diff --git a/Documentation/RelNotes/2.54.0.adoc b/Documentation/RelNotes/2.54.0.adoc
index 7de9f7e7ecf6d2..25affd6a981d61 100644
--- a/Documentation/RelNotes/2.54.0.adoc
+++ b/Documentation/RelNotes/2.54.0.adoc
@@ -227,6 +227,10 @@ Performance, Internal Implementation, Development Support etc.
  * Add a coccinelle rule to break the build when "struct strbuf" gets
    passed by value.
 
+ * Further work on incremental repacking using MIDX/bitmap
+
+ * The logic to count objects has been cleaned up.
+
 
 Fixes since v2.53
 -----------------
diff --git a/Documentation/git-multi-pack-index.adoc b/Documentation/git-multi-pack-index.adoc
index 2f642697e9e106..612568301412d6 100644
--- a/Documentation/git-multi-pack-index.adoc
+++ b/Documentation/git-multi-pack-index.adoc
@@ -9,7 +9,14 @@ git-multi-pack-index - Write and verify multi-pack-indexes
 SYNOPSIS
 --------
 [verse]
-'git multi-pack-index' [--object-dir=<dir>] [--[no-]bitmap] <sub-command>
+'git multi-pack-index' [<options>] write [--preferred-pack=<pack>]
+		         [--[no-]bitmap] [--[no-]incremental] [--[no-]stdin-packs]
+		         [--refs-snapshot=<path>]
+'git multi-pack-index' [<options>] compact [--[no-]incremental]
+		         [--[no-]bitmap] <from> <to>
+'git multi-pack-index' [<options>] verify
+'git multi-pack-index' [<options>] expire
+'git multi-pack-index' [<options>] repack [--batch-size=<size>]
 
 DESCRIPTION
 -----------
@@ -18,6 +25,8 @@ Write or verify a multi-pack-index (MIDX) file.
 OPTIONS
 -------
 
+The following command-line options are applicable to all sub-commands:
+
 --object-dir=<dir>::
 	Use given directory for the location of Git objects. We check
 	`<dir>/packs/multi-pack-index` for the current MIDX file, and
@@ -73,7 +82,21 @@ marker).
 		Write an incremental MIDX file containing only objects
 		and packs not present in an existing MIDX layer.
 		Migrates non-incremental MIDXs to incremental ones when
-		necessary. Incompatible with `--bitmap`.
+		necessary.
+--
+
+compact::
+	Write a new MIDX layer containing only objects and packs present
+	in the range `<from>` to `<to>`, where both arguments are
+	checksums of existing layers in the MIDX chain.
++
+--
+	--incremental::
+		Write the result to a MIDX chain instead of writing a
+		stand-alone MIDX.
+
+	--[no-]bitmap::
+		Control whether or not a multi-pack bitmap is written.
 --
 
 verify::
diff --git a/Documentation/gitformat-pack.adoc b/Documentation/gitformat-pack.adoc
index 1b4db4aa611e83..3416edceab82e9 100644
--- a/Documentation/gitformat-pack.adoc
+++ b/Documentation/gitformat-pack.adoc
@@ -374,7 +374,9 @@ HEADER:
 	    The signature is: {'M', 'I', 'D', 'X'}
 
 	1-byte version number:
-	    Git only writes or recognizes version 1.
+	    Git writes the version specified by the "midx.version"
+	    configuration option, which defaults to 2. It recognizes
+	    both versions 1 and 2.
 
 	1-byte Object Id Version
 	    We infer the length of object IDs (OIDs) from this value:
@@ -413,7 +415,9 @@ CHUNK DATA:
 	    strings. There is no extra padding between the filenames,
 	    and they are listed in lexicographic order. The chunk itself
 	    is padded at the end with between 0 and 3 NUL bytes to make the
-	    chunk size a multiple of 4 bytes.
+	    chunk size a multiple of 4 bytes. Version 1 MIDXs are required to
+	    list their packs in lexicographic order, but version 2 MIDXs may
+	    list their packs in any arbitrary order.
 
 	Bitmapped Packfiles (ID: {'B', 'T', 'M', 'P'})
 	    Stores a table of two 4-byte unsigned integers in network order.
diff --git a/builtin/gc.c b/builtin/gc.c
index 5d8d358f7a511d..3a71e314c975af 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -467,37 +467,19 @@ static int rerere_gc_condition(struct gc_config *cfg UNUSED)
 static int too_many_loose_objects(int limit)
 {
 	/*
-	 * Quickly check if a "gc" is needed, by estimating how
-	 * many loose objects there are.  Because SHA-1 is evenly
-	 * distributed, we can check only one and get a reasonable
-	 * estimate.
+	 * This is weird, but stems from legacy behaviour: the GC auto
+	 * threshold was always essentially interpreted as if it was rounded up
+	 * to the next multiple 256 of, so we retain this behaviour for now.
 	 */
-	DIR *dir;
-	struct dirent *ent;
-	int auto_threshold;
-	int num_loose = 0;
-	int needed = 0;
-	const unsigned hexsz_loose = the_hash_algo->hexsz - 2;
-	char *path;
-
-	path = repo_git_path(the_repository, "objects/17");
-	dir = opendir(path);
-	free(path);
-	if (!dir)
+	int auto_threshold = DIV_ROUND_UP(limit, 256) * 256;
+	unsigned long loose_count;
+
+	if (odb_source_loose_count_objects(the_repository->objects->sources,
+					   ODB_COUNT_OBJECTS_APPROXIMATE,
+					   &loose_count) < 0)
 		return 0;
 
-	auto_threshold = DIV_ROUND_UP(limit, 256);
-	while ((ent = readdir(dir)) != NULL) {
-		if (strspn(ent->d_name, "0123456789abcdef") != hexsz_loose ||
-		    ent->d_name[hexsz_loose] != '\0')
-			continue;
-		if (++num_loose > auto_threshold) {
-			needed = 1;
-			break;
-		}
-	}
-	closedir(dir);
-	return needed;
+	return loose_count > auto_threshold;
 }
 
 static struct packed_git *find_base_packs(struct string_list *packs,
@@ -592,9 +574,13 @@ static uint64_t total_ram(void)
 static uint64_t estimate_repack_memory(struct gc_config *cfg,
 				       struct packed_git *pack)
 {
-	unsigned long nr_objects = repo_approximate_object_count(the_repository);
+	unsigned long nr_objects;
 	size_t os_cache, heap;
 
+	if (odb_count_objects(the_repository->objects,
+			      ODB_COUNT_OBJECTS_APPROXIMATE, &nr_objects) < 0)
+		return 0;
+
 	if (!pack || !nr_objects)
 		return 0;
 
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index 5f364aa816ba25..0f72d96c02da4c 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -9,12 +9,18 @@
 #include "strbuf.h"
 #include "trace2.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "replace-object.h"
 #include "repository.h"
 
 #define BUILTIN_MIDX_WRITE_USAGE \
-	N_("git multi-pack-index [<options>] write [--preferred-pack=<pack>]" \
-	   "[--refs-snapshot=<path>]")
+	N_("git multi-pack-index [<options>] write [--preferred-pack=<pack>]\n" \
+	   "  [--[no-]bitmap] [--[no-]incremental] [--[no-]stdin-packs]\n" \
+	   "  [--refs-snapshot=<path>]")
+
+#define BUILTIN_MIDX_COMPACT_USAGE \
+	N_("git multi-pack-index [<options>] compact [--[no-]incremental]\n" \
+	   "  [--[no-]bitmap] <from> <to>")
 
 #define BUILTIN_MIDX_VERIFY_USAGE \
 	N_("git multi-pack-index [<options>] verify")
@@ -29,6 +35,10 @@ static char const * const builtin_multi_pack_index_write_usage[] = {
 	BUILTIN_MIDX_WRITE_USAGE,
 	NULL
 };
+static char const * const builtin_multi_pack_index_compact_usage[] = {
+	BUILTIN_MIDX_COMPACT_USAGE,
+	NULL
+};
 static char const * const builtin_multi_pack_index_verify_usage[] = {
 	BUILTIN_MIDX_VERIFY_USAGE,
 	NULL
@@ -43,6 +53,7 @@ static char const * const builtin_multi_pack_index_repack_usage[] = {
 };
 static char const * const builtin_multi_pack_index_usage[] = {
 	BUILTIN_MIDX_WRITE_USAGE,
+	BUILTIN_MIDX_COMPACT_USAGE,
 	BUILTIN_MIDX_VERIFY_USAGE,
 	BUILTIN_MIDX_EXPIRE_USAGE,
 	BUILTIN_MIDX_REPACK_USAGE,
@@ -84,6 +95,8 @@ static struct option common_opts[] = {
 	  N_("directory"),
 	  N_("object directory containing set of packfile and pack-index pairs"),
 	  parse_object_dir),
+	OPT_BIT(0, "progress", &opts.flags, N_("force progress reporting"),
+		MIDX_PROGRESS),
 	OPT_END(),
 };
 
@@ -138,8 +151,6 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 			   N_("pack for reuse when computing a multi-pack bitmap")),
 		OPT_BIT(0, "bitmap", &opts.flags, N_("write multi-pack bitmap"),
 			MIDX_WRITE_BITMAP | MIDX_WRITE_REV_INDEX),
-		OPT_BIT(0, "progress", &opts.flags,
-			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_BIT(0, "incremental", &opts.flags,
 			N_("write a new incremental MIDX"), MIDX_WRITE_INCREMENTAL),
 		OPT_BOOL(0, "stdin-packs", &opts.stdin_packs,
@@ -194,14 +205,78 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 	return ret;
 }
 
+static int cmd_multi_pack_index_compact(int argc, const char **argv,
+					const char *prefix,
+					struct repository *repo)
+{
+	struct multi_pack_index *m, *cur;
+	struct multi_pack_index *from_midx = NULL;
+	struct multi_pack_index *to_midx = NULL;
+	struct odb_source *source;
+	int ret;
+
+	struct option *options;
+	static struct option builtin_multi_pack_index_compact_options[] = {
+		OPT_BIT(0, "bitmap", &opts.flags, N_("write multi-pack bitmap"),
+			MIDX_WRITE_BITMAP | MIDX_WRITE_REV_INDEX),
+		OPT_BIT(0, "incremental", &opts.flags,
+			N_("write a new incremental MIDX"), MIDX_WRITE_INCREMENTAL),
+		OPT_END(),
+	};
+
+	repo_config(repo, git_multi_pack_index_write_config, NULL);
+
+	options = add_common_options(builtin_multi_pack_index_compact_options);
+
+	trace2_cmd_mode(argv[0]);
+
+	if (isatty(2))
+		opts.flags |= MIDX_PROGRESS;
+	argc = parse_options(argc, argv, prefix,
+			     options, builtin_multi_pack_index_compact_usage,
+			     0);
+
+	if (argc != 2)
+		usage_with_options(builtin_multi_pack_index_compact_usage,
+				   options);
+	source = handle_object_dir_option(the_repository);
+
+	FREE_AND_NULL(options);
+
+	m = get_multi_pack_index(source);
+
+	for (cur = m; cur && !(from_midx && to_midx); cur = cur->base_midx) {
+		const char *midx_csum = midx_get_checksum_hex(cur);
+
+		if (!from_midx && !strcmp(midx_csum, argv[0]))
+			from_midx = cur;
+		if (!to_midx && !strcmp(midx_csum, argv[1]))
+			to_midx = cur;
+	}
+
+	if (!from_midx)
+		die(_("could not find MIDX: %s"), argv[0]);
+	if (!to_midx)
+		die(_("could not find MIDX: %s"), argv[1]);
+	if (from_midx == to_midx)
+		die(_("MIDX compaction endpoints must be unique"));
+
+	for (m = from_midx; m; m = m->base_midx) {
+		if (m == to_midx)
+			die(_("MIDX %s must be an ancestor of %s"), argv[0], argv[1]);
+	}
+
+	ret = write_midx_file_compact(source, from_midx, to_midx, opts.flags);
+
+	return ret;
+}
+
 static int cmd_multi_pack_index_verify(int argc, const char **argv,
 				       const char *prefix,
 				       struct repository *repo UNUSED)
 {
 	struct option *options;
 	static struct option builtin_multi_pack_index_verify_options[] = {
-		OPT_BIT(0, "progress", &opts.flags,
-			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
 	struct odb_source *source;
@@ -231,8 +306,6 @@ static int cmd_multi_pack_index_expire(int argc, const char **argv,
 {
 	struct option *options;
 	static struct option builtin_multi_pack_index_expire_options[] = {
-		OPT_BIT(0, "progress", &opts.flags,
-			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
 	struct odb_source *source;
@@ -264,8 +337,6 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 	static struct option builtin_multi_pack_index_repack_options[] = {
 		OPT_UNSIGNED(0, "batch-size", &opts.batch_size,
 		  N_("during repack, collect pack-files of smaller size into a batch that is larger than this size")),
-		OPT_BIT(0, "progress", &opts.flags,
-		  N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
 	struct odb_source *source;
@@ -300,6 +371,7 @@ int cmd_multi_pack_index(int argc,
 	struct option builtin_multi_pack_index_options[] = {
 		OPT_SUBCOMMAND("repack", &fn, cmd_multi_pack_index_repack),
 		OPT_SUBCOMMAND("write", &fn, cmd_multi_pack_index_write),
+		OPT_SUBCOMMAND("compact", &fn, cmd_multi_pack_index_compact),
 		OPT_SUBCOMMAND("verify", &fn, cmd_multi_pack_index_verify),
 		OPT_SUBCOMMAND("expire", &fn, cmd_multi_pack_index_expire),
 		OPT_END(),
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index ff8b05d1bafbe3..2f589e3b378d3f 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -29,6 +29,7 @@
 #include "object-file.h"
 #include "object-name.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "advice.h"
 #include "branch.h"
 #include "list-objects-filter-options.h"
diff --git a/commit-graph.c b/commit-graph.c
index f8e24145a513b0..c0300033304404 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -2607,7 +2607,8 @@ int write_commit_graph(struct odb_source *source,
 			replace = ctx.opts->split_flags & COMMIT_GRAPH_SPLIT_REPLACE;
 	}
 
