Expose the incremental MIDX repacking mode (implemented in an earlier
commit) via a new --write-midx=incremental option for `git repack`.
Add "incremental" as a recognized argument to the --write-midx
OPT_CALLBACK, mapping it to REPACK_WRITE_MIDX_INCREMENTAL. When this
mode is active and --geometric is in use, set the midx_layer_threshold
on the pack geometry so that only packs in sufficiently large tip layers
are considered for repacking.
Two new configuration options control the compaction behavior:
- repack.midxSplitFactor (default: 2): the factor used in the
geometric merging condition for MIDX layers.
- repack.midxNewLayerThreshold (default: 8): the minimum number of
packs in the tip MIDX layer before its packs are considered as
candidates for geometric repacking.
Add tests exercising the new mode across a variety of scenarios
including basic geometric violations, multi-round chain integrity,
branching and merging histories, cross-layer object uniqueness, and
threshold-based compaction.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Implement the `write_midx_incremental()` function, which builds and
maintains an incremental MIDX chain as part of the geometric repacking
process.
Unlike the default mode which writes a single flat MIDX, the incremental
mode constructs a compaction plan that determines which MIDX layers to
write, compact, or copy, and then executes each step using `git
multi-pack-index` subcommands with the --checksum-only flag.
The repacking strategy works as follows:
* Acquire the lock guarding the multi-pack-index-chain.
* A new MIDX layer is always written containing the newly created
pack(s). If the tip MIDX layer was rewritten during geometric
repacking, any surviving packs from that layer are also included.
* Starting from the new layer, adjacent MIDX layers are merged together
as long as the accumulated object count exceeds half the object count
of the next deeper layer (controlled by 'repack.midxSplitFactor').
* Remaining layers in the chain are evaluated pairwise and either
compacted or copied as-is, following the same merging condition.
* Write the contents of the new multi-pack-index chain, atomically move
it into place, and then release the lock.
* Delete any now-unused MIDX layers.
After writing the new layer, the strategy is evaluated among the
existing MIDX layers in order from oldest to newest. Each step that
writes a new MIDX layer uses "--checksum-only" to avoid updating the
multi-pack-index-chain file. After all steps are complete, the new chain
file is written and then atomically moved into place.
At present, this functionality is exposed behind a new enum value,
`REPACK_WRITE_MIDX_INCREMENTAL`, but has no external callers. A
subsequent commit will expose this mode via `git repack
--write-midx=incremental`.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change the --write-midx (-m) flag from an OPT_BOOL to an OPT_CALLBACK
that accepts an optional mode argument. Introduce an enum with
REPACK_WRITE_MIDX_NONE and REPACK_WRITE_MIDX_DEFAULT to distinguish
between the two states, and update all existing boolean checks
accordingly.
For now, passing no argument (or just `-m`) selects the default mode,
preserving existing behavior. A subsequent commit will add a new mode
for writing incremental MIDXs.
Extract repack_write_midx() as a dispatcher that selects the
appropriate MIDX-writing implementation based on the mode.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Teach `pack_geometry_init()` to optionally restrict the set of
repacking candidates to only packs in the tip MIDX layer when a
`midx_layer_threshold` is configured. If the tip layer has fewer packs
than the threshold, those packs are excluded entirely; otherwise only
packs in that layer participate in the geometric repack.
Also track whether any tip-layer packs were included in the rollup
(`midx_tip_rewritten`), which a subsequent commit will use to decide
how to update the MIDX chain after repacking.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Store the ODB source in the `existing_packs` struct and use that in
place of the raw `repo->objects->sources` access within `cmd_repack()`.
The source used is still assigned from the first source in the list, so
there are no functional changes in this commit. The changes instead
serve two purposes (one immediate, one not):
- The incremental MIDX-based repacking machinery will need to know what
source is being used to read the existing MIDX/chain (should one
exist).
- In the future, if "git repack" is taught how to operate on other
object sources, this field will serve as the authoritative value for
that source.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When performing a fetch with an object filter, we mark the resulting
packfile as a promisor pack. An object part of such a pack may miss any
of its referenced objects, and Git knows to handle this case by fetching
any such missing objects from the promisor remote.
The "promisor" property needs to be retained going forward. So every
time we pack a promisor object, the resulting pack must be marked as a
promisor pack. git-repack(1) does this already: when a repository has a
promisor remote, it knows to pass "--exclude-promisor-objects" to the
git-pack-objects(1) child process. Promisor packs are written separately
when doing an all-into-one repack via `repack_promisor_objects()`.
But we don't support promisor objects when doing a geometric repack yet.
Promisor packs do not get any special treatment there, as we simply
merge promisor and non-promisor packs. The resulting pack is not even
marked as a promisor pack, which essentially corrupts the repository.
This corruption couldn't happen in the real world though: we pass both
"--exclude-promisor-objects" and "--stdin-packs" to git-pack-objects(1)
if a repository has a promisor remote, but as those options are mutually
exclusive we always end up dying. And while we made those flags
compatible with one another in a preceding commit, we still end up dying
in case git-pack-objects(1) is asked to repack a promisor pack.
There's multiple ways to fix this:
- We can exclude promisor packs from the geometric progression
altogether. This would have the consequence that we never repack
promisor packs at all. But in a partial clone it is quite likely
that the user generates a bunch of promisor packs over time, as
every backfill fetch would create another one. So this doesn't
really feel like a sensible option.
- We can adapt git-pack-objects(1) to support repacking promisor packs
and include them in the normal geometric progression. But this would
mean that the set of promisor objects expands over time as the packs
are merged with normal packs.
- We can use a separate geometric progression to repack promisor
packs.
