From 8434e85d5f9602a82f6b34ba82a9cb9e559a2d3b Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:22 -0700
Subject: [PATCH 01/12] repack: refactor pack deletion for future use

The repack builtin deletes redundant pack-files and their
associated .idx, .promisor, .bitmap, and .keep files. We will want
to re-use this logic in the future for other types of repack, so
pull the logic into 'unlink_pack_path()' in packfile.c.

The 'ignore_keep' parameter is enabled for the use in repack, but
will be important for a future caller.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/repack.c | 14 ++------------
 packfile.c       | 28 ++++++++++++++++++++++++++++
 packfile.h       |  7 +++++++
 3 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/builtin/repack.c b/builtin/repack.c
index caca113927..3ea0583d02 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -129,19 +129,9 @@ static void get_non_kept_pack_filenames(struct string_list *fname_list,
 
 static void remove_redundant_pack(const char *dir_name, const char *base_name)
 {
-	const char *exts[] = {".pack", ".idx", ".keep", ".bitmap", ".promisor"};
-	int i;
 	struct strbuf buf = STRBUF_INIT;
-	size_t plen;
-
-	strbuf_addf(&buf, "%s/%s", dir_name, base_name);
-	plen = buf.len;
-
-	for (i = 0; i < ARRAY_SIZE(exts); i++) {
-		strbuf_setlen(&buf, plen);
-		strbuf_addstr(&buf, exts[i]);
-		unlink(buf.buf);
-	}
+	strbuf_addf(&buf, "%s/%s.pack", dir_name, base_name);
+	unlink_pack_path(buf.buf, 1);
 	strbuf_release(&buf);
 }
 
diff --git a/packfile.c b/packfile.c
index 49c8544ff4..020e61a3b6 100644
--- a/packfile.c
+++ b/packfile.c
@@ -352,6 +352,34 @@ void close_all_packs(struct raw_object_store *o)
 	}
 }
 
+void unlink_pack_path(const char *pack_name, int force_delete)
+{
+	static const char *exts[] = {".pack", ".idx", ".keep", ".bitmap", ".promisor"};
+	int i;
+	struct strbuf buf = STRBUF_INIT;
+	size_t plen;
+
+	strbuf_addstr(&buf, pack_name);
+	strip_suffix_mem(buf.buf, &buf.len, ".pack");
+	plen = buf.len;
+
+	if (!force_delete) {
+		strbuf_addstr(&buf, ".keep");
+		if (!access(buf.buf, F_OK)) {
+			strbuf_release(&buf);
+			return;
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(exts); i++) {
+		strbuf_setlen(&buf, plen);
+		strbuf_addstr(&buf, exts[i]);
+		unlink(buf.buf);
+	}
+
+	strbuf_release(&buf);
+}
+
 /*
  * The LRU pack is the one with the oldest MRU window, preferring packs
  * with no used windows, or the oldest mtime if it has no windows allocated.
diff --git a/packfile.h b/packfile.h
index b678d35c0b..3c436c124f 100644
--- a/packfile.h
+++ b/packfile.h
@@ -95,6 +95,13 @@ void unuse_pack(struct pack_window **);
 void clear_delta_base_cache(void);
 struct packed_git *add_packed_git(const char *path, size_t path_len, int local);
 
+/*
+ * Unlink the .pack and associated extension files.
+ * Does not unlink if 'force_delete' is false and the pack-file is
+ * marked as ".keep".
+ */
+extern void unlink_pack_path(const char *pack_name, int force_delete);
+
 /*
  * Make sure that a pointer access into an mmap'd index file is within bounds,
  * and can provide at least 8 bytes of data.

From 81efa161546d8fc9a89f2565d912137df8cc6c89 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:22 -0700
Subject: [PATCH 02/12] Docs: rearrange subcommands for multi-pack-index
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

We will add new subcommands to the multi-pack-index, and that will
make the documentation a bit messier. Clean up the 'verb'
descriptions by renaming the concept to 'subcommand' and removing
the reference to the object directory.

Helped-by: Stefan Beller <sbeller@google.com>
Helped-by: Szeder Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-multi-pack-index.txt | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index f7778a2c85..1af406aca2 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -9,7 +9,7 @@ git-multi-pack-index - Write and verify multi-pack-indexes
 SYNOPSIS
 --------
 [verse]
-'git multi-pack-index' [--object-dir=<dir>] <verb>
+'git multi-pack-index' [--object-dir=<dir>] <subcommand>
 
 DESCRIPTION
 -----------
@@ -23,13 +23,13 @@ OPTIONS
 	`<dir>/packs/multi-pack-index` for the current MIDX file, and
 	`<dir>/packs` for the pack-files to index.
 
+The following subcommands are available:
+
 write::
-	When given as the verb, write a new MIDX file to
-	`<dir>/packs/multi-pack-index`.
+	Write a new MIDX file.
 
 verify::
-	When given as the verb, verify the contents of the MIDX file
-	at `<dir>/packs/multi-pack-index`.
+	Verify the contents of the MIDX file.
 
 
 EXAMPLES

From cff97116160e57741c9a954a51bfcb0057b3e89d Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:23 -0700
Subject: [PATCH 03/12] multi-pack-index: prepare for 'expire' subcommand

The multi-pack-index tracks objects in a collection of pack-files.
Only one copy of each object is indexed, using the modified time
of the pack-files to determine tie-breakers. It is possible to
have a pack-file with no referenced objects because all objects
have a duplicate in a newer pack-file.

Introduce a new 'expire' subcommand to the multi-pack-index builtin.
This subcommand will delete these unused pack-files and rewrite the
multi-pack-index to no longer refer to those files. More details
about the specifics will follow as the method is implemented.

Add a test that verifies the 'expire' subcommand is correctly wired,
but will still be valid when the verb is implemented. Specifically,
create a set of packs that should all have referenced objects and
should not be removed during an 'expire' operation. The packs are
created carefully to ensure they have a specific order when sorted
by size. This will be important in a later test.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-multi-pack-index.txt |  5 +++
 builtin/multi-pack-index.c             |  4 ++-
 midx.c                                 |  5 +++
 midx.h                                 |  1 +
 t/t5319-multi-pack-index.sh            | 49 ++++++++++++++++++++++++++
 5 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index 1af406aca2..6186c4c936 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -31,6 +31,11 @@ write::
 verify::
 	Verify the contents of the MIDX file.
 
