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Merge branch 'ds/commit-graph-incremental' 

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
maint
Junio C Hamano 2019-07-19 11:30:20 -07:00
parent 209f075593 5b15eb397d
commit 92b1ea66b9
10 changed files with 1419 additions and 79 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
Documentation/git-commit-graph.txt
View File

@ -10,7 +10,7 @@ SYNOPSIS
--------
[verse]
'git commit-graph read' [--object-dir <dir>]
'git commit-graph verify' [--object-dir <dir>]
'git commit-graph verify' [--object-dir <dir>] [--shallow]
'git commit-graph write' <options> [--object-dir <dir>]


@ -26,7 +26,7 @@ OPTIONS
Use given directory for the location of packfiles and commit-graph
file. This parameter exists to specify the location of an alternate
that only has the objects directory, not a full `.git` directory. The
commit-graph file is expected to be at `<dir>/info/commit-graph` and
commit-graph file is expected to be in the `<dir>/info` directory and
the packfiles are expected to be in `<dir>/pack`.


@ -51,6 +51,25 @@ or `--stdin-packs`.)
+
With the `--append` option, include all commits that are present in the
existing commit-graph file.
+
With the `--split` option, write the commit-graph as a chain of multiple
commit-graph files stored in `<dir>/info/commit-graphs`. The new commits
not already in the commit-graph are added in a new "tip" file. This file
is merged with the existing file if the following merge conditions are
met:
+
* If `--size-multiple=<X>` is not specified, let `X` equal 2. If the new
tip file would have `N` commits and the previous tip has `M` commits and
`X` times `N` is greater than `M`, instead merge the two files into a
single file.
+
* If `--max-commits=<M>` is specified with `M` a positive integer, and the
new tip file would have more than `M` commits, then instead merge the new
tip with the previous tip.
+
Finally, if `--expire-time=<datetime>` is not specified, let `datetime`
be the current time. After writing the split commit-graph, delete all
unused commit-graph whose modified times are older than `datetime`.

'read'::

@ -61,6 +80,9 @@ Used for debugging purposes.

Read the commit-graph file and verify its contents against the object
database. Used to check for corrupted data.
+
With the `--shallow` option, only check the tip commit-graph file in
a chain of split commit-graphs.


EXAMPLES

11
Documentation/technical/commit-graph-format.txt
View File

@ -44,8 +44,9 @@ HEADER:

1-byte number (C) of "chunks"

1-byte (reserved for later use)
Current clients should ignore this value.
1-byte number (B) of base commit-graphs
We infer the length (H*B) of the Base Graphs chunk
from this value.

CHUNK LOOKUP:

@ -92,6 +93,12 @@ CHUNK DATA:
positions for the parents until reaching a value with the most-significant
bit on. The other bits correspond to the position of the last parent.

Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
This list of H-byte hashes describe a set of B commit-graph files that
form a commit-graph chain. The graph position for the ith commit in this
file's OID Lookup chunk is equal to i plus the number of commits in all
base graphs. If B is non-zero, this chunk must exist.

TRAILER:

H-byte HASH-checksum of all of the above.

195
Documentation/technical/commit-graph.txt
View File

@ -127,6 +127,197 @@ Design Details
helpful for these clones, anyway. The commit-graph will not be read or
written when shallow commits are present.

Commit Graphs Chains
--------------------

Typically, repos grow with near-constant velocity (commits per day). Over time,
the number of commits added by a fetch operation is much smaller than the
number of commits in the full history. By creating a "chain" of commit-graphs,
we enable fast writes of new commit data without rewriting the entire commit
history -- at least, most of the time.

## File Layout

A commit-graph chain uses multiple files, and we use a fixed naming convention
to organize these files. Each commit-graph file has a name
`$OBJDIR/info/commit-graphs/graph-{hash}.graph` where `{hash}` is the hex-
valued hash stored in the footer of that file (which is a hash of the file's
contents before that hash). For a chain of commit-graph files, a plain-text
file at `$OBJDIR/info/commit-graphs/commit-graph-chain` contains the
hashes for the files in order from "lowest" to "highest".