-	ctx.approx_nr_objects = repo_approximate_object_count(r);
+	if (odb_count_objects(r->objects, ODB_COUNT_OBJECTS_APPROXIMATE, &ctx.approx_nr_objects) < 0)
+		ctx.approx_nr_objects = 0;
 
 	if (ctx.append && g) {
 		for (i = 0; i < g->num_commits; i++) {
diff --git a/midx-write.c b/midx-write.c
index 6485cb67068553..0ff2e45aa7abdd 100644
--- a/midx-write.c
+++ b/midx-write.c
@@ -36,10 +36,13 @@ extern int cmp_idx_or_pack_name(const char *idx_or_pack_name,
 
 static size_t write_midx_header(const struct git_hash_algo *hash_algo,
 				struct hashfile *f, unsigned char num_chunks,
-				uint32_t num_packs)
+				uint32_t num_packs, int version)
 {
+	if (version != MIDX_VERSION_V1 && version != MIDX_VERSION_V2)
+		BUG("unexpected MIDX version: %d", version);
+
 	hashwrite_be32(f, MIDX_SIGNATURE);
-	hashwrite_u8(f, MIDX_VERSION);
+	hashwrite_u8(f, version);
 	hashwrite_u8(f, oid_version(hash_algo));
 	hashwrite_u8(f, num_chunks);
 	hashwrite_u8(f, 0); /* unused */
@@ -105,15 +108,29 @@ struct write_midx_context {
 
 	uint32_t preferred_pack_idx;
 
+	int version; /* must be MIDX_VERSION_V1 or _V2 */
+
 	int incremental;
 	uint32_t num_multi_pack_indexes_before;
 
+	struct multi_pack_index *compact_from;
+	struct multi_pack_index *compact_to;
+	int compact;
+
 	struct string_list *to_include;
 
 	struct repository *repo;
 	struct odb_source *source;
 };
 
+static uint32_t midx_pack_perm(struct write_midx_context *ctx,
+			       uint32_t orig_pack_int_id)
+{
+	if (ctx->compact)
+		orig_pack_int_id -= ctx->compact_from->num_packs_in_base;
+	return ctx->pack_perm[orig_pack_int_id];
+}
+
 static int should_include_pack(const struct write_midx_context *ctx,
 			       const char *file_name)
 {
@@ -257,18 +274,14 @@ static void midx_fanout_sort(struct midx_fanout *fanout)
 	QSORT(fanout->entries, fanout->nr, midx_oid_compare);
 }
 
-static void midx_fanout_add_midx_fanout(struct midx_fanout *fanout,
-					struct multi_pack_index *m,
-					uint32_t cur_fanout,
-					uint32_t preferred_pack)
+static void midx_fanout_add_midx_fanout_1(struct midx_fanout *fanout,
+					  struct multi_pack_index *m,
+					  uint32_t cur_fanout,
+					  uint32_t preferred_pack)
 {
 	uint32_t start = m->num_objects_in_base, end;
 	uint32_t cur_object;
 
-	if (m->base_midx)
-		midx_fanout_add_midx_fanout(fanout, m->base_midx, cur_fanout,
-					    preferred_pack);
-
 	if (cur_fanout)
 		start += ntohl(m->chunk_oid_fanout[cur_fanout - 1]);
 	end = m->num_objects_in_base + ntohl(m->chunk_oid_fanout[cur_fanout]);
@@ -292,6 +305,17 @@ static void midx_fanout_add_midx_fanout(struct midx_fanout *fanout,
 	}
 }
 
+static void midx_fanout_add_midx_fanout(struct midx_fanout *fanout,
+					struct multi_pack_index *m,
+					uint32_t cur_fanout,
+					uint32_t preferred_pack)
+{
+	if (m->base_midx)
+		midx_fanout_add_midx_fanout(fanout, m->base_midx, cur_fanout,
+					    preferred_pack);
+	midx_fanout_add_midx_fanout_1(fanout, m, cur_fanout, preferred_pack);
+}
+
 static void midx_fanout_add_pack_fanout(struct midx_fanout *fanout,
 					struct pack_info *info,
 					uint32_t cur_pack,
@@ -317,6 +341,45 @@ static void midx_fanout_add_pack_fanout(struct midx_fanout *fanout,
 	}
 }
 
+static void midx_fanout_add(struct midx_fanout *fanout,
+			    struct write_midx_context *ctx,
+			    uint32_t start_pack,
+			    uint32_t cur_fanout)
+{
+	uint32_t cur_pack;
+
+	if (ctx->m && !ctx->incremental)
+		midx_fanout_add_midx_fanout(fanout, ctx->m, cur_fanout,
+					    ctx->preferred_pack_idx);
+
+	for (cur_pack = start_pack; cur_pack < ctx->nr; cur_pack++) {
+		int preferred = cur_pack == ctx->preferred_pack_idx;
+		midx_fanout_add_pack_fanout(fanout, ctx->info, cur_pack,
+					    preferred, cur_fanout);
+	}
+
+	if (ctx->preferred_pack_idx != NO_PREFERRED_PACK &&
+	    ctx->preferred_pack_idx < start_pack)
+		midx_fanout_add_pack_fanout(fanout, ctx->info,
+					    ctx->preferred_pack_idx, 1,
+					    cur_fanout);
+}
+
+static void midx_fanout_add_compact(struct midx_fanout *fanout,
+				    struct write_midx_context *ctx,
+				    uint32_t cur_fanout)
+{
+	struct multi_pack_index *m = ctx->compact_to;
+
+	ASSERT(ctx->compact);
+
+	while (m && m != ctx->compact_from->base_midx) {
+		midx_fanout_add_midx_fanout_1(fanout, m, cur_fanout,
+					      NO_PREFERRED_PACK);
+		m = m->base_midx;
+	}
+}
+
 /*
  * It is possible to artificially get into a state where there are many
  * duplicate copies of objects. That can create high memory pressure if
@@ -335,6 +398,9 @@ static void compute_sorted_entries(struct write_midx_context *ctx,
 	size_t alloc_objects, total_objects = 0;
 	struct midx_fanout fanout = { 0 };
 
+	if (ctx->compact)
+		ASSERT(!start_pack);
+
 	for (cur_pack = start_pack; cur_pack < ctx->nr; cur_pack++)
 		total_objects = st_add(total_objects,
 				       ctx->info[cur_pack].p->num_objects);
@@ -353,23 +419,10 @@ static void compute_sorted_entries(struct write_midx_context *ctx,
 	for (cur_fanout = 0; cur_fanout < 256; cur_fanout++) {
 		fanout.nr = 0;
 
-		if (ctx->m && !ctx->incremental)
-			midx_fanout_add_midx_fanout(&fanout, ctx->m, cur_fanout,
-						    ctx->preferred_pack_idx);
-
-		for (cur_pack = start_pack; cur_pack < ctx->nr; cur_pack++) {
-			int preferred = cur_pack == ctx->preferred_pack_idx;
-			midx_fanout_add_pack_fanout(&fanout,
-						    ctx->info, cur_pack,
-						    preferred, cur_fanout);
-		}
-
-		if (ctx->preferred_pack_idx != NO_PREFERRED_PACK &&
-		    ctx->preferred_pack_idx < start_pack)
-			midx_fanout_add_pack_fanout(&fanout, ctx->info,
-						    ctx->preferred_pack_idx, 1,
-						    cur_fanout);
-
+		if (ctx->compact)
+			midx_fanout_add_compact(&fanout, ctx, cur_fanout);
+		else
+			midx_fanout_add(&fanout, ctx, start_pack, cur_fanout);
 		midx_fanout_sort(&fanout);
 
 		/*
@@ -410,7 +463,9 @@ static int write_midx_pack_names(struct hashfile *f, void *data)
 		if (ctx->info[i].expired)
 			continue;
 
-		if (i && strcmp(ctx->info[i].pack_name, ctx->info[i - 1].pack_name) <= 0)
+		if (ctx->version == MIDX_VERSION_V1 &&
+		    i && strcmp(ctx->info[i].pack_name,
+				ctx->info[i - 1].pack_name) <= 0)
 			BUG("incorrect pack-file order: %s before %s",
 			    ctx->info[i - 1].pack_name,
 			    ctx->info[i].pack_name);
@@ -514,12 +569,12 @@ static int write_midx_object_offsets(struct hashfile *f,
 	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *obj = list++;
 
-		if (ctx->pack_perm[obj->pack_int_id] == PACK_EXPIRED)
+		if (midx_pack_perm(ctx, obj->pack_int_id) == PACK_EXPIRED)
 			BUG("object %s is in an expired pack with int-id %d",
 			    oid_to_hex(&obj->oid),
 			    obj->pack_int_id);
 
-		hashwrite_be32(f, ctx->pack_perm[obj->pack_int_id]);
+		hashwrite_be32(f, midx_pack_perm(ctx, obj->pack_int_id));
 
 		if (ctx->large_offsets_needed && obj->offset >> 31)
 			hashwrite_be32(f, MIDX_LARGE_OFFSET_NEEDED | nr_large_offset++);
@@ -620,8 +675,8 @@ static uint32_t *midx_pack_order(struct write_midx_context *ctx)
 	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *e = &ctx->entries[i];
 		data[i].nr = i;
-		data[i].pack = ctx->pack_perm[e->pack_int_id];
-		if (!e->preferred)
+		data[i].pack = midx_pack_perm(ctx, e->pack_int_id);
+		if (!e->preferred || ctx->compact)
 			data[i].pack |= (1U << 31);
 		data[i].offset = e->offset;
 	}
@@ -630,14 +685,14 @@ static uint32_t *midx_pack_order(struct write_midx_context *ctx)
 
