Merge branch 'jk/loose-object-cache'

Code clean-up with optimization for the codepath that checks
(non-)existence of loose objects.

* jk/loose-object-cache:
  odb_load_loose_cache: fix strbuf leak
  fetch-pack: drop custom loose object cache
  sha1-file: use loose object cache for quick existence check
  object-store: provide helpers for loose_objects_cache
  sha1-file: use an object_directory for the main object dir
  handle alternates paths the same as the main object dir
  sha1_file_name(): overwrite buffer instead of appending
  rename "alternate_object_database" to "object_directory"
  submodule--helper: prefer strip_suffix() to ends_with()
  fsck: do not reuse child_process structs

18 files changed, 211 insertions, 274 deletions

diff --git a/builtin/count-objects.c b/builtin/count-objects.c
index a7cad052c6..3fae474f6f 100644
--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@@ -78,10 +78,10 @@ static int count_cruft(const char *basename, const char *path, void *data)
 	return 0;
 }
 
-static int print_alternate(struct alternate_object_database *alt, void *data)
+static int print_alternate(struct object_directory *odb, void *data)
 {
 	printf("alternate: ");
-	quote_c_style(alt->path, NULL, stdout, 0);
+	quote_c_style(odb->path, NULL, stdout, 0);
 	putchar('\n');
 	return 0;
 }
diff --git a/builtin/fsck.c b/builtin/fsck.c
index a281d7cd12..c03a9c42db 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -739,7 +739,7 @@ static struct option fsck_opts[] = {
 int cmd_fsck(int argc, const char **argv, const char *prefix)
 {
 	int i;
-	struct alternate_object_database *alt;
+	struct object_directory *odb;
 
 	/* fsck knows how to handle missing promisor objects */
 	fetch_if_missing = 0;
@@ -775,14 +775,9 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		for_each_loose_object(mark_loose_for_connectivity, NULL, 0);
 		for_each_packed_object(mark_packed_for_connectivity, NULL, 0);
 	} else {
-		struct alternate_object_database *alt_odb_list;
-
-		fsck_object_dir(get_object_directory());
-
 		prepare_alt_odb(the_repository);
-		alt_odb_list = the_repository->objects->alt_odb_list;
-		for (alt = alt_odb_list; alt; alt = alt->next)
-			fsck_object_dir(alt->path);
+		for (odb = the_repository->objects->odb; odb; odb = odb->next)
+			fsck_object_dir(odb->path);
 
 		if (check_full) {
 			struct packed_git *p;
@@ -884,15 +879,13 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		struct child_process commit_graph_verify = CHILD_PROCESS_INIT;
 		const char *verify_argv[] = { "commit-graph", "verify", NULL, NULL, NULL };
 
-		commit_graph_verify.argv = verify_argv;
-		commit_graph_verify.git_cmd = 1;
-		if (run_command(&commit_graph_verify))
-			errors_found |= ERROR_COMMIT_GRAPH;
-
 		prepare_alt_odb(the_repository);
-		for (alt =  the_repository->objects->alt_odb_list; alt; alt = alt->next) {
+		for (odb = the_repository->objects->odb; odb; odb = odb->next) {
+			child_process_init(&commit_graph_verify);
+			commit_graph_verify.argv = verify_argv;
+			commit_graph_verify.git_cmd = 1;
 			verify_argv[2] = "--object-dir";
-			verify_argv[3] = alt->path;
+			verify_argv[3] = odb->path;
 			if (run_command(&commit_graph_verify))
 				errors_found |= ERROR_COMMIT_GRAPH;
 		}
@@ -902,15 +895,13 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		struct child_process midx_verify = CHILD_PROCESS_INIT;
 		const char *midx_argv[] = { "multi-pack-index", "verify", NULL, NULL, NULL };
 
-		midx_verify.argv = midx_argv;
-		midx_verify.git_cmd = 1;
-		if (run_command(&midx_verify))
-			errors_found |= ERROR_COMMIT_GRAPH;
-
 		prepare_alt_odb(the_repository);
-		for (alt =  the_repository->objects->alt_odb_list; alt; alt = alt->next) {
+		for (odb = the_repository->objects->odb; odb; odb = odb->next) {
+			child_process_init(&midx_verify);
+			midx_verify.argv = midx_argv;
+			midx_verify.git_cmd = 1;
 			midx_argv[2] = "--object-dir";
-			midx_argv[3] = alt->path;
+			midx_argv[3] = odb->path;
 			if (run_command(&midx_verify))
 				errors_found |= ERROR_COMMIT_GRAPH;
 		}
diff --git a/builtin/grep.c b/builtin/grep.c
index 71df52a333..bad9c0a3d5 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -437,7 +437,7 @@ static int grep_submodule(struct grep_opt *opt, struct repository *superproject,
 	 * store is no longer global and instead is a member of the repository
 	 * object.
 	 */
-	add_to_alternates_memory(submodule.objects->objectdir);
+	add_to_alternates_memory(submodule.objects->odb->path);
 	grep_read_unlock();
 
 	if (oid) {
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index d38113a31a..b45514be31 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1265,19 +1265,20 @@ struct submodule_alternate_setup {
 	SUBMODULE_ALTERNATE_ERROR_IGNORE, NULL }
 
 static int add_possible_reference_from_superproject(
-		struct alternate_object_database *alt, void *sas_cb)
+		struct object_directory *odb, void *sas_cb)
 {
 	struct submodule_alternate_setup *sas = sas_cb;
+	size_t len;
 