+expire::
+	Delete the pack-files that are tracked 	by the MIDX file, but
+	have no objects referenced by the MIDX. Rewrite the MIDX file
+	afterward to remove all references to these pack-files.
+
 
 EXAMPLES
 --------
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index 72dfd3dadc..ad10d40512 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -6,7 +6,7 @@
 #include "trace2.h"
 
 static char const * const builtin_multi_pack_index_usage[] = {
-	N_("git multi-pack-index [--object-dir=<dir>] (write|verify)"),
+	N_("git multi-pack-index [--object-dir=<dir>] (write|verify|expire)"),
 	NULL
 };
 
@@ -47,6 +47,8 @@ int cmd_multi_pack_index(int argc, const char **argv,
 		return write_midx_file(opts.object_dir);
 	if (!strcmp(argv[0], "verify"))
 		return verify_midx_file(the_repository, opts.object_dir);
+	if (!strcmp(argv[0], "expire"))
+		return expire_midx_packs(the_repository, opts.object_dir);
 
 	die(_("unrecognized verb: %s"), argv[0]);
 }
diff --git a/midx.c b/midx.c
index e7e1fe4d65..3b7da1a360 100644
--- a/midx.c
+++ b/midx.c
@@ -1140,3 +1140,8 @@ int verify_midx_file(struct repository *r, const char *object_dir)
 
 	return verify_midx_error;
 }
+
+int expire_midx_packs(struct repository *r, const char *object_dir)
+{
+	return 0;
+}
diff --git a/midx.h b/midx.h
index 3eb29731f2..505f1431b7 100644
--- a/midx.h
+++ b/midx.h
@@ -50,6 +50,7 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 int write_midx_file(const char *object_dir);
 void clear_midx_file(struct repository *r);
 int verify_midx_file(struct repository *r, const char *object_dir);
+int expire_midx_packs(struct repository *r, const char *object_dir);
 
 void close_midx(struct multi_pack_index *m);
 
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 1ebf19ec3c..1b2d32f475 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -363,4 +363,53 @@ test_expect_success 'verify incorrect 64-bit offset' '
 		"incorrect object offset"
 '
 
+test_expect_success 'setup expire tests' '
+	mkdir dup &&
+	(
+		cd dup &&
+		git init &&
+		test-tool genrandom "data" 4096 >large_file.txt &&
+		git update-index --add large_file.txt &&
+		for i in $(test_seq 1 20)
+		do
+			test_commit $i
+		done &&
+		git branch A HEAD &&
+		git branch B HEAD~8 &&
+		git branch C HEAD~13 &&
+		git branch D HEAD~16 &&
+		git branch E HEAD~18 &&
+		git pack-objects --revs .git/objects/pack/pack-A <<-EOF &&
+		refs/heads/A
+		^refs/heads/B
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-B <<-EOF &&
+		refs/heads/B
+		^refs/heads/C
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-C <<-EOF &&
+		refs/heads/C
+		^refs/heads/D
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-D <<-EOF &&
+		refs/heads/D
+		^refs/heads/E
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-E <<-EOF &&
+		refs/heads/E
+		EOF
+		git multi-pack-index write
+	)
+'
+
+test_expect_success 'expire does not remove any packs' '
+	(
+		cd dup &&
+		ls .git/objects/pack >expect &&
+		git multi-pack-index expire &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done

From dba6175c64cdc9485198395b4c3c715fd2402230 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:24 -0700
Subject: [PATCH 04/12] midx: simplify computation of pack name lengths

Before writing the multi-pack-index, we compute the length of the
pack-index names concatenated together. This forms the data in the
pack name chunk, and we precompute it to compute chunk offsets.
The value is also modified to fit alignment needs.

Previously, this computation was coupled with adding packs from
the existing multi-pack-index and the remaining packs in the object
dir not already covered by the multi-pack-index.

In anticipation of this becoming more complicated with the 'expire'
subcommand, simplify the computation by centralizing it to a single
loop before writing the file.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 midx.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/midx.c b/midx.c
index 3b7da1a360..62404620ad 100644
--- a/midx.c
+++ b/midx.c
@@ -433,7 +433,6 @@ struct pack_list {
 	uint32_t nr;
 	uint32_t alloc_list;
 	uint32_t alloc_names;
-	size_t pack_name_concat_len;
 	struct multi_pack_index *m;
 };
 
@@ -468,7 +467,6 @@ static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 		}
 
 		packs->names[packs->nr] = xstrdup(file_name);
-		packs->pack_name_concat_len += strlen(file_name) + 1;
 		packs->nr++;
 	}
 }
@@ -812,6 +810,7 @@ int write_midx_file(const char *object_dir)
 	uint32_t nr_entries, num_large_offsets = 0;
 	struct pack_midx_entry *entries = NULL;
 	int large_offsets_needed = 0;
+	int pack_name_concat_len = 0;
 
 	midx_name = get_midx_filename(object_dir);
 	if (safe_create_leading_directories(midx_name)) {
@@ -827,7 +826,6 @@ int write_midx_file(const char *object_dir)
 	packs.alloc_names = packs.alloc_list;
 	packs.list = NULL;
 	packs.names = NULL;
-	packs.pack_name_concat_len = 0;
 	ALLOC_ARRAY(packs.list, packs.alloc_list);
 	ALLOC_ARRAY(packs.names, packs.alloc_names);
 
@@ -838,7 +836,6 @@ int write_midx_file(const char *object_dir)
 
 			packs.list[packs.nr] = NULL;
 			packs.names[packs.nr] = xstrdup(packs.m->pack_names[i]);
-			packs.pack_name_concat_len += strlen(packs.names[packs.nr]) + 1;
 			packs.nr++;
 		}
 	}
@@ -848,10 +845,6 @@ int write_midx_file(const char *object_dir)
 	if (packs.m && packs.nr == packs.m->num_packs)
 		goto cleanup;
 
-	if (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
-		packs.pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
-					      (packs.pack_name_concat_len % MIDX_CHUNK_ALIGNMENT);
-
 	ALLOC_ARRAY(pack_perm, packs.nr);
 	sort_packs_by_name(packs.names, packs.nr, pack_perm);
 
@@ -864,6 +857,13 @@ int write_midx_file(const char *object_dir)
 			large_offsets_needed = 1;
 	}
 
+	for (i = 0; i < packs.nr; i++)
+		pack_name_concat_len += strlen(packs.names[i]) + 1;
+
+	if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
+		pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
+					(pack_name_concat_len % MIDX_CHUNK_ALIGNMENT);
+
 	hold_lock_file_for_update(&lk, midx_name, LOCK_DIE_ON_ERROR);
 	f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
 	FREE_AND_NULL(midx_name);
@@ -881,7 +881,7 @@ int write_midx_file(const char *object_dir)
 
 	cur_chunk++;
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_OIDFANOUT;
-	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + packs.pack_name_concat_len;
+	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + pack_name_concat_len;
 
 	cur_chunk++;
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_OIDLOOKUP;

From d01bf2e609bf792820023fc0f4ef5048bc689327 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:24 -0700
Subject: [PATCH 05/12] midx: refactor permutation logic and pack sorting

In anticipation of the expire subcommand, refactor the way we sort
the packfiles by name. This will greatly simplify our approach to
dropping expired packs from the list.

First, create 'struct pack_info' to replace 'struct pack_pair'.
This struct contains the necessary information about a pack,
including its name, a pointer to its packfile struct (if not
already in the multi-pack-index), and the original pack-int-id.

Second, track the pack information using an array of pack_info
structs in the pack_list struct. This simplifies the logic around
the multiple arrays we were tracking in that struct.

Finally, update get_sorted_entries() to not permute the pack-int-id
and instead supply the permutation to write_midx_object_offsets().
This requires sorting the packs after get_sorted_entries().

