When using split commit-graphs, it is sometimes useful to completely
replace the commit-graph chain with a new base.
For example, consider a scenario in which a repository builds a new
commit-graph incremental for each push. Occasionally (say, after some
fixed number of pushes), they may wish to rebuild the commit-graph chain
with all reachable commits.
They can do so with
$ git commit-graph write --reachable
but this removes the chain entirely and replaces it with a single
commit-graph in 'objects/info/commit-graph'. Unfortunately, this means
that the next push will have to move this commit-graph into the first
layer of a new chain, and then write its new commits on top.
Avoid such copying entirely by allowing the caller to specify that they
wish to replace the entirety of their commit-graph chain, while also
specifying that the new commit-graph should become the basis of a fresh,
length-one chain.
This addresses the above situation by making it possible for the caller
to instead write:
$ git commit-graph write --reachable --split=replace
which writes a new length-one chain to 'objects/info/commit-graphs',
making the commit-graph incremental generated by the subsequent push
relatively cheap by avoiding the aforementioned copy.
In order to do this, remove an assumption in 'write_commit_graph_file'
that chains are always at least two incrementals long.
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
Documentation/git-commit-graph.txt | 7 ++--
builtin/commit-graph.c | 2 ++
commit-graph.c | 53 ++++++++++++++++++++++--------
commit-graph.h | 3 +-
t/t5324-split-commit-graph.sh | 19 +++++++++++
5 files changed, 66 insertions(+), 18 deletions(-)
diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index a4c4a641e5..46f7f7c573 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -64,9 +64,10 @@ strategy and other splitting options. 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 `--split=no-merge` is specified, a merge is never performed, and
-the remaining options are ignored. A bare `--split` defers to the
-remaining options. (Note that merging a chain of commit graphs replaces
-the existing chain with a length-1 chain where the first and only
+the remaining options are ignored. `--split=replace` overwrites the
+existing chain with a new one. A bare `--split` defers to the remaining
+options. (Note that merging a chain of commit graphs replaces the
+existing chain with a length-1 chain where the first and only
incremental holds the entire graph).
+
* If `--size-multiple=<X>` is not specified, let `X` equal 2. If the new
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 42182ed71c..922f876bfa 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -129,6 +129,8 @@ static int write_option_parse_split(const struct option *opt, const char *arg,
if (!strcmp(arg, "no-merge"))
*flags = COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED;
+ else if (!strcmp(arg, "replace"))
+ *flags = COMMIT_GRAPH_SPLIT_REPLACE;
else
die(_("unrecognized --split argument, %s"), arg);
diff --git a/commit-graph.c b/commit-graph.c
index af3fe20bb5..c598508d7f 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -866,7 +866,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
if (edge_value >= 0)
edge_value += ctx->new_num_commits_in_base;
- else {
+ else if (ctx->new_base_graph) {
uint32_t pos;
if (find_commit_in_graph(parent->item,
ctx->new_base_graph,
@@ -897,7 +897,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
if (edge_value >= 0)
edge_value += ctx->new_num_commits_in_base;
- else {
+ else if (ctx->new_base_graph) {
uint32_t pos;
if (find_commit_in_graph(parent->item,
ctx->new_base_graph,
@@ -964,7 +964,7 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
if (edge_value >= 0)
edge_value += ctx->new_num_commits_in_base;
- else {
+ else if (ctx->new_base_graph) {
uint32_t pos;
if (find_commit_in_graph(parent->item,
ctx->new_base_graph,
@@ -1037,6 +1037,8 @@ static void close_reachable(struct write_commit_graph_context *ctx)
{
int i;
struct commit *commit;
+ enum commit_graph_split_flags flags = ctx->split_opts ?
+ ctx->split_opts->flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;
if (ctx->report_progress)
ctx->progress = start_delayed_progress(
@@ -1066,8 +1068,9 @@ static void close_reachable(struct write_commit_graph_context *ctx)
if (!commit)
continue;
if (ctx->split) {
- if (!parse_commit(commit) &&
- commit->graph_pos == COMMIT_NOT_FROM_GRAPH)
+ if ((!parse_commit(commit) &&
+ commit->graph_pos == COMMIT_NOT_FROM_GRAPH) ||
+ flags == COMMIT_GRAPH_SPLIT_REPLACE)
add_missing_parents(ctx, commit);
} else if (!parse_commit_no_graph(commit))
add_missing_parents(ctx, commit);
@@ -1287,6 +1290,8 @@ static uint32_t count_distinct_commits(struct write_commit_graph_context *ctx)
static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
{
uint32_t i;
+ enum commit_graph_split_flags flags = ctx->split_opts ?