For example, if the `commit-graph-chain` file contains the lines

```
{hash0}
{hash1}
{hash2}
```

then the commit-graph chain looks like the following diagram:

+-----------------------+
| graph-{hash2}.graph |
+-----------------------+
|
+-----------------------+
| |
| graph-{hash1}.graph |
| |
+-----------------------+
|
+-----------------------+
| |
| |
| |
| graph-{hash0}.graph |
| |
| |
| |
+-----------------------+

Let X0 be the number of commits in `graph-{hash0}.graph`, X1 be the number of
commits in `graph-{hash1}.graph`, and X2 be the number of commits in
`graph-{hash2}.graph`. If a commit appears in position i in `graph-{hash2}.graph`,
then we interpret this as being the commit in position (X0 + X1 + i), and that
will be used as its "graph position". The commits in `graph-{hash2}.graph` use these
positions to refer to their parents, which may be in `graph-{hash1}.graph` or
`graph-{hash0}.graph`. We can navigate to an arbitrary commit in position j by checking
its containment in the intervals [0, X0), [X0, X0 + X1), [X0 + X1, X0 + X1 +
X2).

Each commit-graph file (except the base, `graph-{hash0}.graph`) contains data
specifying the hashes of all files in the lower layers. In the above example,
`graph-{hash1}.graph` contains `{hash0}` while `graph-{hash2}.graph` contains
`{hash0}` and `{hash1}`.

## Merging commit-graph files

If we only added a new commit-graph file on every write, we would run into a
linear search problem through many commit-graph files. Instead, we use a merge
strategy to decide when the stack should collapse some number of levels.

The diagram below shows such a collapse. As a set of new commits are added, it
is determined by the merge strategy that the files should collapse to
`graph-{hash1}`. Thus, the new commits, the commits in `graph-{hash2}` and
the commits in `graph-{hash1}` should be combined into a new `graph-{hash3}`
file.

+---------------------+
| |
| (new commits) |
| |
+---------------------+
| |
+-----------------------+ +---------------------+
| graph-{hash2} |->| |
+-----------------------+ +---------------------+
| | |
+-----------------------+ +---------------------+
| | | |
| graph-{hash1} |->| |
| | | |
+-----------------------+ +---------------------+
| tmp_graphXXX
+-----------------------+
| |
| |
| |
| graph-{hash0} |
| |
| |
| |
+-----------------------+

During this process, the commits to write are combined, sorted and we write the
contents to a temporary file, all while holding a `commit-graph-chain.lock`
lock-file. When the file is flushed, we rename it to `graph-{hash3}`
according to the computed `{hash3}`. Finally, we write the new chain data to
`commit-graph-chain.lock`:

```
{hash3}
{hash0}
```

We then close the lock-file.

## Merge Strategy

When writing a set of commits that do not exist in the commit-graph stack of
height N, we default to creating a new file at level N + 1. We then decide to
merge with the Nth level if one of two conditions hold:

1. `--size-multiple=<X>` is specified or X = 2, and the number of commits in
level N is less than X times the number of commits in level N + 1.

2. `--max-commits=<C>` is specified with non-zero C and the number of commits
in level N + 1 is more than C commits.

This decision cascades down the levels: when we merge a level we create a new
set of commits that then compares to the next level.

The first condition bounds the number of levels to be logarithmic in the total
number of commits. The second condition bounds the total number of commits in
a `graph-{hashN}` file and not in the `commit-graph` file, preventing
significant performance issues when the stack merges and another process only
partially reads the previous stack.

The merge strategy values (2 for the size multiple, 64,000 for the maximum
number of commits) could be extracted into config settings for full
flexibility.

## Deleting graph-{hash} files

After a new tip file is written, some `graph-{hash}` files may no longer
be part of a chain. It is important to remove these files from disk, eventually.
The main reason to delay removal is that another process could read the
`commit-graph-chain` file before it is rewritten, but then look for the
`graph-{hash}` files after they are deleted.

