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The packfile_store data structure is moved from object store to odb
source.
* ps/packfile-store-in-odb-source:
packfile: move MIDX into packfile store
packfile: refactor `find_pack_entry()` to work on the packfile store
packfile: inline `find_kept_pack_entry()`
packfile: only prepare owning store in `packfile_store_prepare()`
packfile: only prepare owning store in `packfile_store_get_packs()`
packfile: move packfile store into object source
packfile: refactor misleading code when unusing pack windows
packfile: refactor kept-pack cache to work with packfile stores
packfile: pass source to `prepare_pack()`
packfile: create store via its owning source
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The multi-pack index still is tracked as a member of the object database
source, but ultimately the MIDX is always tied to one specific packfile
store.
Move the structure into `struct packfile_store` accordingly. This
ensures that the packfile store now keeps track of all data related to
packfiles.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The packfile store is a member of `struct object_database`, which means
that we have a single store per database. This doesn't really make much
sense though: each source connected to the database has its own set of
packfiles, so there is a conceptual mismatch here. This hasn't really
caused much of a problem in the past, but with the advent of pluggable
object databases this is becoming more of a problem because some of the
sources may not even use packfiles in the first place.
Move the packfile store down by one level from the object database into
the object database source. This ensures that each source now has its
own packfile store, and we can eventually start to abstract it away
entirely so that the caller doesn't even know what kind of store it
uses.
Note that we only need to adjust a relatively small number of callers,
way less than one might expect. This is because most callers are using
`repo_for_each_pack()`, which handles enumeration of all packfiles that
exist in the repository. So for now, none of these callers need to be
adapted. The remaining callers that iterate through the packfiles
directly and that need adjustment are those that are a bit more tangled
with packfiles. These will be adjusted over time.
Note that this patch only moves the packfile store, and there is still a
bunch of functions that seemingly operate on a packfile store but that
end up iterating over all sources. These will be adjusted in subsequent
commits.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Even when there is no changes in the packfile and no need to
recompute bitmaps, "git repack" recomputed and updated the MIDX
file, which has been corrected.
* ps/repack-avoid-noop-midx-rewrite:
midx-write: skip rewriting MIDX with `--stdin-packs` unless needed
midx-write: extract function to test whether MIDX needs updating
midx: fix `BUG()` when getting preferred pack without a reverse index
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The function `midx_preferred_pack()` returns the preferred pack for a
given multi-pack index. To compute the preferred pack we:
1. Take the first position indexed by the MIDX in pseudo-pack order.
2. Convert this pseudo-pack position into the MIDX position.
3. We then look up the pack that corresponds to this MIDX position.
This reliably returns the preferred pack given that all of its contained
objects will be up front in pseudo-pack order.
The second step that turns the pseudo-pack order into MIDX order
requires the reverse index though, which may not exist for example when
the MIDX does not have a bitmap. And in that case one may easily hit a
bug:
BUG: ../pack-revindex.c:491: pack_pos_to_midx: reverse index not yet loaded
In theory, `midx_preferred_pack()` already knows to handle the case
where no reverse index exists, as it calls `load_midx_revindex()` before
calling into `midx_preferred_pack()`. But we only check for negative
return values there, even though the function returns a positive error
code in case the reverse index does not exist.
Fix the issue by testing for a non-zero return value instead, same as
all the other callers of this function already do. While at it, document
the return value of `load_midx_revindex()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When preparing the packfile store we know to also prepare the MRU list
of packfiles with all packs that are currently loaded in the store via
`packfile_store_prepare_mru()`. So we know that the list of packs in the
MRU list should match the list of packs in the non-MRU list.
But there are some direct or indirect callsites that add a packfile to
the store via `packfile_store_add_pack()` without adding the pack to the
MRU. And while functions that access the MRU (e.g. `find_pack_entry()`)
know to call `packfile_store_prepare()`, which knows to prepare the MRU
via `packfile_store_prepare_mru()`, that operation will be turned into a
no-op because the packfile store is already prepared. So this will not
cause us to add the packfile to the MRU, and consequently we won't be
able to find the packfile in our MRU list.
There are only a handful of callers outside of "packfile.c" that add a
packfile to the store:
- "builtin/fast-import.c" adds multiple packs of imported objects, but
it knows to look up objects via `packfile_store_get_packs()`. This
function does not use the MRU, so we're good.
- "builtin/index-pack.c" adds the indexed pack to the store in case it
needs to perform consistency checks on its objects.
- "http.c" adds the fetched pack to the store so that we can access
its objects.
