The `expire` sub-command unlinks any packs that are (a) contained in the
MIDX, but (b) have no objects referenced by the MIDX.
This sub-command ignores `.keep` packs, which remain on-disk even if
they have no objects referenced by the MIDX. Cruft packs, however,
aren't given the same treatment: if none of the objects contained in the
cruft pack are selected from the cruft pack by the MIDX, then the cruft
pack is eligible to be expired.
This is less than desireable, since the cruft pack has important
metadata about the individual object mtimes, which is useful to
determine how quickly an object should age out of the repository when
pruning.
Ordinarily, we wouldn't expect the contents of a cruft pack to
duplicated across non-cruft packs (and we'd expect to see the MIDX
select all cruft objects from other sources even less often). But
nonetheless, it is still possible to trick the `expire` sub-command into
removing the `.mtimes` file in this circumstance.
Teach the `expire` sub-command to ignore cruft packs in the same manner
as it does `.keep` packs, in order to keep their metadata around, even
when they are unreferenced by the MIDX.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `expire` sub-command of `git multi-pack-index` will never expire
`.keep` packs, regardless of whether or not any of their objects were
selected in the MIDX.
This has always been the case since 19575c7c8e (multi-pack-index:
implement 'expire' subcommand, 2019-06-10), which came after cff9711616
(multi-pack-index: prepare for 'expire' subcommand, 2019-06-10), when
this documentation was originally written.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Remove the extra space character between "tracked" and "by", which dates
back to when this paragraph was originally written in cff9711616
(multi-pack-index: prepare for 'expire' subcommand, 2019-06-10).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Continue the move of existing Documentation/technical/* protocol and
file-format documentation into our main documentation space by moving
the various documentation pertaining to the *.pack format and related
files, and updating things that refer to it to link to the new
location.
By moving these we can properly link from the newly created
gitformat-commit-graph to a gitformat-chunk-format page.
Integrating "Documentation/technical/bitmap-format.txt" and
"Documentation/technical/cruft-packs.txt" might logically be part of
this change, but as those cover parts of the wider "pack
format" (including associated files) that's documented outside of
"Documentation/technical/pack-format.txt" let's leave those for now,
subsequent commit(s) will address those.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We prefer "directory" over "folder" when discussing the file system
concept. In all of our documentation, these are the only spots where we
refer to the `.git` directory as a folder. Switch to "directory", and
while doing so, add backticks to the ".git" filename to set it in
monospace.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git repack" has been taught to generate multi-pack reachability
bitmaps.
* tb/repack-write-midx:
test-read-midx: fix leak of bitmap_index struct
builtin/repack.c: pass `--refs-snapshot` when writing bitmaps
builtin/repack.c: make largest pack preferred
builtin/repack.c: support writing a MIDX while repacking
builtin/repack.c: extract showing progress to a variable
builtin/repack.c: rename variables that deal with non-kept packs
builtin/repack.c: keep track of existing packs unconditionally
midx: preliminary support for `--refs-snapshot`
builtin/multi-pack-index.c: support `--stdin-packs` mode
midx: expose `write_midx_file_only()` publicly
Regression in "git commit-graph" command line parsing has been
corrected.
* tb/commit-graph-usage-fix:
builtin/multi-pack-index.c: disable top-level --[no-]progress
builtin/commit-graph.c: don't accept common --[no-]progress
To figure out which commits we can write a bitmap for, the multi-pack
index/bitmap code does a reachability traversal, marking any commit
which can be found in the MIDX as eligible to receive a bitmap.
This approach will cause a problem when multi-pack bitmaps are able to
be generated from `git repack`, since the reference tips can change
during the repack. Even though we ignore commits that don't exist in
the MIDX (when doing a scan of the ref tips), it's possible that a
commit in the MIDX reaches something that isn't.
This can happen when a multi-pack index contains some pack which refers
to loose objects (e.g., if a pack was pushed after starting the repack
but before generating the MIDX which depends on an object which is
stored as loose in the repository, and by definition isn't included in
the multi-pack index).
By taking a snapshot of the references before we start repacking, we can
close that race window. In the above scenario (where we have a packed
object pointing at a loose one), we'll either (a) take a snapshot of the
references before seeing the packed one, or (b) take it after, at which
point we can guarantee that the loose object will be packed and included
in the MIDX.
This patch does just that. It writes a temporary "reference snapshot",
which is a list of OIDs that are at the ref tips before writing a
multi-pack bitmap. References that are "preferred" (i.e,. are a suffix
of at least one value of the 'pack.preferBitmapTips' configuration) are
marked with a special '+'.
The format is simple: one line per commit at each tip, with an optional
'+' at the beginning (for preferred references, as described above).
When provided, the reference snapshot is used to drive bitmap selection
instead of the MIDX code doing its own traversal. When it isn't
provided, the usual traversal takes place instead.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
To power a new `--write-midx` mode, `git repack` will want to write a
multi-pack index containing a certain set of packs in the repository.
This new option will be used by `git repack` to write a MIDX which
contains only the packs which will survive after the repack (that is, it
will exclude any packs which are about to be deleted).
