diff --git a/Makefile b/Makefile
index 4c95affadb5e265a98ffcf485f8c13a6c3a7e167..d25d4255f8a7ebf8abfed5c5ae61a11baedc74c7 100644
--- a/Makefile
+++ b/Makefile
@@ -974,7 +974,6 @@ LIB_OBJS += blame.o
 LIB_OBJS += blob.o
 LIB_OBJS += bloom.o
 LIB_OBJS += branch.o
-LIB_OBJS += bulk-checkin.o
 LIB_OBJS += bundle-uri.o
 LIB_OBJS += bundle.o
 LIB_OBJS += cache-tree.o
diff --git a/builtin/add.c b/builtin/add.c
index 0235854f8099c49328a00aadad4adbbbdfc0579b..bf312c40be9789cf2bda329d48d53c49c0e12470 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -14,13 +14,14 @@
 #include "gettext.h"
 #include "pathspec.h"
 #include "run-command.h"
+#include "object-file.h"
+#include "odb.h"
 #include "parse-options.h"
 #include "path.h"
 #include "preload-index.h"
 #include "diff.h"
 #include "read-cache.h"
 #include "revision.h"
-#include "bulk-checkin.h"
 #include "strvec.h"
 #include "submodule.h"
 #include "add-interactive.h"
@@ -389,6 +390,7 @@ int cmd_add(int argc,
 	char *seen = NULL;
 	char *ps_matched = NULL;
 	struct lock_file lock_file = LOCK_INIT;
+	struct odb_transaction *transaction;
 
 	repo_config(repo, add_config, NULL);
 
@@ -574,7 +576,7 @@ int cmd_add(int argc,
 		string_list_clear(&only_match_skip_worktree, 0);
 	}
 
-	begin_odb_transaction();
+	transaction = odb_transaction_begin(repo->objects);
 
 	ps_matched = xcalloc(pathspec.nr, 1);
 	if (add_renormalize)
@@ -593,7 +595,7 @@ int cmd_add(int argc,
 
 	if (chmod_arg && pathspec.nr)
 		exit_status |= chmod_pathspec(repo, &pathspec, chmod_arg[0], show_only);
-	end_odb_transaction();
+	odb_transaction_commit(transaction);
 
 finish:
 	if (write_locked_index(repo->index, &lock_file,
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 7ae7c82b6c05a6a6b09e77766ef7226c0c4ddcd4..ef79e43715d362d2907c23b5613d6fdaf9a96c80 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -2,7 +2,6 @@
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "builtin.h"
-#include "bulk-checkin.h"
 #include "config.h"
 #include "environment.h"
 #include "gettext.h"
@@ -584,6 +583,7 @@ static void unpack_all(void)
 {
 	int i;
 	unsigned char *hdr = fill(sizeof(struct pack_header));
+	struct odb_transaction *transaction;
 
 	if (get_be32(hdr) != PACK_SIGNATURE)
 		die("bad pack file");
@@ -599,12 +599,12 @@ static void unpack_all(void)
 		progress = start_progress(the_repository,
 					  _("Unpacking objects"), nr_objects);
 	CALLOC_ARRAY(obj_list, nr_objects);
-	begin_odb_transaction();
+	transaction = odb_transaction_begin(the_repository->objects);
 	for (i = 0; i < nr_objects; i++) {
 		unpack_one(i);
 		display_progress(progress, i + 1);
 	}
-	end_odb_transaction();
+	odb_transaction_commit(transaction);
 	stop_progress(&progress);
 
 	if (delta_list)
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 2380f3ccd68c8ce0ac4b221dbf84f18b9a430811..8a5907767bf297eefcb0c6de5441cabd567536fd 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -8,7 +8,6 @@
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "builtin.h"
-#include "bulk-checkin.h"
 #include "config.h"
 #include "environment.h"
 #include "gettext.h"
@@ -19,6 +18,7 @@
 #include "cache-tree.h"
 #include "tree-walk.h"
 #include "object-file.h"
+#include "odb.h"
 #include "refs.h"
 #include "resolve-undo.h"
 #include "parse-options.h"
@@ -70,14 +70,6 @@ static void report(const char *fmt, ...)
 	if (!verbose)
 		return;
 
-	/*
-	 * It is possible, though unlikely, that a caller could use the verbose
-	 * output to synchronize with addition of objects to the object
-	 * database. The current implementation of ODB transactions leaves
-	 * objects invisible while a transaction is active, so flush the
-	 * transaction here before reporting a change made by update-index.
-	 */
-	flush_odb_transaction();
 	va_start(vp, fmt);
 	vprintf(fmt, vp);
 	putchar('\n');
@@ -940,6 +932,7 @@ int cmd_update_index(int argc,
 	strbuf_getline_fn getline_fn;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
 	struct repository *r = the_repository;
+	struct odb_transaction *transaction;
 	struct option options[] = {
 		OPT_BIT('q', NULL, &refresh_args.flags,
 			N_("continue refresh even when index needs update"),
@@ -1130,7 +1123,7 @@ int cmd_update_index(int argc,
 	 * Allow the object layer to optimize adding multiple objects in
 	 * a batch.
 	 */
-	begin_odb_transaction();
+	transaction = odb_transaction_begin(the_repository->objects);
 	while (ctx.argc) {
 		if (parseopt_state != PARSE_OPT_DONE)
 			parseopt_state = parse_options_step(&ctx, options,
@@ -1149,6 +1142,21 @@ int cmd_update_index(int argc,
 			const char *path = ctx.argv[0];
 			char *p;
 
