[PATCH] allow OFS_DELTA objects during a push
From: Nicolas Pitre <hidden>
Date: 2016-06-15 22:46:41
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <redacted> --- On Wed, 29 Apr 2009, Junio C Hamano wrote:
Nicolas Pitre [off-list ref] writes:quoted
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; };