In all of these cases we actually want to access the contained objects.
And luckily, reading these objects works as expected:
1. We eventually end up in `do_oid_object_info_extended()`.
2. Calling `find_pack_entry()` fails because the MRU list doesn't
contain the newly added packfile.
3. The callers don't pass `OBJECT_INFO_QUICK`, so we end up
repreparing the object database. This will also cause us to
reprepare the MRU list.
4. We now retry reading the object via `find_pack_entry()`, and now we
succeed because the MRU list got populated.
This logic feels quite fragile: we intentionally add the packfile to the
store, but we then ultimately rely on repreparing the entire store only
to make the packfile accessible. While we do the correct thing in
`do_oid_object_info_extended()`, other sites that access the MRU may not
know to reprepare.
But besides being fragile it's also a waste of resources: repreparing
the object database requires us to re-read the alternates file and
discard any caches.
Refactor the code so that we unconditionally add packfiles to the MRU
when adding them to a packfile store. This makes the logic less fragile
and ensures that we don't have to reprepare the store to make the pack
accessible.
Note that this does not allow us to drop `packfile_store_prepare_mru()`
just yet: while the MRU list is already populated with all packs now,
the order in which we add these packs is indeterministic for most of the
part. So by first calling `sort_pack()` on the other packfile list and
then re-preparing the MRU list we inherit its sorting.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Packfiles have two lists associated to them:
- A list that keeps track of packfiles in the order that they were
added to a packfile store.
- A list that keeps track of packfiles in most-recently-used order so
that packfiles that are more likely to contain a specific object are
ordered towards the front.
Both of these lists are hosted by `struct packed_git` itself, So to
identify all packfiles in a repository you simply need to grab the first
packfile and then iterate the `->next` pointers or the MRU list. This
pattern has the problem that all packfiles are part of the same list,
regardless of whether or not they belong to the same object source.
With the upcoming pluggable object database effort this needs to change:
packfiles should be contained by a single object source, and reading an
object from any such packfile should use that source to look up the
object. Consequently, we need to break up the global lists of packfiles
into per-object-source lists.
A first step towards this goal is to move those lists out of `struct
packed_git` and into the packfile store. While the packfile store is
currently sitting on the `struct object_database` level, the intent is
to push it down one level into the `struct odb_source` in a subsequent
patch series.
Introduce a new `struct packfile_list` that is used to manage lists of
packfiles and use it to store the list of most-recently-used packfiles
in `struct packfile_store`. For now, the new list type is only used in a
single spot, but we'll expand its usage in subsequent patches.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `get_multi_pack_index()` function is declared and implemented in the
packfile subsystem, even though it really belongs into the multi-pack
index subsystem. The reason for this is likely that it needs to call
`packfile_store_prepare()`, which is not exposed by the packfile system.
In a subsequent commit we're about to add another caller outside of the
packfile system though, so we'll have to expose the function anyway.
Do so now already and move `get_multi_pack_index()` into the MIDX
subsystem.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We have a recurring pattern where we essentially perform an upsert of a
packfile in case it isn't yet known by the packfile store. The logic to
do so is non-trivial as we have to reconstruct the packfile's key, check
the map of packfiles, then create the new packfile and finally add it to
the store.
Introduce a new function that does this dance for us. Refactor callsites
to use it.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `install_packed_git()` functions adds a packfile to a specific
object store. Refactor it to accept a packfile store instead of a
repository to clarify its scope.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The object database tracks the list of packfiles in most-recently-used
order, which is mostly used to favor reading from packfiles that contain
most of the objects that we're currently accessing. With the
introduction of the `struct packfile_store` we have a better place to
host this list though.
Move the list accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The object database tracks a map of packfiles by their respective paths,
which is used to figure out whether a given packfile has already been
loaded. With the introduction of the `struct packfile_store` we have a
better place to host this list though.
Move the map accordingly.
`pack_map_entry_cmp()` isn't used anywhere but in "packfile.c" anymore
after this change, so we convert it to a static function, as well. Note
that we also drop the `inline` hint: the function is used as a callback
function exclusively, and callbacks cannot be inlined.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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With the preceding commits we started to always have the object database
source available when we load, write or access multi-pack indices. With
this in place we can change how MIDX paths are computed so that we don't
have to pass in the combination of a hash algorithm and object directory
anymore, but only the object database source.
Refactor the code accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Multi-pack indices store some information that is redundant with their
owning source:
- The locality bit that tracks whether the source is the primary
object source or an alternate.
