index-pack: repack local links into promisor packs
Teach index-pack to, when processing the objects in a pack with --promisor specified on the CLI, repack local objects (and the local objects that they refer to, recursively) referenced by these objects into promisor packs. This prevents the situation in which, when fetching from a promisor remote, we end up with promisor objects (newly fetched) referring to non-promisor objects (locally created prior to the fetch). This situation may arise if the client had previously pushed objects to the remote, for example. One issue that arises in this situation is that, if the non-promisor objects become inaccessible except through promisor objects (for example, if the branch pointing to them has moved to point to the promisor object that refers to them), then GC will garbage collect them. There are other ways to solve this, but the simplest seems to be to enforce the invariant that we don't have promisor objects referring to non-promisor objects. This repacking is done from index-pack to minimize the performance impact. During a fetch, the only time most objects are fully inflated in memory is when their object ID is computed, so we also scan the objects (to see which objects they refer to) during this time. Also to minimize the performance impact, an object is calculated to be local if it's a loose object or present in a non-promisor pack. (If it's also in a promisor pack or referred to by an object in a promisor pack, it is technically already a promisor object. But a misidentification of a promisor object as a non-promisor object is relatively benign here - we will thus repack that promisor object into a promisor pack, duplicating it in the object store, but there is no correctness issue, just an issue of inefficiency.) Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jonathan Tan committed
Nov 1, 2024 at 13:11 UTC
c08589efdc57604590c5892b52c6820d00f6e0fd
4 files changed
+172
-2
Documentation/git-index-pack.txt
+5
@@ -139,6 +139,11 @@ include::object-format-disclaimer.txt[]
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written. If a `<message>` is provided, then that content will be
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written to the .promisor file for future reference. See
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link:technical/partial-clone.html[partial clone] for more information.
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++
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+Also, if there are objects in the given pack that references non-promisor
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+objects (in the repo), repacks those non-promisor objects into a promisor
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+pack. This avoids a situation in which a repo has non-promisor objects that are
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+accessible through promisor objects.
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148
NOTES
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-----
builtin/index-pack.c
+109
-2
@@ -9,6 +9,7 @@
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#include "csum-file.h"
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#include "blob.h"
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#include "commit.h"
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+#include "tag.h"
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#include "tree.h"
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#include "progress.h"
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#include "fsck.h"
@@ -20,9 +21,14 @@
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#include "object-file.h"
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#include "object-store-ll.h"
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#include "oid-array.h"
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+#include "oidset.h"
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+#include "path.h"
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#include "replace-object.h"
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+#include "tree-walk.h"
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#include "promisor-remote.h"
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+#include "run-command.h"
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#include "setup.h"
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+#include "strvec.h"
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static const char index_pack_usage[] =
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"git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--[no-]rev-index] [--verify] [--strict[=<msg-id>=<severity>...]] [--fsck-objects[=<msg-id>=<severity>...]] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
@@ -148,6 +154,13 @@ static uint32_t input_crc32;
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static int input_fd, output_fd;
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static const char *curr_pack;
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+/*
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+ * local_links is guarded by read_mutex, and record_local_links is read-only in
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+ * a thread.
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+ */
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+static struct oidset local_links = OIDSET_INIT;
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+static int record_local_links;
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+
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static struct thread_local *thread_data;
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static int nr_dispatched;
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static int threads_active;
@@ -799,6 +812,44 @@ static int check_collison(struct object_entry *entry)
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return 0;
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}
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815
+static void record_if_local_object(const struct object_id *oid)
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+{
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+ struct object_info info = OBJECT_INFO_INIT;
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+ if (oid_object_info_extended(the_repository, oid, &info, 0))
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+ /* Missing; assume it is a promisor object */
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+ return;
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+ if (info.whence == OI_PACKED && info.u.packed.pack->pack_promisor)
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+ return;
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+ oidset_insert(&local_links, oid);
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+}
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+
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+static void do_record_local_links(struct object *obj)
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+{
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+ if (obj->type == OBJ_TREE) {
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+ struct tree *tree = (struct tree *)obj;
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+ struct tree_desc desc;
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+ struct name_entry entry;
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+ if (init_tree_desc_gently(&desc, &tree->object.oid,
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+ tree->buffer, tree->size, 0))
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+ /*
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+ * Error messages are given when packs are
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+ * verified, so do not print any here.