To allow holding old split commit-graphs for a while after they are unreferenced,
we update the modified times of the files when they become unreferenced. Then,
we scan the `$OBJDIR/info/commit-graphs/` directory for `graph-{hash}`
files whose modified times are older than a given expiry window. This window
defaults to zero, but can be changed using command-line arguments or a config
setting.

## Chains across multiple object directories

In a repo with alternates, we look for the `commit-graph-chain` file starting
in the local object directory and then in each alternate. The first file that
exists defines our chain. As we look for the `graph-{hash}` files for
each `{hash}` in the chain file, we follow the same pattern for the host
directories.

This allows commit-graphs to be split across multiple forks in a fork network.
The typical case is a large "base" repo with many smaller forks.

As the base repo advances, it will likely update and merge its commit-graph
chain more frequently than the forks. If a fork updates their commit-graph after
the base repo, then it should "reparent" the commit-graph chain onto the new
chain in the base repo. When reading each `graph-{hash}` file, we track
the object directory containing it. During a write of a new commit-graph file,
we check for any changes in the source object directory and read the
`commit-graph-chain` file for that source and create a new file based on those
files. During this "reparent" operation, we necessarily need to collapse all
levels in the fork, as all of the files are invalid against the new base file.

It is crucial to be careful when cleaning up "unreferenced" `graph-{hash}.graph`
files in this scenario. It falls to the user to define the proper settings for
their custom environment:

1. When merging levels in the base repo, the unreferenced files may still be
referenced by chains from fork repos.

2. The expiry time should be set to a length of time such that every fork has
time to recompute their commit-graph chain to "reparent" onto the new base
file(s).

3. If the commit-graph chain is updated in the base, the fork will not have
access to the new chain until its chain is updated to reference those files.
(This may change in the future [5].)

Related Links
-------------
[0] https://bugs.chromium.org/p/git/issues/detail?id=8
@ -153,3 +344,7 @@ Related Links

[4] https://public-inbox.org/git/20180108154822.54829-1-git@jeffhostetler.com/T/#u
A patch to remove the ahead-behind calculation from 'status'.

[5] https://public-inbox.org/git/f27db281-abad-5043-6d71-cbb083b1c877@gmail.com/
A discussion of a "two-dimensional graph position" that can allow reading
multiple commit-graph chains at the same time.

58
builtin/commit-graph.c
View File

@ -5,17 +5,18 @@
#include "parse-options.h"
#include "repository.h"
#include "commit-graph.h"
#include "object-store.h"

static char const * const builtin_commit_graph_usage[] = {
N_("git commit-graph [--object-dir <objdir>]"),
N_("git commit-graph read [--object-dir <objdir>]"),
N_("git commit-graph verify [--object-dir <objdir>]"),
N_("git commit-graph write [--object-dir <objdir>] [--append] [--reachable|--stdin-packs|--stdin-commits]"),
N_("git commit-graph verify [--object-dir <objdir>] [--shallow]"),
N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] <split options>"),
NULL
};

static const char * const builtin_commit_graph_verify_usage[] = {
N_("git commit-graph verify [--object-dir <objdir>]"),
N_("git commit-graph verify [--object-dir <objdir>] [--shallow]"),
NULL
};

@ -25,7 +26,7 @@ static const char * const builtin_commit_graph_read_usage[] = {
};

static const char * const builtin_commit_graph_write_usage[] = {
N_("git commit-graph write [--object-dir <objdir>] [--append] [--reachable|--stdin-packs|--stdin-commits]"),
N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] <split options>"),
NULL
};

