fetch: add fetch.writeCommitGraph config setting

The commit-graph feature is now on by default, and is being
written during 'git gc' by default. Typically, Git only writes
a commit-graph when a 'git gc --auto' command passes the gc.auto
setting to actualy do work. This means that a commit-graph will
typically fall behind the commits that are being used every day.

To stay updated with the latest commits, add a step to 'git
fetch' to write a commit-graph after fetching new objects. The
fetch.writeCommitGraph config setting enables writing a split
commit-graph, so on average the cost of writing this file is
very small. Occasionally, the commit-graph chain will collapse
to a single level, and this could be slow for very large repos.

For additional use, adjust the default to be true when
feature.experimental is enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/repository.h b/repository.h
index 4da275e73f..fe0b5f5dc6 100644
--- a/repository.h
+++ b/repository.h
@@ -30,6 +30,7 @@ struct repo_settings {
 
 	int core_commit_graph;
 	int gc_write_commit_graph;
+	int fetch_write_commit_graph;
 
 	int index_version;
 	enum untracked_cache_setting core_untracked_cache;