 	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *e = &ctx->entries[data[i].nr];
-		struct pack_info *pack = &ctx->info[ctx->pack_perm[e->pack_int_id]];
+		struct pack_info *pack = &ctx->info[midx_pack_perm(ctx, e->pack_int_id)];
 		if (pack->bitmap_pos == BITMAP_POS_UNKNOWN)
 			pack->bitmap_pos = i + base_objects;
 		pack->bitmap_nr++;
 		pack_order[i] = data[i].nr;
 	}
 	for (i = 0; i < ctx->nr; i++) {
-		struct pack_info *pack = &ctx->info[ctx->pack_perm[i]];
+		struct pack_info *pack = &ctx->info[i];
 		if (pack->bitmap_pos == BITMAP_POS_UNKNOWN)
 			pack->bitmap_pos = 0;
 	}
@@ -691,7 +746,7 @@ static void prepare_midx_packing_data(struct packing_data *pdata,
 		struct object_entry *to = packlist_alloc(pdata, &from->oid);
 
 		oe_set_in_pack(pdata, to,
-			       ctx->info[ctx->pack_perm[from->pack_int_id]].p);
+			       ctx->info[midx_pack_perm(ctx, from->pack_int_id)].p);
 	}
 
 	trace2_region_leave("midx", "prepare_midx_packing_data", ctx->repo);
@@ -900,6 +955,21 @@ static int write_midx_bitmap(struct write_midx_context *ctx,
 	return ret;
 }
 
+static int fill_pack_from_midx(struct pack_info *info,
+			       struct multi_pack_index *m,
+			       uint32_t pack_int_id)
+{
+	if (prepare_midx_pack(m, pack_int_id))
+		return error(_("could not load pack %d"), pack_int_id);
+
+	fill_pack_info(info,
+		       m->packs[pack_int_id - m->num_packs_in_base],
+		       m->pack_names[pack_int_id - m->num_packs_in_base],
+		       pack_int_id);
+
+	return 0;
+}
+
 static int fill_packs_from_midx(struct write_midx_context *ctx)
 {
 	struct multi_pack_index *m;
@@ -907,19 +977,88 @@ static int fill_packs_from_midx(struct write_midx_context *ctx)
 	for (m = ctx->m; m; m = m->base_midx) {
 		uint32_t i;
 
-		for (i = 0; i < m->num_packs; i++) {
-			if (prepare_midx_pack(m, m->num_packs_in_base + i))
-				return error(_("could not load pack"));
-
+		for (i = m->num_packs_in_base;
+		     i < m->num_packs_in_base + m->num_packs; i++) {
 			ALLOC_GROW(ctx->info, ctx->nr + 1, ctx->alloc);
-			fill_pack_info(&ctx->info[ctx->nr++], m->packs[i],
-				       m->pack_names[i],
-				       m->num_packs_in_base + i);
+
+			if (fill_pack_from_midx(&ctx->info[ctx->nr], m, i) < 0)
+				return -1;
+
+			ctx->nr++;
 		}
 	}
 	return 0;
 }
 
+static uint32_t compactible_packs_between(const struct multi_pack_index *from,
+					  const struct multi_pack_index *to)
+{
+	uint32_t nr;
+
+	ASSERT(from && to);
+
+	if (unsigned_add_overflows(to->num_packs, to->num_packs_in_base))
+		die(_("too many packs, unable to compact"));
+
+	nr = to->num_packs + to->num_packs_in_base;
+	if (nr < from->num_packs_in_base)
+		BUG("unexpected number of packs in base during compaction: "
+		    "%"PRIu32" < %"PRIu32, nr, from->num_packs_in_base);
+
+	return nr - from->num_packs_in_base;
+}
+
+static int fill_packs_from_midx_range(struct write_midx_context *ctx,
+				      int bitmap_order)
+{
+	struct multi_pack_index *m = ctx->compact_to;
+	uint32_t packs_nr;
+
+	ASSERT(ctx->compact && !ctx->nr);
+	ASSERT(ctx->compact_from);
+	ASSERT(ctx->compact_to);
+
+	packs_nr = compactible_packs_between(ctx->compact_from,
+					     ctx->compact_to);
+
+	ALLOC_GROW(ctx->info, packs_nr, ctx->alloc);
+
+	while (m != ctx->compact_from->base_midx) {
+		uint32_t pack_int_id, preferred_pack_id;
+		uint32_t i;
+
+		if (bitmap_order) {
+			if (midx_preferred_pack(m, &preferred_pack_id) < 0)
+				die(_("could not determine preferred pack"));
+		} else {
+			preferred_pack_id = m->num_packs_in_base;
+		}
+
+		pack_int_id = m->num_packs_in_base - ctx->compact_from->num_packs_in_base;
+
+		if (fill_pack_from_midx(&ctx->info[pack_int_id++], m,
+					preferred_pack_id) < 0)
+			return -1;
+
+		for (i = m->num_packs_in_base;
+		     i < m->num_packs_in_base + m->num_packs; i++) {
+			if (preferred_pack_id == i)
+				continue;
+
+			if (fill_pack_from_midx(&ctx->info[pack_int_id++], m,
+						i) < 0)
+				return -1;
+		}
+
+		ctx->nr += m->num_packs;
+		m = m->base_midx;
+	}
+
+	ASSERT(ctx->nr == packs_nr);
+
+	return 0;
+}
+
 static struct {
 	const char *non_split;
 	const char *split;
@@ -946,7 +1085,7 @@ static int link_midx_to_chain(struct multi_pack_index *m)
 	}
 
 	for (i = 0; i < ARRAY_SIZE(midx_exts); i++) {
-		const unsigned char *hash = get_midx_checksum(m);
+		const unsigned char *hash = midx_get_checksum_hash(m);
 
 		get_midx_filename_ext(m->source, &from,
 				      hash, midx_exts[i].non_split);
@@ -1025,6 +1164,12 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c
 	if (!midx_checksum_valid(midx))
 		goto out;
 
+	/*
+	 * If the version differs, we need to update.
+	 */
+	if (midx->version != ctx->version)
+		goto out;
+
 	/*
 	 * Ignore incremental updates for now. The assumption is that any
 	 * incremental update would be either empty (in which case we will bail
@@ -1033,6 +1178,9 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c
 	if (ctx->incremental)
 		goto out;
 
+	if (ctx->compact)
+		goto out; /* Compaction always requires an update. */
+
 	/*
 	 * Otherwise, we need to verify that the packs covered by the existing
 	 * MIDX match the packs that we already have. The logic to do so is way
@@ -1078,14 +1226,31 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c
 	return needed;
 }
 
-static int write_midx_internal(struct odb_source *source,
-			       struct string_list *packs_to_include,
-			       struct string_list *packs_to_drop,
-			       const char *preferred_pack_name,
-			       const char *refs_snapshot,
-			       unsigned flags)
+static int midx_hashcmp(const struct multi_pack_index *a,
+			const struct multi_pack_index *b,
+			const struct git_hash_algo *algop)
 {
-	struct repository *r = source->odb->repo;
+	return hashcmp(midx_get_checksum_hash(a), midx_get_checksum_hash(b),
+		       algop);
+}
+
+struct write_midx_opts {
+	struct odb_source *source; /* non-optional */
+
+	struct string_list *packs_to_include;
+	struct string_list *packs_to_drop;
+
+	struct multi_pack_index *compact_from;
+	struct multi_pack_index *compact_to;
+
+	const char *preferred_pack_name;
+	const char *refs_snapshot;
+	unsigned flags;
+};
+
+static int write_midx_internal(struct write_midx_opts *opts)
+{
+	struct repository *r = opts->source->odb->repo;
 	struct strbuf midx_name = STRBUF_INIT;
 	unsigned char midx_hash[GIT_MAX_RAWSZ];
 	uint32_t start_pack;
@@ -1094,6 +1259,7 @@ static int write_midx_internal(struct odb_source *source,
 	struct tempfile *incr;
 	struct write_midx_context ctx = {
 		.preferred_pack_idx = NO_PREFERRED_PACK,
+		.version = MIDX_VERSION_V2,
 	 };
 	struct multi_pack_index *midx_to_free = NULL;
 	int bitmapped_packs_concat_len = 0;
@@ -1101,27 +1267,45 @@ static int write_midx_internal(struct odb_source *source,
 	int dropped_packs = 0;
 	int result = -1;
 	const char **keep_hashes = NULL;
+	size_t keep_hashes_nr = 0;
 	struct chunkfile *cf;
 
 	trace2_region_enter("midx", "write_midx_internal", r);
 
 	ctx.repo = r;
-	ctx.source = source;
+	ctx.source = opts->source;
 
-	ctx.incremental = !!(flags & MIDX_WRITE_INCREMENTAL);
+	repo_config_get_int(ctx.repo, "midx.version", &ctx.version);
+	if (ctx.version != MIDX_VERSION_V1 && ctx.version != MIDX_VERSION_V2)
+		die(_("unknown MIDX version: %d"), ctx.version);
+
+	ctx.incremental = !!(opts->flags & MIDX_WRITE_INCREMENTAL);
+	ctx.compact = !!(opts->flags & MIDX_WRITE_COMPACT);
+
+	if (ctx.compact) {
+		if (ctx.version != MIDX_VERSION_V2)
+			die(_("cannot perform MIDX compaction with v1 format"));
+		if (!opts->compact_from)
+			BUG("expected non-NULL 'from' MIDX during compaction");
+		if (!opts->compact_to)
+			BUG("expected non-NULL 'to' MIDX during compaction");
+
+		ctx.compact_from = opts->compact_from;
+		ctx.compact_to = opts->compact_to;
+	}
 
 	if (ctx.incremental)
 		strbuf_addf(&midx_name,
 			    "%s/pack/multi-pack-index.d/tmp_midx_XXXXXX",
-			    source->path);
+			    opts->source->path);
 	else
-		get_midx_filename(source, &midx_name);
+		get_midx_filename(opts->source, &midx_name);
 	if (safe_create_leading_directories(r, midx_name.buf))
 		die_errno(_("unable to create leading directories of %s"),
 			  midx_name.buf);
 
-	if (!packs_to_include || ctx.incremental) {
-		struct multi_pack_index *m = get_multi_pack_index(source);
+	if (!opts->packs_to_include || ctx.incremental) {
+		struct multi_pack_index *m = get_multi_pack_index(opts->source);
 		if (m && !midx_checksum_valid(m)) {
 			warning(_("ignoring existing multi-pack-index; checksum mismatch"));
 			m = NULL;
@@ -1136,11 +1320,18 @@ static int write_midx_internal(struct odb_source *source,
 			 */
 			if (ctx.incremental)
 				ctx.base_midx = m;
-			else if (!packs_to_include)
+			if (!opts->packs_to_include)
 				ctx.m = m;
 		}
 	}
 
+	/*
+	 * If compacting MIDX layer(s) in the range [from, to], then the
+	 * compacted MIDX will share the same base MIDX as 'from'.
+	 */
+	if (ctx.compact)
+		ctx.base_midx = ctx.compact_from->base_midx;
+
 	ctx.nr = 0;
 	ctx.alloc = ctx.m ? ctx.m->num_packs + ctx.m->num_packs_in_base : 16;
 	ctx.info = NULL;
@@ -1149,34 +1340,42 @@ static int write_midx_internal(struct odb_source *source,
 	if (ctx.incremental) {
 		struct multi_pack_index *m = ctx.base_midx;
 		while (m) {
-			if (flags & MIDX_WRITE_BITMAP && load_midx_revindex(m)) {
+			if (opts->flags & MIDX_WRITE_BITMAP && load_midx_revindex(m)) {
 				error(_("could not load reverse index for MIDX %s"),
-				      hash_to_hex_algop(get_midx_checksum(m),
-							m->source->odb->repo->hash_algo));
+				      midx_get_checksum_hex(m));
 				goto cleanup;
 			}
 			ctx.num_multi_pack_indexes_before++;
 			m = m->base_midx;
 		}
-	} else if (ctx.m && fill_packs_from_midx(&ctx)) {
+	} else if (ctx.m && !ctx.compact && fill_packs_from_midx(&ctx)) {
 		goto cleanup;
 	}
 
 	start_pack = ctx.nr;
 
 	ctx.pack_paths_checked = 0;
-	if (flags & MIDX_PROGRESS)
+	if (opts->flags & MIDX_PROGRESS)
 		ctx.progress = start_delayed_progress(r,
 						      _("Adding packfiles to multi-pack-index"), 0);
 	else
 		ctx.progress = NULL;
 
