Our current strategy with prune is that an object falls into
one of three categories:
1. Reachable (from ref tips, reflogs, index, etc).
2. Not reachable, but recent (based on the --expire time).
3. Not reachable and not recent.
We keep objects from (1) and (2), but prune objects in (3).
The point of (2) is that these objects may be part of an
in-progress operation that has not yet updated any refs.
However, it is not always the case that objects for an
in-progress operation will have a recent mtime. For example,
the object database may have an old copy of a blob (from an
abandoned operation, a branch that was deleted, etc). If we
create a new tree that points to it, a simultaneous prune
will leave our tree, but delete the blob. Referencing that
tree with a commit will then work (we check that the tree is
in the object database, but not that all of its referred
objects are), as will mentioning the commit in a ref. But
the resulting repo is corrupt; we are missing the blob
reachable from a ref.
One way to solve this is to be more thorough when
referencing a sha1: make sure that not only do we have that
sha1, but that we have objects it refers to, and so forth
recursively. The problem is that this is very expensive.
Creating a parent link would require traversing the entire
object graph!
Instead, this patch pushes the extra work onto prune, which
runs less frequently (and has to look at the whole object
graph anyway). It creates a new category of objects: objects
which are not recent, but which are reachable from a recent
object. We do not prune these objects, just like the
reachable and recent ones.
This lets us avoid the recursive check above, because if we
have an object, even if it is unreachable, we should have
its referent. We can make a simple inductive argument that
with this patch, this property holds (that there are no
objects with missing referents in the repository):
0. When we have no objects, we have nothing to refer or be
referred to, so the property holds.
1. If we add objects to the repository, their direct
referents must generally exist (e.g., if you create a
tree, the blobs it references must exist; if you create
a commit to point at the tree, the tree must exist).
This is already the case before this patch. And it is
not 100% foolproof (you can make bogus objects using
`git hash-object`, for example), but it should be the
case for normal usage.
Therefore for any sequence of object additions, the
property will continue to hold.
2. If we remove objects from the repository, then we will
not remove a child object (like a blob) if an object
that refers to it is being kept. That is the part
implemented by this patch.
Note, however, that our reachability check and the
actual pruning are not atomic. So it _is_ still
possible to violate the property (e.g., an object
becomes referenced just as we are deleting it). This
patch is shooting for eliminating problems where the
mtimes of dependent objects differ by hours or days,
and one is dropped without the other. It does nothing
to help with short races.
Naively, the simplest way to implement this would be to add
all recent objects as tips to the reachability traversal.
However, this does not perform well. In a recently-packed
repository, all reachable objects will also be recent, and
therefore we have to look at each object twice. This patch
instead performs the reachability traversal, then follows up
with a second traversal for recent objects, skipping any
that have already been marked.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we mark all reachable objects for pruning, that
includes blobs mentioned by the index. However, we do not
mark these with the SEEN flag, as we do for objects that we
find by traversing (we also do not add them to the pending
list, but that is because there is nothing further to
traverse with them).
This doesn't cause any problems with prune, because it
checks only that the object exists in the global object
hash, and not its flags. However, let's mark these objects
to be consistent and avoid any later surprises.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We want to add all reflog entries as tips for finding
reachable objects. The revision machinery can already do
this (to support "rev-list --reflog"); we can reuse that
code.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To find the set of reachable objects, we add a bunch of
possible sources to our rev_info, call prepare_revision_walk,
and then launch into a custom walker that handles each
object top. This is a subset of what traverse_commit_list
does, so we can just reuse that code (it can also handle
more complex cases like UNINTERESTING commits and pathspecs,
but we don't use those features).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
HEAD is not explicitly used as a starting commit for
calculating reachability, so if it's detached and reflogs
are disabled it may be pruned.
Add tests which demonstrate it. Test 'prune: prune former HEAD after checking
out branch' also reverts changes to repository.
Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Many code paths will free a tree object's buffer and set it
to NULL after finishing with it in order to keep memory
usage down during a traversal. However, out of 8 sites that
do this, only one actually unsets the "parsed" flag back.
Those sites that don't are setting a trap for later users of
the tree object; even after calling parse_tree, the buffer
will remain NULL, causing potential segfaults.
It is not known whether this is triggerable in the current
code. Most commands do not do an in-memory traversal
followed by actually using the objects again. However, it
does not hurt to be safe for future callers.
In most cases, we can abstract this out to a
"free_tree_buffer" helper. However, there are two
exceptions:
1. The fsck code relies on the parsed flag to know that we
were able to parse the object at one point. We can
switch this to using a flag in the "flags" field.
2. The index-pack code sets the buffer to NULL but does
not free it (it is freed by a caller). We should still
unset the parsed flag here, but we cannot use our
helper, as we do not want to free the buffer.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some call-sites do:
o = parse_object(sha1);
if (!o)
die("bad object %s", some_name);
We can now handle that as a one-liner, and get more
consistent output.
In the third case of this patch, it looks like we are losing
information, as the existing message also outputs the sha1
hex; however, parse_object will already have written a more
specific complaint about the sha1, so there is no point in
repeating it here.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The current progress code really just counts commits.