+			/*
+			 * It is possible, though unlikely, that a caller could
+			 * use the verbose output to synchronize with addition
+			 * of objects to the object database. The current
+			 * implementation of ODB transactions leaves objects
+			 * invisible while a transaction is active, so end the
+			 * transaction here early before processing the next
+			 * update. All further updates are performed outside of
+			 * a transaction.
+			 */
+			if (transaction && verbose) {
+				odb_transaction_commit(transaction);
+				transaction = NULL;
+			}
+
 			setup_work_tree();
 			p = prefix_path(prefix, prefix_length, path);
 			update_one(p);
@@ -1213,7 +1221,7 @@ int cmd_update_index(int argc,
 	/*
 	 * By now we have added all of the new objects
 	 */
-	end_odb_transaction();
+	odb_transaction_commit(transaction);
 
 	if (split_index > 0) {
 		if (repo_config_get_split_index(the_repository) == 0)
diff --git a/bulk-checkin.c b/bulk-checkin.c
deleted file mode 100644
index b2809ab0398136ea0bd18b5d1c90f6a5729415ab..0000000000000000000000000000000000000000
--- a/bulk-checkin.c
+++ /dev/null
@@ -1,391 +0,0 @@
-/*
- * Copyright (c) 2011, Google Inc.
- */
-
-#define USE_THE_REPOSITORY_VARIABLE
-
-#include "git-compat-util.h"
-#include "bulk-checkin.h"
-#include "environment.h"
-#include "gettext.h"
-#include "hex.h"
-#include "lockfile.h"
-#include "repository.h"
-#include "csum-file.h"
-#include "pack.h"
-#include "strbuf.h"
-#include "tmp-objdir.h"
-#include "packfile.h"
-#include "object-file.h"
-#include "odb.h"
-
-static int odb_transaction_nesting;
-
-static struct tmp_objdir *bulk_fsync_objdir;
-
-static struct bulk_checkin_packfile {
-	char *pack_tmp_name;
-	struct hashfile *f;
-	off_t offset;
-	struct pack_idx_option pack_idx_opts;
-
-	struct pack_idx_entry **written;
-	uint32_t alloc_written;
-	uint32_t nr_written;
-} bulk_checkin_packfile;
-
-static void finish_tmp_packfile(struct strbuf *basename,
-				const char *pack_tmp_name,
-				struct pack_idx_entry **written_list,
-				uint32_t nr_written,
-				struct pack_idx_option *pack_idx_opts,
-				unsigned char hash[])
-{
-	char *idx_tmp_name = NULL;
-
-	stage_tmp_packfiles(the_repository, basename, pack_tmp_name,
-			    written_list, nr_written, NULL, pack_idx_opts, hash,
-			    &idx_tmp_name);
-	rename_tmp_packfile_idx(the_repository, basename, &idx_tmp_name);
-
-	free(idx_tmp_name);
-}
-
-static void flush_bulk_checkin_packfile(struct bulk_checkin_packfile *state)
-{
-	unsigned char hash[GIT_MAX_RAWSZ];
-	struct strbuf packname = STRBUF_INIT;
-
-	if (!state->f)
-		return;
-
-	if (state->nr_written == 0) {
-		close(state->f->fd);
-		free_hashfile(state->f);
-		unlink(state->pack_tmp_name);
-		goto clear_exit;
-	} else if (state->nr_written == 1) {
-		finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK,
-				  CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
-	} else {
-		int fd = finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK, 0);
-		fixup_pack_header_footer(the_hash_algo, fd, hash, state->pack_tmp_name,
-					 state->nr_written, hash,
-					 state->offset);
-		close(fd);
-	}
-
-	strbuf_addf(&packname, "%s/pack/pack-%s.", repo_get_object_directory(the_repository),
-		    hash_to_hex(hash));
-	finish_tmp_packfile(&packname, state->pack_tmp_name,
-			    state->written, state->nr_written,
-			    &state->pack_idx_opts, hash);
-	for (uint32_t i = 0; i < state->nr_written; i++)
-		free(state->written[i]);
-
-clear_exit:
-	free(state->pack_tmp_name);
-	free(state->written);
-	memset(state, 0, sizeof(*state));
-
-	strbuf_release(&packname);
-	/* Make objects we just wrote available to ourselves */
-	reprepare_packed_git(the_repository);
-}
-
-/*
- * Cleanup after batch-mode fsync_object_files.
- */
-static void flush_batch_fsync(void)
-{
-	struct strbuf temp_path = STRBUF_INIT;
-	struct tempfile *temp;
-
-	if (!bulk_fsync_objdir)
-		return;
-
-	/*
-	 * Issue a full hardware flush against a temporary file to ensure
-	 * that all objects are durable before any renames occur. The code in
-	 * fsync_loose_object_bulk_checkin has already issued a writeout
-	 * request, but it has not flushed any writeback cache in the storage
-	 * hardware or any filesystem logs. This fsync call acts as a barrier
-	 * to ensure that the data in each new object file is durable before
-	 * the final name is visible.
-	 */
-	strbuf_addf(&temp_path, "%s/bulk_fsync_XXXXXX", repo_get_object_directory(the_repository));
-	temp = xmks_tempfile(temp_path.buf);
-	fsync_or_die(get_tempfile_fd(temp), get_tempfile_path(temp));
-	delete_tempfile(&temp);
-	strbuf_release(&temp_path);
-
-	/*
-	 * Make the object files visible in the primary ODB after their data is
-	 * fully durable.
-	 */
-	tmp_objdir_migrate(bulk_fsync_objdir);
-	bulk_fsync_objdir = NULL;
-}
-
-static int already_written(struct bulk_checkin_packfile *state, struct object_id *oid)
-{
-	/* The object may already exist in the repository */
-	if (odb_has_object(the_repository->objects, oid,
