When compacting tables, it may happen that we want to compact a set of
tables which are already locked by a concurrent process that compacts
them. In the case where we wanted to perform a full compaction of all
tables it is sensible to bail out in this case, as we cannot fulfill the
requested action.
But when performing auto-compaction it isn't necessarily in our best
interest of us to abort the whole operation. For example, due to the
geometric compacting schema that we use, it may be that process A takes
a lot of time to compact the bulk of all tables whereas process B
appends a bunch of new tables to the stack. B would in this case also
notice that it has to compact the tables that process A is compacting
already and thus also try to compact the same range, probably including
the new tables it has appended. But because those tables are locked
already, it will fail and thus abort the complete auto-compaction. The
consequence is that the stack will grow longer and longer while A isn't
yet done with compaction, which will lead to a growing performance
impact.
Instead of aborting auto-compaction altogether, let's gracefully handle
this situation by instead compacting tables which aren't locked. To do
so, instead of locking from the beginning of the slice-to-be-compacted,
we start locking tables from the end of the slice. Once we hit the first
table that is locked already, we abort. If we succeeded to lock two or
more tables, then we simply reduce the slice of tables that we're about
to compact to those which we managed to lock.
This ensures that we can at least make some progress for compaction in
said scenario. It also helps in other scenarios, like for example when a
process died and left a stale lockfile behind. In such a case we can at
least ensure some compaction on a best-effort basis.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The locking employed by compaction uses the following schema:
1. Lock "tables.list" and verify that it matches the version we have
loaded in core.
2. Lock each of the tables in the user-supplied range of tables that
we are supposed to compact. These locks prohibit any concurrent
process to compact those tables while we are doing that.
3. Unlock "tables.list". This enables concurrent processes to add new
tables to the stack, but also allows them to compact tables outside
of the range of tables that we have locked.
4. Perform the compaction.
5. Lock "tables.list" again.
6. Move the compacted table into place.
7. Write the new order of tables, including the compacted table, into
the lockfile.
8. Commit the lockfile into place.
Letting concurrent processes modify the "tables.list" file while we are
doing the compaction is very much part of the design and thus expected.
After all, it may take some time to compact tables in the case where we
are compacting a lot of very large tables.
But there is a bug in the code. Suppose we have two processes which are
compacting two slices of the table. Given that we lock each of the
tables before compacting them, we know that the slices must be disjunct
from each other. But regardless of that, compaction performed by one
process will always impact what the other process needs to write to the
"tables.list" file.
Right now, we do not check whether the "tables.list" has been changed
after we have locked it for the second time in (5). This has the
consequence that we will always commit the old, cached in-core tables to
disk without paying to respect what the other process has written. This
scenario would then lead to data loss and corruption.
This can even happen in the simpler case of one compacting process and
one writing process. The newly-appended table by the writing process
would get discarded by the compacting process because it never sees the
new table.
Fix this bug by re-checking whether our stack is still up to date after
locking for the second time. If it isn't, then we adjust the indices of
tables to replace in the updated stack.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When modifying "tables.list", we need to lock the list before updating
it to ensure that no concurrent writers modify the list at the same
point in time. While we do this via the `lock_file` subsystem when
compacting the stack, we manually handle the lock when adding a new
table to it. While not wrong, it is at least inconsistent.
Refactor the code to consistently lock "tables.list" via the `lock_file`
subsytem.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We use `fsync_component_or_die()` when committing an addition to the
"tables.list" lock file, which unsurprisingly dies in case the fsync
fails. Given that this is part of the reftable library, we should never
die and instead let callers handle the error.
Adapt accordingly and use `fsync_component()` instead.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When compacting tables, we store the locks of all tables we are about to
compact in the `table_locks` array. As we currently only ever compact
all tables in the user-provided range or none, we simply track those
locks via the indices of the respective tables in the merged stack.
This is about to change though, as we will introduce a mode where auto
compaction gracefully handles the case of already-locked files. In this
case, it may happen that we only compact a subset of the user-supplied
range of tables. In this case, the indices will not necessarily match
the lock indices anymore.