 	/*
 	 * If the alternate object store is another repository, try the
 	 * standard layout with .git/(modules/<name>)+/objects
 	 */
-	if (ends_with(alt->path, "/objects")) {
+	if (strip_suffix(odb->path, "/objects", &len)) {
 		char *sm_alternate;
 		struct strbuf sb = STRBUF_INIT;
 		struct strbuf err = STRBUF_INIT;
-		strbuf_add(&sb, alt->path, strlen(alt->path) - strlen("objects"));
+		strbuf_add(&sb, odb->path, len);
 
 		/*
 		 * We need to end the new path with '/' to mark it as a dir,
@@ -1285,7 +1286,7 @@ static int add_possible_reference_from_superproject(
 		 * as the last part of a missing submodule reference would
 		 * be taken as a file name.
 		 */
-		strbuf_addf(&sb, "modules/%s/", sas->submodule_name);
+		strbuf_addf(&sb, "/modules/%s/", sas->submodule_name);
 
 		sm_alternate = compute_alternate_path(sb.buf, &err);
 		if (sm_alternate) {
diff --git a/commit-graph.c b/commit-graph.c
index 40c855f185..99163c244b 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -230,8 +230,7 @@ static void prepare_commit_graph_one(struct repository *r, const char *obj_dir)
  */
 static int prepare_commit_graph(struct repository *r)
 {
-	struct alternate_object_database *alt;
-	char *obj_dir;
+	struct object_directory *odb;
 	int config_value;
 
 	if (r->objects->commit_graph_attempted)
@@ -252,13 +251,11 @@ static int prepare_commit_graph(struct repository *r)
 	if (!commit_graph_compatible(r))
 		return 0;
 
-	obj_dir = r->objects->objectdir;
-	prepare_commit_graph_one(r, obj_dir);
 	prepare_alt_odb(r);
-	for (alt = r->objects->alt_odb_list;
-	     !r->objects->commit_graph && alt;
-	     alt = alt->next)
-		prepare_commit_graph_one(r, alt->path);
+	for (odb = r->objects->odb;
+	     !r->objects->commit_graph && odb;
+	     odb = odb->next)
+		prepare_commit_graph_one(r, odb->path);
 	return !!r->objects->commit_graph;
 }
 
diff --git a/environment.c b/environment.c
index 3465597707..0e37741d83 100644
--- a/environment.c
+++ b/environment.c
@@ -274,9 +274,9 @@ const char *get_git_work_tree(void)
 
 char *get_object_directory(void)
 {
-	if (!the_repository->objects->objectdir)
+	if (!the_repository->objects->odb)
 		BUG("git environment hasn't been setup");
-	return the_repository->objects->objectdir;
+	return the_repository->objects->odb->path;
 }
 
 int odb_mkstemp(struct strbuf *temp_filename, const char *pattern)
diff --git a/fetch-pack.c b/fetch-pack.c
index 9691046e64..dd6700bda9 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -637,23 +637,6 @@ struct loose_object_iter {
 };
 
 /*
- *  If the number of refs is not larger than the number of loose objects,
- *  this function stops inserting.
- */
-static int add_loose_objects_to_set(const struct object_id *oid,
-				    const char *path,
-				    void *data)
-{
-	struct loose_object_iter *iter = data;
-	oidset_insert(iter->loose_object_set, oid);
-	if (iter->refs == NULL)
-		return 1;
-
-	iter->refs = iter->refs->next;
-	return 0;
-}
-
-/*
  * Mark recent commits available locally and reachable from a local ref as
  * COMPLETE. If args->no_dependents is false, also mark COMPLETE remote refs as
  * COMMON_REF (otherwise, we are not planning to participate in negotiation, and
@@ -670,30 +653,14 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 	struct ref *ref;
 	int old_save_commit_buffer = save_commit_buffer;
 	timestamp_t cutoff = 0;
-	struct oidset loose_oid_set = OIDSET_INIT;
-	int use_oidset = 0;
-	struct loose_object_iter iter = {&loose_oid_set, *refs};
-
-	/* Enumerate all loose objects or know refs are not so many. */
-	use_oidset = !for_each_loose_object(add_loose_objects_to_set,
-					    &iter, 0);
 
 	save_commit_buffer = 0;
 
 	for (ref = *refs; ref; ref = ref->next) {
 		struct object *o;
-		unsigned int flags = OBJECT_INFO_QUICK;
 