-			   HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
-		return 1;
-
-	/* Might want to keep the list sorted */
-	for (uint32_t i = 0; i < state->nr_written; i++)
-		if (oideq(&state->written[i]->oid, oid))
-			return 1;
-
-	/* This is a new object we need to keep */
-	return 0;
-}
-
-/*
- * Read the contents from fd for size bytes, streaming it to the
- * packfile in state while updating the hash in ctx. Signal a failure
- * by returning a negative value when the resulting pack would exceed
- * the pack size limit and this is not the first object in the pack,
- * so that the caller can discard what we wrote from the current pack
- * by truncating it and opening a new one. The caller will then call
- * us again after rewinding the input fd.
- *
- * The already_hashed_to pointer is kept untouched by the caller to
- * make sure we do not hash the same byte when we are called
- * again. This way, the caller does not have to checkpoint its hash
- * status before calling us just in case we ask it to call us again
- * with a new pack.
- */
-static int stream_blob_to_pack(struct bulk_checkin_packfile *state,
-			       struct git_hash_ctx *ctx, off_t *already_hashed_to,
-			       int fd, size_t size, const char *path,
-			       unsigned flags)
-{
-	git_zstream s;
-	unsigned char ibuf[16384];
-	unsigned char obuf[16384];
-	unsigned hdrlen;
-	int status = Z_OK;
-	int write_object = (flags & INDEX_WRITE_OBJECT);
-	off_t offset = 0;
-
-	git_deflate_init(&s, pack_compression_level);
-
-	hdrlen = encode_in_pack_object_header(obuf, sizeof(obuf), OBJ_BLOB, size);
-	s.next_out = obuf + hdrlen;
-	s.avail_out = sizeof(obuf) - hdrlen;
-
-	while (status != Z_STREAM_END) {
-		if (size && !s.avail_in) {
-			size_t rsize = size < sizeof(ibuf) ? size : sizeof(ibuf);
-			ssize_t read_result = read_in_full(fd, ibuf, rsize);
-			if (read_result < 0)
-				die_errno("failed to read from '%s'", path);
-			if ((size_t)read_result != rsize)
-				die("failed to read %u bytes from '%s'",
-				    (unsigned)rsize, path);
-			offset += rsize;
-			if (*already_hashed_to < offset) {
-				size_t hsize = offset - *already_hashed_to;
-				if (rsize < hsize)
-					hsize = rsize;
-				if (hsize)
-					git_hash_update(ctx, ibuf, hsize);
-				*already_hashed_to = offset;
-			}
-			s.next_in = ibuf;
-			s.avail_in = rsize;
-			size -= rsize;
-		}
-
-		status = git_deflate(&s, size ? 0 : Z_FINISH);
-
-		if (!s.avail_out || status == Z_STREAM_END) {
-			if (write_object) {
-				size_t written = s.next_out - obuf;
-
-				/* would we bust the size limit? */
-				if (state->nr_written &&
-				    pack_size_limit_cfg &&
-				    pack_size_limit_cfg < state->offset + written) {
-					git_deflate_abort(&s);
-					return -1;
-				}
-
-				hashwrite(state->f, obuf, written);
-				state->offset += written;
-			}
-			s.next_out = obuf;
-			s.avail_out = sizeof(obuf);
-		}
-
-		switch (status) {
-		case Z_OK:
-		case Z_BUF_ERROR:
-		case Z_STREAM_END:
-			continue;
-		default:
-			die("unexpected deflate failure: %d", status);
-		}
-	}
-	git_deflate_end(&s);
-	return 0;
-}
-
-/* Lazily create backing packfile for the state */
-static void prepare_to_stream(struct bulk_checkin_packfile *state,
-			      unsigned flags)
-{
-	if (!(flags & INDEX_WRITE_OBJECT) || state->f)
-		return;
-
-	state->f = create_tmp_packfile(the_repository, &state->pack_tmp_name);
-	reset_pack_idx_option(&state->pack_idx_opts);
-
-	/* Pretend we are going to write only one object */
-	state->offset = write_pack_header(state->f, 1);
-	if (!state->offset)
-		die_errno("unable to write pack header");
-}
-
-static int deflate_blob_to_pack(struct bulk_checkin_packfile *state,
-				struct object_id *result_oid,
-				int fd, size_t size,
-				const char *path, unsigned flags)
-{
-	off_t seekback, already_hashed_to;
-	struct git_hash_ctx ctx;
-	unsigned char obuf[16384];
-	unsigned header_len;
-	struct hashfile_checkpoint checkpoint;
-	struct pack_idx_entry *idx = NULL;
-
-	seekback = lseek(fd, 0, SEEK_CUR);
-	if (seekback == (off_t) -1)
-		return error("cannot find the current offset");
-
-	header_len = format_object_header((char *)obuf, sizeof(obuf),
-					  OBJ_BLOB, size);
-	the_hash_algo->init_fn(&ctx);
-	git_hash_update(&ctx, obuf, header_len);
-
-	/* Note: idx is non-NULL when we are writing */
-	if ((flags & INDEX_WRITE_OBJECT) != 0) {
-		CALLOC_ARRAY(idx, 1);
-
-		prepare_to_stream(state, flags);
-		hashfile_checkpoint_init(state->f, &checkpoint);
-	}
-
-	already_hashed_to = 0;
-
-	while (1) {
-		prepare_to_stream(state, flags);
-		if (idx) {
-			hashfile_checkpoint(state->f, &checkpoint);
-			idx->offset = state->offset;
-			crc32_begin(state->f);
-		}
-		if (!stream_blob_to_pack(state, &ctx, &already_hashed_to,
-					 fd, size, path, flags))
-			break;
-		/*
-		 * Writing this object to the current pack will make
-		 * it too big; we need to truncate it, start a new
-		 * pack, and write into it.
-		 */
-		if (!idx)
-			BUG("should not happen");
-		hashfile_truncate(state->f, &checkpoint);
