diff --git a/builtin/fsck.c b/builtin/fsck.c
index a6c054e45b..892c5661d9 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -1069,7 +1069,6 @@ int cmd_fsck(int argc,
 		odb_for_each_object(repo->objects, NULL,
 				    mark_object_for_connectivity, repo, 0);
 	} else {
-		odb_prepare_alternates(repo->objects);
 		for (source = repo->objects->sources; source; source = source->next)
 			fsck_source(repo, source);
 
@@ -1155,7 +1154,6 @@ int cmd_fsck(int argc,
 	if (repo->settings.core_commit_graph) {
 		struct child_process commit_graph_verify = CHILD_PROCESS_INIT;
 
-		odb_prepare_alternates(repo->objects);
 		for (source = repo->objects->sources; source; source = source->next) {
 			child_process_init(&commit_graph_verify);
 			commit_graph_verify.git_cmd = 1;
@@ -1173,7 +1171,6 @@ int cmd_fsck(int argc,
 	if (repo->settings.core_multi_pack_index) {
 		struct child_process midx_verify = CHILD_PROCESS_INIT;
 
-		odb_prepare_alternates(repo->objects);
 		for (source = repo->objects->sources; source; source = source->next) {
 			child_process_init(&midx_verify);
 			midx_verify.git_cmd = 1;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 8ce3d0045a..2cad5b5a16 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1780,8 +1780,6 @@ static int want_object_in_pack_mtime(const struct object_id *oid,
 		*found_offset = 0;
 	}
 
-	odb_prepare_alternates(the_repository->objects);
-
 	for (source = the_repository->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		struct multi_pack_index *m = get_multi_pack_index(files->packed);
@@ -4520,7 +4518,6 @@ static void add_objects_in_unpacked_packs(void)
 		.source_infop = &source_info,
 	};
 
-	odb_prepare_alternates(to_pack.repo->objects);
 	for (source = to_pack.repo->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 
diff --git a/commit-graph.c b/commit-graph.c
index 49e8f63930..983c11ce85 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -651,8 +651,6 @@ struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
 	count = st->st_size / (odb->repo->hash_algo->hexsz + 1);
 	CALLOC_ARRAY(oids, count);
 
-	odb_prepare_alternates(odb);
-
 	for (i = 0; i < count; i++) {
 		struct odb_source *source;
 
@@ -768,7 +766,6 @@ static struct commit_graph *prepare_commit_graph(struct repository *r)
 	if (!commit_graph_compatible(r))
 		return NULL;
 
-	odb_prepare_alternates(r->objects);
 	for (source = r->objects->sources; source; source = source->next) {
 		r->objects->commit_graph = read_commit_graph_one(source);
 		if (r->objects->commit_graph)
@@ -2018,7 +2015,6 @@ static void fill_oids_from_all_packs(struct write_commit_graph_context *ctx)
 			_("Finding commits for commit graph among packed objects"),
 			ctx->approx_nr_objects);
 
-	odb_prepare_alternates(ctx->r->objects);
 	for (source = ctx->r->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		odb_source_for_each_object(&files->packed->base, &oi, add_packed_commits_oi,
diff --git a/loose.c b/loose.c
index aa3cb1b4fc..c159d29d2d 100644
--- a/loose.c
+++ b/loose.c
@@ -115,7 +115,6 @@ int repo_read_loose_object_map(struct repository *repo)
 {
 	struct odb_source *source;
 
-	odb_prepare_alternates(repo->objects);
 	for (source = repo->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		if (loose_object_map_load(files->loose) < 0)
diff --git a/object-name.c b/object-name.c
index 026ff8c6dd..4eda8c8eac 100644
--- a/object-name.c
+++ b/object-name.c
@@ -280,7 +280,6 @@ static int init_object_disambiguation(struct repository *r,
 
 	ds->len = len;
 	ds->repo = r;
-	odb_prepare_alternates(r->objects);
 	return 0;
 }
 
diff --git a/odb.c b/odb.c
index 22417601ed..a70171251d 100644
--- a/odb.c
+++ b/odb.c
@@ -2,11 +2,10 @@
 #include "abspath.h"
 #include "commit-graph.h"
 #include "config.h"
-#include "dir.h"
 #include "environment.h"
 #include "gettext.h"
+#include "hashmap.h"
 #include "hex.h"
-#include "khash.h"
 #include "lockfile.h"
 #include "loose.h"
 #include "midx.h"
@@ -28,8 +27,47 @@
 #include "trace2.h"
 #include "write-or-die.h"
 