This patch effectively exposes the function implemented in the previous
commit via the `git multi-pack-index` builtin. An alternative approach
would have been to call that function from the `git repack` builtin
directly, but this introduces awkward problems around closing and
reopening the object store, so the MIDX will be written out-of-process.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a similar spirit as the previous patch, let sub-commands which
support showing or hiding a progress meter handle parsing the
`--progress` or `--no-progress` option, but do not expose it as an
option to the top-level `multi-pack-index` builtin.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Write multi-pack bitmaps in the format described by
Documentation/technical/bitmap-format.txt, inferring their presence with
the absence of '--bitmap'.
To write a multi-pack bitmap, this patch attempts to reuse as much of
the existing machinery from pack-objects as possible. Specifically, the
MIDX code prepares a packing_data struct that pretends as if a single
packfile has been generated containing all of the objects contained
within the MIDX.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Opening multiple instance of the same MIDX can lead to problems like two
separate packed_git structures which represent the same pack being added
to the repository's object store.
The above scenario can happen because prepare_midx_pack() checks if
`m->packs[pack_int_id]` is NULL in order to determine if a pack has been
opened and installed in the repository before. But a caller can
construct two copies of the same MIDX by calling get_multi_pack_index()
and load_multi_pack_index() since the former manipulates the
object store directly but the latter is a lower-level routine which
allocates a new MIDX for each call.
So if prepare_midx_pack() is called on multiple MIDXs with the same
pack_int_id, then that pack will be installed twice in the object
store's packed_git pointer.
This can lead to problems in, for e.g., the pack-bitmap code, which does
something like the following (in pack-bitmap.c:open_pack_bitmap()):
struct bitmap_index *bitmap_git = ...;
for (p = get_all_packs(r); p; p = p->next) {
if (open_pack_bitmap_1(bitmap_git, p) == 0)
ret = 0;
}
which is a problem if two copies of the same pack exist in the
packed_git list because pack-bitmap.c:open_pack_bitmap_1() contains a
conditional like the following:
if (bitmap_git->pack || bitmap_git->midx) {
/* ignore extra bitmap file; we can only handle one */
warning("ignoring extra bitmap file: %s", packfile->pack_name);
close(fd);
return -1;
}
Avoid this scenario by not letting write_midx_internal() open a MIDX
that isn't also pointed at by the object store. So long as this is the
case, other routines should prefer to open MIDXs with
get_multi_pack_index() or reprepare_packed_git() instead of creating
instances on their own. Because get_multi_pack_index() returns
`r->object_store->multi_pack_index` if it is non-NULL, we'll only have
one instance of a MIDX open at one time, avoiding these problems.
To encourage this, drop the `struct multi_pack_index *` parameter from
`write_midx_internal()`, and rely instead on the `object_dir` to find
(or initialize) the correct MIDX instance.
Likewise, replace the call to `close_midx()` with
`close_object_store()`, since we're about to replace the MIDX with a new
one and should invalidate the object store's memory of any MIDX that
might have existed beforehand.
Note that this now forbids passing object directories that don't belong
to alternate repositories over `--object-dir`, since before we would
have happily opened a MIDX in any directory, but now restrict ourselves
to only those reachable by `r->objects->multi_pack_index` (and alternate
MIDXs that we can see by walking the `next` pointer).
As far as I can tell, supporting arbitrary directories with
`--object-dir` was a historical accident, since even the documentation
says `<alt>` when referring to the value passed to this option.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The soon-to-be-implemented multi-pack bitmap treats object in the first
bit position specially by assuming that all objects in the pack it was
selected from are also represented from that pack in the MIDX. In other
words, the pack from which the first object was selected must also have
all of its other objects selected from that same pack in the MIDX in
case of any duplicates.
But this assumption relies on the fact that there is at least one object
in that pack to begin with; otherwise the object in the first bit
position isn't from a preferred pack, in which case we can no longer
assume that all objects in that pack were also selected from the same
pack.
Guard this assumption by checking the number of objects in the given
preferred pack, and failing if the given pack is empty.
To make sure we can safely perform this check, open any packs which are
contained in an existing MIDX via prepare_midx_pack(). The same is done
for new packs via the add_pack_to_midx() callback, but packs picked up
from a previous MIDX will not yet have these opened.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When multiple packs in the multi-pack index contain the same object, the
MIDX machinery must make a choice about which pack it associates with
that object. Prior to this patch, the lowest-ordered[1] pack was always
selected.
Pack selection for duplicate objects is relatively unimportant today,
but it will become important for multi-pack bitmaps. This is because we
can only invoke the pack-reuse mechanism when all of the bits for reused
objects come from the reuse pack (in order to ensure that all reused
deltas can find their base objects in the same pack).
To encourage the pack selection process to prefer one pack over another
(the pack to be preferred is the one a caller would like to later use as
a reuse pack), introduce the concept of a "preferred pack". When
provided, the MIDX code will always prefer an object found in a
preferred pack over any other.
No format changes are required to store the preferred pack, since it
will be able to be inferred with a corresponding MIDX bitmap, by looking
up the pack associated with the object in the first bit position (this
ordering is described in detail in a subsequent commit).