-		if (use_oidset &&
-		    !oidset_contains(&loose_oid_set, &ref->old_oid)) {
-			/*
-			 * I know this does not exist in the loose form,
-			 * so check if it exists in a non-loose form.
-			 */
-			flags |= OBJECT_INFO_IGNORE_LOOSE;
-		}
-
-		if (!has_object_file_with_flags(&ref->old_oid, flags))
+		if (!has_object_file_with_flags(&ref->old_oid,
+						OBJECT_INFO_QUICK))
 			continue;
 		o = parse_object(the_repository, &ref->old_oid);
 		if (!o)
@@ -710,8 +677,6 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 		}
 	}
 
-	oidset_clear(&loose_oid_set);
-
 	if (!args->deepen) {
 		for_each_ref(mark_complete_oid, NULL);
 		for_each_cached_alternate(NULL, mark_alternate_complete);
diff --git a/http-walker.c b/http-walker.c
index b3334bf657..0a392c85b6 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -547,7 +547,7 @@ static int fetch_object(struct walker *walker, unsigned char *sha1)
 		ret = error("File %s has bad hash", hex);
 	} else if (req->rename < 0) {
 		struct strbuf buf = STRBUF_INIT;
-		sha1_file_name(the_repository, &buf, req->sha1);
+		loose_object_path(the_repository, &buf, req->sha1);
 		ret = error("unable to write sha1 filename %s", buf.buf);
 		strbuf_release(&buf);
 	}
diff --git a/http.c b/http.c
index b8258fc78f..0b6807cef9 100644
--- a/http.c
+++ b/http.c
@@ -2353,7 +2353,7 @@ struct http_object_request *new_http_object_request(const char *base_url,
 	hashcpy(freq->sha1, sha1);
 	freq->localfile = -1;
 
-	sha1_file_name(the_repository, &filename, sha1);
+	loose_object_path(the_repository, &filename, sha1);
 	strbuf_addf(&freq->tmpfile, "%s.temp", filename.buf);
 
 	strbuf_addf(&prevfile, "%s.prev", filename.buf);
@@ -2504,7 +2504,7 @@ int finish_http_object_request(struct http_object_request *freq)
 		unlink_or_warn(freq->tmpfile.buf);
 		return -1;
 	}
-	sha1_file_name(the_repository, &filename, freq->sha1);
+	loose_object_path(the_repository, &filename, freq->sha1);
 	freq->rename = finalize_object_file(freq->tmpfile.buf, filename.buf);
 	strbuf_release(&filename);
 
diff --git a/midx.c b/midx.c
index 2a6a24fcd7..8a505fd423 100644
--- a/midx.c
+++ b/midx.c
@@ -931,7 +931,7 @@ cleanup:
 
 void clear_midx_file(struct repository *r)
 {
-	char *midx = get_midx_filename(r->objects->objectdir);
+	char *midx = get_midx_filename(r->objects->odb->path);
 
 	if (r->objects && r->objects->multi_pack_index) {
 		close_midx(r->objects->multi_pack_index);
diff --git a/object-store.h b/object-store.h
index 63b7605a3e..60758efad8 100644
--- a/object-store.h
+++ b/object-store.h
@@ -7,19 +7,17 @@
 #include "sha1-array.h"
 #include "strbuf.h"
 
-struct alternate_object_database {
-	struct alternate_object_database *next;
-
-	/* see alt_scratch_buf() */
-	struct strbuf scratch;
-	size_t base_len;
+struct object_directory {
+	struct object_directory *next;
 
 	/*
-	 * Used to store the results of readdir(3) calls when searching
-	 * for unique abbreviated hashes.  This cache is never
-	 * invalidated, thus it's racy and not necessarily accurate.
-	 * That's fine for its purpose; don't use it for tasks requiring
-	 * greater accuracy!
+	 * Used to store the results of readdir(3) calls when we are OK
+	 * sacrificing accuracy due to races for speed. That includes
+	 * object existence with OBJECT_INFO_QUICK, as well as
+	 * our search for unique abbreviated hashes. Don't use it for tasks
+	 * requiring greater accuracy!
+	 *
+	 * Be sure to call odb_load_loose_cache() before using.
 	 */
 	char loose_objects_subdir_seen[256];
 	struct oid_array loose_objects_cache;
@@ -28,20 +26,15 @@ struct alternate_object_database {
 	 * Path to the alternative object store. If this is a relative path,
 	 * it is relative to the current working directory.
 	 */
-	char path[FLEX_ARRAY];
+	char *path;
 };
+
 void prepare_alt_odb(struct repository *r);
 char *compute_alternate_path(const char *path, struct strbuf *err);
-typedef int alt_odb_fn(struct alternate_object_database *, void *);
+typedef int alt_odb_fn(struct object_directory *, void *);
 int foreach_alt_odb(alt_odb_fn, void*);
 
 /*
- * Allocate a "struct alternate_object_database" but do _not_ actually
- * add it to the list of alternates.
- */
-struct alternate_object_database *alloc_alt_odb(const char *dir);
-
-/*
  * Add the directory to the on-disk alternates file; the new entry will also
  * take effect in the current process.
  */
@@ -55,12 +48,11 @@ void add_to_alternates_file(const char *dir);
 void add_to_alternates_memory(const char *dir);
 