Refactor the code such that we track the number of locks via a separate
variable. The resulting code is expected to perform the same, but will
make it easier to perform the described change.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When auto-compaction fails due to a locking error, we update the
statistics to indicate this failure. We're not doing the same when
performing a full compaction.
Fix this inconsistency by using `stack_compact_range_stats()`, which
handles the stat update for us.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We're lacking test coverage for compacting tables when some of the
tables that we are about to compact are locked. Add two tests that
exercise this, one for auto-compaction and one for full compaction.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We're about to add two tests, and both of them will want to initialize
the reftable stack with a set of N tables. Introduce a new function that
handles this and refactor existing tests that use such a setup to use
it.
Note that this changes the exact records contained in the preexisting
tests. This is fine though as we only care about the shape of the stack
here, not the shape of each table.
Furthermore, with this change we now start to disable auto compaction
when writing the tables, as otherwise we might not end up with the
expected amount of new tables added. This also slightly changes the
behaviour of these tests, but the properties we care for remain intact.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Refactor the function that gathers table sizes to be more idiomatic. For
one, use `REFTABLE_CALLOC_ARRAY()` instead of `reftable_calloc()`.
Second, avoid using an integer to iterate through the tables in the
reftable stack given that `stack_len` itself is using a `size_t`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The git-fsck(1) only implicitly checks the reference, it does not fully
check refs with bad format name such as standalone "@".
However, a file ending with ".lock" should not be marked as having a bad
ref name. It is expected that concurrent writers may have such lock files.
We currently ignore this situation. But for bare ".lock" file, we will
report it as error.
In order to provide such checks, add a new fsck message id "badRefName"
with default ERROR type. Use existing "check_refname_format" to explicit
check the ref name. And add a new unit test to verify the functionality.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
For refs and reflogs, we need to scan its corresponding directories to
check every regular file or symbolic link which shares the same pattern.
Introduce a unified interface for scanning directories for
files-backend.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a new subcommand "verify" in git-refs(1) to allow the user to
check the reference database consistency and also this subcommand will
be used as the entry point of checking refs for "git-fsck(1)".
Add "verbose" field into "fsck_options" to indicate whether we should
print verbose messages when checking refs and objects consistency.
Remove bit-field for "strict" field, this is because we cannot take
address of a bit-field which makes it unhandy to set member variables
when parsing the command line options.
The "git-fsck(1)" declares "fsck_options" variable with "static"
identifier which avoids complaint by the leak-checker. However, in
"git-refs verify", we need to do memory clean manually. Thus add
"fsck_options_clear" function in "fsck.c" to provide memory clean
operation.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "struct ref_store" is the base class which contains the "be" pointer
which provides backend-specific functions whose interfaces are defined
in the "ref_storage_be". We could reuse this polymorphism to define only
one interface. For every backend, we need to provide its own function
pointer.
The interfaces defined in the `ref_storage_be` are carefully structured
in semantic. It's organized as the five parts:
1. The name and the initialization interfaces.
2. The ref transaction interfaces.
3. The ref internal interfaces (pack, rename and copy).
4. The ref filesystem interfaces.
5. The reflog related interfaces.
To keep consistent with the git-fsck(1), add a new interface named
"fsck_refs_fn" to the end of "ref_storage_be". This semantic cannot be
grouped into any above five categories. Explicitly add blank line to
make it different from others.
Last, implement placeholder functions for each ref backends.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a new struct "fsck_ref_report" to contain the information we
need when reporting refs-related messages.
With the new "fsck_vreport" function, add a new function
"fsck_report_ref" to report refs-related fsck error message. Unlike
"report" function uses the exact parameters, we simply pass "struct
fsck_ref_report *report" as the parameter. This is because at current we
don't know exactly how many fields we need. By passing this parameter,
we don't need to change this function prototype when we want to add more
information into "fsck_ref_report".
