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"git backfill" is capable of auto-detecting a sparsely checked out
working tree, which was broken.
* th/backfill-auto-detect-sparseness-fix:
backfill: auto-detect sparse-checkout from config
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Commit 85127bcdea ("backfill: assume --sparse when sparse-checkout is
enabled") intended for 'git backfill' to consult the repository
configuration when the user does not pass '--sparse' or
'--no-sparse' on the command line. It added the sentinel check:
if (ctx->sparse < 0)
ctx->sparse = cfg->apply_sparse_checkout;
However, the ctx->sparse field is initialized to 0 instead of -1,
so this guard never triggers. Consequently, the repository config
(core.sparseCheckout) is never checked, and the command always
performs a full backfill even when sparse-checkout is enabled.
Fix this by initializing ctx->sparse to -1, ensuring the existing
fallback logic correctly reads the repository configuration when
no explicit flags are provided.
Add a test to verify that 'git backfill' automatically respects
sparse-checkout settings when no flags are passed.
Signed-off-by: Trieu Huynh <vikingtc4@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Before the recent changes to parse rev-list arguments inside of 'git
backfill', the builtin would take arbitrary arguments without complaint (and
ignore them). This was noticed and a patch was sent [1] which motivates
this change.
[1] https://lore.kernel.org/git/20260321031643.5185-1-r.siddharth.shrimali@gmail.com/
Note that the revision machinery can output an "ambiguous argument"
warning if a value not starting with '--' is found and doesn't make
sense as a reference or a pathspec. For unrecognized arguments starting
with '--' we need to add logic into builtin/backfill.c to catch leftover
arguments.
Reported-by: Siddharth Shrimali <r.siddharth.shrimali@gmail.com>
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Previously, walk_objects_by_path() silently ignored pathspecs containing
wildcards or magic by clearing them. This caused all blobs to be
downloaded regardless of the given pathspec. Wildcard pathspecs like
"d/file.*.txt" are useful for narrowing which blobs to process (e.g.,
during 'git backfill').
Support wildcard pathspecs by making two changes:
1. Add an 'exact_pathspecs' flag to path_walk_context. When the
pathspec has no wildcards or magic, set this flag and use the
existing fast-path prefix matching in add_tree_entries(). When
wildcards are present, skip that block since prefix matching
cannot handle glob patterns.
2. Add a match_pathspec() check in walk_path() to filter out blobs
whose full path does not match the pathspec. This provides the
actual blob-level filtering for wildcard pathspecs.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The previous change allowed specifying revision arguments over the 'git
backfill' command-line. This created the opportunity for restricting the
initial commit set by filtering the revision walk through a pathspec. Other
than filtering the commit set (and thereby the root trees), this did not
restrict the path-walk implementation of 'git backfill' and did not restrict
the blobs that were downloaded to only those matching the pathspec.
Update the path-walk API to accept certain kinds of pathspecs and to
silently ignore anything too complex, for now. We will update this in the
next change to properly restrict to even complex pathspecs.
The current behavior focuses on pathspecs that match paths exactly. This
includes exact filenames, including directory names as prefixes. Pathspecs
containing wildcards or magic are cleared so the path walk downloads all
blobs, as before.
The reason for this restriction is to allow for a faster execution by
pruning the path walk to only trees that could contribute towards one of
those paths as a parent directory.
The test directory 'd/f/' (next to 'd/file*.txt') was prepared in a
previous commit to exercise the subtlety in prefix matching.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The existing implementation of 'git backfill' only includes downloading
missing blobs reachable from HEAD. Advanced uses may desire more general
commit limiting options, such as '--all' for all references, specifying a
commit range via negative references, or specifying a recency of use such as
with '--since=<date>'.
All of these options are available if we use setup_revisions() to parse the
unknown arguments with the revision machinery. This opens up a large number
of possibilities, only a small set of which are tested here.
For documentation, we avoid duplicating the option documentation and instead
link to the documentation of 'git rev-list'.
Note that these arguments currently allow specifying a pathspec, which
modifies the commit history checks but does not limit the paths used in the
backfill logic. This will be updated in a future change.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Prepare the test infrastructure for upcoming changes that teach 'git
backfill' to accept revision arguments and pathspecs.
Add test_tick before each commit in the setup loop so that commit dates
are deterministic. This enables reliable testing with '--since'.
