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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>
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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>
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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>
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Since cd57bc41bb (builtin/multi-pack-index.c: display usage on
unrecognized command, 2021-03-30) we have used a "usage" label to avoid
having two separate callers of usage_with_options (one when no arguments
are given, and another for unrecognized sub-commands).
But the first caller has been broken since cd57bc41bb, since it will
happily jump to usage without arguments, and then pass argv[0] to the
"unrecognized subcommand" error.
Many compilers will save us from a segfault here, but the end result is
ugly, since it mentions an unrecognized subcommand when we didn't even
pass one, and (on GCC) includes "(null)" in its output.
Move the "usage" label down past the error about unrecognized
subcommands so that it is only triggered when it should be. While we're
at it, bulk up our test coverage in this area, too.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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When given a sub-command that it doesn't understand, 'git
multi-pack-index' dies with the following message:
$ git multi-pack-index bogus
fatal: unrecognized subcommand: bogus
Instead of 'die()'-ing, we can display the usage text, which is much
more helpful:
$ git.compile multi-pack-index bogus
error: unrecognized subcommand: bogus
usage: git multi-pack-index [<options>] write
or: git multi-pack-index [<options>] verify
or: git multi-pack-index [<options>] expire
or: git multi-pack-index [<options>] repack [--batch-size=<size>]
--object-dir <file> object directory containing set of packfile and pack-index pairs
--progress force progress reporting
While we're at it, clean up some duplication between the "no sub-command"
and "unrecognized sub-command" conditionals.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Even before the recent refactoring, 'git multi-pack-index' calls
'trace2_cmd_mode()' before verifying that the sub-command is recognized.
Push this call down into the individual sub-commands so that we don't
enter a bogus command mode.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Handle sub-commands of the 'git multi-pack-index' builtin (e.g.,
"write", "repack", etc.) separately from one another. This allows
sub-commands with unique options, without forcing cmd_multi_pack_index()
to reject invalid combinations itself.
This comes at the cost of some duplication and boilerplate. Luckily, the
duplication is reduced to a minimum, since common options are shared
among sub-commands due to a suggestion by Ævar. (Sub-commands do have to
retain the common options, too, since this builtin accepts common
options on either side of the sub-command).
Roughly speaking, cmd_multi_pack_index() parses options (including
common ones), and stops at the first non-option, which is the
sub-command. It then dispatches to the appropriate sub-command, which
parses the remaining options (also including common options).
Unknown options are kept by the sub-commands in order to detect their
presence (and complain that too many arguments were given).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Factor out the usage message into pieces corresponding to each mode.
This avoids options specific to one sub-command from being shared with
another in the usage.
A subsequent commit will use these #define macros to have usage
variables for each sub-command without duplicating their contents.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that there is a shared 'flags' member in the options structure,
there is no need to keep track of whether to force progress or not,
since ultimately the decision of whether or not to show a progress meter
is controlled by a bit in the flags member.
Manipulate that bit directly, and drop the now-unnecessary 'progress'
field while we're at it.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Subcommands of the 'git multi-pack-index' command (e.g., 'write',
'verify', etc.) will want to optionally change a set of shared flags
that are eventually passed to the MIDX libraries.
Right now, options and flags are handled separately. That's fine, since
the options structure is never passed around. But a future patch will
make it so that common options shared by all sub-commands are defined in
a common location. That means that "flags" would have to become a global
variable.
Group it with the options structure so that we reduce the number of
global variables we have overall.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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Add the MIDX_PROGRESS flag and update the
write|verify|expire|repack functions in midx.h
to accept a flags parameter. The MIDX_PROGRESS
flag indicates whether the caller of the function
would like progress information to be displayed.
This patch only changes the method prototypes
and does not change the functionality. The
functionality change will be handled by a later patch.
Signed-off-by: William Baker <William.Baker@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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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>
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Much of the multi-pack-index code focuses on the multi_pack_index
struct, and so we only pass a pointer to the current one. However,
we will insert a dependency on the packed_git linked list in a
future change, so we will need a repository reference. Inserting
these parameters is a significant enough change to split out.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Log multi-pack-index command mode.
Log number of objects and packfiles in the midx.
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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The multi-pack-index builtin has a very simple command-line
interface. Instead of simply reporting usage, give the user a
hint to why the arguments failed.
Reported-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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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>
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