-KHASH_INIT(odb_path_map, const char * /* key: odb_path */,
-	struct odb_source *, 1, fspathhash, fspatheq)
+/*
+ * NEEDSWORK: we're using "core.ignoreCase" to deduplicate alternates that
+ * _may_ be the same. This requires quite a bit of boilerplate for dubious
+ * benefit:
+ *
+ *   - Duplicating alternates should really only lead to regressed performance.
+ *
+ *   - We don't properly resolve symlinks or mointpoints, so we may still end
+ *     up duplicating alternates.
+ *
+ *   - The value may be lying, in which case we might deduplicate alternates
+ *     that are in fact not mapping to the same directory.
+ *
+ * We should investigate whether we can remove this whole mechanism outright.
+ */
+static int odb_source_paths_cmp(struct object_database *o,
+				const char *a, const char *b)
+{
+	if (o->source_paths_icase < 0) {
+		int icase = 0;
+		repo_config_get_bool(o->repo, "core.ignorecase", &icase);
+		o->source_paths_icase = icase;
+	}
+
+	return o->source_paths_icase ? strcasecmp(a, b) : strcmp(a, b);
+}
+
+static int odb_source_by_path_cmp(const void *cb_data,
+				  const struct hashmap_entry *entry,
+				  const struct hashmap_entry *entry_or_key,
+				  const void *keydata)
+{
+	struct object_database *o = (struct object_database *)cb_data;
+	const struct odb_source *source = container_of(entry, const struct odb_source, by_path_entry);
+	const char *path = keydata;
+
+	if (!path)
+		path = container_of(entry_or_key, const struct odb_source, by_path_entry)->path;
+
+	return odb_source_paths_cmp(o, source->path, path);
+}
 
 int odb_mkstemp(struct object_database *odb,
 		struct strbuf *temp_filename, const char *pattern)
@@ -57,8 +95,8 @@ int odb_mkstemp(struct object_database *odb,
  */
 static bool odb_is_source_usable(struct object_database *o, const char *path)
 {
-	int r;
 	struct strbuf normalized_objdir = STRBUF_INIT;
+	struct hashmap_entry key;
 	bool usable = false;
 
 	strbuf_realpath(&normalized_objdir, o->sources->path, 1);
@@ -75,20 +113,18 @@ static bool odb_is_source_usable(struct object_database *o, const char *path)
 	 * Prevent the common mistake of listing the same
 	 * thing twice, or object directory itself.
 	 */
-	if (!o->source_by_path) {
-		khiter_t p;
-
-		o->source_by_path = kh_init_odb_path_map();
+	if (!hashmap_get_size(&o->source_by_path)) {
 		assert(!o->sources->next);
-		p = kh_put_odb_path_map(o->source_by_path, o->sources->path, &r);
-		assert(r == 1); /* never used */
-		kh_value(o->source_by_path, p) = o->sources;
+		hashmap_entry_init(&o->sources->by_path_entry,
+				   strihash(o->sources->path));
+		hashmap_add(&o->source_by_path, &o->sources->by_path_entry);
 	}
 
-	if (fspatheq(path, normalized_objdir.buf))
+	if (!odb_source_paths_cmp(o, path, normalized_objdir.buf))
 		goto out;
 
-	if (kh_get_odb_path_map(o->source_by_path, path) < kh_end(o->source_by_path))
+	hashmap_entry_init(&key, strihash(path));
+	if (hashmap_get(&o->source_by_path, &key, path))
 		goto out;
 
 	usable = true;
@@ -171,8 +207,6 @@ static struct odb_source *odb_add_alternate_recursively(struct object_database *
 {
 	struct odb_source *alternate = NULL;
 	struct strvec sources = STRVEC_INIT;
-	khiter_t pos;
-	int ret;
 
 	if (!odb_is_source_usable(odb, source))
 		goto error;
@@ -183,10 +217,11 @@ static struct odb_source *odb_add_alternate_recursively(struct object_database *
 	*odb->sources_tail = alternate;
 	odb->sources_tail = &(alternate->next);
 
-	pos = kh_put_odb_path_map(odb->source_by_path, alternate->path, &ret);
-	if (!ret)
+	hashmap_entry_init(&alternate->by_path_entry, strihash(alternate->path));
+	if (hashmap_get(&odb->source_by_path, &alternate->by_path_entry,
+			alternate->path))
 		BUG("source must not yet exist");
-	kh_value(odb->source_by_path, pos) = alternate;
+	hashmap_add(&odb->source_by_path, &alternate->by_path_entry);
 
