update index for the respective reflog entries to maintain
that ordering.
These update indices must be respected when writing table headers, which
encode the minimum and maximum update index of contained records in the
header and footer. This logic was added in commit bc67b4ab5f (reftable:
write correct max_update_index to header, 2025-01-15), which started to
use `reftable_writer_set_limits()` to propagate the mininum and maximum
update index of all records contained in a ref transaction.
However, we only set the maximum update index for the first transaction
argument, even though there can be multiple such arguments. This is the
case when we write to multiple stacks in a single transaction, e.g. when
updating references in two different worktrees at once. Consequently,
the update index for all but the first argument remain uninitialized,
which may cause undefined behaviour.
Fix this by moving the assignment of the maximum update index in
`reftable_be_transaction_finish()` inside the loop, which ensures that
all elements of the array are correctly initialized.
Furthermore, initialize the `max_index` field to 0 when queueing a new
transaction argument. This is not strictly necessary, as all elements of
`write_transaction_table_arg.max_index` are now assigned correctly.
However, this initialization is added for consistency and to safeguard
against potential future changes that might inadvertently introduce
uninitialized memory access.
Reported-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Back when Git was in its infancy, remotes were configured via separate
files in "branches/" (back in 2005). This mechanism was replaced later
that year with the "remotes/" directory. Both mechanisms have eventually
been replaced by config-based remotes, and it is very unlikely that
anybody still uses these directories to configure their remotes.
Both of these directories have been marked as deprecated, one in 2005
and the other one in 2011. Follow through with the deprecation and
finally announce the removal of these features in Git 3.0.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
[jc: with a small tweak to the help message]
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Document that it is insecure to use Personal Access Tokens, which
some hosting providers take as username/password, embedded in URLs.
* mh/doc-credential-helpers-with-pat:
docs: discuss caching personal access tokens
docs: list popular credential helpers
The "instaweb" bound only to local IP address without "--local" and
to all addresses with "--local", which was the other way around, when
using Python's http.server class, which has been corrected.
* ak/instaweb-python-port-binding-fix:
instaweb: fix ip binding for the python http.server
The meson build procedure for Documentation/technical/ hierarchy was
missing necessary dependencies, which has been corrected.
* sj/meson-doc-technical-dependency-fix:
meson: fix missing deps for technical articles
The meson build procedure looked for the 'version-def.h' file in a
wrong directory, which has been corrected.
* tc/meson-use-our-version-def-h:
meson: ensure correct version-def.h is used
Extended SHA-1 expression parser did not work well when a branch
with an unusual name (e.g. "foo{bar") is involved.
* en/object-name-with-funny-refname-fix:
object-name: be more strict in parsing describe-like output
object-name: fix resolution of object names containing curly braces
* ds/path-walk-1:
path-walk: drop redundant parse_tree() call
path-walk: reorder object visits
path-walk: mark trees and blobs as UNINTERESTING
path-walk: visit tags and cached objects
path-walk: allow consumer to specify object types
t6601: add helper for testing path-walk API
test-lib-functions: add test_cmp_sorted
path-walk: introduce an object walk by path
Now that all callers have been converted from:
the_hash_algo->unsafe_init_fn();
to
unsafe_hash_algo(the_hash_algo)->init_fn();
and similar, we can remove the scaffolding for the unsafe_ function
variants and force callers to use the new unsafe_hash_algo() mechanic
instead.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 106140a99f (builtin/fast-import: fix segfault with unsafe SHA1
backend, 2024-12-30) and 9218c0bfe1 (bulk-checkin: fix segfault with
unsafe SHA1 backend, 2024-12-30), we observed the effects of failing to
initialize a hashfile_checkpoint with the same hash function
implementation as is used by the hashfile it is used to checkpoint.
While both 106140a99f and 9218c0bfe1 work around the immediate crash,
changing the hash function implementation within the hashfile API to,
for example, the non-unsafe variant would re-introduce the crash. This
is a result of the tight coupling between initializing hashfiles and
hashfile_checkpoints.
Introduce and use a new function which ensures that both parts of a
hashfile and hashfile_checkpoint pair use the same hash function
implementation to avoid such crashes.
A few things worth noting:
- In the change to builtin/fast-import.c::stream_blob(), we can see
that by removing the explicit reference to
'the_hash_algo->unsafe_init_fn()', we are hardened against the
hashfile API changing away from the_hash_algo (or its unsafe
variant) in the future.