-		state->offset = checkpoint.offset;
-		flush_bulk_checkin_packfile(state);
-		if (lseek(fd, seekback, SEEK_SET) == (off_t) -1)
-			return error("cannot seek back");
-	}
-	git_hash_final_oid(result_oid, &ctx);
-	if (!idx)
-		return 0;
-
-	idx->crc32 = crc32_end(state->f);
-	if (already_written(state, result_oid)) {
-		hashfile_truncate(state->f, &checkpoint);
-		state->offset = checkpoint.offset;
-		free(idx);
-	} else {
-		oidcpy(&idx->oid, result_oid);
-		ALLOC_GROW(state->written,
-			   state->nr_written + 1,
-			   state->alloc_written);
-		state->written[state->nr_written++] = idx;
-	}
-	return 0;
-}
-
-void prepare_loose_object_bulk_checkin(void)
-{
-	/*
-	 * We lazily create the temporary object directory
-	 * the first time an object might be added, since
-	 * callers may not know whether any objects will be
-	 * added at the time they call begin_odb_transaction.
-	 */
-	if (!odb_transaction_nesting || bulk_fsync_objdir)
-		return;
-
-	bulk_fsync_objdir = tmp_objdir_create(the_repository, "bulk-fsync");
-	if (bulk_fsync_objdir)
-		tmp_objdir_replace_primary_odb(bulk_fsync_objdir, 0);
-}
-
-void fsync_loose_object_bulk_checkin(int fd, const char *filename)
-{
-	/*
-	 * If we have an active ODB transaction, we issue a call that
-	 * cleans the filesystem page cache but avoids a hardware flush
-	 * command. Later on we will issue a single hardware flush
-	 * before renaming the objects to their final names as part of
-	 * flush_batch_fsync.
-	 */
-	if (!bulk_fsync_objdir ||
-	    git_fsync(fd, FSYNC_WRITEOUT_ONLY) < 0) {
-		if (errno == ENOSYS)
-			warning(_("core.fsyncMethod = batch is unsupported on this platform"));
-		fsync_or_die(fd, filename);
-	}
-}
-
-int index_blob_bulk_checkin(struct object_id *oid,
-			    int fd, size_t size,
-			    const char *path, unsigned flags)
-{
-	int status = deflate_blob_to_pack(&bulk_checkin_packfile, oid, fd, size,
-					  path, flags);
-	if (!odb_transaction_nesting)
-		flush_bulk_checkin_packfile(&bulk_checkin_packfile);
-	return status;
-}
-
-void begin_odb_transaction(void)
-{
-	odb_transaction_nesting += 1;
-}
-
-void flush_odb_transaction(void)
-{
-	flush_batch_fsync();
-	flush_bulk_checkin_packfile(&bulk_checkin_packfile);
-}
-
-void end_odb_transaction(void)
-{
-	odb_transaction_nesting -= 1;
-	if (odb_transaction_nesting < 0)
-		BUG("Unbalanced ODB transaction nesting");
-
-	if (odb_transaction_nesting)
-		return;
-
-	flush_odb_transaction();
-}
diff --git a/bulk-checkin.h b/bulk-checkin.h
deleted file mode 100644
index 7246ea58dcf3481e026560f987138b1efe112390..0000000000000000000000000000000000000000
--- a/bulk-checkin.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- * Copyright (c) 2011, Google Inc.
- */
-#ifndef BULK_CHECKIN_H
-#define BULK_CHECKIN_H
-
-#include "object.h"
-
-void prepare_loose_object_bulk_checkin(void);
-void fsync_loose_object_bulk_checkin(int fd, const char *filename);
-
-/*
- * This creates one packfile per large blob unless bulk-checkin
- * machinery is "plugged".
- *
- * This also bypasses the usual "convert-to-git" dance, and that is on
- * purpose. We could write a streaming version of the converting
- * functions and insert that before feeding the data to fast-import
- * (or equivalent in-core API described above). However, that is
- * somewhat complicated, as we do not know the size of the filter
- * result, which we need to know beforehand when writing a git object.
- * Since the primary motivation for trying to stream from the working
- * tree file and to avoid mmaping it in core is to deal with large
- * binary blobs, they generally do not want to get any conversion, and
- * callers should avoid this code path when filters are requested.
- */
-int index_blob_bulk_checkin(struct object_id *oid,
-			    int fd, size_t size,
-			    const char *path, unsigned flags);
-
-/*
- * Tell the object database to optimize for adding
- * multiple objects. end_odb_transaction must be called
- * to make new objects visible. Transactions can be nested,
- * and objects are only visible after the outermost transaction
- * is complete or the transaction is flushed.
- */
-void begin_odb_transaction(void);
-
-/*
- * Make any objects that are currently part of a pending object
- * database transaction visible. It is valid to call this function
- * even if no transaction is active.
- */
-void flush_odb_transaction(void);
-
-/*
- * Tell the object database to make any objects from the
- * current transaction visible if this is the final nested
- * transaction.
- */
-void end_odb_transaction(void);
-
-#endif
diff --git a/cache-tree.c b/cache-tree.c
index 66ef2becbe01a4bfe2d41de91d97389487c82f64..2aba47060e95d49463a5de78fc29fd601ae0c281 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -8,7 +8,6 @@
 #include "tree.h"
 #include "tree-walk.h"
 #include "cache-tree.h"
-#include "bulk-checkin.h"
 #include "object-file.h"
 #include "odb.h"
 #include "read-cache-ll.h"
@@ -474,6 +473,7 @@ static int update_one(struct cache_tree *it,
 