[1]: the ordering is specified by MIDX internals; for our purposes we
can consider the "lowest ordered" pack to be "the one with the
most-recent mtime.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The --batch-size=<size> option of 'git multi-pack-index repack' is
intended to limit the amount of work done by the repack. In the case of
a large repository, this command should repack a number of small
pack-files but leave the large pack-files alone. Most often, the
repository has one large pack-file from a 'git clone' operation and
number of smaller pack-files from incremental 'git fetch' operations.
The issue with '--batch-size' is that it also _prevents_ the repack from
happening if the expected size of the resulting pack-file is too small.
This was intended as a way to avoid frequent churn of small pack-files,
but it has mostly caused confusion when a repository is of "medium"
size. That is, not enormous like the Windows OS repository, but also not
so small that this incremental repack isn't valuable.
The solution presented here is to collect pack-files for repack if their
expected size is smaller than the batch-size parameter until either the
total expected size exceeds the batch-size or all pack-files are
considered. If there are at least two pack-files, then these are
combined to a new pack-file whose size should not be too much larger
than the batch-size.
This new strategy should succeed in keeping the number of pack-files
small in these "medium" size repositories. The concern about churn is
likely not interesting, as the real control over that is the frequency
in which the repack command is run.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When selecting a batch of pack-files to repack in the "git
multi-pack-index repack" command, Git should respect the
repack.packKeptObjects config option. When false, this option says that
the pack-files with an associated ".keep" file should not be repacked.
This config value is "false" by default.
There are two cases for selecting a batch of objects. The first is the
case where the input batch-size is zero, which specifies "repack
everything". The second is with a non-zero batch size, which selects
pack-files using a greedy selection criteria. Both of these cases are
updated and tested.
Reported-by: Son Luong Ngoc <sluongng@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add the --[no-]progress option to git multi-pack-index.
Pass the MIDX_PROGRESS flag to the subcommand functions
when progress should be displayed by multi-pack-index.
The progress feature was added to 'verify' in 144d703
("multi-pack-index: report progress during 'verify'", 2018-09-13)
but some subcommands were not updated to display progress, and
the ability to opt-out was overlooked.
Signed-off-by: William Baker <William.Baker@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In an environment where the multi-pack-index is useful, it is due
to many pack-files and an inability to repack the object store
into a single pack-file. However, it is likely that many of these
pack-files are rather small, and could be repacked into a slightly
larger pack-file without too much effort. It may also be important
to ensure the object store is highly available and the repack
operation does not interrupt concurrent git commands.
Introduce a 'repack' subcommand to 'git multi-pack-index' that
takes a '--batch-size' option. The subcommand will inspect the
multi-pack-index for referenced pack-files whose size is smaller
than the batch size, until collecting a list of pack-files whose
sizes sum to larger than the batch size. Then, a new pack-file
will be created containing the objects from those pack-files that
are referenced by the multi-pack-index. The resulting pack is
likely to actually be smaller than the batch size due to
compression and the fact that there may be objects in the pack-
files that have duplicate copies in other pack-files.
The current change introduces the command-line arguments, and we
add a test that ensures we parse these options properly. Since
we specify a small batch size, we will guarantee that future
implementations do not change the list of pack-files.
In addition, we hard-code the modified times of the packs in
the pack directory to ensure the list of packs sorted by modified
time matches the order if sorted by size (ascending). This will
be important in a future test.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The multi-pack-index tracks objects in a collection of pack-files.
Only one copy of each object is indexed, using the modified time
of the pack-files to determine tie-breakers. It is possible to
have a pack-file with no referenced objects because all objects
have a duplicate in a newer pack-file.
Introduce a new 'expire' subcommand to the multi-pack-index builtin.
This subcommand will delete these unused pack-files and rewrite the
multi-pack-index to no longer refer to those files. More details
about the specifics will follow as the method is implemented.
Add a test that verifies the 'expire' subcommand is correctly wired,
but will still be valid when the verb is implemented. Specifically,
create a set of packs that should all have referenced objects and
should not be removed during an 'expire' operation. The packs are
created carefully to ensure they have a specific order when sorted
by size. This will be important in a later test.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We will add new subcommands to the multi-pack-index, and that will
make the documentation a bit messier. Clean up the 'verb'
descriptions by renaming the concept to 'subcommand' and removing
the reference to the object directory.
Helped-by: Stefan Beller <sbeller@google.com>
Helped-by: Szeder Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The multi-pack-index builtin writes multi-pack-index files, and
uses a 'write' verb to do so. Add a 'verify' verb that checks this
file matches the contents of the pack-indexes it replaces.
The current implementation is a no-op, but will be extended in
small increments in later commits.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In anticipation of writing multi-pack-indexes, add a skeleton
'git multi-pack-index write' subcommand and send the options to a
write_midx_file() method. Also create a skeleton test script that
tests the 'write' subcommand.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This new 'git multi-pack-index' builtin will be the plumbing access
for writing, reading, and checking multi-pack-index files. The
initial implementation is a no-op.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