 /*
- * Returns a scratch strbuf pre-filled with the alternate object directory,
- * including a trailing slash, which can be used to access paths in the
- * alternate. Always use this over direct access to alt->scratch, as it
- * cleans up any previous use of the scratch buffer.
+ * Populate an odb's loose object cache for one particular subdirectory (i.e.,
+ * the one that corresponds to the first byte of objects you're interested in,
+ * from 0 to 255 inclusive).
  */
-struct strbuf *alt_scratch_buf(struct alternate_object_database *alt);
+void odb_load_loose_cache(struct object_directory *odb, int subdir_nr);
 
 struct packed_git {
 	struct packed_git *next;
@@ -92,17 +84,21 @@ struct multi_pack_index;
 
 struct raw_object_store {
 	/*
-	 * Path to the repository's object store.
-	 * Cannot be NULL after initialization.
+	 * Set of all object directories; the main directory is first (and
+	 * cannot be NULL after initialization). Subsequent directories are
+	 * alternates.
 	 */
-	char *objectdir;
+	struct object_directory *odb;
+	struct object_directory **odb_tail;
+	int loaded_alternates;
 
-	/* Path to extra alternate object database if not NULL */
+	/*
+	 * A list of alternate object directories loaded from the environment;
+	 * this should not generally need to be accessed directly, but will
+	 * populate the "odb" list when prepare_alt_odb() is run.
+	 */
 	char *alternate_db;
 
-	struct alternate_object_database *alt_odb_list;
-	struct alternate_object_database **alt_odb_tail;
-
 	/*
 	 * Objects that should be substituted by other objects
 	 * (see git-replace(1)).
@@ -157,7 +153,7 @@ void raw_object_store_clear(struct raw_object_store *o);
  * Put in `buf` the name of the file in the local object database that
  * would be used to store a loose object with the specified sha1.
  */
-void sha1_file_name(struct repository *r, struct strbuf *buf, const unsigned char *sha1);
+const char *loose_object_path(struct repository *r, struct strbuf *buf, const unsigned char *sha1);
 
 void *map_sha1_file(struct repository *r, const unsigned char *sha1, unsigned long *size);
 
diff --git a/object.c b/object.c
index e54160550c..79d636091c 100644
--- a/object.c
+++ b/object.c
@@ -482,27 +482,26 @@ struct raw_object_store *raw_object_store_new(void)
 	return o;
 }
 
-static void free_alt_odb(struct alternate_object_database *alt)
+static void free_object_directory(struct object_directory *odb)
 {
-	strbuf_release(&alt->scratch);
-	oid_array_clear(&alt->loose_objects_cache);
-	free(alt);
+	free(odb->path);
+	oid_array_clear(&odb->loose_objects_cache);
+	free(odb);
 }
 
-static void free_alt_odbs(struct raw_object_store *o)
+static void free_object_directories(struct raw_object_store *o)
 {
-	while (o->alt_odb_list) {
-		struct alternate_object_database *next;
+	while (o->odb) {
+		struct object_directory *next;
 
-		next = o->alt_odb_list->next;
-		free_alt_odb(o->alt_odb_list);
-		o->alt_odb_list = next;
+		next = o->odb->next;
+		free_object_directory(o->odb);
+		o->odb = next;
 	}
 }
 
 void raw_object_store_clear(struct raw_object_store *o)
 {
-	FREE_AND_NULL(o->objectdir);
 	FREE_AND_NULL(o->alternate_db);
 
 	oidmap_free(o->replace_map, 1);
@@ -512,8 +511,9 @@ void raw_object_store_clear(struct raw_object_store *o)
 	o->commit_graph = NULL;
 	o->commit_graph_attempted = 0;
 
-	free_alt_odbs(o);
-	o->alt_odb_tail = NULL;
+	free_object_directories(o);
+	o->odb_tail = NULL;
+	o->loaded_alternates = 0;
 
 	INIT_LIST_HEAD(&o->packed_git_mru);
 	close_all_packs(o);
diff --git a/packfile.c b/packfile.c
index d1e6683ffe..8c6b47cc77 100644
--- a/packfile.c
+++ b/packfile.c
@@ -971,16 +971,16 @@ static void prepare_packed_git_mru(struct repository *r)
 
 static void prepare_packed_git(struct repository *r)
 {
-	struct alternate_object_database *alt;
+	struct object_directory *odb;
 
 	if (r->objects->packed_git_initialized)
 		return;
-	prepare_multi_pack_index_one(r, r->objects->objectdir, 1);
-	prepare_packed_git_one(r, r->objects->objectdir, 1);
+
 	prepare_alt_odb(r);
-	for (alt = r->objects->alt_odb_list; alt; alt = alt->next) {
-		prepare_multi_pack_index_one(r, alt->path, 0);
-		prepare_packed_git_one(r, alt->path, 0);
+	for (odb = r->objects->odb; odb; odb = odb->next) {
+		int local = (odb == r->objects->odb);
+		prepare_multi_pack_index_one(r, odb->path, local);
+		prepare_packed_git_one(r, odb->path, local);
 	}
 	rearrange_packed_git(r);
 