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 midx.c | 156 +++++++++++++++++++++++++--------------------------------
 1 file changed, 69 insertions(+), 87 deletions(-)

diff --git a/midx.c b/midx.c
index 62404620ad..6d4b84e243 100644
--- a/midx.c
+++ b/midx.c
@@ -427,12 +427,23 @@ static size_t write_midx_header(struct hashfile *f,
 	return MIDX_HEADER_SIZE;
 }
 
+struct pack_info {
+	uint32_t orig_pack_int_id;
+	char *pack_name;
+	struct packed_git *p;
+};
+
+static int pack_info_compare(const void *_a, const void *_b)
+{
+	struct pack_info *a = (struct pack_info *)_a;
+	struct pack_info *b = (struct pack_info *)_b;
+	return strcmp(a->pack_name, b->pack_name);
+}
+
 struct pack_list {
-	struct packed_git **list;
-	char **names;
+	struct pack_info *info;
 	uint32_t nr;
-	uint32_t alloc_list;
-	uint32_t alloc_names;
+	uint32_t alloc;
 	struct multi_pack_index *m;
 };
 
@@ -445,66 +456,32 @@ static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 		if (packs->m && midx_contains_pack(packs->m, file_name))
 			return;
 
-		ALLOC_GROW(packs->list, packs->nr + 1, packs->alloc_list);
-		ALLOC_GROW(packs->names, packs->nr + 1, packs->alloc_names);
+		ALLOC_GROW(packs->info, packs->nr + 1, packs->alloc);
 
-		packs->list[packs->nr] = add_packed_git(full_path,
-							full_path_len,
-							0);
+		packs->info[packs->nr].p = add_packed_git(full_path,
+							  full_path_len,
+							  0);
 
-		if (!packs->list[packs->nr]) {
+		if (!packs->info[packs->nr].p) {
 			warning(_("failed to add packfile '%s'"),
 				full_path);
 			return;
 		}
 
-		if (open_pack_index(packs->list[packs->nr])) {
+		if (open_pack_index(packs->info[packs->nr].p)) {
 			warning(_("failed to open pack-index '%s'"),
 				full_path);
-			close_pack(packs->list[packs->nr]);
-			FREE_AND_NULL(packs->list[packs->nr]);
+			close_pack(packs->info[packs->nr].p);
+			FREE_AND_NULL(packs->info[packs->nr].p);
 			return;
 		}
 
-		packs->names[packs->nr] = xstrdup(file_name);
+		packs->info[packs->nr].pack_name = xstrdup(file_name);
+		packs->info[packs->nr].orig_pack_int_id = packs->nr;
 		packs->nr++;
 	}
 }
 
-struct pack_pair {
-	uint32_t pack_int_id;
-	char *pack_name;
-};
-
-static int pack_pair_compare(const void *_a, const void *_b)
-{
-	struct pack_pair *a = (struct pack_pair *)_a;
-	struct pack_pair *b = (struct pack_pair *)_b;
-	return strcmp(a->pack_name, b->pack_name);
-}
-
-static void sort_packs_by_name(char **pack_names, uint32_t nr_packs, uint32_t *perm)
-{
-	uint32_t i;
-	struct pack_pair *pairs;
-
-	ALLOC_ARRAY(pairs, nr_packs);
-
-	for (i = 0; i < nr_packs; i++) {
-		pairs[i].pack_int_id = i;
-		pairs[i].pack_name = pack_names[i];
-	}
-
-	QSORT(pairs, nr_packs, pack_pair_compare);
-
-	for (i = 0; i < nr_packs; i++) {
-		pack_names[i] = pairs[i].pack_name;
-		perm[pairs[i].pack_int_id] = i;
-	}
-
-	free(pairs);
-}
-
 struct pack_midx_entry {
 	struct object_id oid;
 	uint32_t pack_int_id;
@@ -530,7 +507,6 @@ static int midx_oid_compare(const void *_a, const void *_b)
 }
 
 static int nth_midxed_pack_midx_entry(struct multi_pack_index *m,
-				      uint32_t *pack_perm,
 				      struct pack_midx_entry *e,
 				      uint32_t pos)
 {
@@ -538,7 +514,7 @@ static int nth_midxed_pack_midx_entry(struct multi_pack_index *m,
 		return 1;
 
 	nth_midxed_object_oid(&e->oid, m, pos);
-	e->pack_int_id = pack_perm[nth_midxed_pack_int_id(m, pos)];
+	e->pack_int_id = nth_midxed_pack_int_id(m, pos);
 	e->offset = nth_midxed_offset(m, pos);
 
 	/* consider objects in midx to be from "old" packs */
@@ -572,8 +548,7 @@ static void fill_pack_entry(uint32_t pack_int_id,
  * of a packfile containing the object).
  */
 static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
-						  struct packed_git **p,
-						  uint32_t *perm,
+						  struct pack_info *info,
 						  uint32_t nr_packs,
 						  uint32_t *nr_objects)
 {
@@ -584,7 +559,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 	uint32_t start_pack = m ? m->num_packs : 0;
 
 	for (cur_pack = start_pack; cur_pack < nr_packs; cur_pack++)
-		total_objects += p[cur_pack]->num_objects;
+		total_objects += info[cur_pack].p->num_objects;
 
 	/*
 	 * As we de-duplicate by fanout value, we expect the fanout
@@ -609,7 +584,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 
 			for (cur_object = start; cur_object < end; cur_object++) {
 				ALLOC_GROW(entries_by_fanout, nr_fanout + 1, alloc_fanout);
-				nth_midxed_pack_midx_entry(m, perm,
+				nth_midxed_pack_midx_entry(m,
 							   &entries_by_fanout[nr_fanout],
 							   cur_object);
 				nr_fanout++;
@@ -620,12 +595,12 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 			uint32_t start = 0, end;
 
 			if (cur_fanout)
-				start = get_pack_fanout(p[cur_pack], cur_fanout - 1);
-			end = get_pack_fanout(p[cur_pack], cur_fanout);
+				start = get_pack_fanout(info[cur_pack].p, cur_fanout - 1);
+			end = get_pack_fanout(info[cur_pack].p, cur_fanout);
 
 			for (cur_object = start; cur_object < end; cur_object++) {
 				ALLOC_GROW(entries_by_fanout, nr_fanout + 1, alloc_fanout);
-				fill_pack_entry(perm[cur_pack], p[cur_pack], cur_object, &entries_by_fanout[nr_fanout]);
+				fill_pack_entry(cur_pack, info[cur_pack].p, cur_object, &entries_by_fanout[nr_fanout]);
 				nr_fanout++;
 			}
 		}
@@ -654,7 +629,7 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 }
 
 static size_t write_midx_pack_names(struct hashfile *f,
-				    char **pack_names,
+				    struct pack_info *info,
 				    uint32_t num_packs)
 {
 	uint32_t i;
@@ -662,14 +637,14 @@ static size_t write_midx_pack_names(struct hashfile *f,
 	size_t written = 0;
 
 	for (i = 0; i < num_packs; i++) {
-		size_t writelen = strlen(pack_names[i]) + 1;
+		size_t writelen = strlen(info[i].pack_name) + 1;
 
-		if (i && strcmp(pack_names[i], pack_names[i - 1]) <= 0)
+		if (i && strcmp(info[i].pack_name, info[i - 1].pack_name) <= 0)
 			BUG("incorrect pack-file order: %s before %s",
-			    pack_names[i - 1],
-			    pack_names[i]);
+			    info[i - 1].pack_name,
+			    info[i].pack_name);
 
