The fetching of OFS_DELTA objects has been negotiated between both peers
since git version 1.4.4. However, this was missing from the push side
where every OFS_DELTA objects were always converted to REF_DELTA objects
causing an increase in transferred data.
To fix this, both the client and the server processes have to be
modified: the former to invoke pack-objects with --delta-base-offset
when the server provides the ofs-delta capability, and the later to send
that capability when OFS_DELTA objects are allowed as already indicated
by the repack.usedeltabaseoffset config variable which is TRUE by
default since git v1.6.0.
Signed-off-by: Nicolas Pitre <nico@xxxxxxx>
---
On Wed, 29 Apr 2009, Junio C Hamano wrote:
> Nicolas Pitre <nico@xxxxxxx> writes:
>
> > Hence an average difference of 17 bytes per delta. Given that REF_DELTA
> > objects have a 20-byte SHA1 base reference which is replaced with a
> > variable length encoding of a pack offset in the OFS_DELTA case, we're
> > talking about 2.98 bytes for that offset encoding which feels about
> > right.
> >
> > [...]
> >
> > And the code matches this theory as well. Can you try this patch if you
> > have a chance?
>
> Is there any progress on this?
>
> I think you did a veryclear analysis. 8% size reduction is not only
> unignorable but use of delta offset should also help runtime efficiency,
> right?
Indeed.
Here's the final patch. My initial one didn't work because the server
side didn't advertise the needed capability. So both sides will have to
be updated for pushes with OFS_DELTA to kick in.
builtin-receive-pack.c | 22 +++++++++++++++-------
builtin-send-pack.c | 8 +++++++-
send-pack.h | 1 +
3 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/builtin-receive-pack.c b/builtin-receive-pack.c
index a970b39..4b9d921 100644
--- a/builtin-receive-pack.c
+++ b/builtin-receive-pack.c
@@ -27,10 +27,9 @@ static int receive_unpack_limit = -1;
static int transfer_unpack_limit = -1;
static int unpack_limit = 100;
static int report_status;
+static int prefer_ofs_delta = 1;
static const char *head_name;
-
-static char capabilities[] = " report-status delete-refs ";
-static int capabilities_sent;
+static char *capabilities_to_send;
static enum deny_action parse_deny_action(const char *var, const char *value)
{
@@ -84,24 +83,29 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
return 0;
}
+ if (strcmp(var, "repack.usedeltabaseoffset") == 0) {
+ prefer_ofs_delta = git_config_bool(var, value);
+ return 0;
+ }
+
return git_default_config(var, value, cb);
}
static int show_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
- if (capabilities_sent)
+ if (!capabilities_to_send)
packet_write(1, "%s %s\n", sha1_to_hex(sha1), path);
else
packet_write(1, "%s %s%c%s\n",
- sha1_to_hex(sha1), path, 0, capabilities);
- capabilities_sent = 1;
+ sha1_to_hex(sha1), path, 0, capabilities_to_send);
+ capabilities_to_send = NULL;
return 0;
}
static void write_head_info(void)
{
for_each_ref(show_ref, NULL);
- if (!capabilities_sent)
+ if (capabilities_to_send)
show_ref("capabilities^{}", null_sha1, 0, NULL);
}
@@ -687,6 +691,10 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
else if (0 <= receive_unpack_limit)
unpack_limit = receive_unpack_limit;
+ capabilities_to_send = (prefer_ofs_delta) ?
+ " report-status delete-refs ofs-delta " :
+ " report-status delete-refs ";
+
add_alternate_refs();
write_head_info();
clear_extra_refs();
diff --git a/builtin-send-pack.c b/builtin-send-pack.c
index d5a1c48..473a3de 100644
--- a/builtin-send-pack.c
+++ b/builtin-send-pack.c
@@ -43,12 +43,16 @@ static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *ext
"--stdout",
NULL,
NULL,
+ NULL,
};
struct child_process po;
int i;
+ i = 4;
if (args->use_thin_pack)
- argv[4] = "--thin";
+ argv[i++] = "--thin";
+ if (args->use_ofs_delta)
+ argv[i++] = "--delta-base-offset";
memset(&po, 0, sizeof(po));
po.argv = argv;
po.in = -1;
@@ -315,6 +319,8 @@ int send_pack(struct send_pack_args *args,
ask_for_status_report = 1;
if (server_supports("delete-refs"))
allow_deleting_refs = 1;
+ if (server_supports("ofs-delta"))
+ args->use_ofs_delta = 1;
if (!remote_refs) {
fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
diff --git a/send-pack.h b/send-pack.h
index 83d76c7..1d7b1b3 100644
--- a/send-pack.h
+++ b/send-pack.h
@@ -6,6 +6,7 @@ struct send_pack_args {
send_mirror:1,
force_update:1,
use_thin_pack:1,
+ use_ofs_delta:1,
dry_run:1;
};
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