@ -35,9 +36,10 @@ static struct opts_commit_graph {
int stdin_packs;
int stdin_commits;
int append;
int split;
int shallow;
} opts;


static int graph_verify(int argc, const char **argv)
{
struct commit_graph *graph = NULL;
@ -45,11 +47,14 @@ static int graph_verify(int argc, const char **argv)
int open_ok;
int fd;
struct stat st;
int flags = 0;

static struct option builtin_commit_graph_verify_options[] = {
OPT_STRING(0, "object-dir", &opts.obj_dir,
N_("dir"),
N_("The object directory to store the graph")),
OPT_BOOL(0, "shallow", &opts.shallow,
N_("if the commit-graph is split, only verify the tip file")),
OPT_END(),
};

@ -59,21 +64,27 @@ static int graph_verify(int argc, const char **argv)

if (!opts.obj_dir)
opts.obj_dir = get_object_directory();
if (opts.shallow)
flags |= COMMIT_GRAPH_VERIFY_SHALLOW;

graph_name = get_commit_graph_filename(opts.obj_dir);
open_ok = open_commit_graph(graph_name, &fd, &st);
if (!open_ok && errno == ENOENT)
return 0;
if (!open_ok)
if (!open_ok && errno != ENOENT)
die_errno(_("Could not open commit-graph '%s'"), graph_name);
graph = load_commit_graph_one_fd_st(fd, &st);

FREE_AND_NULL(graph_name);

if (open_ok)
graph = load_commit_graph_one_fd_st(fd, &st);
else
graph = read_commit_graph_one(the_repository, opts.obj_dir);

/* Return failure if open_ok predicted success */
if (!graph)
return 1;
return !!open_ok;

UNLEAK(graph);
return verify_commit_graph(the_repository, graph);
return verify_commit_graph(the_repository, graph, flags);
}

static int graph_read(int argc, const char **argv)
@ -135,6 +146,7 @@ static int graph_read(int argc, const char **argv)
}

extern int read_replace_refs;
static struct split_commit_graph_opts split_opts;

static int graph_write(int argc, const char **argv)
{
@ -156,9 +168,21 @@ static int graph_write(int argc, const char **argv)
N_("start walk at commits listed by stdin")),
OPT_BOOL(0, "append", &opts.append,
N_("include all commits already in the commit-graph file")),
OPT_BOOL(0, "split", &opts.split,
N_("allow writing an incremental commit-graph file")),
OPT_INTEGER(0, "max-commits", &split_opts.max_commits,
N_("maximum number of commits in a non-base split commit-graph")),
OPT_INTEGER(0, "size-multiple", &split_opts.size_multiple,
N_("maximum ratio between two levels of a split commit-graph")),
OPT_EXPIRY_DATE(0, "expire-time", &split_opts.expire_time,
N_("maximum number of commits in a non-base split commit-graph")),
OPT_END(),
};

split_opts.size_multiple = 2;
split_opts.max_commits = 0;
split_opts.expire_time = 0;

argc = parse_options(argc, argv, NULL,
builtin_commit_graph_write_options,
builtin_commit_graph_write_usage, 0);
@ -169,11 +193,16 @@ static int graph_write(int argc, const char **argv)
opts.obj_dir = get_object_directory();
if (opts.append)
flags |= COMMIT_GRAPH_APPEND;
if (opts.split)
flags |= COMMIT_GRAPH_SPLIT;

read_replace_refs = 0;

if (opts.reachable)
return write_commit_graph_reachable(opts.obj_dir, flags);
if (opts.reachable) {
if (write_commit_graph_reachable(opts.obj_dir, flags, &split_opts))
return 1;
return 0;
}

string_list_init(&lines, 0);
if (opts.stdin_packs || opts.stdin_commits) {
@ -193,7 +222,8 @@ static int graph_write(int argc, const char **argv)
if (write_commit_graph(opts.obj_dir,
pack_indexes,
commit_hex,
flags))
flags,
&split_opts))
result = 1;

UNLEAK(lines);

2
builtin/commit.c
View File

@ -1687,7 +1687,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
"not exceeded, and then \"git restore --staged :/\" to recover."));

if (git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
write_commit_graph_reachable(get_object_directory(), 0))
write_commit_graph_reachable(get_object_directory(), 0, NULL))
return 1;

repo_rerere(the_repository, 0);