-	ctx.to_include = packs_to_include;
+	if (ctx.compact) {
+		int bitmap_order = 0;
+		if (opts->preferred_pack_name)
+			bitmap_order |= 1;
+		else if (opts->flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP))
+			bitmap_order |= 1;
 
-	for_each_file_in_pack_dir(source->path, add_pack_to_midx, &ctx);
+		fill_packs_from_midx_range(&ctx, bitmap_order);
+	} else {
+		ctx.to_include = opts->packs_to_include;
+		for_each_file_in_pack_dir(opts->source->path, add_pack_to_midx, &ctx);
+	}
 	stop_progress(&ctx.progress);
 
-	if (!packs_to_drop) {
+	if (!opts->packs_to_drop) {
 		/*
 		 * If there is no MIDX then either it doesn't exist, or we're
 		 * doing a geometric repack. Try to load it from the source to
@@ -1189,7 +1388,7 @@ static int write_midx_internal(struct odb_source *source,
 		if (midx && !midx_needs_update(midx, &ctx)) {
 			struct bitmap_index *bitmap_git;
 			int bitmap_exists;
-			int want_bitmap = flags & MIDX_WRITE_BITMAP;
+			int want_bitmap = opts->flags & MIDX_WRITE_BITMAP;
 
 			bitmap_git = prepare_midx_bitmap_git(midx);
 			bitmap_exists = bitmap_git && bitmap_is_midx(bitmap_git);
@@ -1201,7 +1400,7 @@ static int write_midx_internal(struct odb_source *source,
 				 * corresponding bitmap (or one wasn't requested).
 				 */
 				if (!want_bitmap)
-					clear_midx_files_ext(source, "bitmap", NULL);
+					clear_midx_files_ext(ctx.source, "bitmap", NULL);
 				result = 0;
 				goto cleanup;
 			}
@@ -1216,11 +1415,11 @@ static int write_midx_internal(struct odb_source *source,
 		goto cleanup; /* nothing to do */
 	}
 
-	if (preferred_pack_name) {
+	if (opts->preferred_pack_name) {
 		ctx.preferred_pack_idx = NO_PREFERRED_PACK;
 
 		for (size_t i = 0; i < ctx.nr; i++) {
-			if (!cmp_idx_or_pack_name(preferred_pack_name,
+			if (!cmp_idx_or_pack_name(opts->preferred_pack_name,
 						  ctx.info[i].pack_name)) {
 				ctx.preferred_pack_idx = i;
 				break;
@@ -1229,9 +1428,9 @@ static int write_midx_internal(struct odb_source *source,
 
 		if (ctx.preferred_pack_idx == NO_PREFERRED_PACK)
 			warning(_("unknown preferred pack: '%s'"),
-				preferred_pack_name);
+				opts->preferred_pack_name);
 	} else if (ctx.nr &&
-		   (flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP))) {
+		   (opts->flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP))) {
 		struct packed_git *oldest = ctx.info[0].p;
 		ctx.preferred_pack_idx = 0;
 
@@ -1242,7 +1441,7 @@ static int write_midx_internal(struct odb_source *source,
 		 */
 		open_pack_index(oldest);
 
-		if (packs_to_drop && packs_to_drop->nr)
+		if (opts->packs_to_drop && opts->packs_to_drop->nr)
 			BUG("cannot write a MIDX bitmap during expiration");
 
 		/*
@@ -1302,22 +1501,30 @@ static int write_midx_internal(struct odb_source *source,
 			ctx.large_offsets_needed = 1;
 	}
 
-	QSORT(ctx.info, ctx.nr, pack_info_compare);
+	if (ctx.compact) {
+		if (ctx.version != MIDX_VERSION_V2)
+			BUG("performing MIDX compaction with v1 MIDX");
+	} else {
+		QSORT(ctx.info, ctx.nr, pack_info_compare);
+	}
 
-	if (packs_to_drop && packs_to_drop->nr) {
+	if (opts->packs_to_drop && opts->packs_to_drop->nr) {
 		size_t drop_index = 0;
 		int missing_drops = 0;
 
-		for (size_t i = 0; i < ctx.nr && drop_index < packs_to_drop->nr; i++) {
+		ASSERT(!ctx.compact);
+
+		for (size_t i = 0;
+		     i < ctx.nr && drop_index < opts->packs_to_drop->nr; i++) {
 			int cmp = strcmp(ctx.info[i].pack_name,
-					 packs_to_drop->items[drop_index].string);
+					 opts->packs_to_drop->items[drop_index].string);
 
 			if (!cmp) {
 				drop_index++;
 				ctx.info[i].expired = 1;
 			} else if (cmp > 0) {
 				error(_("did not see pack-file %s to drop"),
-				      packs_to_drop->items[drop_index].string);
+				      opts->packs_to_drop->items[drop_index].string);
 				drop_index++;
 				missing_drops++;
 				i--;
@@ -1338,12 +1545,20 @@ static int write_midx_internal(struct odb_source *source,
 	 */
 	ALLOC_ARRAY(ctx.pack_perm, ctx.nr);
 	for (size_t i = 0; i < ctx.nr; i++) {
+		uint32_t from = ctx.info[i].orig_pack_int_id;
+		uint32_t to;
+
 		if (ctx.info[i].expired) {
+			to = PACK_EXPIRED;
 			dropped_packs++;
-			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = PACK_EXPIRED;
 		} else {
-			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = i - dropped_packs;
+			to = i - dropped_packs;
 		}
+
+		if (ctx.compact)
+			from -= ctx.compact_from->num_packs_in_base;
+
+		ctx.pack_perm[from] = to;
 	}
 
 	for (size_t i = 0; i < ctx.nr; i++) {
@@ -1354,16 +1569,16 @@ static int write_midx_internal(struct odb_source *source,
 	}
 
 	/* Check that the preferred pack wasn't expired (if given). */
-	if (preferred_pack_name) {
-		struct pack_info *preferred = bsearch(preferred_pack_name,
+	if (opts->preferred_pack_name) {
+		struct pack_info *preferred = bsearch(opts->preferred_pack_name,
 						      ctx.info, ctx.nr,
 						      sizeof(*ctx.info),
 						      idx_or_pack_name_cmp);
 		if (preferred) {
-			uint32_t perm = ctx.pack_perm[preferred->orig_pack_int_id];
+			uint32_t perm = midx_pack_perm(&ctx, preferred->orig_pack_int_id);
 			if (perm == PACK_EXPIRED)
 				warning(_("preferred pack '%s' is expired"),
-					preferred_pack_name);
+					opts->preferred_pack_name);
 		}
 	}
 
@@ -1377,15 +1592,15 @@ static int write_midx_internal(struct odb_source *source,
 	}
 
 	if (!ctx.entries_nr) {
-		if (flags & MIDX_WRITE_BITMAP)
+		if (opts->flags & MIDX_WRITE_BITMAP)
 			warning(_("refusing to write multi-pack .bitmap without any objects"));
-		flags &= ~(MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP);
+		opts->flags &= ~(MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP);
 	}
 
 	if (ctx.incremental) {
 		struct strbuf lock_name = STRBUF_INIT;
 
-		get_midx_chain_filename(source, &lock_name);
+		get_midx_chain_filename(opts->source, &lock_name);
 		hold_lock_file_for_update(&lk, lock_name.buf, LOCK_DIE_ON_ERROR);
 		strbuf_release(&lock_name);
 
@@ -1428,7 +1643,7 @@ static int write_midx_internal(struct odb_source *source,
 				MIDX_CHUNK_LARGE_OFFSET_WIDTH),
 			write_midx_large_offsets);
 
-	if (flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP)) {
+	if (opts->flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP)) {
 		ctx.pack_order = midx_pack_order(&ctx);
 		add_chunk(cf, MIDX_CHUNKID_REVINDEX,
 			  st_mult(ctx.entries_nr, sizeof(uint32_t)),
@@ -1439,18 +1654,18 @@ static int write_midx_internal(struct odb_source *source,
 	}
 
 	write_midx_header(r->hash_algo, f, get_num_chunks(cf),
-			  ctx.nr - dropped_packs);
+			  ctx.nr - dropped_packs, ctx.version);
 	write_chunkfile(cf, &ctx);
 
 	finalize_hashfile(f, midx_hash, FSYNC_COMPONENT_PACK_METADATA,
 			  CSUM_FSYNC | CSUM_HASH_IN_STREAM);
 	free_chunkfile(cf);
 
-	if (flags & MIDX_WRITE_REV_INDEX &&
+	if (opts->flags & MIDX_WRITE_REV_INDEX &&
 	    git_env_bool("GIT_TEST_MIDX_WRITE_REV", 0))
 		write_midx_reverse_index(&ctx, midx_hash);
 
-	if (flags & MIDX_WRITE_BITMAP) {
+	if (opts->flags & MIDX_WRITE_BITMAP) {
 		struct packing_data pdata;
 		struct commit_stack commits = COMMIT_STACK_INIT;
 
@@ -1459,7 +1674,7 @@ static int write_midx_internal(struct odb_source *source,
 
 		prepare_midx_packing_data(&pdata, &ctx);
 
-		find_commits_for_midx_bitmap(&commits, refs_snapshot, &ctx);
+		find_commits_for_midx_bitmap(&commits, opts->refs_snapshot, &ctx);
 
 		/*
 		 * The previous steps translated the information from
@@ -1470,8 +1685,8 @@ static int write_midx_internal(struct odb_source *source,
 		FREE_AND_NULL(ctx.entries);
 		ctx.entries_nr = 0;
 
-		if (write_midx_bitmap(&ctx, midx_hash, &pdata,
-				      commits.items, commits.nr, flags) < 0) {
+		if (write_midx_bitmap(&ctx, midx_hash, &pdata, commits.items,
+				      commits.nr, opts->flags) < 0) {
 			error(_("could not write multi-pack bitmap"));
 			clear_packing_data(&pdata);
 			commit_stack_clear(&commits);
@@ -1489,7 +1704,24 @@ static int write_midx_internal(struct odb_source *source,
 	if (ctx.num_multi_pack_indexes_before == UINT32_MAX)
 		die(_("too many multi-pack-indexes"));
 
-	CALLOC_ARRAY(keep_hashes, ctx.num_multi_pack_indexes_before + 1);
+	if (ctx.compact) {
+		struct multi_pack_index *m;
+
+		/*
+		 * Keep all MIDX layers excluding those in the range [from, to].
+		 */
+		for (m = ctx.base_midx; m; m = m->base_midx)
+			keep_hashes_nr++;
+		for (m = ctx.m;
+		     m && midx_hashcmp(m, ctx.compact_to, r->hash_algo);
+		     m = m->base_midx)
+			keep_hashes_nr++;
+
+		keep_hashes_nr++; /* include the compacted layer */
+	} else {
+		keep_hashes_nr = ctx.num_multi_pack_indexes_before + 1;
+	}
+	CALLOC_ARRAY(keep_hashes, keep_hashes_nr);
 
 	if (ctx.incremental) {
 		FILE *chainf = fdopen_lock_file(&lk, "w");
@@ -1504,7 +1736,7 @@ static int write_midx_internal(struct odb_source *source,
 		if (link_midx_to_chain(ctx.base_midx) < 0)
 			goto cleanup;
 
-		get_split_midx_filename_ext(source, &final_midx_name,
+		get_split_midx_filename_ext(opts->source, &final_midx_name,
 					    midx_hash, MIDX_EXT_MIDX);
 
 		if (rename_tempfile(&incr, final_midx_name.buf) < 0) {
@@ -1514,18 +1746,47 @@ static int write_midx_internal(struct odb_source *source,
 
 		strbuf_release(&final_midx_name);
 
