The code to write split commit-graph file(s) upon fetching computed
bogus value for the parameter used in splitting the resulting
files, which has been corrected.
* ds/commit-graph-set-size-mult:
commit-graph: prefer default size_mult when given zero
In 50f26bd ("fetch: add fetch.writeCommitGraph config setting",
2019-09-02), the fetch builtin added the capability to write a
commit-graph using the "--split" feature. This feature creates
multiple commit-graph files, and those can merge based on a set
of "split options" including a size multiple. The default size
multiple is 2, which intends to provide a log_2 N depth of the
commit-graph chain where N is the number of commits.
However, I noticed during dogfooding that my commit-graph chains
were becoming quite large when left only to builds by 'git fetch'.
It turns out that in split_graph_merge_strategy(), we default the
size_mult variable to 2 except we override it with the context's
split_opts if they exist. In builtin/fetch.c, we create such a
split_opts, but do not populate it with values.
This problem is due to two failures:
1. It is unclear that we can add the flag COMMIT_GRAPH_WRITE_SPLIT
with a NULL split_opts.
2. If we have a non-NULL split_opts, then we override the default
values even if a zero value is given.
Correct both of these issues. First, do not override size_mult when
the options provide a zero value. Second, stop creating a split_opts
in the fetch builtin.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
One kind of progress messages were always given during commit-graph
generation, instead of following the "if it takes more than two
seconds, show progress" pattern, which has been corrected.
* ds/commit-graph-delay-gen-progress:
commit-graph: use start_delayed_progress()
progress: create GIT_PROGRESS_DELAY
Docfix.
* en/doc-typofix:
Fix spelling errors in no-longer-updated-from-upstream modules
multimail: fix a few simple spelling errors
sha1dc: fix trivial comment spelling error
Fix spelling errors in test commands
Fix spelling errors in messages shown to users
Fix spelling errors in names of tests
Fix spelling errors in comments of testcases
Fix spelling errors in code comments
Fix spelling errors in documentation outside of Documentation/
Documentation: fix a bunch of typos, both old and new
Crufty code and logic accumulated over time around the object
parsing and low-level object access used in "git fsck" have been
cleaned up.
* jk/cleanup-object-parsing-and-fsck: (23 commits)
fsck: accept an oid instead of a "struct tree" for fsck_tree()
fsck: accept an oid instead of a "struct commit" for fsck_commit()
fsck: accept an oid instead of a "struct tag" for fsck_tag()
fsck: rename vague "oid" local variables
fsck: don't require an object struct in verify_headers()
fsck: don't require an object struct for fsck_ident()
fsck: drop blob struct from fsck_finish()
fsck: accept an oid instead of a "struct blob" for fsck_blob()
fsck: don't require an object struct for report()
fsck: only require an oid for skiplist functions
fsck: only provide oid/type in fsck_error callback
fsck: don't require object structs for display functions
fsck: use oids rather than objects for object_name API
fsck_describe_object(): build on our get_object_name() primitive
fsck: unify object-name code
fsck: require an actual buffer for non-blobs
fsck: stop checking tag->tagged
fsck: stop checking commit->parent counts
fsck: stop checking commit->tree value
commit, tag: don't set parsed bit for parse failures
...
When writing a commit-graph, we show progress along several commit
walks. When we use start_delayed_progress(), the progress line will
only appear if that step takes a decent amount of time.
However, one place was missed: computing generation numbers. This is
normally a very fast operation as all commits have been parsed in a
previous step. But, this is showing up for all users no matter how few
commits are being added.
The tests that check for the progress output have already been updated
to use GIT_PROGRESS_DELAY=0 to force the expected output.
Helped-by: Jeff King <peff@peff.net>
Reported-by: ryenus <ryenus@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If we can't parse a commit, then parse_commit() will return an error
code. But it _also_ sets the "parsed" flag, which tells us not to bother
trying to re-parse the object. That means that subsequent parses have no
idea that the information in the struct may be bogus. I.e., doing this:
parse_commit(commit);
...
if (parse_commit(commit) < 0)
die("commit is broken");
will never trigger the die(). The second parse_commit() will see the
"parsed" flag and quietly return success.
There are two obvious ways to fix this:
1. Stop setting "parsed" until we've successfully parsed.
2. Keep a second "corrupt" flag to indicate that we saw an error (and
when the parsed flag is set, return 0/-1 depending on the corrupt
flag).