 int cache_tree_update(struct index_state *istate, int flags)
 {
+	struct odb_transaction *transaction;
 	int skip, i;
 
 	i = verify_cache(istate, flags);
@@ -489,10 +489,10 @@ int cache_tree_update(struct index_state *istate, int flags)
 
 	trace_performance_enter();
 	trace2_region_enter("cache_tree", "update", the_repository);
-	begin_odb_transaction();
+	transaction = odb_transaction_begin(the_repository->objects);
 	i = update_one(istate->cache_tree, istate->cache, istate->cache_nr,
 		       "", 0, &skip, flags);
-	end_odb_transaction();
+	odb_transaction_commit(transaction);
 	trace2_region_leave("cache_tree", "update", the_repository);
 	trace_performance_leave("cache_tree_update");
 	if (i < 0)
diff --git a/meson.build b/meson.build
index b3dfcc04972601cbc3d05222f72070ddf0c2356f..fccb6d2eeca050e72c0db0193fea3ae104376696 100644
--- a/meson.build
+++ b/meson.build
@@ -287,7 +287,6 @@ libgit_sources = [
   'blob.c',
   'bloom.c',
   'branch.c',
-  'bulk-checkin.c',
   'bundle-uri.c',
   'bundle.c',
   'cache-tree.c',
diff --git a/object-file.c b/object-file.c
index 2bc36ab3ee8cbf2d83c4b3204a7c5df132b934d6..17a236d2fe121bc447f73138c9db4a651b07ca22 100644
--- a/object-file.c
+++ b/object-file.c
@@ -10,7 +10,6 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "git-compat-util.h"
-#include "bulk-checkin.h"
 #include "convert.h"
 #include "dir.h"
 #include "environment.h"
@@ -28,6 +27,8 @@
 #include "read-cache-ll.h"
 #include "setup.h"
 #include "streaming.h"
+#include "tempfile.h"
+#include "tmp-objdir.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -666,6 +667,93 @@ void hash_object_file(const struct git_hash_algo *algo, const void *buf,
 	write_object_file_prepare(algo, buf, len, type, oid, hdr, &hdrlen);
 }
 
+struct transaction_packfile {
+	char *pack_tmp_name;
+	struct hashfile *f;
+	off_t offset;
+	struct pack_idx_option pack_idx_opts;
+
+	struct pack_idx_entry **written;
+	uint32_t alloc_written;
+	uint32_t nr_written;
+};
+
+struct odb_transaction {
+	struct object_database *odb;
+
+	struct tmp_objdir *objdir;
+	struct transaction_packfile packfile;
+};
+
+static void prepare_loose_object_transaction(struct odb_transaction *transaction)
+{
+	/*
+	 * We lazily create the temporary object directory
+	 * the first time an object might be added, since
+	 * callers may not know whether any objects will be
+	 * added at the time they call object_file_transaction_begin.
+	 */
+	if (!transaction || transaction->objdir)
+		return;
+
+	transaction->objdir = tmp_objdir_create(transaction->odb->repo, "bulk-fsync");
+	if (transaction->objdir)
+		tmp_objdir_replace_primary_odb(transaction->objdir, 0);
+}
+
+static void fsync_loose_object_transaction(struct odb_transaction *transaction,
+					   int fd, const char *filename)
+{
+	/*
+	 * If we have an active ODB transaction, we issue a call that
+	 * cleans the filesystem page cache but avoids a hardware flush
+	 * command. Later on we will issue a single hardware flush
+	 * before renaming the objects to their final names as part of
+	 * flush_batch_fsync.
+	 */
+	if (!transaction || !transaction->objdir ||
+	    git_fsync(fd, FSYNC_WRITEOUT_ONLY) < 0) {
+		if (errno == ENOSYS)
+			warning(_("core.fsyncMethod = batch is unsupported on this platform"));
+		fsync_or_die(fd, filename);
+	}
+}
+
+/*
+ * Cleanup after batch-mode fsync_object_files.
+ */
+static void flush_loose_object_transaction(struct odb_transaction *transaction)
+{
+	struct strbuf temp_path = STRBUF_INIT;
+	struct tempfile *temp;
+
+	if (!transaction->objdir)
+		return;
+
+	/*
+	 * Issue a full hardware flush against a temporary file to ensure
+	 * that all objects are durable before any renames occur. The code in
+	 * fsync_loose_object_transaction has already issued a writeout
+	 * request, but it has not flushed any writeback cache in the storage
+	 * hardware or any filesystem logs. This fsync call acts as a barrier
+	 * to ensure that the data in each new object file is durable before
+	 * the final name is visible.
+	 */
+	strbuf_addf(&temp_path, "%s/bulk_fsync_XXXXXX",
+		    repo_get_object_directory(transaction->odb->repo));
+	temp = xmks_tempfile(temp_path.buf);
+	fsync_or_die(get_tempfile_fd(temp), get_tempfile_path(temp));
+	delete_tempfile(&temp);
+	strbuf_release(&temp_path);
+
+	/*
+	 * Make the object files visible in the primary ODB after their data is
+	 * fully durable.
+	 */
+	tmp_objdir_migrate(transaction->objdir);
+	transaction->objdir = NULL;
+}
+
 /* Finalize a file on disk, and close it. */
 static void close_loose_object(struct odb_source *source,
 			       int fd, const char *filename)
@@ -674,7 +762,7 @@ static void close_loose_object(struct odb_source *source,
 		goto out;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		fsync_loose_object_bulk_checkin(fd, filename);
+		fsync_loose_object_transaction(source->odb->transaction, fd, filename);
 	else if (fsync_object_files > 0)
 		fsync_or_die(fd, filename);
 	else
@@ -852,7 +940,7 @@ static int write_loose_object(struct odb_source *source,
 	static struct strbuf filename = STRBUF_INIT;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		prepare_loose_object_bulk_checkin();
+		prepare_loose_object_transaction(source->odb->transaction);
 
 	odb_loose_path(source, &filename, oid);
 
@@ -941,7 +1029,7 @@ int stream_loose_object(struct odb_source *source,
 	int hdrlen;
 
 	if (batch_fsync_enabled(FSYNC_COMPONENT_LOOSE_OBJECT))
-		prepare_loose_object_bulk_checkin();
+		prepare_loose_object_transaction(source->odb->transaction);
 