-		keep_hashes[ctx.num_multi_pack_indexes_before] =
-			xstrdup(hash_to_hex_algop(midx_hash, r->hash_algo));
+		if (ctx.compact) {
+			struct multi_pack_index *m;
+			uint32_t num_layers_before_from = 0;
+			uint32_t i;
+
+			for (m = ctx.base_midx; m; m = m->base_midx)
+				num_layers_before_from++;
+
+			m = ctx.base_midx;
+			for (i = 0; i < num_layers_before_from; i++) {
+				uint32_t j = num_layers_before_from - i - 1;
 
-		for (uint32_t i = 0; i < ctx.num_multi_pack_indexes_before; i++) {
-			uint32_t j = ctx.num_multi_pack_indexes_before - i - 1;
+				keep_hashes[j] = xstrdup(midx_get_checksum_hex(m));
+				m = m->base_midx;
+			}
 
-			keep_hashes[j] = xstrdup(hash_to_hex_algop(get_midx_checksum(m),
+			keep_hashes[i] = xstrdup(hash_to_hex_algop(midx_hash,
 								   r->hash_algo));
-			m = m->base_midx;
+
+			i = 0;
+			for (m = ctx.m;
+			     m && midx_hashcmp(m, ctx.compact_to, r->hash_algo);
+			     m = m->base_midx) {
+				keep_hashes[keep_hashes_nr - i - 1] =
+					xstrdup(midx_get_checksum_hex(m));
+				i++;
+			}
+		} else {
+			keep_hashes[ctx.num_multi_pack_indexes_before] =
+				xstrdup(hash_to_hex_algop(midx_hash,
+							  r->hash_algo));
+
+			for (uint32_t i = 0; i < ctx.num_multi_pack_indexes_before; i++) {
+				uint32_t j = ctx.num_multi_pack_indexes_before - i - 1;
+
+				keep_hashes[j] = xstrdup(midx_get_checksum_hex(m));
+				m = m->base_midx;
+			}
 		}
 
-		for (uint32_t i = 0; i <= ctx.num_multi_pack_indexes_before; i++)
+		for (uint32_t i = 0; i < keep_hashes_nr; i++)
 			fprintf(get_lock_file_fp(&lk), "%s\n", keep_hashes[i]);
 	} else {
 		keep_hashes[ctx.num_multi_pack_indexes_before] =
@@ -1538,8 +1799,7 @@ static int write_midx_internal(struct odb_source *source,
 	if (commit_lock_file(&lk) < 0)
 		die_errno(_("could not write multi-pack-index"));
 
-	clear_midx_files(source, keep_hashes,
-			 ctx.num_multi_pack_indexes_before + 1,
+	clear_midx_files(opts->source, keep_hashes, keep_hashes_nr,
 			 ctx.incremental);
 	result = 0;
 
@@ -1557,7 +1817,7 @@ static int write_midx_internal(struct odb_source *source,
 	free(ctx.pack_perm);
 	free(ctx.pack_order);
 	if (keep_hashes) {
-		for (uint32_t i = 0; i <= ctx.num_multi_pack_indexes_before; i++)
+		for (uint32_t i = 0; i < keep_hashes_nr; i++)
 			free((char *)keep_hashes[i]);
 		free(keep_hashes);
 	}
@@ -1573,9 +1833,14 @@ int write_midx_file(struct odb_source *source,
 		    const char *preferred_pack_name,
 		    const char *refs_snapshot, unsigned flags)
 {
-	return write_midx_internal(source, NULL, NULL,
-				   preferred_pack_name, refs_snapshot,
-				   flags);
+	struct write_midx_opts opts = {
+		.source = source,
+		.preferred_pack_name = preferred_pack_name,
+		.refs_snapshot = refs_snapshot,
+		.flags = flags,
+	};
+
+	return write_midx_internal(&opts);
 }
 
 int write_midx_file_only(struct odb_source *source,
@@ -1583,8 +1848,30 @@ int write_midx_file_only(struct odb_source *source,
 			 const char *preferred_pack_name,
 			 const char *refs_snapshot, unsigned flags)
 {
-	return write_midx_internal(source, packs_to_include, NULL,
-				   preferred_pack_name, refs_snapshot, flags);
+	struct write_midx_opts opts = {
+		.source = source,
+		.packs_to_include = packs_to_include,
+		.preferred_pack_name = preferred_pack_name,
+		.refs_snapshot = refs_snapshot,
+		.flags = flags,
+	};
+
+	return write_midx_internal(&opts);
+}
+
+int write_midx_file_compact(struct odb_source *source,
+			    struct multi_pack_index *from,
+			    struct multi_pack_index *to,
+			    unsigned flags)
+{
+	struct write_midx_opts opts = {
+		.source = source,
+		.compact_from = from,
+		.compact_to = to,
+		.flags = flags | MIDX_WRITE_COMPACT,
+	};
+
+	return write_midx_internal(&opts);
 }
 
 int expire_midx_packs(struct odb_source *source, unsigned flags)
@@ -1643,9 +1930,14 @@ int expire_midx_packs(struct odb_source *source, unsigned flags)
 
 	free(count);
 
-	if (packs_to_drop.nr)
-		result = write_midx_internal(source, NULL,
-					     &packs_to_drop, NULL, NULL, flags);
+	if (packs_to_drop.nr) {
+		struct write_midx_opts opts = {
+			.source = source,
+			.packs_to_drop = &packs_to_drop,
+			.flags = flags & MIDX_PROGRESS,
+		};
+		result = write_midx_internal(&opts);
+	}
 
 	string_list_clear(&packs_to_drop, 0);
 
@@ -1778,6 +2070,10 @@ int midx_repack(struct odb_source *source, size_t batch_size, unsigned flags)
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	FILE *cmd_in;
 	struct multi_pack_index *m = get_multi_pack_index(source);
+	struct write_midx_opts opts = {
+		.source = source,
+		.flags = flags,
+	};
 
 	/*
 	 * When updating the default for these configuration
@@ -1852,8 +2148,7 @@ int midx_repack(struct odb_source *source, size_t batch_size, unsigned flags)
 		goto cleanup;
 	}
 
-	result = write_midx_internal(source, NULL, NULL, NULL, NULL,
-				     flags);
+	result = write_midx_internal(&opts);
 
 cleanup:
 	free(include_pack);
diff --git a/midx.c b/midx.c
index ab8e2611d1fe58..81d6ab11e6eb0e 100644
--- a/midx.c
+++ b/midx.c
@@ -24,7 +24,13 @@ void clear_incremental_midx_files_ext(struct odb_source *source, const char *ext
 int cmp_idx_or_pack_name(const char *idx_or_pack_name,
 			 const char *idx_name);
 
-const unsigned char *get_midx_checksum(struct multi_pack_index *m)
+const char *midx_get_checksum_hex(const struct multi_pack_index *m)
+{
+	return hash_to_hex_algop(midx_get_checksum_hash(m),
+				 m->source->odb->repo->hash_algo);
+}
+
+const unsigned char *midx_get_checksum_hash(const struct multi_pack_index *m)
 {
 	return m->data + m->data_len - m->source->odb->repo->hash_algo->rawsz;
 }
@@ -144,7 +150,7 @@ static struct multi_pack_index *load_multi_pack_index_one(struct odb_source *sou
 		      m->signature, MIDX_SIGNATURE);
 
 	m->version = m->data[MIDX_BYTE_FILE_VERSION];
-	if (m->version != MIDX_VERSION)
+	if (m->version != MIDX_VERSION_V1 && m->version != MIDX_VERSION_V2)
 		die(_("multi-pack-index version %d not recognized"),
 		      m->version);
 
@@ -205,7 +211,8 @@ static struct multi_pack_index *load_multi_pack_index_one(struct odb_source *sou
 			die(_("multi-pack-index pack-name chunk is too short"));
 		cur_pack_name = end + 1;
 
-		if (i && strcmp(m->pack_names[i], m->pack_names[i - 1]) <= 0)
+		if (m->version == MIDX_VERSION_V1 &&
+		    i && strcmp(m->pack_names[i], m->pack_names[i - 1]) <= 0)
 			die(_("multi-pack-index pack names out of order: '%s' before '%s'"),
 			      m->pack_names[i - 1],
 			      m->pack_names[i]);
@@ -406,6 +413,7 @@ void close_midx(struct multi_pack_index *m)
 	}
 	FREE_AND_NULL(m->packs);
 	FREE_AND_NULL(m->pack_names);
+	FREE_AND_NULL(m->pack_names_sorted);
 	free(m);
 }
 
@@ -651,17 +659,40 @@ int cmp_idx_or_pack_name(const char *idx_or_pack_name,
 	return strcmp(idx_or_pack_name, idx_name);
 }
 
+
+static int midx_pack_names_cmp(const void *a, const void *b, void *m_)
+{
+	struct multi_pack_index *m = m_;
+	return strcmp(m->pack_names[*(const size_t *)a],
+		      m->pack_names[*(const size_t *)b]);
+}
+
 static int midx_contains_pack_1(struct multi_pack_index *m,
 				const char *idx_or_pack_name)
 {
 	uint32_t first = 0, last = m->num_packs;
 
+	if (m->version == MIDX_VERSION_V2 && !m->pack_names_sorted) {
+		uint32_t i;
+
+		ALLOC_ARRAY(m->pack_names_sorted, m->num_packs);
+
+		for (i = 0; i < m->num_packs; i++)
+			m->pack_names_sorted[i] = i;
+
+		QSORT_S(m->pack_names_sorted, m->num_packs, midx_pack_names_cmp,
+			m);
+	}
+
 	while (first < last) {
 		uint32_t mid = first + (last - first) / 2;
 		const char *current;
 		int cmp;
 
-		current = m->pack_names[mid];
+		if (m->pack_names_sorted)
+			current = m->pack_names[m->pack_names_sorted[mid]];
+		else
+			current = m->pack_names[mid];
 		cmp = cmp_idx_or_pack_name(idx_or_pack_name, current);
 		if (!cmp)
 			return 1;
diff --git a/midx.h b/midx.h
index 6e54d73503d560..08f3728e5204b8 100644
--- a/midx.h
+++ b/midx.h
@@ -11,7 +11,8 @@ struct git_hash_algo;
 struct odb_source;
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
-#define MIDX_VERSION 1
+#define MIDX_VERSION_V1 1
+#define MIDX_VERSION_V2 2
 #define MIDX_BYTE_FILE_VERSION 4
 #define MIDX_BYTE_HASH_VERSION 5
 #define MIDX_BYTE_NUM_CHUNKS 6
@@ -71,6 +72,7 @@ struct multi_pack_index {
 	uint32_t num_packs_in_base;
 
 	const char **pack_names;
+	size_t *pack_names_sorted;
 	struct packed_git **packs;
 };
 
@@ -80,12 +82,14 @@ struct multi_pack_index {
 #define MIDX_WRITE_BITMAP_HASH_CACHE (1 << 3)
 #define MIDX_WRITE_BITMAP_LOOKUP_TABLE (1 << 4)
 #define MIDX_WRITE_INCREMENTAL (1 << 5)
+#define MIDX_WRITE_COMPACT (1 << 6)
 
 #define MIDX_EXT_REV "rev"
 #define MIDX_EXT_BITMAP "bitmap"
 #define MIDX_EXT_MIDX "midx"
 