- The object directory path the multi-pack index is located in.
- The pointer to the owning parent directory.
All of this information is already contained in `struct odb_source`. So
now that we always have that struct available when loading a multi-pack
index we have it readily accessible.
Drop the redundant information and instead store a pointer to the object
source.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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To load a multi-pack index the caller is expected to pass both the
repository and the object directory where the multi-pack index is
located. While this works, this layout has a couple of downsides:
- We need to pass in information reduntant with the owning source,
namely its object directory and whether the source is local or not.
- We don't have access to the source when loading the multi-pack
index. If we had that access, we could store a pointer to the owning
source in the MIDX and thus deduplicate some information.
- Multi-pack indices are inherently specific to the object source and
its format. With the goal of pluggable object backends in mind we
will eventually want the backends to own the logic of reading and
writing multi-pack indices. Making the logic work on top of object
sources is a step into that direction.
Refactor loading of multi-pack indices accordingly.
This surfaces one small problem though: git-multi-pack-index(1) and our
MIDX test helper both know to read and write multi-pack-indices located
in a different object directory. This issue is addressed by adding the
user-provided object directory as an in-memory alternate.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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There are a couple of functions that take both a `struct repository` and
a `struct multi_pack_index`. This provides redundant information though
without much benefit given that the multi-pack index already has a
pointer to its owning repository.
Drop the `struct repository` parameter from such functions. While at it,
reorder the list of parameters of `fill_midx_entry()` so that the MIDX
comes first to better align with our coding guidelines.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Object database sources are classified either as:
- Local, which means that the source is the repository's primary
source. This is typically ".git/objects".
- Non-local, which is everything else. Most importantly this includes
alternates and quarantine directories.
This locality is often computed ad-hoc by checking whether a given
object source is the first one. This works, but it is quite roundabout.
Refactor the code so that we store locality when creating the sources in
the first place. This makes it both more accessible and robust.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In the preceding commits we have migrated all users of the linked list
of multi-pack indices to instead use those stored in the object database
sources. Remove those now-unused pointers.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When calling `close_midx()` we not only close the multi-pack index for
one object source, but instead we iterate through the whole linked list
of MIDXs to close all of them. This linked list is about to go away in
favor of using the new per-source pointer to its respective MIDX.
Refactor the function to iterate through sources instead.
Note that after this patch, there's a couple of callsites left that
continue to use `close_midx()` without iterating through all sources.
These are all cases where we don't care about the MIDX from other
sources though, so it's fine to keep them as-is.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Multi-pack indices are tracked via `struct multi_pack_index`. This data
structure is stored as a linked list inside `struct object_database`,
which is the global database that spans across all of the object
sources.
This layout causes two problems:
- Object databases consist of multiple object sources (e.g. one source
per alternate object directory), where each multi-pack index is
specific to one of those sources. Regardless of that though, the
MIDX is not tracked per source, but tracked globally for the whole
object database. This creates a mismatch between the on-disk layout
and how things are organized in the object database subsystems and
makes some parts, like figuring out whether a source has an MIDX,
quite awkward.
- Multi-pack indices are an implementation detail of how efficient
access for packfiles work. As such, they are neither relevant in the
context of loose objects, nor in a potential future where we have
pluggable backends.
Refactor `prepare_multi_pack_index_one()` so that it works on a specific
source, which allows us to easily store a pointer to the multi-pack
index inside of it. For now, this pointer exists next to the existing
linked list we have in the object database. Users will be adjusted in
subsequent patches to instead use the per-source pointers.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `object_directory` structure is used as an access point for a single
object directory like ".git/objects". While the structure isn't yet
fully self-contained, the intent is for it to eventually contain all
information required to access objects in one specific location.
While the name "object directory" is a good fit for now, this will
change over time as we continue with the agenda to make pluggable object
databases a thing. Eventually, objects may not be accessed via any kind
of directory at all anymore, but they could instead be backed by any
kind of durable storage mechanism. While it seems quite far-fetched for
now, it is thinkable that eventually this might even be some form of a
database, for example.
As such, the current name of this structure will become worse over time
as we evolve into the direction of pluggable ODBs. Immediate next steps
will start to carve out proper self-contained object directories, which
requires us to pass in these object directories as parameters. Based on
our modern naming schema this means that those functions should then be
named after their subsystem, which means that we would start to bake the
current name into the codebase more and more.
Let's preempt this by renaming the structure. There have been a couple
alternatives that were discussed:
- `odb_backend` was discarded because it led to the association that
one object database has a single backend, but the model is that one
alternate has one backend. Furthermore, "backend" is more about the
actual backing implementation and less about the high-level concept.