@@ -992,6 +992,14 @@ static void prepare_packed_git(struct repository *r)
 
 void reprepare_packed_git(struct repository *r)
 {
+	struct object_directory *odb;
+
+	for (odb = r->objects->odb; odb; odb = odb->next) {
+		oid_array_clear(&odb->loose_objects_cache);
+		memset(&odb->loose_objects_subdir_seen, 0,
+		       sizeof(odb->loose_objects_subdir_seen));
+	}
+
 	r->objects->approximate_object_count_valid = 0;
 	r->objects->packed_git_initialized = 0;
 	prepare_packed_git(r);
diff --git a/path.c b/path.c
index dc3294c71e..03ab712839 100644
--- a/path.c
+++ b/path.c
@@ -385,7 +385,7 @@ static void adjust_git_path(const struct repository *repo,
 		strbuf_splice(buf, 0, buf->len,
 			      repo->index_file, strlen(repo->index_file));
 	else if (dir_prefix(base, "objects"))
-		replace_dir(buf, git_dir_len + 7, repo->objects->objectdir);
+		replace_dir(buf, git_dir_len + 7, repo->objects->odb->path);
 	else if (git_hooks_path && dir_prefix(base, "hooks"))
 		replace_dir(buf, git_dir_len + 5, git_hooks_path);
 	else if (repo->different_commondir)
diff --git a/repository.c b/repository.c
index 5dd1486718..7b02e1dffa 100644
--- a/repository.c
+++ b/repository.c
@@ -63,8 +63,14 @@ void repo_set_gitdir(struct repository *repo,
 	free(old_gitdir);
 
 	repo_set_commondir(repo, o->commondir);
-	expand_base_dir(&repo->objects->objectdir, o->object_dir,
+
+	if (!repo->objects->odb) {
+		repo->objects->odb = xcalloc(1, sizeof(*repo->objects->odb));
+		repo->objects->odb_tail = &repo->objects->odb->next;
+	}
+	expand_base_dir(&repo->objects->odb->path, o->object_dir,
 			repo->commondir, "objects");
+
 	free(repo->objects->alternate_db);
 	repo->objects->alternate_db = xstrdup_or_null(o->alternate_db);
 	expand_base_dir(&repo->graft_file, o->graft_file,
diff --git a/sha1-file.c b/sha1-file.c
index 5bd11c85bc..5a272f70de 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -346,25 +346,21 @@ static void fill_sha1_path(struct strbuf *buf, const unsigned char *sha1)
 	}
 }
 
-void sha1_file_name(struct repository *r, struct strbuf *buf, const unsigned char *sha1)
+static const char *odb_loose_path(struct object_directory *odb,
+				  struct strbuf *buf,
+				  const unsigned char *sha1)
 {
-	strbuf_addstr(buf, r->objects->objectdir);
+	strbuf_reset(buf);
+	strbuf_addstr(buf, odb->path);
 	strbuf_addch(buf, '/');
 	fill_sha1_path(buf, sha1);
+	return buf->buf;
 }
 
-struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
-{
-	strbuf_setlen(&alt->scratch, alt->base_len);
-	return &alt->scratch;
-}
-
-static const char *alt_sha1_path(struct alternate_object_database *alt,
-				 const unsigned char *sha1)
+const char *loose_object_path(struct repository *r, struct strbuf *buf,
+			      const unsigned char *sha1)
 {
-	struct strbuf *buf = alt_scratch_buf(alt);
-	fill_sha1_path(buf, sha1);
-	return buf->buf;
+	return odb_loose_path(r->objects->odb, buf, sha1);
 }
 
 /*
@@ -374,7 +370,7 @@ static int alt_odb_usable(struct raw_object_store *o,
 			  struct strbuf *path,
 			  const char *normalized_objdir)
 {
-	struct alternate_object_database *alt;
+	struct object_directory *odb;
 
 	/* Detect cases where alternate disappeared */
 	if (!is_directory(path->buf)) {
@@ -388,8 +384,8 @@ static int alt_odb_usable(struct raw_object_store *o,
 	 * Prevent the common mistake of listing the same
 	 * thing twice, or object directory itself.
 	 */
-	for (alt = o->alt_odb_list; alt; alt = alt->next) {
-		if (!fspathcmp(path->buf, alt->path))
+	for (odb = o->odb; odb; odb = odb->next) {
+		if (!fspathcmp(path->buf, odb->path))
 			return 0;
 	}
 	if (!fspathcmp(path->buf, normalized_objdir))
@@ -402,7 +398,7 @@ static int alt_odb_usable(struct raw_object_store *o,
  * Prepare alternate object database registry.
  *
  * The variable alt_odb_list points at the list of struct
- * alternate_object_database.  The elements on this list come from
+ * object_directory.  The elements on this list come from
  * non-empty elements from colon separated ALTERNATE_DB_ENVIRONMENT
  * environment variable, and $GIT_OBJECT_DIRECTORY/info/alternates,
  * whose contents is similar to that environment variable but can be
@@ -419,7 +415,7 @@ static void read_info_alternates(struct repository *r,
 static int link_alt_odb_entry(struct repository *r, const char *entry,
 	const char *relative_base, int depth, const char *normalized_objdir)
 {
-	struct alternate_object_database *ent;
+	struct object_directory *ent;
 	struct strbuf pathbuf = STRBUF_INIT;
 
 	if (!is_absolute_path(entry) && relative_base) {
@@ -447,11 +443,12 @@ static int link_alt_odb_entry(struct repository *r, const char *entry,
 		return -1;
 	}
 