 	/* Since oid is not determined, save tmp file to odb path. */
 	strbuf_addf(&filename, "%s/", source->path);
@@ -1243,6 +1331,274 @@ static int index_core(struct index_state *istate,
 	return ret;
 }
 
+static int already_written(struct odb_transaction *transaction,
+			   struct object_id *oid)
+{
+	/* The object may already exist in the repository */
+	if (odb_has_object(transaction->odb, oid,
+			   HAS_OBJECT_RECHECK_PACKED | HAS_OBJECT_FETCH_PROMISOR))
+		return 1;
+
+	/* Might want to keep the list sorted */
+	for (uint32_t i = 0; i < transaction->packfile.nr_written; i++)
+		if (oideq(&transaction->packfile.written[i]->oid, oid))
+			return 1;
+
+	/* This is a new object we need to keep */
+	return 0;
+}
+
+/* Lazily create backing packfile for the state */
+static void prepare_packfile_transaction(struct odb_transaction *transaction,
+					 unsigned flags)
+{
+	struct transaction_packfile *state = &transaction->packfile;
+	if (!(flags & INDEX_WRITE_OBJECT) || state->f)
+		return;
+
+	state->f = create_tmp_packfile(transaction->odb->repo,
+				       &state->pack_tmp_name);
+	reset_pack_idx_option(&state->pack_idx_opts);
+
+	/* Pretend we are going to write only one object */
+	state->offset = write_pack_header(state->f, 1);
+	if (!state->offset)
+		die_errno("unable to write pack header");
+}
+
+/*
+ * Read the contents from fd for size bytes, streaming it to the
+ * packfile in state while updating the hash in ctx. Signal a failure
+ * by returning a negative value when the resulting pack would exceed
+ * the pack size limit and this is not the first object in the pack,
+ * so that the caller can discard what we wrote from the current pack
+ * by truncating it and opening a new one. The caller will then call
+ * us again after rewinding the input fd.
+ *
+ * The already_hashed_to pointer is kept untouched by the caller to
+ * make sure we do not hash the same byte when we are called
+ * again. This way, the caller does not have to checkpoint its hash
+ * status before calling us just in case we ask it to call us again
+ * with a new pack.
+ */
+static int stream_blob_to_pack(struct transaction_packfile *state,
+			       struct git_hash_ctx *ctx, off_t *already_hashed_to,
+			       int fd, size_t size, const char *path,
+			       unsigned flags)
+{
+	git_zstream s;
+	unsigned char ibuf[16384];
+	unsigned char obuf[16384];
+	unsigned hdrlen;
+	int status = Z_OK;
+	int write_object = (flags & INDEX_WRITE_OBJECT);
+	off_t offset = 0;
+
+	git_deflate_init(&s, pack_compression_level);
+
+	hdrlen = encode_in_pack_object_header(obuf, sizeof(obuf), OBJ_BLOB, size);
+	s.next_out = obuf + hdrlen;
+	s.avail_out = sizeof(obuf) - hdrlen;
+
+	while (status != Z_STREAM_END) {
+		if (size && !s.avail_in) {
+			size_t rsize = size < sizeof(ibuf) ? size : sizeof(ibuf);
+			ssize_t read_result = read_in_full(fd, ibuf, rsize);
+			if (read_result < 0)
+				die_errno("failed to read from '%s'", path);
+			if ((size_t)read_result != rsize)
+				die("failed to read %u bytes from '%s'",
+				    (unsigned)rsize, path);
+			offset += rsize;
+			if (*already_hashed_to < offset) {
+				size_t hsize = offset - *already_hashed_to;
+				if (rsize < hsize)
+					hsize = rsize;
+				if (hsize)
+					git_hash_update(ctx, ibuf, hsize);
+				*already_hashed_to = offset;
+			}
+			s.next_in = ibuf;
+			s.avail_in = rsize;
+			size -= rsize;
+		}
+
+		status = git_deflate(&s, size ? 0 : Z_FINISH);
+
+		if (!s.avail_out || status == Z_STREAM_END) {
+			if (write_object) {
+				size_t written = s.next_out - obuf;
+
+				/* would we bust the size limit? */
+				if (state->nr_written &&
+				    pack_size_limit_cfg &&
+				    pack_size_limit_cfg < state->offset + written) {
+					git_deflate_abort(&s);
+					return -1;
+				}
+
+				hashwrite(state->f, obuf, written);
+				state->offset += written;
+			}
+			s.next_out = obuf;
+			s.avail_out = sizeof(obuf);
+		}
+
+		switch (status) {
+		case Z_OK:
+		case Z_BUF_ERROR:
+		case Z_STREAM_END:
+			continue;
+		default:
+			die("unexpected deflate failure: %d", status);
+		}
+	}
+	git_deflate_end(&s);
+	return 0;
+}
+
+static void flush_packfile_transaction(struct odb_transaction *transaction)
+{
+	struct transaction_packfile *state = &transaction->packfile;
+	struct repository *repo = transaction->odb->repo;
+	unsigned char hash[GIT_MAX_RAWSZ];
+	struct strbuf packname = STRBUF_INIT;
+	char *idx_tmp_name = NULL;
+
+	if (!state->f)
+		return;
+
+	if (state->nr_written == 0) {
+		close(state->f->fd);
+		free_hashfile(state->f);
+		unlink(state->pack_tmp_name);
+		goto clear_exit;
+	} else if (state->nr_written == 1) {
+		finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK,
+				  CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
+	} else {
+		int fd = finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK, 0);
+		fixup_pack_header_footer(repo->hash_algo, fd, hash, state->pack_tmp_name,
+					 state->nr_written, hash,
+					 state->offset);
+		close(fd);
+	}
+
+	strbuf_addf(&packname, "%s/pack/pack-%s.",
+		    repo_get_object_directory(transaction->odb->repo),
+		    hash_to_hex_algop(hash, repo->hash_algo));
+
+	stage_tmp_packfiles(repo, &packname, state->pack_tmp_name,
+			    state->written, state->nr_written, NULL,
+			    &state->pack_idx_opts, hash, &idx_tmp_name);
+	rename_tmp_packfile_idx(repo, &packname, &idx_tmp_name);
+
+	for (uint32_t i = 0; i < state->nr_written; i++)
+		free(state->written[i]);
+
+clear_exit:
+	free(idx_tmp_name);
+	free(state->pack_tmp_name);
+	free(state->written);
+	memset(state, 0, sizeof(*state));
+
+	strbuf_release(&packname);
+	/* Make objects we just wrote available to ourselves */
+	reprepare_packed_git(repo);
+}
+
+/*
+ * This writes the specified object to a packfile. Objects written here
+ * during the same transaction are written to the same packfile. The