 	/* recursively add alternates */
 	odb_source_read_alternates(alternate, &sources);
@@ -209,18 +244,12 @@ void odb_add_to_alternates_file(struct object_database *odb,
 	int ret = odb_source_write_alternate(odb->sources, dir);
 	if (ret < 0)
 		die(NULL);
-	if (odb->loaded_alternates)
-		odb_add_alternate_recursively(odb, dir, 0);
+	odb_add_alternate_recursively(odb, dir, 0);
 }
 
 struct odb_source *odb_add_to_alternates_memory(struct object_database *odb,
 						const char *dir)
 {
-	/*
-	 * Make sure alternates are initialized, or else our entry may be
-	 * overwritten when they are.
-	 */
-	odb_prepare_alternates(odb);
 	return odb_add_alternate_recursively(odb, dir, 0);
 }
 
@@ -229,12 +258,6 @@ struct odb_source *odb_set_temporary_primary_source(struct object_database *odb,
 {
 	struct odb_source *source;
 
-	/*
-	 * Make sure alternates are initialized, or else our entry may be
-	 * overwritten when they are.
-	 */
-	odb_prepare_alternates(odb);
-
 	/*
 	 * Make a new primary odb and link the old primary ODB in as an
 	 * alternate
@@ -340,7 +363,6 @@ struct odb_source *odb_find_source(struct object_database *odb, const char *obj_
 	char *obj_dir_real = real_pathdup(obj_dir, 1);
 	struct strbuf odb_path_real = STRBUF_INIT;
 
-	odb_prepare_alternates(odb);
 	for (source = odb->sources; source; source = source->next) {
 		strbuf_realpath(&odb_path_real, source->path, 1);
 		if (!strcmp(obj_dir_real, odb_path_real.buf))
@@ -474,7 +496,6 @@ int odb_for_each_alternate(struct object_database *odb,
 	struct odb_source *alternate;
 	int r = 0;
 
-	odb_prepare_alternates(odb);
 	for (alternate = odb->sources->next; alternate; alternate = alternate->next) {
 		r = cb(alternate, payload);
 		if (r)
@@ -483,26 +504,22 @@ int odb_for_each_alternate(struct object_database *odb,
 	return r;
 }
 
-void odb_prepare_alternates(struct object_database *odb)
+static void odb_prepare_alternates(struct object_database *odb,
+				   const char *alternate_db)
 {
 	struct strvec sources = STRVEC_INIT;
 
-	if (odb->loaded_alternates)
-		return;
-
-	parse_alternates(odb->alternate_db, PATH_SEP, NULL, &sources);
+	parse_alternates(alternate_db, PATH_SEP, NULL, &sources);
 	odb_source_read_alternates(odb->sources, &sources);
+
 	for (size_t i = 0; i < sources.nr; i++)
 		odb_add_alternate_recursively(odb, sources.v[i], 0);
 
-	odb->loaded_alternates = 1;
-
 	strvec_clear(&sources);
 }
 
 int odb_has_alternates(struct object_database *odb)
 {
-	odb_prepare_alternates(odb);
 	return !!odb->sources->next;
 }
 
@@ -565,8 +582,6 @@ static enum odb_read_status do_oid_object_info_extended(struct object_database *
 	if (!odb_source_read_object_info(odb->inmemory_objects, oid, oi, flags, NULL))
 		return 0;
 
-	odb_prepare_alternates(odb);
-
 	while (1) {
 		struct odb_source *source;
 
@@ -846,7 +861,6 @@ int odb_freshen_object(struct object_database *odb,
 		       const struct object_id *oid)
 {
 	struct odb_source *source;
-	odb_prepare_alternates(odb);
 	for (source = odb->sources; source; source = source->next)
 		if (odb_source_freshen_object(source, oid, NULL))
 			return 1;
@@ -861,7 +875,6 @@ int odb_for_each_object_ext(struct object_database *odb,
 {
 	int ret;
 
-	odb_prepare_alternates(odb);
 	for (struct odb_source *source = odb->sources; source; source = source->next) {
 		if (opts->flags & ODB_FOR_EACH_OBJECT_LOCAL_ONLY && !source->local)
 			continue;
@@ -899,7 +912,6 @@ int odb_count_objects(struct object_database *odb,
 		return 0;
 	}
 