-const unsigned char *get_midx_checksum(struct multi_pack_index *m);
+const char *midx_get_checksum_hex(const struct multi_pack_index *m) /* static buffer */;
+const unsigned char *midx_get_checksum_hash(const struct multi_pack_index *m);
 void get_midx_filename(struct odb_source *source, struct strbuf *out);
 void get_midx_filename_ext(struct odb_source *source, struct strbuf *out,
 			   const unsigned char *hash, const char *ext);
@@ -128,6 +132,10 @@ int write_midx_file_only(struct odb_source *source,
 			 struct string_list *packs_to_include,
 			 const char *preferred_pack_name,
 			 const char *refs_snapshot, unsigned flags);
+int write_midx_file_compact(struct odb_source *source,
+			    struct multi_pack_index *from,
+			    struct multi_pack_index *to,
+			    unsigned flags);
 void clear_midx_file(struct repository *r);
 int verify_midx_file(struct odb_source *source, unsigned flags);
 int expire_midx_packs(struct odb_source *source, unsigned flags);
diff --git a/object-file.c b/object-file.c
index c62e5496e0795d..f0b029ff0b2cb0 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1868,6 +1868,64 @@ int odb_source_loose_for_each_object(struct odb_source *source,
 					     NULL, NULL, &data);
 }
 
+static int count_loose_object(const struct object_id *oid UNUSED,
+			      struct object_info *oi UNUSED,
+			      void *payload)
+{
+	unsigned long *count = payload;
+	(*count)++;
+	return 0;
+}
+
+int odb_source_loose_count_objects(struct odb_source *source,
+				   enum odb_count_objects_flags flags,
+				   unsigned long *out)
+{
+	const unsigned hexsz = source->odb->repo->hash_algo->hexsz - 2;
+	char *path = NULL;
+	DIR *dir = NULL;
+	int ret;
+
+	if (flags & ODB_COUNT_OBJECTS_APPROXIMATE) {
+		unsigned long count = 0;
+		struct dirent *ent;
+
+		path = xstrfmt("%s/17", source->path);
+
+		dir = opendir(path);
+		if (!dir) {
+			if (errno == ENOENT) {
+				*out = 0;
+				ret = 0;
+				goto out;
+			}
+
+			ret = error_errno("cannot open object shard '%s'", path);
+			goto out;
+		}
+
+		while ((ent = readdir(dir)) != NULL) {
+			if (strspn(ent->d_name, "0123456789abcdef") != hexsz ||
+			    ent->d_name[hexsz] != '\0')
+				continue;
+			count++;
+		}
+
+		*out = count * 256;
+		ret = 0;
+	} else {
+		*out = 0;
+		ret = odb_source_loose_for_each_object(source, NULL, count_loose_object,
+						       out, 0);
+	}
+
+out:
+	if (dir)
+		closedir(dir);
+	free(path);
+	return ret;
+}
+
 static int append_loose_object(const struct object_id *oid,
 			       const char *path UNUSED,
 			       void *data)
diff --git a/object-file.h b/object-file.h
index ff6da6529640dc..f8d8805a18cc8c 100644
--- a/object-file.h
+++ b/object-file.h
@@ -139,6 +139,20 @@ int odb_source_loose_for_each_object(struct odb_source *source,
 				     void *cb_data,
 				     unsigned flags);
 
+/*
+ * Count the number of loose objects in this source.
+ *
+ * The object count is approximated by opening a single sharding directory for
+ * loose objects and scanning its contents. The result is then extrapolated by
+ * 256. This should generally work as a reasonable estimate given that the
+ * object hash is supposed to be indistinguishable from random.
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
+int odb_source_loose_count_objects(struct odb_source *source,
+				   enum odb_count_objects_flags flags,
+				   unsigned long *out);
+
 /**
  * format_object_header() is a thin wrapper around s xsnprintf() that
  * writes the initial "<type> <obj-len>" part of the loose object
diff --git a/object-name.c b/object-name.c
index 7b14c3bf9b9b48..e5adec4c9d5084 100644
--- a/object-name.c
+++ b/object-name.c
@@ -837,7 +837,11 @@ int repo_find_unique_abbrev_r(struct repository *r, char *hex,
 	const unsigned hexsz = algo->hexsz;
 
 	if (len < 0) {
-		unsigned long count = repo_approximate_object_count(r);
+		unsigned long count;
+
+		if (odb_count_objects(r->objects, ODB_COUNT_OBJECTS_APPROXIMATE, &count) < 0)
+			count = 0;
+
 		/*
 		 * Add one because the MSB only tells us the highest bit set,
 		 * not including the value of all the _other_ bits (so "15"
diff --git a/odb.c b/odb.c
index 84a31084d3884b..350e23f3c0798d 100644
--- a/odb.c
+++ b/odb.c
@@ -917,6 +917,41 @@ int odb_for_each_object(struct object_database *odb,
 	return 0;
 }
 
+int odb_count_objects(struct object_database *odb,
+		      enum odb_count_objects_flags flags,
+		      unsigned long *out)
+{
+	struct odb_source *source;
+	unsigned long count = 0;
+	int ret;
+
+	if (odb->object_count_valid && odb->object_count_flags == flags) {
+		*out = odb->object_count;
+		return 0;
+	}
+
+	odb_prepare_alternates(odb);
+	for (source = odb->sources; source; source = source->next) {
+		unsigned long c;
+
+		ret = odb_source_count_objects(source, flags, &c);
+		if (ret < 0)
+			goto out;
+
+		count += c;
+	}
+
+	odb->object_count = count;
+	odb->object_count_valid = 1;
+	odb->object_count_flags = flags;
+
+	*out = count;
+	ret = 0;
+
+out:
+	return ret;
+}
+
 void odb_assert_oid_type(struct object_database *odb,
 			 const struct object_id *oid, enum object_type expect)
 {
@@ -1030,7 +1065,7 @@ void odb_reprepare(struct object_database *o)
 	for (source = o->sources; source; source = source->next)
 		odb_source_reprepare(source);
 
-	o->approximate_object_count_valid = 0;
+	o->object_count_valid = 0;
 
 	obj_read_unlock();
 }
diff --git a/odb.h b/odb.h
index 86e0365c243863..9aee260105ae54 100644
--- a/odb.h
+++ b/odb.h
@@ -3,7 +3,6 @@
 
 #include "hashmap.h"
 #include "object.h"
-#include "odb/source.h"
 #include "oidset.h"
 #include "oidmap.h"
 #include "string-list.h"
@@ -12,6 +11,7 @@
 struct oidmap;
 struct oidtree;
 struct strbuf;
+struct strvec;
 struct repository;
 struct multi_pack_index;
 
@@ -110,10 +110,11 @@ struct object_database {
 	/*
 	 * A fast, rough count of the number of objects in the repository.
 	 * These two fields are not meant for direct access. Use
-	 * repo_approximate_object_count() instead.
+	 * odb_count_objects() instead.
 	 */
-	unsigned long approximate_object_count;
-	unsigned approximate_object_count_valid : 1;
+	unsigned long object_count;
+	unsigned object_count_flags;
+	unsigned object_count_valid : 1;
 
 	/*
 	 * Submodule source paths that will be added as additional sources to
@@ -339,6 +340,42 @@ struct object_info {
  */
 #define OBJECT_INFO_INIT { 0 }
 
+/* Flags that can be passed to `odb_read_object_info_extended()`. */
+enum object_info_flags {
+	/* Invoke lookup_replace_object() on the given hash. */
+	OBJECT_INFO_LOOKUP_REPLACE = (1 << 0),
+
+	/* Do not reprepare object sources when the first lookup has failed. */
+	OBJECT_INFO_QUICK = (1 << 1),
+
+	/*
+	 * Do not attempt to fetch the object if missing (even if fetch_is_missing is
+	 * nonzero).
+	 */
+	OBJECT_INFO_SKIP_FETCH_OBJECT = (1 << 2),
+
+	/* Die if object corruption (not just an object being missing) was detected. */
+	OBJECT_INFO_DIE_IF_CORRUPT = (1 << 3),
+
+	/*
+	 * We have already tried reading the object, but it couldn't be found
+	 * via any of the attached sources, and are now doing a second read.
+	 * This second read asks the individual sources to also evaluate
+	 * whether any on-disk state may have changed that may have caused the
+	 * object to appear.
+	 *
+	 * This flag is for internal use, only. The second read only occurs
+	 * when `OBJECT_INFO_QUICK` was not passed.
+	 */
+	OBJECT_INFO_SECOND_READ = (1 << 4),
+
+	/*
+	 * This is meant for bulk prefetching of missing blobs in a partial
+	 * clone. Implies OBJECT_INFO_SKIP_FETCH_OBJECT and OBJECT_INFO_QUICK.
+	 */
+	OBJECT_INFO_FOR_PREFETCH = (OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_QUICK),
+};
+
 /*
  * Read object info from the object database and populate the `object_info`
  * structure. Returns 0 on success, a negative error code otherwise.
@@ -432,6 +469,18 @@ enum odb_for_each_object_flags {
 	ODB_FOR_EACH_OBJECT_SKIP_ON_DISK_KEPT_PACKS = (1<<4),
 };
 
+/*
+ * A callback function that can be used to iterate through objects. If given,
+ * the optional `oi` parameter will be populated the same as if you would call
+ * `odb_read_object_info()`.
+ *
+ * Returning a non-zero error code will cause iteration to abort. The error
+ * code will be propagated.
+ */
+typedef int (*odb_for_each_object_cb)(const struct object_id *oid,
+				      struct object_info *oi,
+				      void *cb_data);
+
 /*
  * Iterate through all objects contained in the object database. Note that
  * objects may be iterated over multiple times in case they are either stored
@@ -452,6 +501,27 @@ int odb_for_each_object(struct object_database *odb,
 			void *cb_data,
 			unsigned flags);
 
+enum odb_count_objects_flags {
+	/*
+	 * Instead of providing an accurate count, allow the number of objects
+	 * to be approximated. Details of how this approximation works are
+	 * subject to the specific source's implementation.
+	 */
+	ODB_COUNT_OBJECTS_APPROXIMATE = (1 << 0),
+};
+
+/*
+ * Count the number of objects in the given object database. This object count
+ * may double-count objects that are stored in multiple backends, or which are
+ * stored multiple times in a single backend.
+ *
+ * Returns 0 on success, a negative error code otherwise. The number of objects
+ * will be assigned to the `out` pointer on success.
+ */
+int odb_count_objects(struct object_database *odb,
+		      enum odb_count_objects_flags flags,
+		      unsigned long *out);
+
 enum {
 	/*
 	 * By default, `odb_write_object()` does not actually write anything
diff --git a/odb/source-files.c b/odb/source-files.c
index 14cb9adecadd99..c08d8993e378a0 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -93,6 +93,35 @@ static int odb_source_files_for_each_object(struct odb_source *source,
 	return 0;
 }
 
+static int odb_source_files_count_objects(struct odb_source *source,
+					  enum odb_count_objects_flags flags,
+					  unsigned long *out)
+{
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	unsigned long count;
+	int ret;
+
+	ret = packfile_store_count_objects(files->packed, flags, &count);
+	if (ret < 0)
+		goto out;
+
+	if (!(flags & ODB_COUNT_OBJECTS_APPROXIMATE)) {
+		unsigned long loose_count;
+
+		ret = odb_source_loose_count_objects(source, flags, &loose_count);
+		if (ret < 0)
+			goto out;
+
+		count += loose_count;
+	}
+
+	*out = count;
+	ret = 0;
+
+out:
+	return ret;
+}
+
 static int odb_source_files_freshen_object(struct odb_source *source,
 					   const struct object_id *oid)
 {
@@ -220,6 +249,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->base.read_object_info = odb_source_files_read_object_info;
 	files->base.read_object_stream = odb_source_files_read_object_stream;
 	files->base.for_each_object = odb_source_files_for_each_object;
+	files->base.count_objects = odb_source_files_count_objects;
 	files->base.freshen_object = odb_source_files_freshen_object;
 	files->base.write_object = odb_source_files_write_object;
 	files->base.write_object_stream = odb_source_files_write_object_stream;
diff --git a/odb/source.h b/odb/source.h
index caac5581495ece..96c906e7a1b350 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -2,6 +2,7 @@
 #define ODB_SOURCE_H
 
 #include "object.h"
+#include "odb.h"
 
 enum odb_source_type {
 	/*
@@ -14,61 +15,10 @@ enum odb_source_type {
 	ODB_SOURCE_FILES,
 };
 