This patch does option 1. The obvious downside versus option 2 is that
we might continually re-parse a broken object. But in practice,
corruption like this is rare, and we typically die() or return an error
in the caller. So it's OK not to worry about optimizing for corruption.
And it's much simpler: we don't need to use an extra bit in the object
struct, and callers which check the "parsed" flag don't need to learn
about the corrupt bit, too.
There's no new test here, because this case is already covered in t5318.
Note that we do need to update the expected message there, because we
now detect the problem in the return from "parse_commit()", and not with
a separate check for a NULL tree. In fact, we can now ditch that
explicit tree check entirely, as we're covered robustly by this change
(and the previous recent change to treat a NULL tree as a parse error).
We'll also give tags the same treatment. I don't know offhand of any
cases where the problem can be triggered (it implies somebody ignoring a
parse error earlier in the process), but consistently returning an error
should cause the least surprise.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous commit includes a failing test for an issue around
fetch.writeCommitGraph and fetching in a repo with a submodule. Here, we
fix that bug and set the test to "test_expect_success".
The problem arises with this set of commands when the remote repo at
<url> has a submodule. Note that --recurse-submodules is not needed to
demonstrate the bug.
$ git clone <url> test
$ cd test
$ git -c fetch.writeCommitGraph=true fetch origin
Computing commit graph generation numbers: 100% (12/12), done.
BUG: commit-graph.c:886: missing parent <hash1> for commit <hash2>
Aborted (core dumped)
As an initial fix, I converted the code in builtin/fetch.c that calls
write_commit_graph_reachable() to instead launch a "git commit-graph
write --reachable --split" process. That code worked, but is not how we
want the feature to work long-term.
That test did demonstrate that the issue must be something to do with
internal state of the 'git fetch' process.
The write_commit_graph() method in commit-graph.c ensures the commits we
plan to write are "closed under reachability" using close_reachable().
This method walks from the input commits, and uses the UNINTERESTING
flag to mark which commits have already been visited. This allows the
walk to take O(N) time, where N is the number of commits, instead of
O(P) time, where P is the number of paths. (The number of paths can be
exponential in the number of commits.)
However, the UNINTERESTING flag is used in lots of places in the
codebase. This flag usually means some barrier to stop a commit walk,
such as in revision-walking to compare histories. It is not often
cleared after the walk completes because the starting points of those
walks do not have the UNINTERESTING flag, and clear_commit_marks() would
stop immediately.
This is happening during a 'git fetch' call with a remote. The fetch
negotiation is comparing the remote refs with the local refs and marking
some commits as UNINTERESTING.
I tested running clear_commit_marks_many() to clear the UNINTERESTING
flag inside close_reachable(), but the tips did not have the flag, so
that did nothing.
It turns out that the calculate_changed_submodule_paths() method is at
fault. Thanks, Peff, for pointing out this detail! More specifically,
for each submodule, the collect_changed_submodules() runs a revision
walk to essentially do file-history on the list of submodules. That
revision walk marks commits UNININTERESTING if they are simplified away
by not changing the submodule.
Instead, I finally arrived on the conclusion that I should use a flag
that is not used in any other part of the code. In commit-reach.c, a
number of flags were defined for commit walk algorithms. The REACHABLE
flag seemed like it made the most sense, and it seems it was not
actually used in the file. The REACHABLE flag was used in early versions
of commit-reach.c, but was removed by 4fbcca4 (commit-reach: make
can_all_from_reach... linear, 2018-07-20).
Add the REACHABLE flag to commit-graph.c and use it instead of
UNINTERESTING in close_reachable(). This fixes the bug in manual
testing.
Reported-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Szeder Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Miscellaneous code clean-ups.
* ah/cleanups:
git_mkstemps_mode(): replace magic numbers with computed value
wrapper: use a loop instead of repetitive statements
diffcore-break: use a goto instead of a redundant if statement
commit-graph: remove a duplicate assignment
The code to parse and use the commit-graph file has been made more
robust against corrupted input.
* tb/commit-graph-harden:
commit-graph.c: handle corrupt/missing trees
commit-graph.c: handle commit parsing errors
t/t5318: introduce failing 'git commit-graph write' tests
The "upload-pack" (the counterpart of "git fetch") needs to disable
commit-graph when responding to a shallow clone/fetch request, but
the way this was done made Git panic, which has been corrected.
