[PATCH] Don't allow fast-import tree delta chains to exceed maximum depth
- From
Shawn O. Pearce <spearce@spearce.org>
- Date
- Nov 14, 2007, 04:48 UTC
- Message-ID
- <20071114044842.GA6876@spearce.org>
Brian Downing noticed fast-import can produce tree depths of up to 6,035 objects and even deeper. Long delta chains can create very small packfiles but cause problems during repacking as git needs to unpack each tree to count the reachable blobs.
What's happening here is the active branch cache isn't big enough. We're swapping out the branch and thus recycling the tree information (struct tree_content) back into the free pool. When we later reload the tree we set the delta_depth to 0 but we kept the tree we just reloaded as a delta base.
So if the tree we reloaded was already at the maximum depth we wouldn't know it and make the new tree a delta. Multiply the number of times the branch cache has to swap out the tree times max_depth (10) and you get the maximum delta depth of a tree created by fast-import. In Brian's case above the active branch cache had to swap the branch out 603/604 times during this import to produce a tree with a delta depth of 6035.
Acked-by: Brian Downing <bdowning@lavos.net> Signed-off-by: Shawn O. Pearce <spearce@spearce.org> ---
Junio, this patch is against maint. It will apply cleanly to maint but is also crafted to ensure it should apply to next with git-am -3. Its a real bug that's lasted a long time in fast-import. I think it is maint material.
My fast-import tree is quite behind yours so I would appreciate it if you could apply this to your own tree instead of trying to fetch things from me. Thanks.
fast-import.c | 17 ++++++++++++----- 1 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/fast-import.c b/fast-import.c index c07e3d8..7544949 100644 --- a/fast-import.c +++ b/fast-import.c @@ -154,13 +154,16 @@ Format of STDIN stream: #define PACK_ID_BITS 16 #define MAX_PACK_ID ((1<<PACK_ID_BITS)-1) +#define DEPTH_BITS 13 +#define MAX_DEPTH ((1<<DEPTH_BITS)-1) struct object_entry { struct object_entry *next; uint32_t offset; - unsigned type : TYPE_BITS; - unsigned pack_id : PACK_ID_BITS; + uint32_t type : TYPE_BITS, + pack_id : PACK_ID_BITS, + depth : DEPTH_BITS; unsigned char sha1[20]; }; @@ -1105,7 +1108,7 @@ static int store_object( unsigned pos = sizeof(hdr) - 1; delta_count_by_type[type]++; - last->depth++; + e->depth = ++last->depth++; hdrlen = encode_header(OBJ_OFS_DELTA, deltalen, hdr); write_or_die(pack_data->pack_fd, hdr, hdrlen); @@ -1117,6 +1120,7 @@ static int store_object( write_or_die(pack_data->pack_fd, hdr + pos, sizeof(hdr) - pos); pack_size += sizeof(hdr) - pos; } else { + e->depth = 0; if (last) last->depth = 0; hdrlen = encode_header(type, datlen, hdr); @@ -1181,7 +1185,7 @@ static void load_tree(struct tree_entry *root) if (myoe && myoe->pack_id != MAX_PACK_ID) { if (myoe->type != OBJ_TREE) die("Not a tree: %s", sha1_to_hex(sha1)); - t->delta_depth = 0; + t->delta_depth = myoe->depth; buf = gfi_unpack_entry(myoe, &size); } else { enum object_type type; @@ -2347,8 +2351,11 @@ int main(int argc, const char **argv) } else if (!prefixcmp(a, "--max-pack-size=")) max_packsize = strtoumax(a + 16, NULL, 0) * 1024 * 1024; - else if (!prefixcmp(a, "--depth=")) + else if (!prefixcmp(a, "--depth=")) { max_depth = strtoul(a + 8, NULL, 0); + if (max_depth > MAX_DEPTH) + die("--depth cannot exceed %u", MAX_DEPTH); + } else if (!prefixcmp(a, "--active-branches=")) max_active_branches = strtoul(a + 18, NULL, 0); else if (!prefixcmp(a, "--import-marks="))
-- 1.5.3.5.1728.g34b3e