- `odb_alternate` was discarded because it is a bit of a stretch to
also call the main object directory an "alternate".
Instead, pick `odb_source` as the new name. It makes it sufficiently
clear that there can be multiple sources and does not cause confusion
when mixed with the already-existing "alternate" terminology.
In the future, this change allows us to easily introduce for example a
`odb_files_source` and other format-specific implementations.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The multi-pack index acts as a cache across a set of packfiles so that
we can quickly look up which of those packfiles contains a given object.
As such, the multi-pack index naturally needs to be updated every time
one of the packfiles goes away, or otherwise the multi-pack index has
grown stale.
A stale multi-pack index should be handled gracefully by Git though, and
in fact it is: if the indexed pack cannot be found we simply ignore it
and eventually we fall back to doing the object lookup by just iterating
through all packs, even if those aren't indexed.
But while this fallback works, it has one significant downside: we don't
cache the fact that a pack has vanished. This leads to us repeatedly
trying to look up the same pack only to realize that it (still) doesn't
exist.
This issue can be easily demonstrated by creating a repository with a
stale multi-pack index and a couple of objects. We do so by creating a
repository with two packfiles, both of which are indexed by the
multi-pack index, and then repack those two packfiles. Note that we have
to move the multi-pack-index before doing the final repack, as Git knows
to delete it otherwise.
$ git init repo
$ cd repo/
$ git config set maintenance.auto false
$ for i in $(seq 1000); do printf "%d-original" $i >file-$i; done
$ git add .
$ git commit -moriginal
$ git repack -dl
$ for i in $(seq 1000); do printf "%d-modified" $i >file-$i; done
$ git commit -a -mmodified
$ git repack -dl
$ git multi-pack-index write
$ mv .git/objects/pack/multi-pack-index .
$ git repack -Adl
$ mv multi-pack-index .git/objects/pack/
Commands that cause a lot of objects lookups will now repeatedly invoke
`add_packed_git()`, which leads to three failed access(3p) calls as well
as one failed stat(3p) call. The following strace for example is done
for `git log --patch` in the above repository:
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
74.67 0.024693 1 18038 18031 access
25.33 0.008378 1 6045 6017 newfstatat
------ ----------- ----------- --------- --------- ----------------
100.00 0.033071 1 24083 24048 total
Fix the issue by introducing a negative lookup cache for indexed packs.
This cache works by simply storing an invalid pointer for a missing pack
when `prepare_midx_pack()` fails to look up the pack. Most users of the
`packs` array don't need to be adjusted, either, as they all know to
call `prepare_midx_pack()` before accessing the array.
With this change in place we can now see a significantly reduced number
of syscalls:
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
73.58 0.000323 5 60 28 newfstatat
26.42 0.000116 5 23 16 access
------ ----------- ----------- --------- --------- ----------------
100.00 0.000439 5 83 44 total
Furthermore, this change also results in a speedup:
Benchmark 1: git log --patch (revision = HEAD~)
Time (mean ± σ): 50.4 ms ± 2.5 ms [User: 22.0 ms, System: 24.4 ms]
Range (min … max): 45.4 ms … 54.9 ms 53 runs
Benchmark 2: git log --patch (revision = HEAD)
Time (mean ± σ): 12.7 ms ± 0.4 ms [User: 11.1 ms, System: 1.6 ms]
Range (min … max): 12.4 ms … 15.0 ms 191 runs
Summary
git log --patch (revision = HEAD) ran
3.96 ± 0.22 times faster than git log --patch (revision = HEAD~)
In the end, it should in theory never be necessary to have this negative
lookup cache given that we know to update the multi-pack index together
with repacks. But as the change is quite contained and as the speedup
can be significant as demonstrated above, it does feel sensible to have
the negative lookup cache regardless.
Based-on-patch-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `git_open_cloexec()` wrapper function provides the ability to open a
file with `O_CLOEXEC` in a platform-agnostic way. This function is
provided by "object-file.c" even though it is not specific to the object
subsystem at all.
Move the file into "compat/open.c". This file already exists before this
commit, but has only been compiled conditionally depending on whether or
not open(3p) may return EINTR. With this change we now unconditionally
compile the object, but wrap `git_open_with_retry()` in an ifdef.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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There are multiple sites in "csum-file.c" where we use the global
`the_repository` variable, either explicitly or implicitly by using
`the_hash_algo`.