* jk/disable-commit-graph-during-upload-pack:
upload-pack: disable commit graph more gently for shallow traversal
commit-graph: bump DIE_ON_LOAD check to actual load-time
A pair of small fixups to "git commit-graph" have been applied.
* jk/commit-graph-cleanup:
commit-graph: turn off save_commit_buffer
commit-graph: don't show progress percentages while expanding reachable commits
Leave the variable 'g' uninitialized before it is set just before its
first use in front of a loop, which is a much more appropriate place to
indicate what it is used for.
Also initialize the variable 'num_commits' just before the loop instead
of at the beginning of the function for the same reason.
Reviewed-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add --[no-]progress to git commit-graph write and verify.
The progress feature was introduced in 7b0f229
("commit-graph write: add progress output", 2018-09-17) but
the ability to opt-out was overlooked.
Signed-off-by: Garima Singh <garima.singh@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Let commit_list_count() count the number of parents instead of
duplicating it. Also store the result in an unsigned int, as that's
what the function returns, and the count is never negative.
Signed-off-by: René Scharfe <l.s.r@web.de>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When the client has asked for certain shallow options like
"deepen-since", we do a custom rev-list walk that pretends to be
shallow. Before doing so, we have to disable the commit-graph, since it
is not compatible with the shallow view of the repository. That's
handled by 829a321569 (commit-graph: close_commit_graph before shallow
walk, 2018-08-20). That commit literally closes and frees our
repo->objects->commit_graph struct.
That creates an interesting problem for commits that have _already_ been
parsed using the commit graph. Their commit->object.parsed flag is set,
their commit->graph_pos is set, but their commit->maybe_tree may still
be NULL. When somebody later calls repo_get_commit_tree(), we see that
we haven't loaded the tree oid yet and try to get it from the commit
graph. But since it has been freed, we segfault!
So the root of the issue is a data dependency between the commit's
lazy-load of the tree oid and the fact that the commit graph can go
away mid-process. How can we resolve it?
There are a couple of general approaches:
1. The obvious answer is to avoid loading the tree from the graph when
we see that it's NULL. But then what do we return for the tree oid?
If we return NULL, our caller in do_traverse() will rightly
complain that we have no tree. We'd have to fallback to loading the
actual commit object and re-parsing it. That requires teaching
parse_commit_buffer() to understand re-parsing (i.e., not starting
from a clean slate and not leaking any allocated bits like parent
list pointers).
2. When we close the commit graph, walk through the set of in-memory
objects and clear any graph_pos pointers. But this means we also
have to "unparse" any such commits so that we know they still need
to open the commit object to fill in their trees. So it's no less
complicated than (1), and is more expensive (since we clear objects
we might not later need).
3. Stop freeing the commit-graph struct. Continue to let it be used
for lazy-loads of tree oids, but let upload-pack specify that it
shouldn't be used for further commit parsing.
4. Push the whole shallow rev-list out to its own sub-process, with
the commit-graph disabled from the start, giving it a clean memory
space to work from.
I've chosen (3) here. Options (1) and (2) would work, but are
non-trivial to implement. Option (4) is more expensive, and I'm not sure
how complicated it is (shelling out for the actual rev-list part is
easy, but we do then parse the resulting commits internally, and I'm not
clear which parts need to be handling shallow-ness).
The new test in t5500 triggers this segfault, but see the comments there
for how horribly intimate it has to be with how both upload-pack and
commit graphs work.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Commit 43d3561805 (commit-graph write: don't die if the existing graph
is corrupt, 2019-03-25) added an environment variable we use only in the
test suite, $GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD. But it put the check for
this variable at the very top of prepare_commit_graph(), which is called
every time we want to use the commit graph. Most importantly, it comes
_before_ we check the fast-path "did we already try to load?", meaning
we end up calling getenv() for every single use of the commit graph,
rather than just when we load.
getenv() is allowed to have unexpected side effects, but that shouldn't
be a problem here; we're lazy-loading the graph so it's clear that at
least _one_ invocation of this function is going to call it.
But it is inefficient. getenv() typically has to do a linear search
through the environment space.