- The bulk-checkin code no longer needs to explicitly zero-initialize
the hashfile_checkpoint, since it is now done as a result of calling
'hashfile_checkpoint_init()'.
- Also in the bulk-checkin code, we add an additional call to
prepare_to_stream() outside of the main loop in order to initialize
'state->f' so we know which hash function implementation to use when
calling 'hashfile_checkpoint_init()'.
This is OK, since subsequent 'prepare_to_stream()' calls are noops.
However, we only need to call 'prepare_to_stream()' when we have the
HASH_WRITE_OBJECT bit set in our flags. Without that bit, calling
'prepare_to_stream()' does not assign 'state->f', so we have nothing
to initialize.
- Other uses of the 'checkpoint' in 'deflate_blob_to_pack()' are
appropriately guarded.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove a series of conditionals within the shared cmd_hash_impl() helper
that powers the 'sha1' and 'sha1-unsafe' helpers.
Instead, replace them with a single conditional that transforms the
specified hash algorithm into its unsafe variant. Then all subsequent
calls can directly use whatever function it wants to call without having
to decide between the safe and unsafe variants.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Instead of calling the unsafe_ hash function variants directly, make use
of the shared 'algop' pointer by initializing it to:
f->algop = unsafe_hash_algo(the_hash_algo);
, thus making all calls use the unsafe variants directly.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 253ed9ecff (hash.h: scaffolding for _unsafe hashing variants,
2024-09-26), we introduced "unsafe" variants of the SHA-1 hashing
functions by introducing new functions like "unsafe_init_fn()" and so
on.
This approach has a major shortcoming that callers must remember to
consistently use one variant or the other. Failing to consistently use
(or not use) the unsafe variants can lead to crashes at best, or subtle
memory corruption issues at worst.
In the hashfile API, this isn't difficult to achieve, but verifying that
all callers consistently use the unsafe variants is somewhat of a chore
given how spread out all of the callers are. In the sha1 and sha1-unsafe
test helpers, all of the calls to various hash functions are guarded by
an "if (unsafe)" conditional, which is repetitive and cumbersome.
Address these issues by introducing a new pattern whereby one
'git_hash_algo' can return a pointer to another 'git_hash_algo' that
represents the unsafe version of itself. So instead of having something
like:
if (unsafe)
the_hash_algo->init_fn(...);
the_hash_algo->update_fn(...);
the_hash_algo->final_fn(...);
else
the_hash_algo->unsafe_init_fn(...);
the_hash_algo->unsafe_update_fn(...);
the_hash_algo->unsafe_final_fn(...);
we can instead write:
struct git_hash_algo *algop = the_hash_algo;
if (unsafe)
algop = unsafe_hash_algo(algop);
algop->init_fn(...);
algop->update_fn(...);
algop->final_fn(...);
This removes the existing shortcoming by no longer forcing the caller to
"remember" which variant of the hash functions it wants to call, only to
hold onto a 'struct git_hash_algo' pointer that is initialized once.
Similarly, while there currently is still a way to "mix" safe and unsafe
functions, this too will go away after subsequent commits remove all
direct calls to the unsafe_ variants.
Note that hash_algo_by_ptr() needs an adjustment to allow passing in the
unsafe variant of a hash function. All other query functions on the
hash_algos array will continue to return the safe variants of any
function.
Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Perform a similar transformation as in the previous commit, but focused
instead on hashfile_checksum_valid(). This function does not work with a
hashfile structure itself, and instead validates the raw contents of a
file written using the hashfile API.
We'll want to be prepared for a similar change to this function in the
future, so prepare ourselves for that by extracting 'the_hash_algo' into
its own field for use within this function.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Throughout the hashfile API, we rely on a reference to 'the_hash_algo',
and call its _unsafe function variants directly.
Prepare for a future change where we may use a different 'git_hash_algo'
pointer (instead of just relying on 'the_hash_algo' throughout) by
making the 'git_hash_algo' pointer a member of the 'hashfile' structure
itself.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
With the new "unsafe" SHA-1 build knob, it is convenient to have a
test-tool that can exercise Git's unsafe SHA-1 wrappers for testing,
similar to 't/helper/test-tool sha1'.
Implement that helper by altering the implementation of that test-tool
(in cmd_hash_impl(), which is generic and parameterized over different
hash functions) to conditionally run the unsafe variants of the chosen
hash function, and expose the new behavior via a new 'sha1-unsafe' test
helper.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