-		hashwrite(f, pack_names[i], writelen);
+		hashwrite(f, info[i].pack_name, writelen);
 		written += writelen;
 	}
 
@@ -740,6 +715,7 @@ static size_t write_midx_oid_lookup(struct hashfile *f, unsigned char hash_len,
 }
 
 static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_needed,
+					uint32_t *perm,
 					struct pack_midx_entry *objects, uint32_t nr_objects)
 {
 	struct pack_midx_entry *list = objects;
@@ -749,7 +725,7 @@ static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_nee
 	for (i = 0; i < nr_objects; i++) {
 		struct pack_midx_entry *obj = list++;
 
-		hashwrite_be32(f, obj->pack_int_id);
+		hashwrite_be32(f, perm[obj->pack_int_id]);
 
 		if (large_offset_needed && obj->offset >> 31)
 			hashwrite_be32(f, MIDX_LARGE_OFFSET_NEEDED | nr_large_offset++);
@@ -822,20 +798,17 @@ int write_midx_file(const char *object_dir)
 	packs.m = load_multi_pack_index(object_dir, 1);
 
 	packs.nr = 0;
-	packs.alloc_list = packs.m ? packs.m->num_packs : 16;
-	packs.alloc_names = packs.alloc_list;
-	packs.list = NULL;
-	packs.names = NULL;
-	ALLOC_ARRAY(packs.list, packs.alloc_list);
-	ALLOC_ARRAY(packs.names, packs.alloc_names);
+	packs.alloc = packs.m ? packs.m->num_packs : 16;
+	packs.info = NULL;
+	ALLOC_ARRAY(packs.info, packs.alloc);
 
 	if (packs.m) {
 		for (i = 0; i < packs.m->num_packs; i++) {
-			ALLOC_GROW(packs.list, packs.nr + 1, packs.alloc_list);
-			ALLOC_GROW(packs.names, packs.nr + 1, packs.alloc_names);
+			ALLOC_GROW(packs.info, packs.nr + 1, packs.alloc);
 
-			packs.list[packs.nr] = NULL;
-			packs.names[packs.nr] = xstrdup(packs.m->pack_names[i]);
+			packs.info[packs.nr].orig_pack_int_id = i;
+			packs.info[packs.nr].pack_name = xstrdup(packs.m->pack_names[i]);
+			packs.info[packs.nr].p = NULL;
 			packs.nr++;
 		}
 	}
@@ -845,10 +818,7 @@ int write_midx_file(const char *object_dir)
 	if (packs.m && packs.nr == packs.m->num_packs)
 		goto cleanup;
 
-	ALLOC_ARRAY(pack_perm, packs.nr);
-	sort_packs_by_name(packs.names, packs.nr, pack_perm);
-
-	entries = get_sorted_entries(packs.m, packs.list, pack_perm, packs.nr, &nr_entries);
+	entries = get_sorted_entries(packs.m, packs.info, packs.nr, &nr_entries);
 
 	for (i = 0; i < nr_entries; i++) {
 		if (entries[i].offset > 0x7fffffff)
@@ -857,8 +827,21 @@ int write_midx_file(const char *object_dir)
 			large_offsets_needed = 1;
 	}
 
+	QSORT(packs.info, packs.nr, pack_info_compare);
+
+	/*
+	 * pack_perm stores a permutation between pack-int-ids from the
+	 * previous multi-pack-index to the new one we are writing:
+	 *
+	 * pack_perm[old_id] = new_id
+	 */
+	ALLOC_ARRAY(pack_perm, packs.nr);
+	for (i = 0; i < packs.nr; i++) {
+		pack_perm[packs.info[i].orig_pack_int_id] = i;
+	}
+
 	for (i = 0; i < packs.nr; i++)
-		pack_name_concat_len += strlen(packs.names[i]) + 1;
+		pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
 
 	if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
 		pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
@@ -929,7 +912,7 @@ int write_midx_file(const char *object_dir)
 
 		switch (chunk_ids[i]) {
 			case MIDX_CHUNKID_PACKNAMES:
-				written += write_midx_pack_names(f, packs.names, packs.nr);
+				written += write_midx_pack_names(f, packs.info, packs.nr);
 				break;
 
 			case MIDX_CHUNKID_OIDFANOUT:
@@ -941,7 +924,7 @@ int write_midx_file(const char *object_dir)
 				break;
 
 			case MIDX_CHUNKID_OBJECTOFFSETS:
-				written += write_midx_object_offsets(f, large_offsets_needed, entries, nr_entries);
+				written += write_midx_object_offsets(f, large_offsets_needed, pack_perm, entries, nr_entries);
 				break;
 
 			case MIDX_CHUNKID_LARGEOFFSETS:
@@ -964,15 +947,14 @@ int write_midx_file(const char *object_dir)
 
 cleanup:
 	for (i = 0; i < packs.nr; i++) {
-		if (packs.list[i]) {
-			close_pack(packs.list[i]);
-			free(packs.list[i]);
+		if (packs.info[i].p) {
+			close_pack(packs.info[i].p);
+			free(packs.info[i].p);
 		}
-		free(packs.names[i]);
+		free(packs.info[i].pack_name);
 	}
 
-	free(packs.list);
-	free(packs.names);
+	free(packs.info);
 	free(entries);
 	free(pack_perm);
 	free(midx_name);

From 19575c7c8e60c95c6714e51039ee9a21721cc31d Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:25 -0700
Subject: [PATCH 06/12] multi-pack-index: implement 'expire' subcommand

The 'git multi-pack-index expire' subcommand looks at the existing
mult-pack-index, counts the number of objects referenced in each
pack-file, deletes the pack-fils with no referenced objects, and
rewrites the multi-pack-index to no longer reference those packs.

Refactor the write_midx_file() method to call write_midx_internal()
which now takes an existing 'struct multi_pack_index' and a list
of pack-files to drop (as specified by the names of their pack-
indexes). As we write the new multi-pack-index, we drop those
file names from the list of known pack-files.

The expire_midx_packs() method removes the unreferenced pack-files
after carefully closing the packs to avoid open handles.

Test that a new pack-file that covers the contents of two other
pack-files leads to those pack-files being deleted during the
expire subcommand. Be sure to read the multi-pack-index to ensure
it no longer references those packs.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 midx.c                      | 119 +++++++++++++++++++++++++++++++++---
 t/t5319-multi-pack-index.sh |  20 ++++++
 2 files changed, 129 insertions(+), 10 deletions(-)

diff --git a/midx.c b/midx.c
index 6d4b84e243..9b0b4c1520 100644
--- a/midx.c
+++ b/midx.c
@@ -34,6 +34,8 @@
 #define MIDX_CHUNK_LARGE_OFFSET_WIDTH (sizeof(uint64_t))
 #define MIDX_LARGE_OFFSET_NEEDED 0x80000000
 