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+ */
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+ return;
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+ while (tree_entry_gently(&desc, &entry))
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+ record_if_local_object(&entry.oid);
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+ } else if (obj->type == OBJ_COMMIT) {
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+ struct commit *commit = (struct commit *) obj;
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+ struct commit_list *parents = commit->parents;
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+
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+ for (; parents; parents = parents->next)
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+ record_if_local_object(&parents->item->object.oid);
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+ } else if (obj->type == OBJ_TAG) {
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+ struct tag *tag = (struct tag *) obj;
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+ record_if_local_object(get_tagged_oid(tag));
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+ }
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+}
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+
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static void sha1_object(const void *data, struct object_entry *obj_entry,
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unsigned long size, enum object_type type,
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const struct object_id *oid)
@@ -845,7 +896,7 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
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free(has_data);
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}
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848
- if (strict || do_fsck_object) {
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+ if (strict || do_fsck_object || record_local_links) {
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read_lock();
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if (type == OBJ_BLOB) {
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struct blob *blob = lookup_blob(the_repository, oid);
@@ -877,6 +928,8 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
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die(_("fsck error in packed object"));
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if (strict && fsck_walk(obj, NULL, &fsck_options))
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die(_("Not all child objects of %s are reachable"), oid_to_hex(&obj->oid));
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+ if (record_local_links)
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+ do_record_local_links(obj);
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if (obj->type == OBJ_TREE) {
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struct tree *item = (struct tree *) obj;
@@ -1719,6 +1772,58 @@ static void show_pack_info(int stat_only)
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free(chain_histogram);
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}
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+static void repack_local_links(void)
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+{
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+ struct child_process cmd = CHILD_PROCESS_INIT;
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+ FILE *out;
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+ struct strbuf line = STRBUF_INIT;
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+ struct oidset_iter iter;
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+ struct object_id *oid;
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+ char *base_name;
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+
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+ if (!oidset_size(&local_links))
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+ return;
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+
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+ base_name = mkpathdup("%s/pack/pack", repo_get_object_directory(the_repository));
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+
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+ strvec_push(&cmd.args, "pack-objects");
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+ strvec_push(&cmd.args, "--exclude-promisor-objects-best-effort");
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+ strvec_push(&cmd.args, base_name);
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+ cmd.git_cmd = 1;
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+ cmd.in = -1;
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+ cmd.out = -1;
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+ if (start_command(&cmd))
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+ die(_("could not start pack-objects to repack local links"));
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+
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+ oidset_iter_init(&local_links, &iter);
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+ while ((oid = oidset_iter_next(&iter))) {
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+ if (write_in_full(cmd.in, oid_to_hex(oid), the_hash_algo->hexsz) < 0 ||
1801
+ write_in_full(cmd.in, "\n", 1) < 0)
1802
+ die(_("failed to feed local object to pack-objects"));
1803
+ }
1804
+ close(cmd.in);
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+
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+ out = xfdopen(cmd.out, "r");
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+ while (strbuf_getline_lf(&line, out) != EOF) {
1808
+ unsigned char binary[GIT_MAX_RAWSZ];
1809
+ if (line.len != the_hash_algo->hexsz ||
1810
+ !hex_to_bytes(binary, line.buf, line.len))
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+ die(_("index-pack: Expecting full hex object ID lines only from pack-objects."));
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+
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+ /*
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+ * pack-objects creates the .pack and .idx files, but not the
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+ * .promisor file. Create the .promisor file, which is empty.
1816
+ */
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+ write_special_file("promisor", "", NULL, binary, NULL);
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+ }