We could memoize the call, but it's simpler still to just bump the check
down to the actual loading step. That's fine for our sole user in t5318,
and produces this minor real-world speedup:
[before]
Benchmark #1: git -C linux rev-list HEAD >/dev/null
Time (mean ± σ): 1.460 s ± 0.017 s [User: 1.174 s, System: 0.285 s]
Range (min … max): 1.440 s … 1.491 s 10 runs
[after]
Benchmark #1: git -C linux rev-list HEAD >/dev/null
Time (mean ± σ): 1.391 s ± 0.005 s [User: 1.118 s, System: 0.273 s]
Range (min … max): 1.385 s … 1.399 s 10 runs
Of course that actual speedup depends on how big your environment is. We
can game it like this:
for i in $(seq 10000); do
export dummy$i=$i
done
in which case I get:
[before]
Benchmark #1: git -C linux rev-list HEAD >/dev/null
Time (mean ± σ): 6.257 s ± 0.061 s [User: 6.005 s, System: 0.250 s]
Range (min … max): 6.174 s … 6.337 s 10 runs
[after]
Benchmark #1: git -C linux rev-list HEAD >/dev/null
Time (mean ± σ): 1.403 s ± 0.005 s [User: 1.146 s, System: 0.256 s]
Range (min … max): 1.396 s … 1.412 s 10 runs
So this is really more about avoiding the pathological case than
providing a big real-world speedup.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A mechanism to affect the default setting for a (related) group of
configuration variables is introduced.
* ds/feature-macros:
repo-settings: create feature.experimental setting
repo-settings: create feature.manyFiles setting
repo-settings: parse core.untrackedCache
commit-graph: turn on commit-graph by default
t6501: use 'git gc' in quiet mode
repo-settings: consolidate some config settings
Commit 49bbc57a57 (commit-graph write: emit a percentage for all
progress, 2019-01-19) was a bit overeager when it added progress
percentages to the "Expanding reachable commits in commit graph" phase
as well, because most of the time the number of commits that phase has
to iterate over is not known in advance and grows significantly, and,
consequently, we end up with nonsensical numbers:
$ git commit-graph write --reachable
Expanding reachable commits in commit graph: 138606% (824706/595), done.
[...]
$ git rev-parse v5.0 | git commit-graph write --stdin-commits
Expanding reachable commits in commit graph: 81264400% (812644/1), done.
[...]
Even worse, because the percentage grows so quickly, the progress code
outputs much more often than it should (because it ticks every second,
or every 1%), slowing the whole process down. My time for "git
commit-graph write --reachable" on linux.git went from 13.463s to
12.521s with this patch, ~7% savings.
Therefore, don't show progress percentages in the "Expanding reachable
commits in commit graph" phase.
Note that the current code does sometimes do the right thing, if we
picked up all commits initially (e.g., omitting "--reachable" in a
fully-packed repository would get the correct count without any parent
traversal). So it may be possible to come up with a way to tell when we
could use a percentage here. But in the meantime, let's make sure we
robustly avoid printing nonsense.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Apply similar treatment as in the previous commit to handle an unchecked
call to 'get_commit_tree_oid()'. Previously, a NULL return value from
this function would be immediately dereferenced with '->hash', and then
cause a segfault.
Before dereferencing to access the 'hash' member, check the return value
of 'get_commit_tree_oid()' to make sure that it is not NULL.
To make this check correct, a related change is also needed in
'commit.c', which is to check the return value of 'get_commit_tree'
before taking its address. If 'get_commit_tree' returns NULL, we
encounter an undefined behavior when taking the address of the return
value of 'get_commit_tree' and then taking '->object.oid'. (On my system,
this is memory address 0x8, which is obviously wrong).
Fix this by making sure that 'get_commit_tree' returns something
non-NULL before digging through a structure that is not there, thus
preventing a segfault down the line in the commit graph code.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To write a commit graph chunk, 'write_graph_chunk_data()' takes a list
of commits to write and parses each one before writing the necessary
data, and continuing on to the next commit in the list.
Since the majority of these commits are not parsed ahead of time (an
exception is made for the *last* commit in the list, which is parsed
early within 'copy_oids_to_commits'), it is possible that calling
'parse_commit_no_graph()' on them may return an error. Failing to catch
these errors before de-referencing later calls can result in a undefined
memory access and a SIGSEGV.