+#define PACK_EXPIRED UINT_MAX
+
 static char *get_midx_filename(const char *object_dir)
 {
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
@@ -431,6 +433,7 @@ struct pack_info {
 	uint32_t orig_pack_int_id;
 	char *pack_name;
 	struct packed_git *p;
+	unsigned expired : 1;
 };
 
 static int pack_info_compare(const void *_a, const void *_b)
@@ -478,6 +481,7 @@ static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 
 		packs->info[packs->nr].pack_name = xstrdup(file_name);
 		packs->info[packs->nr].orig_pack_int_id = packs->nr;
+		packs->info[packs->nr].expired = 0;
 		packs->nr++;
 	}
 }
@@ -637,13 +641,17 @@ static size_t write_midx_pack_names(struct hashfile *f,
 	size_t written = 0;
 
 	for (i = 0; i < num_packs; i++) {
-		size_t writelen = strlen(info[i].pack_name) + 1;
+		size_t writelen;
+
+		if (info[i].expired)
+			continue;
 
 		if (i && strcmp(info[i].pack_name, info[i - 1].pack_name) <= 0)
 			BUG("incorrect pack-file order: %s before %s",
 			    info[i - 1].pack_name,
 			    info[i].pack_name);
 
+		writelen = strlen(info[i].pack_name) + 1;
 		hashwrite(f, info[i].pack_name, writelen);
 		written += writelen;
 	}
@@ -725,6 +733,11 @@ static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_nee
 	for (i = 0; i < nr_objects; i++) {
 		struct pack_midx_entry *obj = list++;
 
+		if (perm[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, perm[obj->pack_int_id]);
 
 		if (large_offset_needed && obj->offset >> 31)
@@ -771,7 +784,8 @@ static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_off
 	return written;
 }
 
-int write_midx_file(const char *object_dir)
+static int write_midx_internal(const char *object_dir, struct multi_pack_index *m,
+			       struct string_list *packs_to_drop)
 {
 	unsigned char cur_chunk, num_chunks = 0;
 	char *midx_name;
@@ -787,6 +801,8 @@ int write_midx_file(const char *object_dir)
 	struct pack_midx_entry *entries = NULL;
 	int large_offsets_needed = 0;
 	int pack_name_concat_len = 0;
+	int dropped_packs = 0;
+	int result = 0;
 
 	midx_name = get_midx_filename(object_dir);
 	if (safe_create_leading_directories(midx_name)) {
@@ -795,7 +811,10 @@ int write_midx_file(const char *object_dir)
 			  midx_name);
 	}
 
-	packs.m = load_multi_pack_index(object_dir, 1);
+	if (m)
+		packs.m = m;
+	else
+		packs.m = load_multi_pack_index(object_dir, 1);
 
 	packs.nr = 0;
 	packs.alloc = packs.m ? packs.m->num_packs : 16;
@@ -809,13 +828,14 @@ int write_midx_file(const char *object_dir)
 			packs.info[packs.nr].orig_pack_int_id = i;
 			packs.info[packs.nr].pack_name = xstrdup(packs.m->pack_names[i]);
 			packs.info[packs.nr].p = NULL;
+			packs.info[packs.nr].expired = 0;
 			packs.nr++;
 		}
 	}
 
 	for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &packs);
 
-	if (packs.m && packs.nr == packs.m->num_packs)
+	if (packs.m && packs.nr == packs.m->num_packs && !packs_to_drop)
 		goto cleanup;
 
 	entries = get_sorted_entries(packs.m, packs.info, packs.nr, &nr_entries);
@@ -829,6 +849,34 @@ int write_midx_file(const char *object_dir)
 
 	QSORT(packs.info, packs.nr, pack_info_compare);
 
+	if (packs_to_drop && packs_to_drop->nr) {
+		int drop_index = 0;
+		int missing_drops = 0;
+
+		for (i = 0; i < packs.nr && drop_index < packs_to_drop->nr; i++) {
+			int cmp = strcmp(packs.info[i].pack_name,
+					 packs_to_drop->items[drop_index].string);
+
+			if (!cmp) {
+				drop_index++;
+				packs.info[i].expired = 1;
+			} else if (cmp > 0) {
+				error(_("did not see pack-file %s to drop"),
+				      packs_to_drop->items[drop_index].string);
+				drop_index++;
+				missing_drops++;
+				i--;
+			} else {
+				packs.info[i].expired = 0;
+			}
+		}
+
+		if (missing_drops) {
+			result = 1;
+			goto cleanup;
+		}
+	}
+
 	/*
 	 * pack_perm stores a permutation between pack-int-ids from the
 	 * previous multi-pack-index to the new one we are writing:
@@ -837,11 +885,18 @@ int write_midx_file(const char *object_dir)
 	 */
 	ALLOC_ARRAY(pack_perm, packs.nr);
 	for (i = 0; i < packs.nr; i++) {
-		pack_perm[packs.info[i].orig_pack_int_id] = i;
+		if (packs.info[i].expired) {
+			dropped_packs++;
+			pack_perm[packs.info[i].orig_pack_int_id] = PACK_EXPIRED;
+		} else {
+			pack_perm[packs.info[i].orig_pack_int_id] = i - dropped_packs;
+		}
 	}
 
-	for (i = 0; i < packs.nr; i++)
-		pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+	for (i = 0; i < packs.nr; i++) {
+		if (!packs.info[i].expired)
+			pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+	}
 
 	if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
 		pack_name_concat_len += MIDX_CHUNK_ALIGNMENT -
@@ -857,7 +912,7 @@ int write_midx_file(const char *object_dir)
 	cur_chunk = 0;
 	num_chunks = large_offsets_needed ? 5 : 4;
 
-	written = write_midx_header(f, num_chunks, packs.nr);
+	written = write_midx_header(f, num_chunks, packs.nr - dropped_packs);
 
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
 	chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
@@ -958,7 +1013,12 @@ cleanup:
 	free(entries);
 	free(pack_perm);
 	free(midx_name);
-	return 0;
+	return result;
+}
+
+int write_midx_file(const char *object_dir)
+{
+	return write_midx_internal(object_dir, NULL, NULL);
 }
 
 void clear_midx_file(struct repository *r)
@@ -1125,5 +1185,44 @@ int verify_midx_file(struct repository *r, const char *object_dir)
 
 int expire_midx_packs(struct repository *r, const char *object_dir)
 {
-	return 0;
+	uint32_t i, *count, result = 0;
+	struct string_list packs_to_drop = STRING_LIST_INIT_DUP;
+	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+	if (!m)
+		return 0;
+
+	count = xcalloc(m->num_packs, sizeof(uint32_t));
+	for (i = 0; i < m->num_objects; i++) {
+		int pack_int_id = nth_midxed_pack_int_id(m, i);
+		count[pack_int_id]++;
+	}
+
+	for (i = 0; i < m->num_packs; i++) {
+		char *pack_name;
+
+		if (count[i])
+			continue;
+
+		if (prepare_midx_pack(r, m, i))
+			continue;
+
+		if (m->packs[i]->pack_keep)
+			continue;
+
+		pack_name = xstrdup(m->packs[i]->pack_name);
+		close_pack(m->packs[i]);
+
+		string_list_insert(&packs_to_drop, m->pack_names[i]);
+		unlink_pack_path(pack_name, 0);
+		free(pack_name);
+	}
+
+	free(count);
+
+	if (packs_to_drop.nr)
+		result = write_midx_internal(object_dir, m, &packs_to_drop);
+
+	string_list_clear(&packs_to_drop, 0);
+	return result;
 }
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 1b2d32f475..12570fe7ac 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -412,4 +412,24 @@ test_expect_success 'expire does not remove any packs' '
 	)
 '
 