We have introduced "fsck_report_ref" function to report the error
message for refs. We still need to add the corresponding callback
function. Create refs-specific "error_func" callback
"fsck_refs_error_function".
Last, add "FSCK_REFS_OPTIONS_DEFAULT" macro to create default options
when checking ref consistency.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The static function "report" provided by "fsck.c" aims at checking error
type and calling the callback "error_func" to report the message. Both
refs and objects need to check the error type of the current fsck
message. In order to extract this common behavior, create a new function
"fsck_vreport". Instead of using "...", provide "va_list" to allow more
flexibility.
Instead of changing "report" prototype to be align with the
"fsck_vreport" function, we leave the "report" prototype unchanged due
to the reason that there are nearly 62 references about "report"
function. Simply change "report" function to use "fsck_vreport" to
report objects related messages.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "fsck_error" callback is designed to report the objects-related
error messages. It accepts two parameter "oid" and "object_type" which
is not generic. In order to provide a unified callback which can report
either objects or refs, remove the objects-related parameters and add
the generic parameter "void *fsck_report".
Create a new "fsck_object_report" structure which incorporates the
removed parameters "oid" and "object_type". Then change the
corresponding references to adapt to new "fsck_error" callback.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The names of objects-related fsck error functions are generic. It's OK
when there is only object database check. However, we are going to
introduce refs database check report function. To avoid ambiguity,
rename object-related fsck error functions to explicitly indicate these
functions are used to report objects-related messages.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "skiplist" field in "fsck_options" is related to objects. Because we
are going to introduce ref consistency check, the "skiplist" name is too
general which will make the caller think "skiplist" is related to both
the refs and objects.
It may seem that for both refs and objects, we should provide a general
"skiplist" here. However, the type for "skiplist" is `struct oidset`
which is totally unsuitable for refs.
To avoid above ambiguity, rename "skiplist" to "skip_oids".
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When calling `raw_object_store_clear()`, we close and free several
resources associated with the object store. Part of that is to close and
free all the packfiles, which is handled by `close_object_store()`.
That function really only ends up closing the packfiles though, but it
doesn't free them. And in fact it can't, as that function is being
called via `run_command()` when `close_object_store = 1`, which is done
e.g. when we execute git-maintenance(1). At that point, other structures
may still have references on those packfiles, and thus we cannot free
them here. So while it is in fact intentional that we really only close
them, the result is a memory leak because `raw_object_store_clear()`
does not free them, either.
Fix the leak by freeing the packfiles in `raw_object_store_clear()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We keep track of submodules we have already seen via a string map such
that we don't process the same submodule twice. We never free that map
though, causing a memory leak.
Fix this leak by clearing the map.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When done with a fetch task used for parallel fetches of submodules, we
need to both call `fetch_task_release()` to release the task's contents
and `free()` to release the task itself. Most sites do this already, but
some only call `fetch_task_release()` and thus leak memory.
While we could trivially fix this by adding the two missing calls to
free(3P), the result would be that we always call both functions. Let's
thus refactor the code such that `fetch_task_release()` also frees the
structure itself. Rename it to `fetch_task_free()` accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Same as with "clone", users may want to add a submodule to a repository
with a non-default ref storage format. Wire up a new `--ref-format=`
option that works the same as for `git submodule clone`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When opening a submodule ref storage we accidentally use the ref storage
format of the owning repository, not of the submodule repository. As
submodules may have a different storage format than their parent repo
this can lead to bugs when trying to access the submodule ref storage
from the parent repository.
One such bug was reported when performing a recursive pull with mixed
ref stores, which fails with:
$ git pull --recursive
fatal: Unable to find current revision in submodule path 'path/to/sub'
The same issue occurs when adding a repository contained in the working
tree with a different ref storage format via `git submodule add`.
Fix the bug by using the submodule repository's ref storage format
instead and add some tests. Note that the test for `git submodule
status` was included as a precaution, only. The command worked alright
even without the bugfix.
Reported-by: Jeppe Øland <joland@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When recursively cloning a repository with a non-default ref storage
format, e.g. by passing the `--ref-format=` option, then only the
top-level repository will end up using that ref storage format, and
all recursively cloned submodules will instead use the default format.