-	odb_prepare_alternates(odb);
 	for (source = odb->sources; source; source = source->next) {
 		unsigned long c;
 
@@ -979,7 +991,6 @@ int odb_find_abbrev_len(struct object_database *odb,
 		goto out;
 	}
 
-	odb_prepare_alternates(odb);
 	for (struct odb_source *source = odb->sources; source; source = source->next) {
 		ret = odb_source_find_abbrev_len(source, oid, len, &len);
 		if (ret)
@@ -1075,6 +1086,8 @@ struct object_database *odb_new(struct repository *repo,
 	o->repo = repo;
 	pthread_mutex_init(&o->replace_mutex, NULL);
 	string_list_init_dup(&o->submodule_source_paths);
+	hashmap_init(&o->source_by_path, odb_source_by_path_cmp, o, 0);
+	o->source_paths_icase = -1;
 
 	if (flags & ODB_NEW_HONOR_ENV) {
 		primary_source = xstrdup_or_null(getenv(DB_ENVIRONMENT));
@@ -1085,9 +1098,11 @@ struct object_database *odb_new(struct repository *repo,
 
 	o->sources = odb_source_new(o, primary_source, true);
 	o->sources_tail = &o->sources->next;
-	o->alternate_db = secondary_sources;
 	o->inmemory_objects = &odb_source_inmemory_new(o)->base;
 
+	odb_prepare_alternates(o, secondary_sources);
+
+	free(secondary_sources);
 	free(primary_source);
 	return o;
 }
@@ -1113,8 +1128,7 @@ static void odb_free_sources(struct object_database *o)
 	odb_source_free(o->inmemory_objects);
 	o->inmemory_objects = NULL;
 
-	kh_destroy_odb_path_map(o->source_by_path);
-	o->source_by_path = NULL;
+	hashmap_clear(&o->source_by_path);
 }
 
 void odb_free(struct object_database *o)
@@ -1122,8 +1136,6 @@ void odb_free(struct object_database *o)
 	if (!o)
 		return;
 
-	free(o->alternate_db);
-
 	oidmap_clear(&o->replace_map, 1);
 	pthread_mutex_destroy(&o->replace_mutex);
 
@@ -1145,14 +1157,14 @@ void odb_prepare(struct object_database *o, enum odb_prepare_flags flags)
 	 * Reprepare alt odbs, in case the alternates file was modified
 	 * during the course of this process. This only _adds_ odbs to
 	 * the linked list, so existing odbs will continue to exist for
-	 * the lifetime of the process.
+	 * the lifetime of the process. Consequently, we don't have to
+	 * reprocess GIT_ALTERNATE_OBJECT_DIRECTORIES here.
 	 */
 	if (flags & ODB_PREPARE_FLUSH_CACHES) {
-		o->loaded_alternates = 0;
+		odb_prepare_alternates(o, NULL);
 		o->object_count_valid = 0;
 	}
 
-	odb_prepare_alternates(o);
 	for (source = o->sources; source; source = source->next)
 		odb_source_prepare(source, flags);
 
diff --git a/odb.h b/odb.h
index c41fb5d07c..1de105d6bd 100644
--- a/odb.h
+++ b/odb.h
@@ -1,6 +1,7 @@
 #ifndef ODB_H
 #define ODB_H
 
+#include "hashmap.h"
 #include "object.h"
 #include "oidset.h"
 #include "oidmap.h"
@@ -54,16 +55,19 @@ struct object_database {
 	 */
 	struct odb_source *sources;
 	struct odb_source **sources_tail;
-	struct kh_odb_path_map *source_by_path;
-
-	int loaded_alternates;
 
 	/*
-	 * A list of alternate object directories loaded from the environment;
-	 * this should not generally need to be accessed directly, but will
-	 * populate the "sources" list when odb_prepare_alternates() is run.
+	 * Map of object database sources, keyed by their respective paths.
+	 * This map is used to detect the case where the same source is
+	 * registered multiple times.
 	 */
-	char *alternate_db;
+	struct hashmap source_by_path;
+
+	/*
+	 * Whether source paths shall be compared case-insensitively, as
+	 * determined by "core.ignoreCase".
+	 */
+	int source_paths_icase;
 
