mirrors/git
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

index-pack: prefetch missing REF_DELTA bases

Browse Source 
When fetching, the client sends "have" commit IDs indicating that the
server does not need to send any object referenced by those commits,
reducing network I/O. When the client is a partial clone, the client
still sends "have"s in this way, even if it does not have every object
referenced by a commit it sent as "have".

If a server omits such an object, it is fine: the client could lazily
fetch that object before this fetch, and it can still do so after.

The issue is when the server sends a thin pack containing an object that
is a REF_DELTA against such a missing object: index-pack fails to fix
the thin pack. When support for lazily fetching missing objects was
added in 8b4c0103a9 ("sha1_file: support lazily fetching missing
objects", 2017-12-08), support in index-pack was turned off in the
belief that it accesses the repo only to do hash collision checks.
However, this is not true: it also needs to access the repo to resolve
REF_DELTA bases.

Support for lazy fetching should still generally be turned off in
index-pack because it is used as part of the lazy fetching process
itself (if not, infinite loops may occur), but we do need to fetch the
REF_DELTA bases. (When fetching REF_DELTA bases, it is unlikely that
those are REF_DELTA themselves, because we do not send "have" when
making such fetches.)

To resolve this, prefetch all missing REF_DELTA bases before attempting
to resolve them. This both ensures that all bases are attempted to be
fetched, and ensures that we make only one request per index-pack
invocation, and not one request per missing object.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jonathan Tan
2019-05-14 14:10:55 -07:00
committed by Junio C Hamano
parent 385d1bfd7a
commit 8a30a1efd1
2 changed files with 85 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
builtin/index-pack.c
View File

@ -14,6 +14,7 @@
#include "thread-utils.h"
#include "packfile.h"
#include "object-store.h"
#include "fetch-object.h"
static const char index_pack_usage[] =
"git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";
@ -1351,6 +1352,25 @@ static void fix_unresolved_deltas(struct hashfile *f)
sorted_by_pos[i] = &ref_deltas[i];
QSORT(sorted_by_pos, nr_ref_deltas, delta_pos_compare);
if (repository_format_partial_clone) {
/*
* Prefetch the delta bases.
*/
struct oid_array to_fetch = OID_ARRAY_INIT;
for (i = 0; i < nr_ref_deltas; i++) {
struct ref_delta_entry *d = sorted_by_pos[i];
if (!oid_object_info_extended(the_repository, &d->oid,
NULL,
OBJECT_INFO_FOR_PREFETCH))
continue;
oid_array_append(&to_fetch, &d->oid);
}
if (to_fetch.nr)
fetch_objects(repository_format_partial_clone,
to_fetch.oid, to_fetch.nr);
oid_array_clear(&to_fetch);
}
for (i = 0; i < nr_ref_deltas; i++) {
struct ref_delta_entry *d = sorted_by_pos[i];
enum object_type type;
@ -1650,8 +1670,10 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
int report_end_of_input = 0;
/*
* index-pack never needs to fetch missing objects, since it only
* accesses the repo to do hash collision checks
* index-pack never needs to fetch missing objects except when
* REF_DELTA bases are missing (which are explicitly handled). It only
* accesses the repo to do hash collision checks and to check which
* REF_DELTA bases need to be fetched.
*/
fetch_if_missing = 0;