3
builtin/gc.c
View File

@ -687,7 +687,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)

if (gc_write_commit_graph &&
write_commit_graph_reachable(get_object_directory(),
!quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0))
!quiet && !daemonized ? COMMIT_GRAPH_PROGRESS : 0,
NULL))
return 1;

if (auto_gc && too_many_loose_objects())

833
commit-graph.c
View File

File diff suppressed because it is too large Load Diff

25
commit-graph.h
View File

@ -47,15 +47,21 @@ struct commit_graph {
unsigned char num_chunks;
uint32_t num_commits;
struct object_id oid;
char *filename;
const char *obj_dir;

uint32_t num_commits_in_base;
struct commit_graph *base_graph;

const uint32_t *chunk_oid_fanout;
const unsigned char *chunk_oid_lookup;
const unsigned char *chunk_commit_data;
const unsigned char *chunk_extra_edges;
const unsigned char *chunk_base_graphs;
};

struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st);

struct commit_graph *read_commit_graph_one(struct repository *r, const char *obj_dir);
struct commit_graph *parse_commit_graph(void *graph_map, int fd,
size_t graph_size);

@ -67,6 +73,13 @@ int generation_numbers_enabled(struct repository *r);

#define COMMIT_GRAPH_APPEND (1 << 0)
#define COMMIT_GRAPH_PROGRESS (1 << 1)
#define COMMIT_GRAPH_SPLIT (1 << 2)

struct split_commit_graph_opts {
int size_multiple;
int max_commits;
timestamp_t expire_time;
};

/*
* The write_commit_graph* methods return zero on success
@ -74,13 +87,17 @@ int generation_numbers_enabled(struct repository *r);
* is not compatible with the commit-graph feature, then the
* methods will return 0 without writing a commit-graph.
*/
int write_commit_graph_reachable(const char *obj_dir, unsigned int flags);
int write_commit_graph_reachable(const char *obj_dir, unsigned int flags,
const struct split_commit_graph_opts *split_opts);
int write_commit_graph(const char *obj_dir,
struct string_list *pack_indexes,
struct string_list *commit_hex,
unsigned int flags);
unsigned int flags,
const struct split_commit_graph_opts *split_opts);

int verify_commit_graph(struct repository *r, struct commit_graph *g);
#define COMMIT_GRAPH_VERIFY_SHALLOW (1 << 0)

int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags);

void close_commit_graph(struct raw_object_store *);
void free_commit_graph(struct commit_graph *);

2
t/t5318-commit-graph.sh
View File

@ -20,7 +20,7 @@ test_expect_success 'verify graph with no graph file' '
test_expect_success 'write graph with no packs' '
cd "$TRASH_DIRECTORY/full" &&
git commit-graph write --object-dir . &&
test_path_is_file info/commit-graph
test_path_is_missing info/commit-graph
'

test_expect_success 'close with correct error on bad input' '

343
t/t5324-split-commit-graph.sh Executable file
View File

@ -0,0 +1,343 @@
#!/bin/sh

test_description='split commit graph'
. ./test-lib.sh

GIT_TEST_COMMIT_GRAPH=0

test_expect_success 'setup repo' '
git init &&
git config core.commitGraph true &&
infodir=".git/objects/info" &&
graphdir="$infodir/commit-graphs" &&
test_oid_init
'

graph_read_expect() {
NUM_BASE=0
if test ! -z $2
then
NUM_BASE=$2
fi
cat >expect <<- EOF
header: 43475048 1 1 3 $NUM_BASE
num_commits: $1
chunks: oid_fanout oid_lookup commit_metadata
EOF
git commit-graph read >output &&
test_cmp expect output
}

test_expect_success 'create commits and write commit-graph' '
for i in $(test_seq 3)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git commit-graph write --reachable &&
test_path_is_file $infodir/commit-graph &&
graph_read_expect 3
'