While mixed-format constellations are expected to work alright, the
outcome still is somewhat surprising as we have essentially ignored
the user's request.
Fix this by propagating the requested ref format to cloned submodules.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As submodules are proper self-contained repositories, it is perfectly
valid for them to have a different ref storage format than their parent
repository. There is no obvious way for users to ask for the ref storage
format when initializing submodules though. Whether the setup of such
mixed-ref-storage-format constellations is all that useful remains to be
seen. But there is no good reason to not expose such an option, and we
will require it in a subsequent patch.
Introduce a new `--ref-format=` option for git-submodule(1) that allows
the user to pick the ref storage format. This option will also be used
in a subsequent commit, where we start to propagate the same flag from
git-clone(1) to cloning submodules with the `--recursive` switch.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
For most of the subcommands of git-submodule(1), we end up passing a
bunch of arguments to the submodule helper. This quickly leads to overly
long lines, where it becomes hard to spot what has changed when one
needs to modify them.
Break up these lines into one argument per line, similarly to how it is
done for the "clone" subcommand already.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Transport URLs can be prefixed with "foo::", which would tell us that
the transport uses a remote helper called "foo". We extract the helper
name by `xstrndup()`ing the prefix before the double-colons, but never
free that string.
Fix this leak by assigning the result to a separate local variable that
we can then free upon returning.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* ps/refs-wo-the-repository:
refs/reftable: stop using `the_repository`
refs/packed: stop using `the_repository`
refs/files: stop using `the_repository`
refs/files: stop using `the_repository` in `parse_loose_ref_contents()`
refs: stop using `the_repository`
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>
Prepare for sub-directories to appear in $GIT_DIR/objects/pack by
adjusting the copy, remove, and chmod invocations to perform their
behavior recursively.
This prepares us for the new $GIT_DIR/objects/pack/multi-pack-index.d
directory which will be added in a following commit.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Two years ago, commit ff1e653c8e (midx: respect
'GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP', 2021-08-31) introduced a new
environment variable which caused the test suite to write MIDX bitmaps
after any 'git repack' invocation.
At the time, this was done to help flush out any bugs with MIDX bitmaps
that weren't explicitly covered in the t5326-multi-pack-bitmap.sh
script.
Two years later, that flag has served us well and is no longer providing
meaningful coverage, as the script in t5326 has matured substantially
and covers many more interesting cases than it did back when ff1e653c8e
was originally written.
Remove the 'GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP' environment variable
as it is no longer serving a useful purpose. More importantly, removing
this variable clears the way for us to introduce a new one to help
similarly flush out bugs related to incremental MIDX chains.
Because these incremental MIDX chains are (for now) incompatible with
MIDX bitmaps, we cannot have both.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
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>
The function `midx_fanout_add_midx_fanout()` is used to help construct
the fanout table when generating a MIDX by reusing data from an existing
MIDX.
Prepare this function to work with incremental MIDXs by making a few
changes:
- The bounds checks need to be adjusted to start object lookups taking
into account the number of objects in the previous MIDX layer (i.e.,
by starting the lookups at position `m->num_objects_in_base` instead
of position 0).
- Likewise, the bounds checks need to end at `m->num_objects_in_base`
objects after `m->num_objects`.
- Finally, `midx_fanout_add_midx_fanout()` needs to recur on earlier
MIDX layers when dealing with an incremental MIDX chain by calling
itself when given a MIDX with a non-NULL `base_midx`.
Note that after 0c5a62f14b (midx-write.c: do not read existing MIDX with
`packs_to_include`, 2024-06-11), we do not use this function with an
existing MIDX (incremental or not) when generating a MIDX with
--stdin-packs, and likewise for incremental MIDXs.
But it is still used when adding the fanout table from an incremental
MIDX when generating a non-incremental MIDX (without --stdin-packs, of
course).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
The function `nth_midxed_pack_int_id()` takes in a object position in
MIDX lexicographic order and returns an identifier of the pack from
which that object was selected in the MIDX.