One such example of this is 'get_commit_tree_oid()', which expects a
parsed object as its input (in this case, the commit-graph code passes
'*list'). If '*list' causes a parse error, the subsequent call will
fail.
Prevent such an issue by checking the return value of
'parse_commit_no_graph()' to avoid passing an unparsed object to a
function which expects a parsed object, thus preventing a segfault.
It is worth noting that this fix is really skirting around the issue in
object.c's 'parse_object()', which makes it difficult to tell how
corrupt an object is without digging into it. Presumably one could
change the meaning of 'parse_object' returns, but this would require
adjusting each callsite accordingly. Instead of that, add an additional
check to the object parsed.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code to write commit-graph over given commit object names has
been made a bit more robust.
* sg/commit-graph-validate:
commit-graph: error out on invalid commit oids in 'write --stdin-commits'
commit-graph: turn a group of write-related macro flags into an enum
t5318-commit-graph: use 'test_expect_code'
There are a few important config settings that are not loaded
during git_default_config. These are instead loaded on-demand.
Centralize these config options to a single scan, and store
all of the values in a repo_settings struct. The values for
each setting are initialized as negative to indicate "unset".
This centralization will be particularly important in a later
change to introduce "meta" config settings that change the
defaults for these config settings.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 1771be90 "commit-graph: merge commit-graph chains" (2019-06-18),
the method sort_and_scan_merged_commits() was added to merge the
commit lists of two commit-graph files in the incremental format.
Unfortunately, there was an off-by-one error in that method around
incrementing num_extra_edges, which leads to an incorrect offset
for the base graph chunk.
When we store an octopus merge in the commit-graph file, we store
the first parent in the normal place, but use the second parent
position to point into the "extra edges" chunk where the remaining
parents exist. This means we should be adding "num_parents - 1"
edges to this list, not "num_parents - 2". That is the basic error.
The reason this was not caught in the test suite is more subtle.
In 5324-split-commit-graph.sh, we test creating an octopus merge
and adding it to the tip of a commit-graph chain, then verify the
result. This _should_ have caught the problem, except that when
we load the commit-graph files we were overly careful to not fail
when the commit-graph chain does not match. This care was on
purpose to avoid race conditions as one process reads the chain
and another process modifies it. In such a case, the reading
process outputs the following message to stderr:
warning: commit-graph chain does not match
These warnings are output in the test suite, but ignored. By
checking the stderr of `git commit-graph verify` to include
the expected progress output, it will now catch this error.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
While 'git commit-graph write --stdin-commits' expects commit object
ids as input, it accepts and silently skips over any invalid commit
object ids, and still exits with success:
# nonsense
$ echo not-a-commit-oid | git commit-graph write --stdin-commits
$ echo $?
0
# sometimes I forgot that refs are not good...
$ echo HEAD | git commit-graph write --stdin-commits
$ echo $?
0
# valid tree OID, but not a commit OID
$ git rev-parse HEAD^{tree} | git commit-graph write --stdin-commits
$ echo $?
0
$ ls -l .git/objects/info/commit-graph
ls: cannot access '.git/objects/info/commit-graph': No such file or directory
Check that all input records are indeed valid commit object ids and
return with error otherwise, the same way '--stdin-packs' handles
invalid input; see e103f7276f (commit-graph: return with errors during
write, 2019-06-12).
Note that it should only return with error when encountering an
invalid commit object id coming from standard input. However,
'--reachable' uses the same code path to process object ids pointed to
by all refs, and that includes tag object ids as well, which should
still be skipped over. Therefore add a new flag to 'enum
commit_graph_write_flags' and a corresponding field to 'struct
write_commit_graph_context', so we can differentiate between those two
cases.
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The commits in a repository can be described by multiple
commit-graph files now, which allows the commit-graph files to be
updated incrementally.
* ds/commit-graph-incremental:
commit-graph: test verify across alternates
commit-graph: normalize commit-graph filenames
commit-graph: test --split across alternate without --split
commit-graph: test octopus merges with --split
commit-graph: clean up chains after flattened write
commit-graph: verify chains with --shallow mode
commit-graph: create options for split files
commit-graph: expire commit-graph files
commit-graph: allow cross-alternate chains
commit-graph: merge commit-graph chains
commit-graph: add --split option to builtin
commit-graph: write commit-graph chains
commit-graph: rearrange chunk count logic
commit-graph: add base graphs chunk
commit-graph: load commit-graph chains
commit-graph: rename commit_compare to oid_compare
commit-graph: prepare for commit-graph chains
commit-graph: document commit-graph chains
Code clean-up to remove hardcoded SHA-1 hash from many places.