graph_git_two_modes() {
git -c core.commitGraph=true $1 >output
git -c core.commitGraph=false $1 >expect
test_cmp expect output
}

graph_git_behavior() {
MSG=$1
BRANCH=$2
COMPARE=$3
test_expect_success "check normal git operations: $MSG" '
graph_git_two_modes "log --oneline $BRANCH" &&
graph_git_two_modes "log --topo-order $BRANCH" &&
graph_git_two_modes "log --graph $COMPARE..$BRANCH" &&
graph_git_two_modes "branch -vv" &&
graph_git_two_modes "merge-base -a $BRANCH $COMPARE"
'
}

graph_git_behavior 'graph exists' commits/3 commits/1

verify_chain_files_exist() {
for hash in $(cat $1/commit-graph-chain)
do
test_path_is_file $1/graph-$hash.graph || return 1
done
}

test_expect_success 'add more commits, and write a new base graph' '
git reset --hard commits/1 &&
for i in $(test_seq 4 5)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git reset --hard commits/2 &&
for i in $(test_seq 6 10)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git reset --hard commits/2 &&
git merge commits/4 &&
git branch merge/1 &&
git reset --hard commits/4 &&
git merge commits/6 &&
git branch merge/2 &&
git commit-graph write --reachable &&
graph_read_expect 12
'

test_expect_success 'fork and fail to base a chain on a commit-graph file' '
test_when_finished rm -rf fork &&
git clone . fork &&
(
cd fork &&
rm .git/objects/info/commit-graph &&
echo "$(pwd)/../.git/objects" >.git/objects/info/alternates &&
test_commit new-commit &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 1 $graphdir/commit-graph-chain &&
verify_chain_files_exist $graphdir
)
'

test_expect_success 'add three more commits, write a tip graph' '
git reset --hard commits/3 &&
git merge merge/1 &&
git merge commits/5 &&
git merge merge/2 &&
git branch merge/3 &&
git commit-graph write --reachable --split &&
test_path_is_missing $infodir/commit-graph &&
test_path_is_file $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 2 graph-files &&
verify_chain_files_exist $graphdir
'

graph_git_behavior 'split commit-graph: merge 3 vs 2' merge/3 merge/2

test_expect_success 'add one commit, write a tip graph' '
test_commit 11 &&
git branch commits/11 &&
git commit-graph write --reachable --split &&
test_path_is_missing $infodir/commit-graph &&
test_path_is_file $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 3 graph-files &&
verify_chain_files_exist $graphdir
'

graph_git_behavior 'three-layer commit-graph: commit 11 vs 6' commits/11 commits/6

test_expect_success 'add one commit, write a merged graph' '
test_commit 12 &&
git branch commits/12 &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 2 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 2 graph-files &&
verify_chain_files_exist $graphdir
'

graph_git_behavior 'merged commit-graph: commit 12 vs 6' commits/12 commits/6

test_expect_success 'create fork and chain across alternate' '
git clone . fork &&
(
cd fork &&
git config core.commitGraph true &&
rm -rf $graphdir &&
echo "$(pwd)/../.git/objects" >.git/objects/info/alternates &&
test_commit 13 &&
git branch commits/13 &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 3 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files &&
git -c core.commitGraph=true rev-list HEAD >expect &&
git -c core.commitGraph=false rev-list HEAD >actual &&
test_cmp expect actual &&
test_commit 14 &&
git commit-graph write --reachable --split --object-dir=.git/objects/ &&
test_line_count = 3 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
)
'

graph_git_behavior 'alternate: commit 13 vs 6' commits/13 commits/6

test_expect_success 'test merge stragety constants' '
git clone . merge-2 &&
(
cd merge-2 &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 14 &&
git commit-graph write --reachable --split --size-multiple=2 &&
test_line_count = 3 $graphdir/commit-graph-chain