+test_expect_success 'expire removes unreferenced packs' '
+	(
+		cd dup &&
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/A
+		^refs/heads/C
+		EOF
+		git multi-pack-index write &&
+		ls .git/objects/pack | grep -v -e pack-[AB] >expect &&
+		git multi-pack-index expire &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual &&
+		ls .git/objects/pack/ | grep idx >expect-idx &&
+		test-tool read-midx .git/objects | grep idx >actual-midx &&
+		test_cmp expect-idx actual-midx &&
+		git multi-pack-index verify &&
+		git fsck
+	)
+'
+
 test_done

From 2af890bb28013ae9edf8f5de7873fac849d39c32 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:26 -0700
Subject: [PATCH 07/12] multi-pack-index: prepare 'repack' subcommand

In an environment where the multi-pack-index is useful, it is due
to many pack-files and an inability to repack the object store
into a single pack-file. However, it is likely that many of these
pack-files are rather small, and could be repacked into a slightly
larger pack-file without too much effort. It may also be important
to ensure the object store is highly available and the repack
operation does not interrupt concurrent git commands.

Introduce a 'repack' subcommand to 'git multi-pack-index' that
takes a '--batch-size' option. The subcommand will inspect the
multi-pack-index for referenced pack-files whose size is smaller
than the batch size, until collecting a list of pack-files whose
sizes sum to larger than the batch size. Then, a new pack-file
will be created containing the objects from those pack-files that
are referenced by the multi-pack-index. The resulting pack is
likely to actually be smaller than the batch size due to
compression and the fact that there may be objects in the pack-
files that have duplicate copies in other pack-files.

The current change introduces the command-line arguments, and we
add a test that ensures we parse these options properly. Since
we specify a small batch size, we will guarantee that future
implementations do not change the list of pack-files.

In addition, we hard-code the modified times of the packs in
the pack directory to ensure the list of packs sorted by modified
time matches the order if sorted by size (ascending). This will
be important in a future test.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-multi-pack-index.txt | 17 +++++++++++++++++
 builtin/multi-pack-index.c             | 12 ++++++++++--
 midx.c                                 |  5 +++++
 midx.h                                 |  1 +
 t/t5319-multi-pack-index.sh            | 20 +++++++++++++++++++-
 5 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index 6186c4c936..233b2b7862 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -36,6 +36,23 @@ expire::
 	have no objects referenced by the MIDX. Rewrite the MIDX file
 	afterward to remove all references to these pack-files.
 
+repack::
+	Create a new pack-file containing objects in small pack-files
+	referenced by the multi-pack-index. If the size given by the
+	`--batch-size=<size>` argument is zero, then create a pack
+	containing all objects referenced by the multi-pack-index. For
+	a non-zero batch size, Select the pack-files by examining packs
+	from oldest-to-newest, computing the "expected size" by counting
+	the number of objects in the pack referenced by the
+	multi-pack-index, then divide by the total number of objects in
+	the pack and multiply by the pack size. We select packs with
+	expected size below the batch size until the set of packs have
+	total expected size at least the batch size. If the total size
+	does not reach the batch size, then do nothing. If a new pack-
+	file is created, rewrite the multi-pack-index to reference the
+	new pack-file. A later run of 'git multi-pack-index expire' will
+	delete the pack-files that were part of this batch.
+
 
 EXAMPLES
 --------
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index ad10d40512..b1ea1a6aa1 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -6,12 +6,13 @@
 #include "trace2.h"
 
 static char const * const builtin_multi_pack_index_usage[] = {
-	N_("git multi-pack-index [--object-dir=<dir>] (write|verify|expire)"),
+	N_("git multi-pack-index [--object-dir=<dir>] (write|verify|expire|repack --batch-size=<size>)"),
 	NULL
 };
 
 static struct opts_multi_pack_index {
 	const char *object_dir;
+	unsigned long batch_size;
 } opts;
 
 int cmd_multi_pack_index(int argc, const char **argv,
@@ -20,6 +21,8 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	static struct option builtin_multi_pack_index_options[] = {
 		OPT_FILENAME(0, "object-dir", &opts.object_dir,
 		  N_("object directory containing set of packfile and pack-index pairs")),
+		OPT_MAGNITUDE(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_END(),
 	};
 
@@ -43,6 +46,11 @@ int cmd_multi_pack_index(int argc, const char **argv,
 
 	trace2_cmd_mode(argv[0]);
 
+	if (!strcmp(argv[0], "repack"))
+		return midx_repack(the_repository, opts.object_dir, (size_t)opts.batch_size);
+	if (opts.batch_size)
+		die(_("--batch-size option is only for 'repack' subcommand"));
+
 	if (!strcmp(argv[0], "write"))
 		return write_midx_file(opts.object_dir);
 	if (!strcmp(argv[0], "verify"))
@@ -50,5 +58,5 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	if (!strcmp(argv[0], "expire"))
 		return expire_midx_packs(the_repository, opts.object_dir);
 
-	die(_("unrecognized verb: %s"), argv[0]);
+	die(_("unrecognized subcommand: %s"), argv[0]);
 }
diff --git a/midx.c b/midx.c
index 9b0b4c1520..fbed8a8adb 100644
--- a/midx.c
+++ b/midx.c
@@ -1226,3 +1226,8 @@ int expire_midx_packs(struct repository *r, const char *object_dir)
 	string_list_clear(&packs_to_drop, 0);
 	return result;
 }
+
+int midx_repack(struct repository *r, const char *object_dir, size_t batch_size)
+{
+	return 0;
+}
diff --git a/midx.h b/midx.h
index 505f1431b7..f0ae656b5d 100644
--- a/midx.h
+++ b/midx.h
@@ -51,6 +51,7 @@ int write_midx_file(const char *object_dir);
 void clear_midx_file(struct repository *r);
 int verify_midx_file(struct repository *r, const char *object_dir);
 int expire_midx_packs(struct repository *r, const char *object_dir);
+int midx_repack(struct repository *r, const char *object_dir, size_t batch_size);
 
 void close_midx(struct multi_pack_index *m);
 
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 12570fe7ac..133d5b7068 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -398,7 +398,8 @@ test_expect_success 'setup expire tests' '
 		git pack-objects --revs .git/objects/pack/pack-E <<-EOF &&
 		refs/heads/E
 		EOF
-		git multi-pack-index write
+		git multi-pack-index write &&
+		cp -r .git/objects/pack .git/objects/pack-backup
 	)
 '
 
@@ -432,4 +433,21 @@ test_expect_success 'expire removes unreferenced packs' '
 	)
 '
 
+test_expect_success 'repack with minimum size does not alter existing packs' '
+	(
+		cd dup &&
+		rm -rf .git/objects/pack &&
+		mv .git/objects/pack-backup .git/objects/pack &&
+		touch -m -t 201901010000 .git/objects/pack/pack-D* &&
+		touch -m -t 201901010001 .git/objects/pack/pack-C* &&
+		touch -m -t 201901010002 .git/objects/pack/pack-B* &&
+		touch -m -t 201901010003 .git/objects/pack/pack-A* &&
+		ls .git/objects/pack >expect &&
+		MINSIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 1) &&
+		git multi-pack-index repack --batch-size=$MINSIZE &&
+		ls .git/objects/pack >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done

From ce1e4a105b4ff2457f2537bc703863175f9195c9 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:27 -0700
Subject: [PATCH 08/12] midx: implement midx_repack()

To repack with a non-zero batch-size, first sort all pack-files by
their modified time. Second, walk those pack-files from oldest
to newest, compute their expected size, and add the packs to a list
if they are smaller than the given batch-size. Stop when the total
expected size is at least the batch size.