Rename the 'd/e/' directory to 'd/f/' so that the prefix 'd/f' is
ambiguous with the files 'd/file.*.txt'. This exercises the subtlety
in prefix pathspec matching that will be added in a later commit.
Create a branched version of the test repository (src-revs) with:
- A 'side' branch merged into main, adding s/file.{1,2}.txt with
two versions (4 new blobs, 52 total from main HEAD).
- An unmerged 'other' branch adding o/file.{1,2}.txt (2 more blobs,
54 total reachable from --all).
This structure makes --all, --first-parent, and --since produce
meaningfully different results when used with 'git backfill'.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The previous change introduced the '--[no-]sparse' option for the 'git
backfill' command, but did not assume it as enabled by default. However,
this is likely the behavior that users will most often want to happen.
Without this default, users with a small sparse-checkout may be confused
when 'git backfill' downloads every version of every object in the full
history.
However, this is left as a separate change so this decision can be reviewed
independently of the value of the '--[no-]sparse' option.
Add a test of adding the '--sparse' option to a repo without sparse-checkout
to make it clear that supplying it without a sparse-checkout is an error.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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One way to significantly reduce the cost of a Git clone and later fetches is
to use a blobless partial clone and combine that with a sparse-checkout that
reduces the paths that need to be populated in the working directory. Not
only does this reduce the cost of clones and fetches, the sparse-checkout
reduces the number of objects needed to download from a promisor remote.
However, history investigations can be expensive as computing blob diffs
will trigger promisor remote requests for one object at a time. This can be
avoided by downloading the blobs needed for the given sparse-checkout using
'git backfill' and its new '--sparse' mode, at a time that the user is
willing to pay that extra cost.
Note that this is distinctly different from the '--filter=sparse:<oid>'
option, as this assumes that the partial clone has all reachable trees and
we are using client-side logic to avoid downloading blobs outside of the
sparse-checkout cone. This avoids the server-side cost of walking trees
while also achieving a similar goal. It also downloads in batches based on
similar path names, presenting a resumable download if things are
interrupted.
This augments the path-walk API to have a possibly-NULL 'pl' member that may
point to a 'struct pattern_list'. This could be more general than the
sparse-checkout definition at HEAD, but 'git backfill --sparse' is currently
the only consumer.
Be sure to test this in both cone mode and not cone mode. Cone mode has the
benefit that the path-walk can skip certain paths once they would expand
beyond the sparse-checkout. Non-cone mode can describe the included files
using both positive and negative patterns, which changes the possible return
values of path_matches_pattern_list(). Test both kinds of matches for
increased coverage.
To test this, we can create a blobless sparse clone, expand the
sparse-checkout slightly, and then run 'git backfill --sparse' to see
how much data is downloaded. The general steps are
1. git clone --filter=blob:none --sparse <url>
2. git sparse-checkout set <dir1> ... <dirN>
3. git backfill --sparse
For the Git repository with the 'builtin' directory in the
sparse-checkout, we get these results for various batch sizes:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|-------|
| (Initial clone) | 3 | 110 MB | |
| 10K | 12 | 192 MB | 17.2s |
| 15K | 9 | 192 MB | 15.5s |
| 20K | 8 | 192 MB | 15.5s |
| 25K | 7 | 192 MB | 14.7s |
This case matters less because a full clone of the Git repository from
GitHub is currently at 277 MB.
Using a copy of the Linux repository with the 'kernel/' directory in the
sparse-checkout, we get these results:
| Batch Size | Pack Count | Pack Size | Time |
|-----------------|------------|-----------|------|
| (Initial clone) | 2 | 1,876 MB | |
| 10K | 11 | 2,187 MB | 46s |
| 25K | 7 | 2,188 MB | 43s |
| 50K | 5 | 2,194 MB | 44s |
| 100K | 4 | 2,194 MB | 48s |
This case is more meaningful because a full clone of the Linux
repository is currently over 6 GB, so this is a valuable way to download
a fraction of the repository and no longer need network access for all
reachable objects within the sparse-checkout.
Choosing a batch size will depend on a lot of factors, including the
user's network speed or reliability, the repository's file structure,
and how many versions there are of the file within the sparse-checkout
scope. There will not be a one-size-fits-all solution.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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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>
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