-	ent = alloc_alt_odb(pathbuf.buf);
+	ent = xcalloc(1, sizeof(*ent));
+	ent->path = xstrdup(pathbuf.buf);
 
 	/* add the alternate entry */
-	*r->objects->alt_odb_tail = ent;
-	r->objects->alt_odb_tail = &(ent->next);
+	*r->objects->odb_tail = ent;
+	r->objects->odb_tail = &(ent->next);
 	ent->next = NULL;
 
 	/* recursively add alternates */
@@ -505,7 +502,7 @@ static void link_alt_odb_entries(struct repository *r, const char *alt,
 		return;
 	}
 
-	strbuf_add_absolute_path(&objdirbuf, r->objects->objectdir);
+	strbuf_add_absolute_path(&objdirbuf, r->objects->odb->path);
 	if (strbuf_normalize_path(&objdirbuf) < 0)
 		die(_("unable to normalize object directory: %s"),
 		    objdirbuf.buf);
@@ -540,18 +537,6 @@ static void read_info_alternates(struct repository *r,
 	free(path);
 }
 
-struct alternate_object_database *alloc_alt_odb(const char *dir)
-{
-	struct alternate_object_database *ent;
-
-	FLEX_ALLOC_STR(ent, path, dir);
-	strbuf_init(&ent->scratch, 0);
-	strbuf_addf(&ent->scratch, "%s/", dir);
-	ent->base_len = ent->scratch.len;
-
-	return ent;
-}
-
 void add_to_alternates_file(const char *reference)
 {
 	struct lock_file lock = LOCK_INIT;
@@ -588,7 +573,7 @@ void add_to_alternates_file(const char *reference)
 		fprintf_or_die(out, "%s\n", reference);
 		if (commit_lock_file(&lock))
 			die_errno(_("unable to move new alternates file into place"));
-		if (the_repository->objects->alt_odb_tail)
+		if (the_repository->objects->loaded_alternates)
 			link_alt_odb_entries(the_repository, reference,
 					     '\n', NULL, 0);
 	}
@@ -684,11 +669,11 @@ out:
 
 int foreach_alt_odb(alt_odb_fn fn, void *cb)
 {
-	struct alternate_object_database *ent;
+	struct object_directory *ent;
 	int r = 0;
 
 	prepare_alt_odb(the_repository);
-	for (ent = the_repository->objects->alt_odb_list; ent; ent = ent->next) {
+	for (ent = the_repository->objects->odb->next; ent; ent = ent->next) {
 		r = fn(ent, cb);
 		if (r)
 			break;
@@ -698,13 +683,13 @@ int foreach_alt_odb(alt_odb_fn fn, void *cb)
 
 void prepare_alt_odb(struct repository *r)
 {
-	if (r->objects->alt_odb_tail)
+	if (r->objects->loaded_alternates)
 		return;
 
-	r->objects->alt_odb_tail = &r->objects->alt_odb_list;
 	link_alt_odb_entries(r, r->objects->alternate_db, PATH_SEP, NULL, 0);
 
-	read_info_alternates(r, r->objects->objectdir, 0);
+	read_info_alternates(r, r->objects->odb->path, 0);
+	r->objects->loaded_alternates = 1;
 }
 
 /* Returns 1 if we have successfully freshened the file, 0 otherwise. */
@@ -731,23 +716,27 @@ int check_and_freshen_file(const char *fn, int freshen)
 	return 1;
 }
 
-static int check_and_freshen_local(const struct object_id *oid, int freshen)
+static int check_and_freshen_odb(struct object_directory *odb,
+				 const struct object_id *oid,
+				 int freshen)
 {
-	static struct strbuf buf = STRBUF_INIT;
-
-	strbuf_reset(&buf);
-	sha1_file_name(the_repository, &buf, oid->hash);
+	static struct strbuf path = STRBUF_INIT;
+	odb_loose_path(odb, &path, oid->hash);
+	return check_and_freshen_file(path.buf, freshen);
+}
 