+ * packfile is not flushed until the transaction is flushed. The caller
+ * is expected to ensure a valid transaction is setup for objects to be
+ * recorded to.
+ *
+ * This also bypasses the usual "convert-to-git" dance, and that is on
+ * purpose. We could write a streaming version of the converting
+ * functions and insert that before feeding the data to fast-import
+ * (or equivalent in-core API described above). However, that is
+ * somewhat complicated, as we do not know the size of the filter
+ * result, which we need to know beforehand when writing a git object.
+ * Since the primary motivation for trying to stream from the working
+ * tree file and to avoid mmaping it in core is to deal with large
+ * binary blobs, they generally do not want to get any conversion, and
+ * callers should avoid this code path when filters are requested.
+ */
+static int index_blob_packfile_transaction(struct odb_transaction *transaction,
+					   struct object_id *result_oid, int fd,
+					   size_t size, const char *path,
+					   unsigned flags)
+{
+	struct transaction_packfile *state = &transaction->packfile;
+	off_t seekback, already_hashed_to;
+	struct git_hash_ctx ctx;
+	unsigned char obuf[16384];
+	unsigned header_len;
+	struct hashfile_checkpoint checkpoint;
+	struct pack_idx_entry *idx = NULL;
+
+	seekback = lseek(fd, 0, SEEK_CUR);
+	if (seekback == (off_t)-1)
+		return error("cannot find the current offset");
+
+	header_len = format_object_header((char *)obuf, sizeof(obuf),
+					  OBJ_BLOB, size);
+	transaction->odb->repo->hash_algo->init_fn(&ctx);
+	git_hash_update(&ctx, obuf, header_len);
+
+	/* Note: idx is non-NULL when we are writing */
+	if ((flags & INDEX_WRITE_OBJECT) != 0) {
+		CALLOC_ARRAY(idx, 1);
+
+		prepare_packfile_transaction(transaction, flags);
+		hashfile_checkpoint_init(state->f, &checkpoint);
+	}
+
+	already_hashed_to = 0;
+
+	while (1) {
+		prepare_packfile_transaction(transaction, flags);
+		if (idx) {
+			hashfile_checkpoint(state->f, &checkpoint);
+			idx->offset = state->offset;
+			crc32_begin(state->f);
+		}
+		if (!stream_blob_to_pack(state, &ctx, &already_hashed_to,
+					 fd, size, path, flags))
+			break;
+		/*
+		 * Writing this object to the current pack will make
+		 * it too big; we need to truncate it, start a new
+		 * pack, and write into it.
+		 */
+		if (!idx)
+			BUG("should not happen");
+		hashfile_truncate(state->f, &checkpoint);
+		state->offset = checkpoint.offset;
+		flush_packfile_transaction(transaction);
+		if (lseek(fd, seekback, SEEK_SET) == (off_t)-1)
+			return error("cannot seek back");
+	}
+	git_hash_final_oid(result_oid, &ctx);
+	if (!idx)
+		return 0;
+
+	idx->crc32 = crc32_end(state->f);
+	if (already_written(transaction, result_oid)) {
+		hashfile_truncate(state->f, &checkpoint);
+		state->offset = checkpoint.offset;
+		free(idx);
+	} else {
+		oidcpy(&idx->oid, result_oid);
+		ALLOC_GROW(state->written,
+			   state->nr_written + 1,
+			   state->alloc_written);
+		state->written[state->nr_written++] = idx;
+	}
+	return 0;
+}
+
 int index_fd(struct index_state *istate, struct object_id *oid,
 	     int fd, struct stat *st,
 	     enum object_type type, const char *path, unsigned flags)
@@ -1253,18 +1609,27 @@ int index_fd(struct index_state *istate, struct object_id *oid,
 	 * Call xsize_t() only when needed to avoid potentially unnecessary
 	 * die() for large files.
 	 */
-	if (type == OBJ_BLOB && path && would_convert_to_git_filter_fd(istate, path))
+	if (type == OBJ_BLOB && path && would_convert_to_git_filter_fd(istate, path)) {
 		ret = index_stream_convert_blob(istate, oid, fd, path, flags);
-	else if (!S_ISREG(st->st_mode))
+	} else if (!S_ISREG(st->st_mode)) {
 		ret = index_pipe(istate, oid, fd, type, path, flags);
-	else if ((st->st_size >= 0 && (size_t) st->st_size <= repo_settings_get_big_file_threshold(istate->repo)) ||
-		 type != OBJ_BLOB ||
-		 (path && would_convert_to_git(istate, path)))
+	} else if ((st->st_size >= 0 &&
+		    (size_t)st->st_size <= repo_settings_get_big_file_threshold(istate->repo)) ||
+		   type != OBJ_BLOB ||
+		   (path && would_convert_to_git(istate, path))) {
 		ret = index_core(istate, oid, fd, xsize_t(st->st_size),
 				 type, path, flags);
-	else
-		ret = index_blob_bulk_checkin(oid, fd, xsize_t(st->st_size), path,
-					     flags);
+	} else {
+		struct odb_transaction *transaction;
+
+		transaction = odb_transaction_begin(the_repository->objects);
+		ret = index_blob_packfile_transaction(the_repository->objects->transaction,
+						      oid, fd,
+						      xsize_t(st->st_size),
+						      path, flags);
+		odb_transaction_commit(transaction);
+	}
+
 	close(fd);
 	return ret;
 }
@@ -1601,3 +1966,32 @@ int read_loose_object(struct repository *repo,
 		munmap(map, mapsize);
 	return ret;
 }
+
+struct odb_transaction *object_file_transaction_begin(struct odb_source *source)
+{
+	struct object_database *odb = source->odb;
+
+	if (odb->transaction)
+		return NULL;
+
+	CALLOC_ARRAY(odb->transaction, 1);
+	odb->transaction->odb = odb;
+
+	return odb->transaction;
+}
+
+void object_file_transaction_commit(struct odb_transaction *transaction)
+{
+	if (!transaction)
+		return;
+
+	/*
+	 * Ensure the transaction ending matches the pending transaction.
+	 */
+	ASSERT(transaction == transaction->odb->transaction);
+
+	flush_loose_object_transaction(transaction);
+	flush_packfile_transaction(transaction);
+	transaction->odb->transaction = NULL;
+	free(transaction);
+}
diff --git a/object-file.h b/object-file.h
index 15d97630d3b11b5b4f94f9f6b9d39502928101df..3fd48dcafbf1dc797efabd489e68720e521a38d2 100644
--- a/object-file.h
+++ b/object-file.h
@@ -218,4 +218,20 @@ int read_loose_object(struct repository *repo,
 		      void **contents,
 		      struct object_info *oi);
 