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+
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+ fclose(out);
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+ if (finish_command(&cmd))
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+ die(_("could not finish pack-objects to repack local links"));
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+ strbuf_release(&line);
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+ free(base_name);
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+}
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+
1827
int cmd_index_pack(int argc,
1828
const char **argv,
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const char *prefix,
@@ -1794,7 +1899,7 @@ int cmd_index_pack(int argc,
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} else if (skip_to_optional_arg(arg, "--keep", &keep_msg)) {
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; /* nothing to do */
1901
} else if (skip_to_optional_arg(arg, "--promisor", &promisor_msg)) {
1797
- ; /* already parsed */
1902
+ record_local_links = 1;
1903
} else if (starts_with(arg, "--threads=")) {
1904
char *end;
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nr_threads = strtoul(arg+10, &end, 0);
@@ -1970,6 +2075,8 @@ int cmd_index_pack(int argc,
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free((void *) curr_index);
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free(curr_rev_index);
2077
2078
+ repack_local_links();
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+
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/*
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* Let the caller know this pack is not self contained
2082
*/
builtin/pack-objects.c
+28
@@ -239,6 +239,7 @@ static enum {
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static uint16_t write_bitmap_options = BITMAP_OPT_HASH_CACHE;
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241
static int exclude_promisor_objects;
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+static int exclude_promisor_objects_best_effort;
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static int use_delta_islands;
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@@ -4312,6 +4313,18 @@ static int option_parse_cruft_expiration(const struct option *opt UNUSED,
4313
return 0;
4314
}
4315
4316
+static int is_not_in_promisor_pack_obj(struct object *obj, void *data UNUSED)
4317
+{
4318
+ struct object_info info = OBJECT_INFO_INIT;
4319
+ if (oid_object_info_extended(the_repository, &obj->oid, &info, 0))
4320
+ BUG("should_include_obj should only be called on existing objects");
4321
+ return info.whence != OI_PACKED || !info.u.packed.pack->pack_promisor;
4322
+}
4323
+
4324
+static int is_not_in_promisor_pack(struct commit *commit, void *data) {
4325
+ return is_not_in_promisor_pack_obj((struct object *) commit, data);
4326
+}
4327
+
4328
int cmd_pack_objects(int argc,
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const char **argv,
4330
const char *prefix,
@@ -4424,6 +4437,9 @@ int cmd_pack_objects(int argc,
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option_parse_missing_action),
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OPT_BOOL(0, "exclude-promisor-objects", &exclude_promisor_objects,
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N_("do not pack objects in promisor packfiles")),
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+ OPT_BOOL(0, "exclude-promisor-objects-best-effort",
4441
+ &exclude_promisor_objects_best_effort,
4442
+ N_("implies --missing=allow-any")),
4443
OPT_BOOL(0, "delta-islands", &use_delta_islands,
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N_("respect islands during delta compression")),
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OPT_STRING_LIST(0, "uri-protocol", &uri_protocols,
@@ -4504,10 +4520,18 @@ int cmd_pack_objects(int argc,
4520
strvec_push(&rp, "--unpacked");
4521
}
4522
4523
+ if (exclude_promisor_objects && exclude_promisor_objects_best_effort)
4524
+ die(_("options '%s' and '%s' cannot be used together"),
4525
+ "--exclude-promisor-objects", "--exclude-promisor-objects-best-effort");
4526
if (exclude_promisor_objects) {
4527
use_internal_rev_list = 1;
4528
fetch_if_missing = 0;
4529
strvec_push(&rp, "--exclude-promisor-objects");
4530
+ } else if (exclude_promisor_objects_best_effort) {
4531
+ use_internal_rev_list = 1;
4532
+ fetch_if_missing = 0;
4533
+ option_parse_missing_action(NULL, "allow-any", 0);
4534
+ /* revs configured below */
4535
}
4536
if (unpack_unreachable || keep_unreachable || pack_loose_unreachable)
4537
use_internal_rev_list = 1;
@@ -4627,6 +4651,10 @@ int cmd_pack_objects(int argc,
4651
4652
repo_init_revisions(the_repository, &revs, NULL);
4653
list_objects_filter_copy(&revs.filter, &filter_options);
4654
+ if (exclude_promisor_objects_best_effort) {
4655
+ revs.include_check = is_not_in_promisor_pack;
4656
+ revs.include_check_obj = is_not_in_promisor_pack_obj;
4657
+ }
4658
get_object_list(&revs, rp.nr, rp.v);
4659
release_revisions(&revs);
4660
}
t/t5616-partial-clone.sh
+30
@@ -694,6 +694,36 @@ test_expect_success 'lazy-fetch in submodule succeeds' '
694
git -C client restore --recurse-submodules --source=HEAD^ :/
695
'
696
697
+test_expect_success 'after fetching descendants of non-promisor commits, gc works' '
698
+ # Setup
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+ git init full &&
700
+ git -C full config uploadpack.allowfilter 1 &&
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+ git -C full config uploadpack.allowanysha1inwant 1 &&
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+ touch full/foo &&
703
+ git -C full add foo &&
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+ git -C full commit -m "commit 1" &&
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+ git -C full checkout --detach &&
706
+
707
+ # Partial clone and push commit to remote
708
+ git clone "file://$(pwd)/full" --filter=blob:none partial &&
709
+ echo "hello" > partial/foo &&
710
+ git -C partial commit -a -m "commit 2" &&
711
+ git -C partial push &&
712
+
713
+ # gc in partial repo
714
+ git -C partial gc --prune=now &&
715
+
716
+ # Create another commit in normal repo
717
+ git -C full checkout main &&
718
+ echo " world" >> full/foo &&
719
+ git -C full commit -a -m "commit 3" &&
720
+
721
+ # Pull from remote in partial repo, and run gc again
722
+ git -C partial pull &&
723
+ git -C partial gc --prune=now
724
+'
725
+
726
+
727
. "$TEST_DIRECTORY"/lib-httpd.sh
728
start_httpd
729