Delta base for blobs is chosen as a previously saved blob. If we
treat cat-blob's blob as a delta base for the next blob, nothing
is likely to become worse.
For fast-import stream producer like svn-fe cat-blob is used like
following:
- svn-fe reads file delta in svn format
- to apply it, svn-fe asks cat-blob 'svn delta base'
- applies 'svn delta' to the response
- produces a blob command to store the result
Currently there is no way for svn-fe to give fast-import a hint on
object delta base. While what's requested in cat-blob is most of
the time a best delta base possible. Of course, it could be not a
good delta base, but we don't know any better one anyway.
So do treat cat-blob's result as a delta base for next blob. The
profit is nice: 2x to 7x reduction in pack size AND 1.2x to 3x
time speedup due to diff_delta being faster on good deltas. git gc
--aggressive can compress it even more, by 10% to 70%, utilizing
more cpu time, real time and 3 cpu cores.
Tested on 213M and 2.7G fast-import streams, resulting packs are 22M
and 113M, import time is 7s and 60s, both streams are produced by
svn-fe, sniffed and then used as raw input for fast-import.
For git-fast-export produced streams there is no change as it doesn't
use cat-blob and doesn't try to reorder blobs in some smart way to
make successive deltas small.
Signed-off-by: Dmitry Ivankov <divanorama@xxxxxxxxx>
---
fast-import.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/fast-import.c b/fast-import.c
index 2b069e3..0480fbf 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2802,7 +2802,12 @@ static void cat_blob(struct object_entry *oe, unsigned char sha1[20])
strbuf_release(&line);
cat_blob_write(buf, size);
cat_blob_write("\n", 1);
- free(buf);
+ if (oe && oe->pack_id == pack_id) {
+ last_blob.offset = oe->idx.offset;
+ strbuf_attach(&last_blob.data, buf, size, size);
+ last_blob.depth = oe->depth;
+ } else
+ free(buf);
}
static void parse_cat_blob(void)
--
1.7.3.4
--
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