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authorVicent Marti <tanoku@gmail.com>2013-12-21 09:00:45 -0500
committerJunio C Hamano <gitster@pobox.com>2013-12-30 12:19:23 -0800
commitae4f07fbccaab6dc93be52c0f34e137dd9fcbcf4 (patch)
tree7318a55faf8d38e4317a82dda8f1c5f465a9ae53 /pack-bitmap.c
parentbbcefa1f3f8355921137dd7a097b3ee3db66f023 (diff)
downloadgit-ae4f07fbccaab6dc93be52c0f34e137dd9fcbcf4.tar.gz
pack-bitmap: implement optional name_hash cache
When we use pack bitmaps rather than walking the object graph, we end up with the list of objects to include in the packfile, but we do not know the path at which any tree or blob objects would be found. In a recently packed repository, this is fine. A fetch would use the paths only as a heuristic in the delta compression phase, and a fully packed repository should not need to do much delta compression. As time passes, though, we may acquire more objects on top of our large bitmapped pack. If clients fetch frequently, then they never even look at the bitmapped history, and all works as usual. However, a client who has not fetched since the last bitmap repack will have "have" tips in the bitmapped history, but "want" newer objects. The bitmaps themselves degrade gracefully in this circumstance. We manually walk the more recent bits of history, and then use bitmaps when we hit them. But we would also like to perform delta compression between the newer objects and the bitmapped objects (both to delta against what we know the user already has, but also between "new" and "old" objects that the user is fetching). The lack of pathnames makes our delta heuristics much less effective. This patch adds an optional cache of the 32-bit name_hash values to the end of the bitmap file. If present, a reader can use it to match bitmapped and non-bitmapped names during delta compression. Here are perf results for p5310: Test origin/master HEAD^ HEAD ------------------------------------------------------------------------------------------------- 5310.2: repack to disk 36.81(37.82+1.43) 47.70(48.74+1.41) +29.6% 47.75(48.70+1.51) +29.7% 5310.3: simulated clone 30.78(29.70+2.14) 1.08(0.97+0.10) -96.5% 1.07(0.94+0.12) -96.5% 5310.4: simulated fetch 3.16(6.10+0.08) 3.54(10.65+0.06) +12.0% 1.70(3.07+0.06) -46.2% 5310.6: partial bitmap 36.76(43.19+1.81) 6.71(11.25+0.76) -81.7% 4.08(6.26+0.46) -88.9% You can see that the time spent on an incremental fetch goes down, as our delta heuristics are able to do their work. And we save time on the partial bitmap clone for the same reason. Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'pack-bitmap.c')
-rw-r--r--pack-bitmap.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 82090a6741..ae0b57b950 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -66,6 +66,9 @@ static struct bitmap_index {
/* Number of bitmapped commits */
uint32_t entry_count;
+ /* Name-hash cache (or NULL if not present). */
+ uint32_t *hashes;
+
/*
* Extended index.
*
@@ -152,6 +155,11 @@ static int load_bitmap_header(struct bitmap_index *index)
if ((flags & BITMAP_OPT_FULL_DAG) == 0)
return error("Unsupported options for bitmap index file "
"(Git requires BITMAP_OPT_FULL_DAG)");
+
+ if (flags & BITMAP_OPT_HASH_CACHE) {
+ unsigned char *end = index->map + index->map_size - 20;
+ index->hashes = ((uint32_t *)end) - index->pack->num_objects;
+ }
}
index->entry_count = ntohl(header->entry_count);
@@ -626,6 +634,9 @@ static void show_objects_for_type(
entry = &bitmap_git.reverse_index->revindex[pos + offset];
sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);
+ if (bitmap_git.hashes)
+ hash = ntohl(bitmap_git.hashes[entry->nr]);
+
show_reach(sha1, object_type, 0, hash, bitmap_git.pack, entry->offset);
}