+ ctx->split_opts->flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;
ctx->num_extra_edges = 0;
if (ctx->report_progress)
@@ -1303,11 +1308,14 @@ static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
ALLOC_GROW(ctx->commits.list, ctx->commits.nr + 1, ctx->commits.alloc);
ctx->commits.list[ctx->commits.nr] = lookup_commit(ctx->r, &ctx->oids.list[i]);
- if (ctx->split &&
+ if (ctx->split && flags != COMMIT_GRAPH_SPLIT_REPLACE &&
ctx->commits.list[ctx->commits.nr]->graph_pos != COMMIT_NOT_FROM_GRAPH)
continue;
- parse_commit_no_graph(ctx->commits.list[ctx->commits.nr]);
+ if (ctx->split && flags == COMMIT_GRAPH_SPLIT_REPLACE)
+ parse_commit(ctx->commits.list[ctx->commits.nr]);
+ else
+ parse_commit_no_graph(ctx->commits.list[ctx->commits.nr]);
num_parents = commit_list_count(ctx->commits.list[ctx->commits.nr]->parents);
if (num_parents > 2)
@@ -1488,8 +1496,12 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
}
if (ctx->base_graph_name) {
- const char *dest = ctx->commit_graph_filenames_after[
- ctx->num_commit_graphs_after - 2];
+ const char *dest;
+ int idx = ctx->num_commit_graphs_after - 1;
+ if (ctx->num_commit_graphs_after > 1)
+ idx--;
+
+ dest = ctx->commit_graph_filenames_after[idx];
if (strcmp(ctx->base_graph_name, dest)) {
result = rename(ctx->base_graph_name, dest);
@@ -1546,9 +1558,13 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
g = ctx->r->objects->commit_graph;
num_commits = ctx->commits.nr;
- ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
+ if (flags == COMMIT_GRAPH_SPLIT_REPLACE)
+ ctx->num_commit_graphs_after = 1;
+ else
+ ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
- if (flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED) {
+ if (flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED &&
+ flags != COMMIT_GRAPH_SPLIT_REPLACE) {
while (g && (g->num_commits <= size_mult * num_commits ||
(max_commits && num_commits > max_commits))) {
if (g->odb != ctx->odb)
@@ -1561,7 +1577,11 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
}
}
- ctx->new_base_graph = g;
+ if (flags != COMMIT_GRAPH_SPLIT_REPLACE)
+ ctx->new_base_graph = g;
+ else if (ctx->num_commit_graphs_after != 1)
+ BUG("split_graph_merge_strategy: num_commit_graphs_after "
+ "should be 1 with --split=replace");
if (ctx->num_commit_graphs_after == 2) {
char *old_graph_name = get_commit_graph_filename(g->odb);
@@ -1768,6 +1788,7 @@ int write_commit_graph(struct object_directory *odb,
struct write_commit_graph_context *ctx;
uint32_t i, count_distinct = 0;
int res = 0;
+ int replace = 0;
if (!commit_graph_compatible(the_repository))
return 0;
@@ -1802,6 +1823,9 @@ int write_commit_graph(struct object_directory *odb,
g = g->base_graph;
}
}
+
+ if (ctx->split_opts)
+ replace = ctx->split_opts->flags & COMMIT_GRAPH_SPLIT_REPLACE;
}
ctx->approx_nr_objects = approximate_object_count();
@@ -1862,13 +1886,14 @@ int write_commit_graph(struct object_directory *odb,
goto cleanup;
}
- if (!ctx->commits.nr)
+ if (!ctx->commits.nr && !replace)
goto cleanup;
if (ctx->split) {
split_graph_merge_strategy(ctx);
- merge_commit_graphs(ctx);
+ if (!replace)
+ merge_commit_graphs(ctx);
} else
ctx->num_commit_graphs_after = 1;
diff --git a/commit-graph.h b/commit-graph.h
index 8752afb88d..718433d79b 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -84,7 +84,8 @@ enum commit_graph_write_flags {
enum commit_graph_split_flags {
COMMIT_GRAPH_SPLIT_UNSPECIFIED = 0,
- COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED = 1
+ COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED = 1,
+ COMMIT_GRAPH_SPLIT_REPLACE = 2
};
struct split_commit_graph_opts {
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 1438d63f24..e5d8d64170 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -362,4 +362,23 @@ test_expect_success '--split=no-merge always writes an incremental' '
test_line_count = 2 $graphdir/commit-graph-chain
'
+test_expect_success '--split=replace replaces the chain' '
+ rm -rf $graphdir $infodir/commit-graph &&
+ git reset --hard commits/3 &&
+ git rev-list -1 HEAD~2 >a &&
+ git rev-list -1 HEAD~1 >b &&
+ git rev-list -1 HEAD >c &&
+ git commit-graph write --split=no-merge --stdin-commits <a &&
+ git commit-graph write --split=no-merge --stdin-commits <b &&
+ git commit-graph write --split=no-merge --stdin-commits <c &&
+ test_line_count = 3 $graphdir/commit-graph-chain &&
+ git commit-graph write --stdin-commits --split=replace <b &&
+ test_path_is_missing $infodir/commit-graph &&
+ test_path_is_file $graphdir/commit-graph-chain &&
+ ls $graphdir/graph-*.graph >graph-files &&
+ test_line_count = 1 graph-files &&
+ verify_chain_files_exist $graphdir &&
+ graph_read_expect 2
+'
+
test_done
--
2.26.0.106.g9fadedd637