* jk/oidhash:
hashmap: convert sha1hash() to oidhash()
hash.h: move object_id definition from cache.h
khash: rename oid helper functions
khash: drop sha1-specific map types
pack-bitmap: convert khash_sha1 maps into kh_oid_map
delta-islands: convert island_marks khash to use oids
khash: rename kh_oid_t to kh_oid_set
khash: drop broken oid_map typedef
object: convert create_object() to use object_id
object: convert internal hash_obj() to object_id
object: convert lookup_object() to use object_id
object: convert lookup_unknown_object() to use object_id
pack-objects: convert locate_object_entry_hash() to object_id
pack-objects: convert packlist_find() to use object_id
pack-bitmap-write: convert some helpers to use object_id
upload-pack: rename a "sha1" variable to "oid"
describe: fix accidental oid/hash type-punning
The commit-graph file is now part of the "files that the runtime
may keep open file descriptors on, all of which would need to be
closed when done with the object store", and the file descriptor to
an existing commit-graph file now is closed before "gc" finalizes a
new instance to replace it.
* ds/close-object-store:
packfile: rename close_all_packs to close_object_store
packfile: close commit-graph in close_all_packs
commit-graph: use raw_object_store when closing
There are no callers left of create_object() that aren't just passing us
the "hash" member of a "struct object_id". Let's take the whole struct,
which gets us closer to removing all raw sha1 variables.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing commit-graph files, we append path data to an
object directory, which may be specified by the user via the
'--object-dir' option. If the user supplies a trailing slash,
or some other alternative path format, the resulting path may
be usable for writing to the correct location. However, when
expiring graph files from the <obj-dir>/info/commit-graphs
directory during a write, we need to compare paths with exact
string matches.
Normalize the commit-graph filenames to avoid ambiguity. This
creates extra allocations, but this is a constant multiple of
the number of commit-graph files, which should be a number in
the single digits.
Further normalize the object directory in the context. Due to
a comparison between g->obj_dir and ctx->obj_dir in
split_graph_merge_strategy(), a trailing slash would prevent
any merging of layers within the same object directory. The
check is there to ensure we do not merge across alternates.
Update the tests to include a case with this trailing slash
problem.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If we write a commit-graph file without the split option, then
we write to $OBJDIR/info/commit-graph and start to ignore
the chains in $OBJDIR/info/commit-graphs/.
Unlink the commit-graph-chain file and expire the graph-{hash}.graph
files in $OBJDIR/info/commit-graphs/ during every write.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If we wrote a commit-graph chain, we only modified the tip file in
the chain. It is valuable to verify what we wrote, but not waste
time checking files we did not write.
Add a '--shallow' option to the 'git commit-graph verify' subcommand
and check that it does not read the base graph in a two-file chain.
Making the verify subcommand read from a chain of commit-graphs takes
some rearranging of the builtin code.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The split commit-graph feature is now fully implemented, but needs
some more run-time configurability. Allow direct callers to 'git
commit-graph write --split' to specify the values used in the
merge strategy and the expire time.
Update the documentation to specify these values.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As we merge commit-graph files in a commit-graph chain, we should clean
up the files that are no longer used.
This change introduces an 'expiry_window' value to the context, which is
always zero (for now). We then check the modified time of each
graph-{hash}.graph file in the $OBJDIR/info/commit-graphs folder and
unlink the files that are older than the expiry_window.
Since this is always zero, this immediately clears all unused graph
files. We will update the value to match a config setting in a future
change.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In an environment like a fork network, it is helpful to have a
commit-graph chain that spans both the base repo and the fork repo. The
fork is usually a small set of data on top of the large repo, but
sometimes the fork is much larger. For example, git-for-windows/git has
almost double the number of commits as git/git because it rebases its
commits on every major version update.