Refactor the code to stop using `the_repository` by adapting functions
to receive required data as parameters. Adapt callsites accordingly by
either using `the_repository->hash_algo`, or by using a context-provided
hash algorithm in case the subsystem already got rid of its dependency
on `the_repository`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Stop using `the_repository` in the "progress" subsystem by passing in a
repository when initializing `struct progress`. Furthermore, store a
pointer to the repository in that struct so that we can pass it to the
trace2 API when logging information.
Adjust callers accordingly by using `the_repository`. While there may be
some callers that have a repository available in their context, this
trivial conversion allows for easier verification and bubbles up the use
of `the_repository` by one level.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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* ps/build-sign-compare:
t/helper: don't depend on implicit wraparound
scalar: address -Wsign-compare warnings
builtin/patch-id: fix type of `get_one_patchid()`
builtin/blame: fix type of `length` variable when emitting object ID
gpg-interface: address -Wsign-comparison warnings
daemon: fix type of `max_connections`
daemon: fix loops that have mismatching integer types
global: trivial conversions to fix `-Wsign-compare` warnings
pkt-line: fix -Wsign-compare warning on 32 bit platform
csum-file: fix -Wsign-compare warning on 32-bit platform
diff.h: fix index used to loop through unsigned integer
config.mak.dev: drop `-Wno-sign-compare`
global: mark code units that generate warnings with `-Wsign-compare`
compat/win32: fix -Wsign-compare warning in "wWinMain()"
compat/regex: explicitly ignore "-Wsign-compare" warnings
git-compat-util: introduce macros to disable "-Wsign-compare" warnings
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Mark code units that generate warnings with `-Wsign-compare`. This
allows for a structured approach to get rid of all such warnings over
time in a way that can be easily measured.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `MIDX_MIN_SIZE` definition is used to check the midx_size in
`local_multi_pack_index_one`. This definition relies on the
`the_hash_algo` global variable. Inline this and remove the global
variable usage.
With this, remove `USE_THE_REPOSITORY_VARIABLE` usage from `midx.c`.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The functions `get_split_midx_filename_ext()`, `get_midx_filename()` and
`get_midx_filename_ext()` use `hash_to_hex()` which internally uses the
`the_hash_algo` global variable.
Remove this dependency on global variables by passing down the
`hash_algo` through to the functions mentioned and instead calling
`hash_to_hex_algop()` along with the obtained `hash_algo`.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `load_multi_pack_index` function in midx uses `the_repository`
variable to access the `repository` struct. Modify the function and its
callee's to send the `repository` field.
This moves usage of `the_repository` to the `test-read-midx.c` file.
While that is not optimal, it is okay, since the upcoming commits will
slowly move the usage of `the_repository` up the layers and remove it
eventually.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In the `midx.c` file, there are multiple usages of `the_repository` and
`the_hash_algo` within static functions of the file. Some of the usages
can be simply swapped out with the available `repository` struct. While
some of them can be swapped out by passing the repository to the
required functions.
This leaves out only some other usages of `the_repository` and
`the_hash_algo` in the file in non-static functions, which we'll tackle
in upcoming commits.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `multi_pack_index` struct represents the MIDX for a repository.
Here, we add a pointer to the repository in this struct, allowing direct
use of the repository variable without relying on the global
`the_repository` struct.
With this addition, we can determine the repository associated with a
`bitmap_index` struct. A `bitmap_index` points to either a `packed_git`
or a `multi_pack_index`, both of which have direct repository
references. To support this, we introduce a static helper function,
`bitmap_repo`, in `pack-bitmap.c`, which retrieves a repository given a
`bitmap_index`.
With this, we clear up all usages of `the_repository` within
`pack-bitmap.c` and also remove the `USE_THE_REPOSITORY_VARIABLE`
definition. Bringing us another step closer to remove all global
variable usage.
Although this change also opens up the potential to clean up `midx.c`,
doing so would require additional refactoring to pass the repository
struct to functions where the MIDX struct is created: a task better
suited for future patches.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The struct `packed_git` holds information regarding a packed object
file. Let's add the repository variable to this object, to represent the
repository that this packfile belongs to. This helps remove dependency
on the global `the_repository` object in `packfile.c` by simply using
repository information now readily available in the struct.
We do need to consider that a packfile could be part of the alternates
of a repository, but considering that we only have one repository struct
and also that we currently anyways use 'the_repository', we should be
OK with this change.
We also modify `alloc_packed_git` to ensure that the repository is added
to newly created `packed_git` structs. This requires modifying the
function and all its callee to pass the repository object down the
levels.
Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The main function we use to search a pack index for an object is
find_pack_entry_one(). That function still takes a bare pointer to the
hash, despite the fact that its underlying bsearch_pack() function needs
an object_id struct. And so we end up making an extra copy of the hash
into the struct just to do a lookup.
As it turns out, all callers but one already have such an object_id. So
we can just take a pointer to that struct and use it directly. This
avoids the extra copy and provides a more type-safe interface.
The one exception is get_delta_base() in packfile.c, when we are chasing
a REF_DELTA from inside the pack (and thus we have a pointer directly to
the mmap'd pack memory, not a struct). We can just bump the hashcpy()
from inside find_pack_entry_one() to this one caller that needs it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
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When we scan a pack directory to load the idx entries we find into the
packed_git list, we skip any of them that are contained in a midx. We
then load them later lazily if we actually need to access the
corresponding pack, referencing them both from the midx struct and the
packed_git list.
The lazy-load in the midx code checks to see if the midx already
mentions the pack, but doesn't otherwise check the packed_git list. This
makes sense, since we should have added any pack to both lists.
But there's a loophole! If we call close_object_store(), that frees the
midx entirely, but _not_ the packed_git structs, which we must keep
around for Reasons[1]. If we then try to look up more objects, we'll
auto-load the midx again, which won't realize that we've already loaded
those packs, and will create duplicate entries in the packed_git list.
This is possibly inefficient, because it means we may open and map the
pack redundantly. But it can also lead to weird user-visible behavior.
The case I found is in "git repack", which closes and reopens the midx
after repacking and then calls update_server_info(). We end up writing
the duplicate entries into objects/info/packs.
We could obviously de-dup them while writing that file, but it seems
like a violation of more core assumptions that we end up with these
duplicate structs at all.
We can avoid the duplicates reasonably efficiently by checking their
names in the pack_map hash. This annoyingly does require a little more
than a straight hash lookup due to the naming conventions, but it should
only happen when we are about to actually open a pack. I don't think one
extra malloc will be noticeable there.
[1] I'm not entirely sure of all the details, except that we generally
assume the packed_git structs never go away. We noted this
restriction in the comment added by 6f1e9394e2 (object: fix leaking
packfiles when closing object store, 2024-08-08), but it's somewhat
vague. At any rate, if you try freeing the structs in
close_object_store(), you can observe segfaults all over the test
suite. So it might be fixable, but it's not trivial.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
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The next commit will need to use the bitmap's MIDX (if one exists) to
translate bit positions into pack-relative positions in the source pack.
Ordinarily, we'd use the "midx" field of the bitmap_index struct. But
since that struct is defined within pack-bitmap.c, and our caller is in
a separate compilation unit, we do not have access to the MIDX field.
Instead, add a "from_midx" field to the bitmapped_pack structure so that
we can use that piece of data from outside of pack-bitmap.c. The caller
that uses this new piece of information will be added in the following
commit.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When loading a chained midx, we build up an array of hashes, one per
layer of the chain. But since the chain is also represented by the
linked list of multi_pack_index structs, nobody actually reads this
array. We pass it to add_midx_to_chain(), but the parameters are
completely ignored.
So we can drop those unused parameters. And then we can see that its
sole caller, load_midx_chain_fd_st(), only cares about one layer hash at a
time (for parsing each line and feeding it to the single-layer midx
code). So we can replace the array with a single object_id on the stack.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that the rest of the MIDX subsystem and relevant callers have been
updated to learn about how to read and process incremental MIDX chains,
let's finally update the implementation in `write_midx_internal()` to be
able to write incremental MIDX chains.
This new feature is available behind the `--incremental` option for the
`multi-pack-index` builtin, like so:
$ git multi-pack-index write --incremental
The implementation for doing so is relatively straightforward, and boils
down to a handful of different kinds of changes implemented in this
patch:
- The `compute_sorted_entries()` function is taught to reject objects
which appear in any existing MIDX layer.
- Functions like `write_midx_revindex()` are adjusted to write
pack_order values which are offset by the number of objects in the
base MIDX layer.
- The end of `write_midx_internal()` is adjusted to move
non-incremental MIDX files when necessary (i.e. when creating an
incremental chain with an existing non-incremental MIDX in the
repository).
There are a handful of other changes that are introduced, like new
functions to clear incremental MIDX files that are unrelated to the
current chain (using the same "keep_hash" mechanism as in the
non-incremental case).