-/* Flags that can be passed to `odb_read_object_info_extended()`. */
-enum object_info_flags {
-	/* Invoke lookup_replace_object() on the given hash. */
-	OBJECT_INFO_LOOKUP_REPLACE = (1 << 0),
-
-	/* Do not reprepare object sources when the first lookup has failed. */
-	OBJECT_INFO_QUICK = (1 << 1),
-
-	/*
-	 * Do not attempt to fetch the object if missing (even if fetch_is_missing is
-	 * nonzero).
-	 */
-	OBJECT_INFO_SKIP_FETCH_OBJECT = (1 << 2),
-
-	/* Die if object corruption (not just an object being missing) was detected. */
-	OBJECT_INFO_DIE_IF_CORRUPT = (1 << 3),
-
-	/*
-	 * We have already tried reading the object, but it couldn't be found
-	 * via any of the attached sources, and are now doing a second read.
-	 * This second read asks the individual sources to also evaluate
-	 * whether any on-disk state may have changed that may have caused the
-	 * object to appear.
-	 *
-	 * This flag is for internal use, only. The second read only occurs
-	 * when `OBJECT_INFO_QUICK` was not passed.
-	 */
-	OBJECT_INFO_SECOND_READ = (1 << 4),
-
-	/*
-	 * This is meant for bulk prefetching of missing blobs in a partial
-	 * clone. Implies OBJECT_INFO_SKIP_FETCH_OBJECT and OBJECT_INFO_QUICK.
-	 */
-	OBJECT_INFO_FOR_PREFETCH = (OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_QUICK),
-};
-
 struct object_id;
-struct object_info;
 struct odb_read_stream;
-struct odb_transaction;
-struct odb_write_stream;
 struct strvec;
 
-/*
- * A callback function that can be used to iterate through objects. If given,
- * the optional `oi` parameter will be populated the same as if you would call
- * `odb_read_object_info()`.
- *
- * Returning a non-zero error code will cause iteration to abort. The error
- * code will be propagated.
- */
-typedef int (*odb_for_each_object_cb)(const struct object_id *oid,
-				      struct object_info *oi,
-				      void *cb_data);
-
 /*
  * The source is the part of the object database that stores the actual
  * objects. It thus encapsulates the logic to read and write the specific
@@ -192,6 +142,21 @@ struct odb_source {
 			       void *cb_data,
 			       unsigned flags);
 
+	/*
+	 * This callback is expected to count objects in the given object
+	 * database source. The callback function does not have to guarantee
+	 * that only unique objects are counted. The result shall be assigned
+	 * to the `out` pointer.
+	 *
+	 * Accepts `enum odb_count_objects_flag` flags to alter the behaviour.
+	 *
+	 * The callback is expected to return 0 on success, or a negative error
+	 * code otherwise.
+	 */
+	int (*count_objects)(struct odb_source *source,
+			     enum odb_count_objects_flags flags,
+			     unsigned long *out);
+
 	/*
 	 * This callback is expected to freshen the given object so that its
 	 * last access time is set to the current time. This is used to ensure
@@ -383,6 +348,18 @@ static inline int odb_source_for_each_object(struct odb_source *source,
 	return source->for_each_object(source, request, cb, cb_data, flags);
 }
 
+/*
+ * Count the number of objects in the given object database source.
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
+static inline int odb_source_count_objects(struct odb_source *source,
+					   enum odb_count_objects_flags flags,
+					   unsigned long *out)
+{
+	return source->count_objects(source, flags, out);
+}
+
 /*
  * Freshen an object in the object database by updating its timestamp.
  * Returns 1 in case the object has been freshened, 0 in case the object does
diff --git a/odb/streaming.c b/odb/streaming.c
index a4355cd2458c38..5927a12954ba59 100644
--- a/odb/streaming.c
+++ b/odb/streaming.c
@@ -7,6 +7,7 @@
 #include "environment.h"
 #include "repository.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "odb/streaming.h"
 #include "replace-object.h"
 
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 22419bfb33dd4e..f6ec18d83afe21 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -441,11 +441,11 @@ char *midx_bitmap_filename(struct multi_pack_index *midx)
 	struct strbuf buf = STRBUF_INIT;
 	if (midx->has_chain)
 		get_split_midx_filename_ext(midx->source, &buf,
-					    get_midx_checksum(midx),
+					    midx_get_checksum_hash(midx),
 					    MIDX_EXT_BITMAP);
 	else
 		get_midx_filename_ext(midx->source, &buf,
-				      get_midx_checksum(midx),
+				      midx_get_checksum_hash(midx),
 				      MIDX_EXT_BITMAP);
 
 	return strbuf_detach(&buf, NULL);
@@ -502,7 +502,7 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	if (load_bitmap_header(bitmap_git) < 0)
 		goto cleanup;
 
-	if (!hasheq(get_midx_checksum(bitmap_git->midx), bitmap_git->checksum,
+	if (!hasheq(midx_get_checksum_hash(bitmap_git->midx), bitmap_git->checksum,
 		    bitmap_repo(bitmap_git)->hash_algo)) {
 		error(_("checksum doesn't match in MIDX and bitmap"));
 		goto cleanup;
@@ -2819,8 +2819,7 @@ void test_bitmap_walk(struct rev_info *revs)
 
 		if (bitmap_is_midx(found))
 			fprintf_ln(stderr, "Located via MIDX '%s'.",
-				   hash_to_hex_algop(get_midx_checksum(found->midx),
-						     revs->repo->hash_algo));
+				   midx_get_checksum_hex(found->midx));
 		else
 			fprintf_ln(stderr, "Located via pack '%s'.",
 				   hash_to_hex_algop(found->pack->hash,
diff --git a/pack-revindex.c b/pack-revindex.c
index 1fe0afe89907c5..1b67863606a75f 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -394,11 +394,11 @@ int load_midx_revindex(struct multi_pack_index *m)
 
 	if (m->has_chain)
 		get_split_midx_filename_ext(m->source, &revindex_name,
-					    get_midx_checksum(m),
+					    midx_get_checksum_hash(m),
 					    MIDX_EXT_REV);
 	else
 		get_midx_filename_ext(m->source, &revindex_name,
-				      get_midx_checksum(m),
+				      midx_get_checksum_hash(m),
 				      MIDX_EXT_REV);
 
 	ret = load_revindex_from_disk(m->source->odb->repo->hash_algo,
diff --git a/packfile.c b/packfile.c
index 215a23e42be0fe..d4de9f3ffe831e 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1101,37 +1101,35 @@ struct packfile_list_entry *packfile_store_get_packs(struct packfile_store *stor
 	return store->packs.head;
 }
 
-/*
- * Give a fast, rough count of the number of objects in the repository. This
- * ignores loose objects completely. If you have a lot of them, then either
- * you should repack because your performance will be awful, or they are
- * all unreachable objects about to be pruned, in which case they're not really
- * interesting as a measure of repo size in the first place.
- */
-unsigned long repo_approximate_object_count(struct repository *r)
+int packfile_store_count_objects(struct packfile_store *store,
+				 enum odb_count_objects_flags flags UNUSED,
+				 unsigned long *out)
 {
-	if (!r->objects->approximate_object_count_valid) {
-		struct odb_source *source;
-		unsigned long count = 0;
-		struct packed_git *p;
+	struct packfile_list_entry *e;
+	struct multi_pack_index *m;
+	unsigned long count = 0;
+	int ret;
 
-		odb_prepare_alternates(r->objects);
+	m = get_multi_pack_index(store->source);
+	if (m)
+		count += m->num_objects + m->num_objects_in_base;
 
-		for (source = r->objects->sources; source; source = source->next) {
-			struct multi_pack_index *m = get_multi_pack_index(source);
-			if (m)
-				count += m->num_objects + m->num_objects_in_base;
+	for (e = packfile_store_get_packs(store); e; e = e->next) {
+		if (e->pack->multi_pack_index)
+			continue;
+		if (open_pack_index(e->pack)) {
+			ret = -1;
+			goto out;
 		}
 
-		repo_for_each_pack(r, p) {
-			if (p->multi_pack_index || open_pack_index(p))
-				continue;
-			count += p->num_objects;
-		}
-		r->objects->approximate_object_count = count;
-		r->objects->approximate_object_count_valid = 1;
+		count += e->pack->num_objects;
 	}
-	return r->objects->approximate_object_count;
+
+	*out = count;
+	ret = 0;
+
+out:
+	return ret;
 }
 
 unsigned long unpack_object_header_buffer(const unsigned char *buf,
diff --git a/packfile.h b/packfile.h
index 8b04a258a7b9d5..a16ec3950d2507 100644
--- a/packfile.h
+++ b/packfile.h
@@ -268,6 +268,16 @@ enum kept_pack_type {
 	KEPT_PACK_IN_CORE = (1 << 1),
 };
 
+/*
+ * Count the number objects contained in the given packfile store. If
+ * successful, the number of objects will be written to the `out` pointer.
+ *
+ * Return 0 on success, a negative error code otherwise.
+ */
+int packfile_store_count_objects(struct packfile_store *store,
+				 enum odb_count_objects_flags flags,
+				 unsigned long *out);
+
 /*
  * Retrieve the cache of kept packs from the given packfile store. Accepts a
  * combination of `kept_pack_type` flags. The cache is computed on demand and
@@ -365,12 +375,6 @@ int packfile_store_for_each_object(struct packfile_store *store,
 #define PACKDIR_FILE_GARBAGE 4
 extern void (*report_garbage)(unsigned seen_bits, const char *path);
 
-/*
- * Give a rough count of objects in the repository. This sacrifices accuracy
- * for speed.
- */
-unsigned long repo_approximate_object_count(struct repository *r);
-
 void pack_report(struct repository *repo);
 
 /*
diff --git a/repository.c b/repository.c
index 0b8f7ec20089e0..9e5537f53961ed 100644
--- a/repository.c
+++ b/repository.c
@@ -3,6 +3,7 @@
 #include "repository.h"
 #include "hook.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "config.h"
 #include "gettext.h"
 #include "object.h"
diff --git a/submodule-config.c b/submodule-config.c
index 1f19fe207741bc..72a46b7a54bc3d 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -14,6 +14,7 @@
 #include "strbuf.h"
 #include "object-name.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "parse-options.h"
 #include "thread-utils.h"
 #include "tree-walk.h"
diff --git a/t/helper/test-read-midx.c b/t/helper/test-read-midx.c
index 6de5d1665afbfc..388d29e2b53db3 100644
--- a/t/helper/test-read-midx.c
+++ b/t/helper/test-read-midx.c
@@ -26,18 +26,22 @@ static int read_midx_file(const char *object_dir, const char *checksum,
 			  int show_objects)
 {
 	uint32_t i;
-	struct multi_pack_index *m;
+	struct multi_pack_index *m, *tip;
+	int ret = 0;
 
-	m = setup_midx(object_dir);
+	m = tip = setup_midx(object_dir);
 
 	if (!m)
 		return 1;
 
 	if (checksum) {
-		while (m && strcmp(hash_to_hex(get_midx_checksum(m)), checksum))
+		while (m && strcmp(midx_get_checksum_hex(m), checksum))
 			m = m->base_midx;
-		if (!m)
-			return 1;
+		if (!m) {
+			ret = error(_("could not find MIDX with checksum %s"),
+				    checksum);
+			goto out;
+		}
 	}
 
 	printf("header: %08x %d %d %d %d\n",
@@ -82,9 +86,10 @@ static int read_midx_file(const char *object_dir, const char *checksum,
 		}
 	}
 
-	close_midx(m);
+out:
+	close_midx(tip);
 
