On Fri, 6 Jul 2007, Linus Torvalds wrote:
>
> If we want to be really aggressive, we migth decide to pass a new flag to
> pack-objects that does something closer to what "aggressive" was meant to
> do: it would use existing delta's if they exist, but _despite_ existing it
> could look if there are even better choices.
This is a totally untested patch that may or may not work.
The reason I say "may not work" is not just that I haven't really tested
it, it's also because I haven't thought it through very well.
In particular, does this possibly cause infinite loops of delta chains?
Probably. It would need code to explicitly make sure that we don't do
that, but I couldn't even convince myself as to why we might not hit that
case _already_ with delta re-use, so maybe there's something going that
protects us against it.
The patch itself is trivial, except for hunk #2, which fixes up the fact
that we didn't fill in the "entry->size" correctly for a delta entry (we
left it at the *delta* size). It didn't use to matter, since the entry
size wasn't ever used for anything, I think (with the possible exception
of the object sorting).
Anyway, consider this a starting point for somebody else who wants to
really try to look into this. But I do think that "git gc --aggressive" is
broken as it stands now.
Linus
---
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 3d396ca..89e9900 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -57,6 +57,7 @@ static struct object_entry *objects;
static struct object_entry **written_list;
static uint32_t nr_objects, nr_alloc, nr_result, nr_written;
+static int aggressive;
static int non_empty;
static int no_reuse_delta, no_reuse_object;
static int local;
@@ -1179,6 +1180,8 @@ static void check_object(struct object_entry *entry)
entry->delta = base_entry;
entry->delta_sibling = base_entry->delta_child;
base_entry->delta_child = entry;
+ entry->size = get_size_from_delta(p, &w_curs,
+ entry->in_pack_offset + entry->in_pack_header_size);
unuse_pack(&w_curs);
return;
}
@@ -1425,7 +1428,7 @@ static void find_deltas(struct object_entry **list, int window, int depth)
if (progress)
display_progress(&progress_state, processed);
- if (entry->delta)
+ if (entry->delta && !aggressive)
/* This happens if we decided to reuse existing
* delta from a pack. "!no_reuse_delta &&" is implied.
*/
@@ -1760,6 +1763,10 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
die("bad %s", arg);
continue;
}
+ if (!strcmp("--aggressive", arg)) {
+ aggressive = 1;
+ continue;
+ }
usage(pack_usage);
}
-
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