-	return check_and_freshen_file(buf.buf, freshen);
+static int check_and_freshen_local(const struct object_id *oid, int freshen)
+{
+	return check_and_freshen_odb(the_repository->objects->odb, oid, freshen);
 }
 
 static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
 {
-	struct alternate_object_database *alt;
+	struct object_directory *odb;
+
 	prepare_alt_odb(the_repository);
-	for (alt = the_repository->objects->alt_odb_list; alt; alt = alt->next) {
-		const char *path = alt_sha1_path(alt, oid->hash);
-		if (check_and_freshen_file(path, freshen))
+	for (odb = the_repository->objects->odb->next; odb; odb = odb->next) {
+		if (check_and_freshen_odb(odb, oid, freshen))
 			return 1;
 	}
 	return 0;
@@ -888,25 +877,17 @@ int git_open_cloexec(const char *name, int flags)
  *
  * The "path" out-parameter will give the path of the object we found (if any).
  * Note that it may point to static storage and is only valid until another
- * call to sha1_file_name(), etc.
+ * call to stat_sha1_file().
  */
 static int stat_sha1_file(struct repository *r, const unsigned char *sha1,
 			  struct stat *st, const char **path)
 {
-	struct alternate_object_database *alt;
+	struct object_directory *odb;
 	static struct strbuf buf = STRBUF_INIT;
 
-	strbuf_reset(&buf);
-	sha1_file_name(r, &buf, sha1);
-	*path = buf.buf;
-
-	if (!lstat(*path, st))
-		return 0;
-
 	prepare_alt_odb(r);
-	errno = ENOENT;
-	for (alt = r->objects->alt_odb_list; alt; alt = alt->next) {
-		*path = alt_sha1_path(alt, sha1);
+	for (odb = r->objects->odb; odb; odb = odb->next) {
+		*path = odb_loose_path(odb, &buf, sha1);
 		if (!lstat(*path, st))
 			return 0;
 	}
@@ -922,25 +903,17 @@ static int open_sha1_file(struct repository *r,
 			  const unsigned char *sha1, const char **path)
 {
 	int fd;
-	struct alternate_object_database *alt;
-	int most_interesting_errno;
+	struct object_directory *odb;
+	int most_interesting_errno = ENOENT;
 	static struct strbuf buf = STRBUF_INIT;
 
-	strbuf_reset(&buf);
-	sha1_file_name(r, &buf, sha1);
-	*path = buf.buf;
-
-	fd = git_open(*path);
-	if (fd >= 0)
-		return fd;
-	most_interesting_errno = errno;
-
 	prepare_alt_odb(r);
-	for (alt = r->objects->alt_odb_list; alt; alt = alt->next) {
-		*path = alt_sha1_path(alt, sha1);
+	for (odb = r->objects->odb; odb; odb = odb->next) {
+		*path = odb_loose_path(odb, &buf, sha1);
 		fd = git_open(*path);
 		if (fd >= 0)
 			return fd;
+
 		if (most_interesting_errno == ENOENT)
 			most_interesting_errno = errno;
 	}
@@ -948,6 +921,24 @@ static int open_sha1_file(struct repository *r,
 	return -1;
 }
 
+static int quick_has_loose(struct repository *r,
+			   const unsigned char *sha1)
+{
+	int subdir_nr = sha1[0];
+	struct object_id oid;
+	struct object_directory *odb;
+
+	hashcpy(oid.hash, sha1);
+
+	prepare_alt_odb(r);
+	for (odb = r->objects->odb; odb; odb = odb->next) {
+		odb_load_loose_cache(odb, subdir_nr);
+		if (oid_array_lookup(&odb->loose_objects_cache, &oid) >= 0)
+			return 1;
+	}
+	return 0;
+}
+
 /*
  * Map the loose object at "path" if it is not NULL, or the path found by
  * searching for a loose object named "sha1".
@@ -1198,6 +1189,8 @@ static int sha1_loose_object_info(struct repository *r,
 	if (!oi->typep && !oi->type_name && !oi->sizep && !oi->contentp) {
 		const char *path;
 		struct stat st;
+		if (!oi->disk_sizep && (flags & OBJECT_INFO_QUICK))
+			return quick_has_loose(r, sha1) ? 0 : -1;
 		if (stat_sha1_file(r, sha1, &st, &path) < 0)
 			return -1;
 		if (oi->disk_sizep)
@@ -1626,8 +1619,7 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 	static struct strbuf tmp_file = STRBUF_INIT;
 	static struct strbuf filename = STRBUF_INIT;
 
-	strbuf_reset(&filename);
-	sha1_file_name(the_repository, &filename, oid->hash);
+	loose_object_path(the_repository, &filename, oid->hash);
 
 	fd = create_tmpfile(&tmp_file, filename.buf);
 	if (fd < 0) {
@@ -2134,43 +2126,50 @@ int for_each_loose_file_in_objdir(const char *path,
 	return r;
 }
 
-struct loose_alt_odb_data {
-	each_loose_object_fn *cb;
-	void *data;
-};
-
-static int loose_from_alt_odb(struct alternate_object_database *alt,
-			      void *vdata)
+int for_each_loose_object(each_loose_object_fn cb, void *data,
+			  enum for_each_object_flags flags)
 {
-	struct loose_alt_odb_data *data = vdata;
-	struct strbuf buf = STRBUF_INIT;
-	int r;
+	struct object_directory *odb;
 