) &&
git clone . merge-10 &&
(
cd merge-10 &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 14 &&
git commit-graph write --reachable --split --size-multiple=10 &&
test_line_count = 1 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
) &&
git clone . merge-10-expire &&
(
cd merge-10-expire &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 15 &&
git commit-graph write --reachable --split --size-multiple=10 --expire-time=1980-01-01 &&
test_line_count = 1 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 3 graph-files
) &&
git clone --no-hardlinks . max-commits &&
(
cd max-commits &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 16 &&
test_commit 17 &&
git commit-graph write --reachable --split --max-commits=1 &&
test_line_count = 1 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
)
'

test_expect_success 'remove commit-graph-chain file after flattening' '
git clone . flatten &&
(
cd flatten &&
test_line_count = 2 $graphdir/commit-graph-chain &&
git commit-graph write --reachable &&
test_path_is_missing $graphdir/commit-graph-chain &&
ls $graphdir >graph-files &&
test_line_count = 0 graph-files
)
'

corrupt_file() {
file=$1
pos=$2
data="${3:-\0}"
chmod a+w "$file" &&
printf "$data" | dd of="$file" bs=1 seek="$pos" conv=notrunc
}

test_expect_success 'verify hashes along chain, even in shallow' '
git clone --no-hardlinks . verify &&
(
cd verify &&
git commit-graph verify &&
base_file=$graphdir/graph-$(head -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" 1760 "\01" &&
test_must_fail git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "incorrect checksum" err
)
'

test_expect_success 'verify --shallow does not check base contents' '
git clone --no-hardlinks . verify-shallow &&
(
cd verify-shallow &&
git commit-graph verify &&
base_file=$graphdir/graph-$(head -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" 1000 "\01" &&
git commit-graph verify --shallow &&
test_must_fail git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "incorrect checksum" err
)
'

test_expect_success 'warn on base graph chunk incorrect' '
git clone --no-hardlinks . base-chunk &&
(
cd base-chunk &&
git commit-graph verify &&
base_file=$graphdir/graph-$(tail -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" 1376 "\01" &&
git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "commit-graph chain does not match" err
)
'

test_expect_success 'verify after commit-graph-chain corruption' '
git clone --no-hardlinks . verify-chain &&
(
cd verify-chain &&
corrupt_file "$graphdir/commit-graph-chain" 60 "G" &&
git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "invalid commit-graph chain" err &&
corrupt_file "$graphdir/commit-graph-chain" 60 "A" &&
git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "unable to find all commit-graph files" err
)
'

test_expect_success 'verify across alternates' '
git clone --no-hardlinks . verify-alt &&
(
cd verify-alt &&
rm -rf $graphdir &&
altdir="$(pwd)/../.git/objects" &&
echo "$altdir" >.git/objects/info/alternates &&
git commit-graph verify --object-dir="$altdir/" &&
test_commit extra &&
git commit-graph write --reachable --split &&
tip_file=$graphdir/graph-$(tail -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$tip_file" 100 "\01" &&
test_must_fail git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "commit-graph has incorrect fanout value" err
)
'

test_expect_success 'add octopus merge' '
git reset --hard commits/10 &&
git merge commits/3 commits/4 &&
git branch merge/octopus &&
git commit-graph write --reachable --split &&
git commit-graph verify &&
test_line_count = 3 $graphdir/commit-graph-chain
'

graph_git_behavior 'graph exists' merge/octopus commits/12

test_expect_success 'split across alternate where alternate is not split' '
git commit-graph write --reachable &&
test_path_is_file .git/objects/info/commit-graph &&
cp .git/objects/info/commit-graph . &&
git clone --no-hardlinks . alt-split &&
(
cd alt-split &&
echo "$(pwd)"/../.git/objects >.git/objects/info/alternates &&
test_commit 18 &&
git commit-graph write --reachable --split &&
test_line_count = 1 $graphdir/commit-graph-chain
) &&
test_cmp commit-graph .git/objects/info/commit-graph
'

test_done