The tests explicitly exercising the new incremental MIDX feature are
relatively limited for two reasons:
1. Most of the "interesting" behavior is already thoroughly covered in
t5319-multi-pack-index.sh, which handles the core logic of reading
objects through a MIDX.
The new tests in t5334-incremental-multi-pack-index.sh are mostly
focused on creating and destroying incremental MIDXs, as well as
stitching their results together across layers.
2. A new GIT_TEST environment variable is added called
"GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL", which modifies the
entire test suite to write incremental MIDXs after repacking when
combined with the "GIT_TEST_MULTI_PACK_INDEX" variable.
This exercises the long tail of other interesting behavior that is
defined implicitly throughout the rest of the CI suite. It is
likewise added to the linux-TEST-vars job.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Teach the verification implementation used by `git multi-pack-index
verify` to perform verification for incremental MIDX chains by
independently validating each layer within the chain.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that the MIDX machinery's internals have been taught to understand
incremental MIDXs over the previous handful of commits, the MIDX
machinery itself can begin reading incremental MIDXs.
(Note that while the on-disk format for incremental MIDXs has been
defined, the writing end has not been implemented. This will take place
in the commit after next.)
The core of this change involves following the order specified in the
MIDX chain in reverse and opening up MIDXs in the chain one-by-one,
adding them to the previous layer's `->base_midx` pointer at each step.
In order to implement this, the `load_multi_pack_index()` function is
taught to call a new `load_multi_pack_index_chain()` function if loading
a non-incremental MIDX failed via `load_multi_pack_index_one()`.
When loading a MIDX chain, `load_midx_chain_fd_st()` reads each line in
the file one-by-one and dispatches calls to
`load_multi_pack_index_one()` to read each layer of the MIDX chain. When
a layer was successfully read, it is added to the MIDX chain by calling
`add_midx_to_chain()` which validates the contents of the `BASE` chunk,
performs some bounds checks on the number of combined packs and objects,
and attaches the new MIDX by assigning its `base_midx` pointer to the
existing part of the chain.
As a supplement to this, introduce a new mode in the test-read-midx
test-tool which allows us to read the information for a specific MIDX in
the chain by specifying its trailing checksum via the command-line
arguments like so:
$ test-tool read-midx .git/objects [checksum]
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The function `midx_preferred_pack()` is used to determine the identity
of the preferred pack, which is the identity of a unique pack within
the MIDX which is used as a tie-breaker when selecting from which pack
to represent an object that appears in multiple packs within the MIDX.
Historically we have said that the MIDX's preferred pack has the unique
property that all objects from that pack are represented in the MIDX.
But that isn't quite true: a more precise statement would be that all
objects from that pack *which appear in the MIDX* are selected from that
pack.
This helps us extend the concept of preferred packs across a MIDX chain,
where some object(s) in the preferred pack may appear in other packs
in an earlier MIDX layer, in which case those object(s) will not appear
in a subsequent MIDX layer from either the preferred pack or any other
pack.
Extend the concept of preferred packs by using the pack which represents
the object at the first position in MIDX pseudo-pack order belonging to
the current MIDX layer (i.e., at position 'm->num_objects_in_base').
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that the `midx_contains_pack()` versus `midx_locate_pack()` debacle
has been cleaned up, teach the former about how to operate in an
incremental MIDX-aware world in a similar fashion as in previous
commits.
Instead of using either of the two `midx_for_object()` or
`midx_for_pack()` helpers, this function is split into two: one that
determines whether a pack is contained in a single MIDX, and another
which calls the former in a loop over all MIDXs.
This approach does not require that we change any of the implementation
in what is now `midx_contains_pack_1()` as it still operates over a
single MIDX.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Commit 307d75bbe6 (midx: implement `midx_locate_pack()`, 2023-12-14)
introduced `midx_locate_pack()`, which was described at the time as a
complement to the function `midx_contains_pack()` which allowed
callers to determine where in the MIDX lexical order a pack appeared, as
opposed to whether or not it was simply contained.
307d75bbe6 suggests that future patches would be added which would
introduce callers for this new function, but none ever were, meaning the
function has gone unused since its introduction.
Clean this up by in effect reverting 307d75bbe6, which removes the
unused functions and inlines its definition back into
`midx_contains_pack()`.
(Looking back through the list archives when 307d75bbe6 was written,
this was in preparation for this[1] patch from back when we had the
concept of "disjoint" packs while developing multi-pack verbatim reuse.
That concept was abandoned before the series was merged, but I never
dropped what would become 307d75bbe6 from the series, leading to the
state prior to this commit).