To allow cross-alternate commit-graph chains, we need a few pieces:
1. When looking for a graph-{hash}.graph file, check all alternates.
2. When merging commit-graph chains, do not merge across alternates.
3. When writing a new commit-graph chain based on a commit-graph file
in another object directory, do not allow success if the base file
has of the name "commit-graph" instead of
"commit-graphs/graph-{hash}.graph".
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When searching for a commit in a commit-graph chain of G graphs with N
commits, the search takes O(G log N) time. If we always add a new tip
graph with every write, the linear G term will start to dominate and
slow the lookup process.
To keep lookups fast, but also keep most incremental writes fast, create
a strategy for merging levels of the commit-graph chain. The strategy is
detailed in the commit-graph design document, but is summarized by these
two conditions:
1. If the number of commits we are adding is more than half the number
of commits in the graph below, then merge with that graph.
2. If we are writing more than 64,000 commits into a single graph,
then merge with all lower graphs.
The numeric values in the conditions above are currently constant, but
can become config options in a future update.
As we merge levels of the commit-graph chain, check that the commits
still exist in the repository. A garbage-collection operation may have
removed those commits from the object store and we do not want to
persist them in the commit-graph chain. This is a non-issue if the
'git gc' process wrote a new, single-level commit-graph file.
After we merge levels, the old graph-{hash}.graph files are no longer
referenced by the commit-graph-chain file. We will expire these files in
a future change.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a new "--split" option to the 'git commit-graph write' subcommand. This
option allows the optional behavior of writing a commit-graph chain.
The current behavior will add a tip commit-graph containing any commits that
are not in the existing commit-graph or commit-graph chain. Later changes
will allow merging the chain and expiring out-dated files.
Add a new test script (t5324-split-commit-graph.sh) that demonstrates this
behavior.
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Extend write_commit_graph() to write a commit-graph chain when given the
COMMIT_GRAPH_SPLIT flag.
This implementation is purposefully simplistic in how it creates a new
chain. The commits not already in the chain are added to a new tip
commit-graph file.
Much of the logic around writing a graph-{hash}.graph file and updating
the commit-graph-chain file is the same as the commit-graph file case.
However, there are several places where we need to do some extra logic
in the split case.
Track the list of graph filenames before and after the planned write.
This will be more important when we start merging graph files, but it
also allows us to upgrade our commit-graph file to the appropriate
graph-{hash}.graph file when we upgrade to a chain of commit-graphs.
Note that we use the eighth byte of the commit-graph header to store the
number of base graph files. This determines the length of the base
graphs chunk.
A subtle change of behavior with the new logic is that we do not write a
commit-graph if we our commit list is empty. This extends to the typical
case, which is reflected in t5318-commit-graph.sh.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The number of chunks in a commit-graph file can change depending on
whether we need the Extra Edges Chunk. We are going to add more optional
chunks, and it will be helpful to rearrange this logic around the chunk
count before doing so.
Specifically, we need to finalize the number of chunks before writing
the commit-graph header. Further, we also need to fill out the chunk
lookup table dynamically and using "num_chunks" as we add optional
chunks is useful for adding optional chunks in the future.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To quickly verify a commit-graph chain is valid on load, we will
read from the new "Base Graphs Chunk" of each file in the chain.
This will prevent accidentally loading incorrect data from manually
editing the commit-graph-chain file or renaming graph-{hash}.graph
files.
The commit_graph struct already had an object_id struct "oid", but
it was never initialized or used. Add a line to read the hash from
the end of the commit-graph file and into the oid member.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Prepare the logic for reading a chain of commit-graphs.
First, look for a file at $OBJDIR/info/commit-graph. If it exists,
then use that file and stop.
Next, look for the chain file at $OBJDIR/info/commit-graphs/commit-graph-chain.
If this file exists, then load the hash values as line-separated values in that
file and load $OBJDIR/info/commit-graphs/graph-{hash[i]}.graph for each hash[i]
in that file. The file is given in order, so the first hash corresponds to the
"base" file and the final hash corresponds to the "tip" file.
This implementation assumes that all of the graph-{hash}.graph files are in
the same object directory as the commit-graph-chain file. This will be updated
in a future change. This change is purposefully simple so we can isolate the
different concerns.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The helper function commit_compare() actually compares object_id
structs, not commits. A future change to commit-graph.c will need
to sort commit structs, so rename this function in advance.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