 	/*
 	 * Objects that should be substituted by other objects
@@ -260,12 +264,6 @@ void odb_for_each_alternate_ref(struct object_database *odb,
 int odb_mkstemp(struct object_database *odb,
 		struct strbuf *temp_filename, const char *pattern);
 
-/*
- * Prepare alternate object sources for the given database by reading
- * "objects/info/alternates" and opening the respective sources.
- */
-void odb_prepare_alternates(struct object_database *odb);
-
 /*
  * Check whether the object database has any alternates. The primary object
  * source does not count as alternate.
diff --git a/odb/source.h b/odb/source.h
index 1aba10eae9..29159a0426 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -1,6 +1,7 @@
 #ifndef ODB_SOURCE_H
 #define ODB_SOURCE_H
 
+#include "hashmap.h"
 #include "object.h"
 #include "odb.h"
 #include "odb/transaction.h"
@@ -51,6 +52,12 @@ struct strvec;
 struct odb_source {
 	struct odb_source *next;
 
+	/*
+	 * Entry in the object database's map of sources, keyed by this
+	 * source's path.
+	 */
+	struct hashmap_entry by_path_entry;
+
 	/* Object database that owns this object source. */
 	struct object_database *odb;
 
diff --git a/odb/streaming.c b/odb/streaming.c
index 9c85ec54f5..8f2143cab5 100644
--- a/odb/streaming.c
+++ b/odb/streaming.c
@@ -184,7 +184,6 @@ static int istream_source(struct odb_stream **out,
 {
 	struct odb_source *source;
 
-	odb_prepare_alternates(odb);
 	for (source = odb->sources; source; source = source->next)
 		if (!odb_source_read_object_stream(out, source, oid))
 			return 0;
diff --git a/pack-bitmap.c b/pack-bitmap.c
index e85bd69ba4..e0fb57d332 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -717,7 +717,6 @@ static int open_bitmap(struct repository *r,
 
 	assert(!bitmap_git->map);
 
-	odb_prepare_alternates(r->objects);
 	for (source = r->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 
@@ -3417,7 +3416,6 @@ int verify_bitmap_files(struct repository *r)
 	struct packed_git *p;
 	int res = 0;
 
-	odb_prepare_alternates(r->objects);
 	for (source = r->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		struct multi_pack_index *m = get_multi_pack_index(files->packed);
diff --git a/packfile.c b/packfile.c
index 047a59ea6c..4fa5fd67c8 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1923,7 +1923,6 @@ int has_object_pack(struct repository *r, const struct object_id *oid)
 {
 	struct odb_source *source;
 
-	odb_prepare_alternates(r->objects);
 	for (source = r->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		if (!odb_source_read_object_info(&files->packed->base, oid, NULL, 0, NULL))
diff --git a/packfile.h b/packfile.h
index 7149ad9f43..6d30d15a00 100644
--- a/packfile.h
+++ b/packfile.h
@@ -77,8 +77,6 @@ static inline struct repo_for_each_pack_data repo_for_eack_pack_data_init(struct
 {
 	struct repo_for_each_pack_data data = { 0 };
 
-	odb_prepare_alternates(repo->objects);
-
 	for (struct odb_source *source = repo->objects->sources; source; source = source->next) {
 		struct odb_source_files *files = odb_source_files_downcast(source);
 		struct packfile_list_entry *entry = packfile_store_get_packs(files->packed);
diff --git a/setup.c b/setup.c
index 22beb86f7a..dfe05d9a03 100644
--- a/setup.c
+++ b/setup.c
@@ -2879,12 +2879,6 @@ int init_db(struct repository *repo,
 	reinit = create_default_files(repo, template_dir, original_git_dir,
 				      &repo_fmt, init_shared_repository);
 
-	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(repo, initial_branch, flags & INIT_DB_QUIET);
-	create_object_database(repo);
-
-	startup_info->have_repository = 1;
-
 	if (repo_settings_get_shared_repository(repo)) {
 		char buf[10];
 		/* We do not spell "group" and such, so that
@@ -2906,6 +2900,12 @@ int init_db(struct repository *repo,
 		repo_config_set(repo, "receive.denyNonFastforwards", "true");
 	}
 
+	if (!(flags & INIT_DB_SKIP_REFDB))
+		create_reference_database(repo, initial_branch, flags & INIT_DB_QUIET);
+	create_object_database(repo);
+
+	startup_info->have_repository = 1;
+
 	if (!(flags & INIT_DB_QUIET)) {
 		int len = strlen(git_dir);