-	return 0;
+	return ret;
 }
 
 static int read_midx_checksum(const char *object_dir)
@@ -94,7 +99,7 @@ static int read_midx_checksum(const char *object_dir)
 	m = setup_midx(object_dir);
 	if (!m)
 		return 1;
-	printf("%s\n", hash_to_hex(get_midx_checksum(m)));
+	printf("%s\n", midx_get_checksum_hex(m));
 
 	close_midx(m);
 	return 0;
diff --git a/t/meson.build b/t/meson.build
index bafb8e63a9363e..919a0ae4cbb38e 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -626,6 +626,7 @@ integration_tests = [
   't5332-multi-pack-reuse.sh',
   't5333-pseudo-merge-bitmaps.sh',
   't5334-incremental-multi-pack-index.sh',
+  't5335-compact-multi-pack-index.sh',
   't5351-unpack-large-objects.sh',
   't5400-send-pack.sh',
   't5401-update-hooks.sh',
diff --git a/t/t0450/adoc-help-mismatches b/t/t0450/adoc-help-mismatches
index 8ee2d3f7c81502..e8d6c13ccd0333 100644
--- a/t/t0450/adoc-help-mismatches
+++ b/t/t0450/adoc-help-mismatches
@@ -33,7 +33,6 @@ merge
 merge-file
 merge-index
 merge-one-file
-multi-pack-index
 name-rev
 notes
 push
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index a7c79225f67526..58e0b685b105f5 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -21,7 +21,7 @@ midx_read_expect () {
 	EXTRA_CHUNKS="$5"
 	{
 		cat <<-EOF &&
-		header: 4d494458 1 $HASH_LEN $NUM_CHUNKS $NUM_PACKS
+		header: 4d494458 2 $HASH_LEN $NUM_CHUNKS $NUM_PACKS
 		chunks: pack-names oid-fanout oid-lookup object-offsets$EXTRA_CHUNKS
 		num_objects: $NUM_OBJECTS
 		packs:
@@ -512,12 +512,7 @@ test_expect_success 'verify invalid chunk offset' '
 		"improper chunk offset(s)"
 '
 
-test_expect_success 'verify packnames out of order' '
-	corrupt_midx_and_verify $MIDX_BYTE_PACKNAME_ORDER "z" $objdir \
-		"pack names out of order"
-'
-
-test_expect_success 'verify packnames out of order' '
+test_expect_success 'verify missing pack' '
 	corrupt_midx_and_verify $MIDX_BYTE_PACKNAME_ORDER "a" $objdir \
 		"failed to load pack"
 '
@@ -578,6 +573,15 @@ test_expect_success 'verify incorrect checksum' '
 		$objdir "incorrect checksum"
 '
 
+test_expect_success 'setup for v1-specific fsck tests' '
+	git -c midx.version=1 multi-pack-index write
+'
+
+test_expect_success 'verify packnames out of order (v1)' '
+	corrupt_midx_and_verify $MIDX_BYTE_PACKNAME_ORDER "z" $objdir \
+		"pack names out of order"
+'
+
 test_expect_success 'repack progress off for redirected stderr' '
 	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir repack 2>err &&
 	test_line_count = 0 err
diff --git a/t/t5335-compact-multi-pack-index.sh b/t/t5335-compact-multi-pack-index.sh
new file mode 100755
index 00000000000000..40f3844282f04e
--- /dev/null
+++ b/t/t5335-compact-multi-pack-index.sh
@@ -0,0 +1,293 @@
+#!/bin/sh
+
+test_description='multi-pack-index compaction'
+
+. ./test-lib.sh
+
+GIT_TEST_MULTI_PACK_INDEX=0
+GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
+GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL=0
+
+objdir=.git/objects
+packdir=$objdir/pack
+midxdir=$packdir/multi-pack-index.d
+midx_chain=$midxdir/multi-pack-index-chain
+
+nth_line() {
+	local n="$1"
+	shift
+	awk "NR==$n" "$@"
+}
+
+write_packs () {
+	for c in "$@"
+	do
+		test_commit "$c" &&
+
+		git pack-objects --all --unpacked $packdir/pack-$c &&
+		git prune-packed &&
+
+		git multi-pack-index write --incremental --bitmap || return 1
+	done
+}
+
+test_midx_layer_packs () {
+	local checksum="$1" &&
+	shift &&
+
+	test-tool read-midx $objdir "$checksum" >out &&
+
+	printf "%s\n" "$@" >expect &&
+	# NOTE: do *not* pipe through sort here, we want to ensure the
+	# order of packs is preserved during compaction.
+	grep "^pack-" out | cut -d"-" -f2 >actual &&
+
+	test_cmp expect actual
+}
+
+test_midx_layer_object_uniqueness () {
+	: >objs.all
+	while read layer
+	do
+		test-tool read-midx --show-objects $objdir "$layer" >out &&
+		grep "\.pack$" out | cut -d" " -f1 | sort >objs.layer &&
+		test_stdout_line_count = 0 comm -12 objs.all objs.layer &&
+		cat objs.all objs.layer | sort >objs.tmp &&
+		mv objs.tmp objs.all || return 1
+	done <$midx_chain
+}
+
+test_expect_success 'MIDX compaction with lex-ordered pack names' '
+	git init midx-compact-lex-order &&
+	(
+		cd midx-compact-lex-order &&
+
+		git config maintenance.auto false &&
+
+		write_packs A B C D E &&
+		test_line_count = 5 $midx_chain &&
+
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+		test_line_count = 3 $midx_chain &&
+
+		test_midx_layer_packs "$(nth_line 1 "$midx_chain")" A &&
+		test_midx_layer_packs "$(nth_line 2 "$midx_chain")" B C D &&
+		test_midx_layer_packs "$(nth_line 3 "$midx_chain")" E &&
+
+		test_midx_layer_object_uniqueness
+	)
+'
+
+test_expect_success 'MIDX compaction with non-lex-ordered pack names' '
+	git init midx-compact-non-lex-order &&
+	(
+		cd midx-compact-non-lex-order &&
+
+		git config maintenance.auto false &&
+
+		write_packs D C A B E &&
+		test_line_count = 5 $midx_chain &&
+
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+		test_line_count = 3 $midx_chain &&
+
+		test_midx_layer_packs "$(nth_line 1 "$midx_chain")" D &&
+		test_midx_layer_packs "$(nth_line 2 "$midx_chain")" C A B &&
+		test_midx_layer_packs "$(nth_line 3 "$midx_chain")" E &&
+
+		test_midx_layer_object_uniqueness
+	)
+'
+
+test_expect_success 'setup for bogus MIDX compaction scenarios' '
+	git init midx-compact-bogus &&
+	(
+		cd midx-compact-bogus &&
+
+		git config maintenance.auto false &&
+
+		write_packs A B C
+	)
+'
+
+test_expect_success 'MIDX compaction with missing endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"<missing>" "<missing>" 2>err &&
+		test_grep "could not find MIDX: <missing>" err &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"<missing>" "$(nth_line 2 "$midx_chain")" 2>err &&
+		test_grep "could not find MIDX: <missing>" err &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$(nth_line 2 "$midx_chain")" "<missing>" 2>err &&
+		test_grep "could not find MIDX: <missing>" err
+	)
+'
+
+test_expect_success 'MIDX compaction with reversed endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		from="$(nth_line 3 "$midx_chain")" &&
+		to="$(nth_line 1 "$midx_chain")" &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$from" "$to" 2>err &&
+
+		test_grep "MIDX $from must be an ancestor of $to" err
+	)
+'
+
+test_expect_success 'MIDX compaction with identical endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		from="$(nth_line 3 "$midx_chain")" &&
+		to="$(nth_line 3 "$midx_chain")" &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$from" "$to" 2>err &&
+
+		test_grep "MIDX compaction endpoints must be unique" err
+	)
+'
+
+test_expect_success 'MIDX compaction with midx.version=1' '
+	(
+		cd midx-compact-bogus &&
+
+		test_must_fail git -c midx.version=1 multi-pack-index compact \
+			"$(nth_line 1 "$midx_chain")" \
+			"$(nth_line 2 "$midx_chain")" 2>err &&
+
+		test_grep "fatal: cannot perform MIDX compaction with v1 format" err
+	)
+'
+
+midx_objs_by_pack () {
+	awk '/\.pack$/ { split($3, a, "-"); print a[2], $1 }' | sort
+}
+
+tag_objs_from_pack () {
+	objs="$(git rev-list --objects --no-object-names "$2")" &&
+	printf "$1 %s\n" $objs | sort
+}
+
+test_expect_success 'MIDX compaction preserves pack object selection' '
+	git init midx-compact-preserve-selection &&
+	(
+		cd midx-compact-preserve-selection &&
+
+		git config maintenance.auto false &&
+
+		test_commit A &&
+		test_commit B &&
+
+		# Create two packs, one containing just the objects from
+		# A, and another containing all objects from the
+		# repository.
+		p1="$(echo A | git pack-objects --revs --delta-base-offset \
+			$packdir/pack-1)" &&
+		p0="$(echo B | git pack-objects --revs --delta-base-offset \
+			$packdir/pack-0)" &&
+
+		echo "pack-1-$p1.idx" | git multi-pack-index write \
+			--incremental --bitmap --stdin-packs &&
+		echo "pack-0-$p0.idx" | git multi-pack-index write \
+			--incremental --bitmap --stdin-packs &&
+
+		write_packs C &&
+
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 1 "$midx_chain")" \
+			"$(nth_line 2 "$midx_chain")" &&
+
+
+		test-tool read-midx --show-objects $objdir \
+			"$(nth_line 1 "$midx_chain")" >AB.info &&
+		test-tool read-midx --show-objects $objdir \
+			"$(nth_line 2 "$midx_chain")" >C.info &&
+
+		midx_objs_by_pack <AB.info >AB.actual &&
+		midx_objs_by_pack <C.info >C.actual &&
+
+		{
+			tag_objs_from_pack 1 A &&
+			tag_objs_from_pack 0 A..B
+		} | sort >AB.expect &&
+		tag_objs_from_pack C B..C >C.expect &&
+
+		test_cmp AB.expect AB.actual &&
+		test_cmp C.expect C.actual
+	)
+'
+
+test_expect_success 'MIDX compaction with bitmaps' '
+	git init midx-compact-with-bitmaps &&
+	(
+		cd midx-compact-with-bitmaps &&
+
+		git config maintenance.auto false &&
+
+		write_packs foo bar baz quux woot &&
+
+		test-tool read-midx --bitmap $objdir >bitmap.expect &&
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+		test-tool read-midx --bitmap $objdir >bitmap.actual &&
+
+		test_cmp bitmap.expect bitmap.actual &&
+
+		true
+	)
+'
+
+test_expect_success 'MIDX compaction with bitmaps (non-trivial)' '
+	git init midx-compact-with-bitmaps-non-trivial &&
+	(
+		cd midx-compact-with-bitmaps-non-trivial &&
+
+		git config maintenance.auto false &&
+
+		git branch -m main &&
+
+		#               D(4)
+		#              /
+		# A(1) --- B(2) --- C(3) --- G(7)
+		#              \
+		#               E(5) --- F(6)
+		write_packs A B C &&
+		git checkout -b side &&
+		write_packs D &&
+		git checkout -b other B &&
+		write_packs E F &&
+		git checkout main &&
+		write_packs G &&
+
+		# Compact layers 2-4, leaving us with:
+		#
+		#  [A, [B, C, D], E, F, G]
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+
+		# Then compact the top two layers, condensing the above
+		# such that the new 4th layer contains F and G.
+		#
+		#  [A, [B, C, D], E, [F, G]]
+		git multi-pack-index compact --incremental --bitmap \
+			"$(nth_line 4 "$midx_chain")" \
+			"$(nth_line 5 "$midx_chain")"
+	)
+'
+
+test_done
diff --git a/tmp-objdir.c b/tmp-objdir.c
index e436eed07e4449..d199d39e7c9d51 100644
--- a/tmp-objdir.c
+++ b/tmp-objdir.c
@@ -11,6 +11,7 @@
 #include "strvec.h"
 #include "quote.h"
 #include "odb.h"
+#include "odb/source.h"
 #include "repository.h"
 
 struct tmp_objdir {