-	strbuf_addstr(&buf, alt->path);
-	r = for_each_loose_file_in_objdir_buf(&buf,
-					      data->cb, NULL, NULL,
-					      data->data);
-	strbuf_release(&buf);
-	return r;
+	prepare_alt_odb(the_repository);
+	for (odb = the_repository->objects->odb; odb; odb = odb->next) {
+		int r = for_each_loose_file_in_objdir(odb->path, cb, NULL,
+						      NULL, data);
+		if (r)
+			return r;
+
+		if (flags & FOR_EACH_OBJECT_LOCAL_ONLY)
+			break;
+	}
+
+	return 0;
 }
 
-int for_each_loose_object(each_loose_object_fn cb, void *data,
-			  enum for_each_object_flags flags)
+static int append_loose_object(const struct object_id *oid, const char *path,
+			       void *data)
 {
-	struct loose_alt_odb_data alt;
-	int r;
+	oid_array_append(data, oid);
+	return 0;
+}
 
-	r = for_each_loose_file_in_objdir(get_object_directory(),
-					  cb, NULL, NULL, data);
-	if (r)
-		return r;
+void odb_load_loose_cache(struct object_directory *odb, int subdir_nr)
+{
+	struct strbuf buf = STRBUF_INIT;
 
-	if (flags & FOR_EACH_OBJECT_LOCAL_ONLY)
-		return 0;
+	if (subdir_nr < 0 ||
+	    subdir_nr >= ARRAY_SIZE(odb->loose_objects_subdir_seen))
+		BUG("subdir_nr out of range");
 
-	alt.cb = cb;
-	alt.data = data;
-	return foreach_alt_odb(loose_from_alt_odb, &alt);
+	if (odb->loose_objects_subdir_seen[subdir_nr])
+		return;
+
+	strbuf_addstr(&buf, odb->path);
+	for_each_file_in_obj_subdir(subdir_nr, &buf,
+				    append_loose_object,
+				    NULL, NULL,
+				    &odb->loose_objects_cache);
+	odb->loose_objects_subdir_seen[subdir_nr] = 1;
+	strbuf_release(&buf);
 }
 
 static int check_stream_sha1(git_zstream *stream,
diff --git a/sha1-name.c b/sha1-name.c
index faa60f69e3..b24502811b 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -83,51 +83,25 @@ static void update_candidates(struct disambiguate_state *ds, const struct object
 	/* otherwise, current can be discarded and candidate is still good */
 }
 
-static int append_loose_object(const struct object_id *oid, const char *path,
-			       void *data)
-{
-	oid_array_append(data, oid);
-	return 0;
-}
-
 static int match_sha(unsigned, const unsigned char *, const unsigned char *);
 
 static void find_short_object_filename(struct disambiguate_state *ds)
 {
 	int subdir_nr = ds->bin_pfx.hash[0];
-	struct alternate_object_database *alt;
-	static struct alternate_object_database *fakeent;
+	struct object_directory *odb;
 
-	if (!fakeent) {
-		/*
-		 * Create a "fake" alternate object database that
-		 * points to our own object database, to make it
-		 * easier to get a temporary working space in
-		 * alt->name/alt->base while iterating over the
-		 * object databases including our own.
-		 */
-		fakeent = alloc_alt_odb(get_object_directory());
-	}
-	fakeent->next = the_repository->objects->alt_odb_list;
-
-	for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
+	for (odb = the_repository->objects->odb;
+	     odb && !ds->ambiguous;
+	     odb = odb->next) {
 		int pos;
 
-		if (!alt->loose_objects_subdir_seen[subdir_nr]) {
-			struct strbuf *buf = alt_scratch_buf(alt);
-			for_each_file_in_obj_subdir(subdir_nr, buf,
-						    append_loose_object,
-						    NULL, NULL,
-						    &alt->loose_objects_cache);
-			alt->loose_objects_subdir_seen[subdir_nr] = 1;
-		}
-
-		pos = oid_array_lookup(&alt->loose_objects_cache, &ds->bin_pfx);
+		odb_load_loose_cache(odb, subdir_nr);
+		pos = oid_array_lookup(&odb->loose_objects_cache, &ds->bin_pfx);
 		if (pos < 0)
 			pos = -1 - pos;
-		while (!ds->ambiguous && pos < alt->loose_objects_cache.nr) {
+		while (!ds->ambiguous && pos < odb->loose_objects_cache.nr) {
 			const struct object_id *oid;
-			oid = alt->loose_objects_cache.oid + pos;
+			oid = odb->loose_objects_cache.oid + pos;
 			if (!match_sha(ds->len, ds->bin_pfx.hash, oid->hash))
 				break;
 			update_candidates(ds, oid);
diff --git a/transport.c b/transport.c
index 5a74b609ff..040e92c134 100644
--- a/transport.c
+++ b/transport.c
@@ -1433,7 +1433,7 @@ struct alternate_refs_data {
 	void *data;
 };
 
-static int refs_from_alternate_cb(struct alternate_object_database *e,
+static int refs_from_alternate_cb(struct object_directory *e,
 				  void *data)
 {
 	struct strbuf path = STRBUF_INIT;