repo-settings: pack.useSparse=true

If a repo is large, then it probably has a very large working
directory. In this case, a typical developer's edits usually impact
many fewer paths than the full path set. The sparse treewalk
algorithm is optimized for this case, speeding up 'git push' calls.

Use pack.useSparse=true when core.featureAdoptionRate is at least
five. This is the first setting where the feature has only been
out for a single major version. This could be moved to the "at
least three" category after another major version.

Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

Documentation/config/core.txt

@@ -623,3 +623,12 @@ not modify the user-facing output of porcelain commands.
 +
 * `index.version=4` uses prefix-compression to reduce the size of the
 .git/index file.
++
+If the value is at least 5, then all of the defaults above are included,
+plus the defaults below. These represent new features that present
+significant performance benefits, but may not have been released for
+multiple major versions.
++
+* `pack.useSparse=true` uses the sparse tree-walk algorithm, which is
+optimized for enumerating objects during linkgit:git-push[1] from a
+client machine.

Documentation/config/pack.txt

@@ -112,7 +112,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames.
+	commits contain certain types of direct renames. Defaults to
+	false, unless `core.featureAdoptionRate` is at least five.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.

builtin/pack-objects.c

@@ -34,6 +34,7 @@
 #include "dir.h"
 #include "midx.h"
 #include "trace2.h"
+#include "repo-settings.h"
 
 #define IN_PACK(obj) oe_in_pack(&to_pack, obj)
 #define SIZE(obj) oe_size(&to_pack, obj)
@@ -2707,10 +2708,6 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
 	}
-	if (!strcmp(k, "pack.usesparse")) {
-		sparse = git_config_bool(k, v);
-		return 0;
-	}
 	if (!strcmp(k, "pack.threads")) {
 		delta_search_threads = git_config_int(k, v);
 		if (delta_search_threads < 0)
@@ -3330,6 +3327,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	read_replace_refs = 0;
 
 	sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
+	prepare_repo_settings(the_repository);
+	if (!sparse && the_repository->settings->pack_use_sparse != -1)
+		sparse = the_repository->settings->pack_use_sparse;
+
 	reset_pack_idx_option(&pack_idx_opts);
 	git_config(git_pack_config, NULL);
 

repo-settings.c

@@ -16,6 +16,9 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 			UPDATE_DEFAULT(rs->gc_write_commit_graph, 1);
 			UPDATE_DEFAULT(rs->index_version, 4);
 		}
+		if (rate >= 5) {
+			UPDATE_DEFAULT(rs->pack_use_sparse, 1);
+		}
 		return 0;
 	}
 	if (!strcmp(key, "core.commitgraph")) {
@@ -26,6 +29,10 @@ static int git_repo_config(const char *key, const char *value, void *cb)
 		rs->gc_write_commit_graph = git_config_bool(key, value);
 		return 0;
 	}
+	if (!strcmp(key, "pack.usesparse")) {
+		rs->pack_use_sparse = git_config_bool(key, value);
+		return 0;
+	}
 	if (!strcmp(key, "index.version")) {
 		rs->index_version = git_config_int(key, value);
 		return 0;
@@ -44,6 +51,7 @@ void prepare_repo_settings(struct repository *r)
 	/* Defaults */
 	r->settings->core_commit_graph = -1;
 	r->settings->gc_write_commit_graph = -1;
+	r->settings->pack_use_sparse = -1;
 	r->settings->index_version = -1;
 
 	repo_config(r, git_repo_config, r->settings);

repo-settings.h

@@ -4,6 +4,7 @@
 struct repo_settings {
 	char core_commit_graph;
 	char gc_write_commit_graph;
+	char pack_use_sparse;
 	int index_version;
 };