If the batch size is zero, select all packs in the multi-pack-index.

Finally, collect the objects from the multi-pack-index that are in
the selected packs and send them to 'git pack-objects'. Write a new
multi-pack-index that includes the new pack.

Using a batch size of zero is very similar to a standard 'git repack'
command, except that we do not delete the old packs and instead rely
on the new multi-pack-index to prevent new processes from reading the
old packs. This does not disrupt other Git processes that are currently
reading the old packs based on the old multi-pack-index.

While first designing a 'git multi-pack-index repack' operation, I
started by collecting the batches based on the actual size of the
objects instead of the size of the pack-files. This allows repacking
a large pack-file that has very few referencd objects. However, this
came at a significant cost of parsing pack-files instead of simply
reading the multi-pack-index and getting the file information for
the pack-files. The "expected size" version provides similar
behavior, but could skip a pack-file if the average object size is
much larger than the actual size of the referenced objects, or
can create a large pack if the actual size of the referenced objects
is larger than the expected size.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 midx.c                      | 151 +++++++++++++++++++++++++++++++++++-
 t/t5319-multi-pack-index.sh |  28 +++++++
 2 files changed, 178 insertions(+), 1 deletion(-)

diff --git a/midx.c b/midx.c
index fbed8a8adb..d649644420 100644
--- a/midx.c
+++ b/midx.c
@@ -9,6 +9,7 @@
 #include "midx.h"
 #include "progress.h"
 #include "trace2.h"
+#include "run-command.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -1227,7 +1228,155 @@ int expire_midx_packs(struct repository *r, const char *object_dir)
 	return result;
 }
 
-int midx_repack(struct repository *r, const char *object_dir, size_t batch_size)
+struct repack_info {
+	timestamp_t mtime;
+	uint32_t referenced_objects;
+	uint32_t pack_int_id;
+};
+
+static int compare_by_mtime(const void *a_, const void *b_)
 {
+	const struct repack_info *a, *b;
+
+	a = (const struct repack_info *)a_;
+	b = (const struct repack_info *)b_;
+
+	if (a->mtime < b->mtime)
+		return -1;
+	if (a->mtime > b->mtime)
+		return 1;
 	return 0;
 }
+
+static int fill_included_packs_all(struct multi_pack_index *m,
+				   unsigned char *include_pack)
+{
+	uint32_t i;
+
+	for (i = 0; i < m->num_packs; i++)
+		include_pack[i] = 1;
+
+	return m->num_packs < 2;
+}
+
+static int fill_included_packs_batch(struct repository *r,
+				     struct multi_pack_index *m,
+				     unsigned char *include_pack,
+				     size_t batch_size)
+{
+	uint32_t i, packs_to_repack;
+	size_t total_size;
+	struct repack_info *pack_info = xcalloc(m->num_packs, sizeof(struct repack_info));
+
+	for (i = 0; i < m->num_packs; i++) {
+		pack_info[i].pack_int_id = i;
+
+		if (prepare_midx_pack(r, m, i))
+			continue;
+
+		pack_info[i].mtime = m->packs[i]->mtime;
+	}
+
+	for (i = 0; batch_size && i < m->num_objects; i++) {
+		uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
+		pack_info[pack_int_id].referenced_objects++;
+	}
+
+	QSORT(pack_info, m->num_packs, compare_by_mtime);
+
+	total_size = 0;
+	packs_to_repack = 0;
+	for (i = 0; total_size < batch_size && i < m->num_packs; i++) {
+		int pack_int_id = pack_info[i].pack_int_id;
+		struct packed_git *p = m->packs[pack_int_id];
+		size_t expected_size;
+
+		if (!p)
+			continue;
+		if (open_pack_index(p) || !p->num_objects)
+			continue;
+
+		expected_size = (size_t)(p->pack_size
+					 * pack_info[i].referenced_objects);
+		expected_size /= p->num_objects;
+
+		if (expected_size >= batch_size)
+			continue;
+
+		packs_to_repack++;
+		total_size += expected_size;
+		include_pack[pack_int_id] = 1;
+	}
+
+	free(pack_info);
+
+	if (total_size < batch_size || packs_to_repack < 2)
+		return 1;
+
+	return 0;
+}
+
+int midx_repack(struct repository *r, const char *object_dir, size_t batch_size)
+{
+	int result = 0;
+	uint32_t i;
+	unsigned char *include_pack;
+	struct child_process cmd = CHILD_PROCESS_INIT;
+	struct strbuf base_name = STRBUF_INIT;
+	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+
+	if (!m)
+		return 0;
+
+	include_pack = xcalloc(m->num_packs, sizeof(unsigned char));
+
+	if (batch_size) {
+		if (fill_included_packs_batch(r, m, include_pack, batch_size))
+			goto cleanup;
+	} else if (fill_included_packs_all(m, include_pack))
+		goto cleanup;
+
+	argv_array_push(&cmd.args, "pack-objects");
+
+	strbuf_addstr(&base_name, object_dir);
+	strbuf_addstr(&base_name, "/pack/pack");
+	argv_array_push(&cmd.args, base_name.buf);
+	strbuf_release(&base_name);
+
+	cmd.git_cmd = 1;
+	cmd.in = cmd.out = -1;
+
+	if (start_command(&cmd)) {
+		error(_("could not start pack-objects"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for (i = 0; i < m->num_objects; i++) {
+		struct object_id oid;
+		uint32_t pack_int_id = nth_midxed_pack_int_id(m, i);
+
+		if (!include_pack[pack_int_id])
+			continue;
+
+		nth_midxed_object_oid(&oid, m, i);
+		xwrite(cmd.in, oid_to_hex(&oid), the_hash_algo->hexsz);
+		xwrite(cmd.in, "\n", 1);
+	}
+	close(cmd.in);
+
+	if (finish_command(&cmd)) {
+		error(_("could not finish pack-objects"));
+		result = 1;
+		goto cleanup;
+	}
+
+	result = write_midx_internal(object_dir, m, NULL);
+	m = NULL;
+
+cleanup:
+	if (m)
+		close_midx(m);
+	free(include_pack);
+	return result;
+}
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 133d5b7068..6e47e5d0b2 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -450,4 +450,32 @@ test_expect_success 'repack with minimum size does not alter existing packs' '
 	)
 '
 
+test_expect_success 'repack creates a new pack' '
+	(
+		cd dup &&
+		ls .git/objects/pack/*idx >idx-list &&
+		test_line_count = 5 idx-list &&
+		THIRD_SMALLEST_SIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 3 | tail -n 1) &&
+		BATCH_SIZE=$(($THIRD_SMALLEST_SIZE + 1)) &&
+		git multi-pack-index repack --batch-size=$BATCH_SIZE &&
+		ls .git/objects/pack/*idx >idx-list &&
+		test_line_count = 6 idx-list &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 6 midx-list
+	)
+'
+
+test_expect_success 'expire removes repacked packs' '
+	(
+		cd dup &&
+		ls -al .git/objects/pack/*pack &&
+		ls -S .git/objects/pack/*pack | head -n 4 >expect &&
+		git multi-pack-index expire &&
+		ls -S .git/objects/pack/*pack >actual &&
+		test_cmp expect actual &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 4 midx-list
+	)
+'
+
 test_done

From d2743315d4d05d2fd4dc83afa2009c0615a94527 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:27 -0700
Subject: [PATCH 09/12] multi-pack-index: test expire while adding packs

During development of the multi-pack-index expire subcommand, a
version went out that improperly computed the pack order if a new
pack was introduced while other packs were being removed. Part of
the subtlety of the bug involved the new pack being placed before
other packs that already existed in the multi-pack-index.