[1]: https://lore.kernel.org/git/3019738b52ba8cd78ea696a3b800fa91e722eb66.1701198172.git.me@ttaylorr.com/
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In a similar fashion as previous commits, teach the `fill_midx_entry()`
function to work in a incremental MIDX-aware fashion.
This function, unlike others which accept an index into either the
lexical order of objects or packs, takes in an object_id, and attempts
to fill a caller-provided 'struct pack_entry' with the remaining pieces
of information about that object from the MIDX.
The function uses `bsearch_midx()` which fills out the frame-local 'pos'
variable, recording the given object_id's lexical position within the
MIDX chain, if found (if no matching object ID was found, we'll return
immediately without filling out the `pack_entry` structure).
Once given that position, we jump back through the `->base_midx` pointer
to ensure that our `m` points at the MIDX layer which contains the given
object_id (and not an ancestor or descendant of it in the chain). Note
that we can drop the bounds check "if (pos >= m->num_objects)" because
`midx_for_object()` performs this check for us.
After that point, we only need to make two special considerations within
this function:
- First, the pack_int_id returned to us by `nth_midxed_pack_int_id()`
is a position in the concatenated lexical order of packs, so we must
ensure that we subtract `m->num_packs_in_base` before accessing the
MIDX-local `packs` array.
- Second, we must avoid translating the `pos` back to a MIDX-local
index, since we use it as an argument to `nth_midxed_offset()` which
expects a position relative to the concatenated lexical order of
objects.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In a similar fashion as in previous commits, teach the function
`nth_midxed_offset()` about incremental MIDXs.
The given object `pos` is used to find the containing MIDX, and
translated back into a MIDX-local position by assigning the return value
of `midx_for_object()` to it.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that the special cases callers of `bsearch_midx()` have been dealt
with, teach `bsearch_midx()` to handle incremental MIDX chains.
The incremental MIDX-aware version of `bsearch_midx()` works by
repeatedly searching for a given OID in each layer along the
`->base_midx` pointer, stopping either when an exact match is found, or
the end of the chain is reached.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `bsearch_midx()` function will be extended in a following commit to
search for the location of a given object ID across all MIDXs in a chain
(or the single non-chain MIDX if no chain is available).
While most callers will naturally want to use the updated
`bsearch_midx()` function, there are a handful of special cases that
will want finer control and will only want to search through a single
MIDX.
For instance, the object abbreviation code, which cares about object IDs
near to where we'd expect to find a match in a MIDX. In that case, we
want to look at the nearby matches in each layer of the MIDX chain, not
just a single one).
Split the more fine-grained control out into a separate function called
`bsearch_one_midx()` which searches only a single MIDX.
At present both `bsearch_midx()` and `bsearch_one_midx()` have identical
behavior, but the following commit will rewrite the former to be aware
of incremental MIDXs for the remaining non-special case callers.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In a similar fashion as in previous commits, teach the function
`nth_bitmapped_pack()` about incremental MIDXs by translating the given
`pack_int_id` from the concatenated lexical order to a MIDX-local
lexical position.
When accessing the containing MIDX's array of packs, use the local pack
ID. Likewise, when reading the 'BTMP' chunk, use the MIDX-local offset
when accessing the data within that chunk.
(Note that the both the call to prepare_midx_pack() and the assignment
of bp->pack_int_id both care about the global pack_int_id, so avoid
shadowing the given 'pack_int_id' parameter).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The function `nth_midxed_object_oid()` returns the object ID for a given
object position in the MIDX lexicographic order.
Teach this function to instead operate over the concatenated
lexicographic order defined in an earlier step so that it is able to be
used with incremental MIDXs.
To do this, we need to both (a) adjust the bounds check for the given
'n', as well as record the MIDX-local position after chasing the
`->base_midx` pointer to find the MIDX which contains that object.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The function `prepare_midx_pack()` is part of the midx.h API and
loads the pack identified by the MIDX-local 'pack_int_id'. This patch
prepares that function to be aware of an incremental MIDX world.
To do this, introduce the second of the two general purpose helpers
mentioned in the previous commit. This commit introduces
`midx_for_pack()`, which is the pack-specific analog of
`midx_for_object()`, and works in the same fashion.
Like `midx_for_object()`, this function chases down the '->base_midx'
field until it finds the MIDX layer within the chain that contains the
given pack.
Use this function within `prepare_midx_pack()` so that the `pack_int_id`
it expects is now relative to the entire MIDX chain, and that it
prepares the given pack in the appropriate MIDX.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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