+struct odb_transaction;
+
+/*
+ * Tell the object database to optimize for adding
+ * multiple objects. object_file_transaction_commit must be called
+ * to make new objects visible. If a transaction is already
+ * pending, NULL is returned.
+ */
+struct odb_transaction *object_file_transaction_begin(struct odb_source *source);
+
+/*
+ * Tell the object database to make any objects from the
+ * current transaction visible.
+ */
+void object_file_transaction_commit(struct odb_transaction *transaction);
+
 #endif /* OBJECT_FILE_H */
diff --git a/odb.c b/odb.c
index 2a92a018c42940f131edd4e7cacd3454e66ee370..af9534bfe1cdf548edb87e25d196ec89a453fac4 100644
--- a/odb.c
+++ b/odb.c
@@ -1051,3 +1051,13 @@ void odb_clear(struct object_database *o)
 	hashmap_clear(&o->pack_map);
 	string_list_clear(&o->submodule_source_paths, 0);
 }
+
+struct odb_transaction *odb_transaction_begin(struct object_database *odb)
+{
+	return object_file_transaction_begin(odb->sources);
+}
+
+void odb_transaction_commit(struct odb_transaction *transaction)
+{
+	object_file_transaction_commit(transaction);
+}
diff --git a/odb.h b/odb.h
index 3dfc66d75a3d20dd64d787d04e3ab4e5f9010e8a..82093753c84ca6125101eb2a7b9762aa30a92369 100644
--- a/odb.h
+++ b/odb.h
@@ -84,6 +84,7 @@ struct odb_source {
 
 struct packed_git;
 struct cached_object_entry;
+struct odb_transaction;
 
 /*
  * The object database encapsulates access to objects in a repository. It
@@ -94,6 +95,13 @@ struct object_database {
 	/* Repository that owns this database. */
 	struct repository *repo;
 
+	/*
+	 * State of current current object database transaction. Only one
+	 * transaction may be pending at a time. Is NULL when no transaction is
+	 * configured.
+	 */
+	struct odb_transaction *transaction;
+
 	/*
 	 * Set of all object directories; the main directory is first (and
 	 * cannot be NULL after initialization). Subsequent directories are
@@ -177,6 +185,19 @@ struct object_database {
 struct object_database *odb_new(struct repository *repo);
 void odb_clear(struct object_database *o);
 
+/*
+ * Starts an ODB transaction. Subsequent objects are written to the transaction
+ * and not committed until odb_transaction_commit() is invoked on the
+ * transaction. If the ODB already has a pending transaction, NULL is returned.
+ */
+struct odb_transaction *odb_transaction_begin(struct object_database *odb);
+
+/*
+ * Commits an ODB transaction making the written objects visible. If the
+ * specified transaction is NULL, the function is a no-op.
+ */
+void odb_transaction_commit(struct odb_transaction *transaction);
+
 /*
  * Find source by its object directory path. Dies in case the source couldn't
  * be found.
diff --git a/read-cache.c b/read-cache.c
index 06ad74db2286aee617b0f7bf5eb3c15cc252a3bf..94098a3861403c400ff45eb87c51ba8cbfcafeab 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -8,7 +8,6 @@
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
-#include "bulk-checkin.h"
 #include "config.h"
 #include "date.h"
 #include "diff.h"
@@ -3947,6 +3946,7 @@ int add_files_to_cache(struct repository *repo, const char *prefix,
 		       const struct pathspec *pathspec, char *ps_matched,
 		       int include_sparse, int flags)
 {
+	struct odb_transaction *transaction;
 	struct update_callback_data data;
 	struct rev_info rev;
 
@@ -3972,9 +3972,9 @@ int add_files_to_cache(struct repository *repo, const char *prefix,
 	 * This function is invoked from commands other than 'add', which
 	 * may not have their own transaction active.
 	 */
-	begin_odb_transaction();
+	transaction = odb_transaction_begin(repo->objects);
 	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
-	end_odb_transaction();
+	odb_transaction_commit(transaction);
 
 	release_revisions(&rev);
 	return !!data.add_errors;