Add a test to t5319-multi-pack-index.sh that catches this issue.
The test adds new packs that cause another pack to be expired, and
creates new packs that are lexicographically sorted before and
after the existing packs.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5319-multi-pack-index.sh | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 6e47e5d0b2..8e04ce2821 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -478,4 +478,36 @@ test_expect_success 'expire removes repacked packs' '
 	)
 '
 
+test_expect_success 'expire works when adding new packs' '
+	(
+		cd dup &&
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/A
+		^refs/heads/B
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/B
+		^refs/heads/C
+		EOF
+		git pack-objects --revs .git/objects/pack/pack-combined <<-EOF &&
+		refs/heads/C
+		^refs/heads/D
+		EOF
+		git multi-pack-index write &&
+		git pack-objects --revs .git/objects/pack/a-pack <<-EOF &&
+		refs/heads/D
+		^refs/heads/E
+		EOF
+		git multi-pack-index write &&
+		git pack-objects --revs .git/objects/pack/z-pack <<-EOF &&
+		refs/heads/E
+		EOF
+		git multi-pack-index expire &&
+		ls .git/objects/pack/ | grep idx >expect &&
+		test-tool read-midx .git/objects | grep idx >actual &&
+		test_cmp expect actual &&
+		git multi-pack-index verify
+	)
+'
+
 test_done

From 10bfa3f7f58406a5799267e4844fcd3f9ec16097 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:28 -0700
Subject: [PATCH 10/12] midx: add test that 'expire' respects .keep files

The 'git multi-pack-index expire' subcommand may delete packs that
are not needed from the perspective of the multi-pack-index. If
a pack has a .keep file, then we should not delete that pack. Add
a test that ensures we preserve a pack that would otherwise be
expired. First, create a new pack that contains every object in
the repo, then add it to the multi-pack-index. Then create a .keep
file for a pack starting with "a-pack" that was added in the
previous test. Finally, expire and verify that the pack remains
and the other packs were expired.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5319-multi-pack-index.sh | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 8e04ce2821..c288901401 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -510,4 +510,22 @@ test_expect_success 'expire works when adding new packs' '
 	)
 '
 
+test_expect_success 'expire respects .keep files' '
+	(
+		cd dup &&
+		git pack-objects --revs .git/objects/pack/pack-all <<-EOF &&
+		refs/heads/A
+		EOF
+		git multi-pack-index write &&
+		PACKA=$(ls .git/objects/pack/a-pack*\.pack | sed s/\.pack\$//) &&
+		touch $PACKA.keep &&
+		git multi-pack-index expire &&
+		ls -S .git/objects/pack/a-pack* | grep $PACKA >a-pack-files &&
+		test_line_count = 3 a-pack-files &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 2 midx-list
+	)
+'
+
+
 test_done

From b526d8cbbb8740faa10411caa757c6586395fcab Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 10 Jun 2019 16:35:29 -0700
Subject: [PATCH 11/12] t5319-multi-pack-index.sh: test batch size zero

The 'git multi-pack-index repack' command can take a batch size of
zero, which creates a new pack-file containing all objects in the
multi-pack-index. The first 'repack' command will create one new
pack-file, and an 'expire' command after that will delete the old
pack-files, as they no longer contain any referenced objects in the
multi-pack-index.

We must remove the .keep file that was added in the previous test
in order to expire that pack-file.

Also test that a 'repack' will do nothing if there is only one
pack-file.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5319-multi-pack-index.sh | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index c288901401..79bfaeafa9 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -527,5 +527,24 @@ test_expect_success 'expire respects .keep files' '
 	)
 '
 
+test_expect_success 'repack --batch-size=0 repacks everything' '
+	(
+		cd dup &&
+		rm .git/objects/pack/*.keep &&
+		ls .git/objects/pack/*idx >idx-list &&
+		test_line_count = 2 idx-list &&
+		git multi-pack-index repack --batch-size=0 &&
+		ls .git/objects/pack/*idx >idx-list &&
+		test_line_count = 3 idx-list &&
+		test-tool read-midx .git/objects | grep idx >midx-list &&
+		test_line_count = 3 midx-list &&
+		git multi-pack-index expire &&
+		ls -al .git/objects/pack/*idx >idx-list &&
+		test_line_count = 1 idx-list &&
+		git multi-pack-index repack --batch-size=0 &&
+		ls -al .git/objects/pack/*idx >new-idx-list &&
+		test_cmp idx-list new-idx-list
+	)
+'
 
 test_done

From 3612c2334af8b70137a2d3f5497b1b6f4e9762a2 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 1 Jul 2019 06:16:19 -0700
Subject: [PATCH 12/12] t5319: use 'test-tool path-utils' instead of 'ls -l'

Using 'ls -l' and parsing the columns to find file sizes is
problematic when the platform could report the owner as a name
with spaces. Instead, use the 'test-tool path-utils file-size'
command to list only the sizes.

Reported-by: Johannes Sixt <j6t@kdbg.org>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5319-multi-pack-index.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 79bfaeafa9..c72ca04399 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -443,7 +443,7 @@ test_expect_success 'repack with minimum size does not alter existing packs' '
 		touch -m -t 201901010002 .git/objects/pack/pack-B* &&
 		touch -m -t 201901010003 .git/objects/pack/pack-A* &&
 		ls .git/objects/pack >expect &&
-		MINSIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 1) &&
+		MINSIZE=$(test-tool path-utils file-size .git/objects/pack/*pack | sort -n | head -n 1) &&
 		git multi-pack-index repack --batch-size=$MINSIZE &&
 		ls .git/objects/pack >actual &&
 		test_cmp expect actual
@@ -455,7 +455,7 @@ test_expect_success 'repack creates a new pack' '
 		cd dup &&
 		ls .git/objects/pack/*idx >idx-list &&
 		test_line_count = 5 idx-list &&
-		THIRD_SMALLEST_SIZE=$(ls -l .git/objects/pack/*pack | awk "{print \$5;}" | sort -n | head -n 3 | tail -n 1) &&
+		THIRD_SMALLEST_SIZE=$(test-tool path-utils file-size .git/objects/pack/*pack | sort -n | head -n 3 | tail -n 1) &&
 		BATCH_SIZE=$(($THIRD_SMALLEST_SIZE + 1)) &&
 		git multi-pack-index repack --batch-size=$BATCH_SIZE &&
 		ls .git/objects/pack/*idx >idx-list &&