This patch makes it count all objects, giving us a "total"
count close to what a repack would show. This is nice when
using "git gc", which will usually have just repacked the
whole repo.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
prune already shows progress meter while pruning. The marking part may
take a few seconds or more, depending on repository size. Show
progress meter during this time too.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The name of the processed object was duplicated for passing it to
add_object(), but that already calls path_name, which allocates a new
string anyway. So the memory allocated by the xstrdup calls just went
nowhere, leaking memory.
This reduces the RSS usage for a "rev-list --all --objects" by about 10% on
the gentoo repo (fully packed) as well as linux-2.6.git:
gentoo:
| old | new
----------------|-------------------------------
RSS | 1537284 | 1388408
VSZ | 1816852 | 1667952
time elapsed | 1:49.62 | 1:48.99
min. page faults| 417178 | 379919
linux-2.6.git:
| old | new
----------------|-------------------------------
RSS | 324452 | 292996
VSZ | 491792 | 460376
time elapsed | 0:14.53 | 0:14.28
min. page faults| 89360 | 81613
Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* mk/maint-parse-careful:
peel_onion: handle NULL
check return value from parse_commit() in various functions
parse_commit: don't fail, if object is NULL
revision.c: handle tag->tagged == NULL
reachable.c::process_tree/blob: check for NULL
process_tag: handle tag->tagged == NULL
check results of parse_commit in merge_bases
list-objects.c::process_tree/blob: check for NULL
reachable.c::add_one_tree: handle NULL from lookup_tree
mark_blob/tree_uninteresting: check for NULL
get_sha1_oneline: check return value of parse_object
read_object_with_reference: don't read beyond the buffer
As these functions are directly called with the result
from lookup_tree/blob, they must handle NULL.
Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A failure in prepare_revision_walk can be caused by
a not parseable object.
Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This converts the index explicitly on read and write to its on-disk
format, allowing the in-core format to contain more flags, and be
simpler.
In particular, the in-core format is now host-endian (as opposed to the
on-disk one that is network endian in order to be able to be shared
across machines) and as a result we can dispense with all the
htonl/ntohl on accesses to the cache_entry fields.
This will make it easier to make use of various temporary flags that do
not exist in the on-disk format.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
I ran git-prune on a repository and got this:
$ git-prune
error: Object 228f8065b930120e35fc0c154c237487ab02d64a is a blob, not a commit
Segmentation fault (core dumped)
This repository was a strange one in that it was being used to provide
its own submodule. That is, the repository was cloned into a
subdirectory, an independent branch checked out in that subdirectory,
and then it was marked as a submodule. git-prune then failed in the
above manner.
The problem was that git-prune was not submodule aware in two areas.
Linus said:
> So what happens is that something traverses a tree object, looks at each
> entry, sees that it's not a tree, and tries to look it up as a blob. But
> subprojects are commits, not blobs, and then when you look at the object
> more closely, you get the above kind of object type confusion.
and included a patch to add an S_ISGITLINK() test to reachable.c's
process_tree() function. That fixed the first git-prune error, and
stopped it from trying to process the gitlink entries in trees as if
they were pointers to other trees (and of course failing, because
gitlinks _aren't_ trees). That part of this patch is his.
The second area is add_cache_refs(). This is called before starting the
reachability analysis, and was calling lookup_blob() on every object
hash found in the index. However, it is no longer true that every hash
in the index is a pointer to a blob, some of them are gitlinks, and are
not backed by any object at all, they are commits in another repository.
Normally this bug was not causing any problems, but in the case of the
self-referencing repository described above, it meant that the gitlink
hash was being marked as being of type OBJ_BLOB by add_cache_refs() call
to lookup_blob(). Then later, because that hash was also pointed to by
a ref, add_one_ref() would treat it as a commit; lookup_commit() would
return a NULL because that object was already noted as being an
OBJ_BLOB, not an OBJ_COMMIT; and parse_commit_buffer() would SEGFAULT on
that NULL pointer.
The fix made by this patch is to not blindly call lookup_blob() in
reachable.c's add_cache_refs(), and instead skip any index entries that
are S_ISGITLINK().
Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This removes slightly more lines than it adds, but the real reason for
doing this is that future optimizations will require more setup of the
tree descriptor, and so we want to do it in one place.
Also renamed the "desc.buf" field to "desc.buffer" just to trigger
compiler errors for old-style manual initializations, making sure I
didn't miss anything.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Currently, the search for all reflogs depends on the existence of
corresponding refs under the .git/refs/ directory. Let's scan the
.git/logs/ directory directly instead.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
It used to ignore the return value of the helper function; now, it
expects it to return 0, and stops iteration upon non-zero return
values; this value is then passed on as the return value of
for_each_reflog_ent().
Further, it makes no sense to force the parsing upon the helper
functions; for_each_reflog_ent() now calls the helper function with
old and new sha1, the email, the timestamp & timezone, and the message.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This moves major part of builtin-prune into a separate file,
reachable.c. It is used to mark the objects that are reachable
from refs, and optionally from reflogs.
The patch looks very large, but if you look at it with diff -C,
which this message is formatted in, most of them are copied
lines and there are very little additions.
Signed-off-by: Junio C Hamano <junkio@cox.net>