Currently, the given object position is an index into the lexicographic
order of objects in a single MIDX. Change this position to instead refer
into the concatenated lexicographic order of all MIDXs in a MIDX chain.
This has two visible effects within the implementation of
`prepare_midx_pack()`:
- First, the given position is now an index into the concatenated
lexicographic order of all MIDXs in the order in which they appear
in the MIDX chain.
- Second the pack ID returned from this function is now also in the
concatenated order of packs among all layers of the MIDX chain in
the same order that they appear in the MIDX chain.
To do this, introduce the first of two general purpose helpers, this one
being `midx_for_object()`. `midx_for_object()` takes a double pointer to
a `struct multi_pack_index` as well as an object `pos` in terms of the
entire MIDX chain[^1].
The function chases down the '->base_midx' field until it finds the MIDX
layer within the chain that contains the given object. It then:
- modifies the double pointer to point to the containing MIDX, instead
of the tip of the chain, and
- returns the MIDX-local position[^2] at which the given object can be
found.
Use this function within `nth_midxed_pack_int_id()` so that the `pos` it
expects is now relative to the entire MIDX chain, and that it returns
the appropriate pack position for that object.
[^1]: As a reminder, this means that the object is identified among the
objects contained in all layers of the incremental MIDX chain, not any
particular layer. For example, consider MIDX chain with two individual
MIDXs, one with 4 objects and another with 3 objects. If the MIDX with
4 objects appears earlier in the chain, then asking for object 6 would
return the second object in the MIDX with 3 objects.
[^2]: Building on the previous example, asking for object 6 in a MIDX
chain with (4, 3) objects, respectively, this would set the double
pointer to point at the MIDX containing three objects, and would
return an index to the second object within that MIDX.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The incremental MIDX chain feature is designed around the idea of
indexing into a concatenated lexicographic ordering of object IDs
present in the MIDX.
When given an object position, the MIDX machinery needs to be able to
locate both (a) which MIDX layer contains the given object, and (b) at
what position *within that MIDX layer* that object appears.
To do this, three new fields are added to the `struct multi_pack_index`:
- struct multi_pack_index *base_midx;
- uint32_t num_objects_in_base;
- uint32_t num_packs_in_base;
These three fields store the pieces of information suggested by their
respective field names. In turn, the `num_objects_in_base` and
`num_packs_in_base` fields are used to crawl backwards along the
`base_midx` pointer to locate the appropriate position for a given
object within the MIDX that contains it.
The following commits will update various parts of the MIDX machinery
(as well as their callers from outside of midx.c and midx-write.c) to be
aware and make use of these fields when performing object lookups.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Prepare to implement incremental multi-pack indexes (MIDXs) over the
next several commits by first describing the relevant prerequisites
(like a new chunk in the MIDX format, the directory structure for
incremental MIDXs, etc.)
The format is described in detail in the patch contents below, but the
high-level description is as follows.
Incremental MIDXs live in $GIT_DIR/objects/pack/multi-pack-index.d, and
each `*.midx` within that directory has a single "parent" MIDX, which is
the MIDX layer immediately before it in the MIDX chain. The chain order
resides in a file 'multi-pack-index-chain' in the same directory.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Many existing tests in this script perform operation(s) and then use
test_when_finished to define how to undo the effect of the
operation(s).
This is backwards. When your operation(s) fail before you manage to
successfully call test_when_finished (remember, that these commands
must be all &&-chained, so a failure of an earlier operation mean
your test_when_finished may not be executed at all). You must
establish how to clean up your mess with test_when_finished before
you create the mess to be cleaned up.
Also make sure that the body of test_when_finished deals with case
where the cruft it wants to remove failed to be created, by using
"rm -f" (instead of "rm") to remove potential cruft files, and
having "|| :" after "git notes remove" to remove potential cruft
notes---both of these by default fail when asked to remove something
that does not exist, instead of being silently idempotent no-ops.
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