The first two options both have significant downsides, so they aren't
really feasible. But the third option fixes both of these downsides: we
make sure that promisor packs get merged, and at the same time we never
expand the set of promisor objects beyond the set of objects that are
already marked as promisor objects.
Implement this strategy so that geometric repacking works in partial
clones.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In an identical fashion as the previous commit, move the function
`write_cruft_pack()` into its own compilation unit, and make the
function visible through the repack.h API.
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, move the function
`write_filtered_pack()` out of the builtin and into its own compilation
unit.
This function is now part of the repack.h API, but implemented in its
own "repack-filtered.c" unit as it is a separate component from other
kinds of repacking operations.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "pack_kept_objects" variable is defined as static to the repack
builtin, but is inherently related to the pack-objects arguments that
the builtin uses when generating new packs.
Move that field into the "struct pack_objects_args", and shuffle around
where we append the corresponding command-line option when preparing a
pack-objects process. Specifically:
- `write_cruft_pack()` always wants to pass "--honor-pack-keep", so
explicitly set the `pack_kept_objects` field to "0" when initializing
the `write_pack_opts` struct before calling `write_cruft_pack()`.
- `write_filtered_pack()` no longer needs to handle writing the
command-line option "--honor-pack-keep" when preparing a pack-objects
process, since its call to `prepare_pack_objects()` will have already
taken care of that.
`write_filtered_pack()` also reads the `pack_kept_objects` field to
determine whether to write the existing kept packs with a leading "^"
character, so update that to read through the `po_args` pointer
instead.
- `cmd_repack()` also no longer has to write the "--honor-pack-keep"
flag explicitly, since this is also handled via its call to
`prepare_pack_objects()`.
Since there is a default value for "pack_kept_objects" that relies on
whether or not we are writing a bitmap (and not writing a MIDX), extract
a default initializer for `struct pack_objects_args` that keeps this
conditional default behavior.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a similar spirit as the previous commit(s), now that the function
`finish_pack_objects_cmd()` has no explicit dependencies within the
repack builtin, let's extract it.
This prepares us to extract the remaining two functions within the
repack builtin that explicitly write packfiles, which are
`write_cruft_pack()` and `write_filtered_pack()`, which will be done in
the future commits.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to the previous commit, the functions `write_cruft_pack()` and
`write_filtered_pack()` both compute a "local" variable via the exact
same mechanism:
const char *scratch;
int local = skip_prefix(opts->destination, opts->packdir, &scratch);
Not only does this cause us to repeat the same pair of lines, it also
introduces an unnecessary "scratch" variable that is common between both
functions.
Instead of repeating ourselves, let's extract that functionality into a
new function in the repack.h API called "write_pack_opts_is_local()".
That function takes a pointer to a "struct write_pack_opts" (which has
as fields both "destination" and "packdir"), and can encapsulate the
dangling "scratch" field.
Extract that function and make it visible within the repack.h API, and
use it within both `write_cruft_pack()` and `write_filtered_pack()`.
While we're at it, match our modern conventions by returning a "bool"
instead of "int", and use `starts_with()` instead of `skip_prefix()` to
avoid storing the dummy "scratch" variable.
The remaining duplication (that is, that both `write_cruft_pack()` and
`write_filtered_pack()` still both call `write_pack_opts_is_local()`)
will be addressed in the following commit.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both callers within the repack builtin which call functions that take a
'write_pack_opts' structure have the following pattern:
struct write_pack_opts opts = {
.packdir = packdir,
.packtmp = packtmp,
.pack_prefix = find_pack_prefix(packdir, packtmp),
/* ... */
};
int ret = write_some_kind_of_pack(&opts, /* ... */);
, but both "packdir" and "packtmp" are fields within the write_pack_opts
struct itself!
Instead of also computing the pack_prefix ahead of time, let's have the
callees compute it themselves by moving `find_pack_prefix()` out of the
repack builtin, and have it take a write_pack_opts pointer instead of
the "packdir" and "packtmp" fields directly.
This avoids the callers having to do some prep work that is common
between the two of them, but also avoids the potential pitfall of
accidentally writing:
.pack_prefix = find_pack_prefix(packtmp, packdir),
(which is well-typed) when the caller meant to instead write:
.pack_prefix = find_pack_prefix(packdir, packtmp),
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are various functions within the 'repack' builtin which are
responsible for writing different kinds of packs. They include:
- `static int write_filtered_pack(...)`
- `static int write_cruft_pack(...)`
as well as the function `finish_pack_objects_cmd()`, which is
responsible for finalizing a new pack write, and recording the checksum
of its contents in the 'names' list.
Both of these `write_` functions have a few things in common. They both
take a pointer to the 'pack_objects_args' struct, as well as a pair of
character pointers for `destination` and `pack_prefix`.
Instead of repeating those arguments for each function, let's extract an
options struct called "write_pack_opts" which has these three parameters
as member fields. While we're at it, add fields for "packdir," and
"packtmp", both of which are static variables within the builtin, and
need to be read from within these two functions.
This will shorten the list of parameters that callers have to provide to
`write_filtered_pack()`, avoid ambiguity when passing multiple variables
of the same type, and provide a unified interface for the two functions
mentioned earlier.
(Note that "pack_prefix" can be derived on the fly as a function of
"packdir" and "packtmp", making it unnecessary to store "pack_prefix"
explicitly. This commit ignores that potential cleanup in the name of
doing as few things as possible, but a later commit will make that
change.)
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have sufficiently cleaned up the write_midx_included_packs()
function, we can move it (along with the struct repack_write_midx_opts)
out of the builtin, and into the repack.h header.
Since this function (and the static ones that it depends on) are
MIDX-specific details of the repacking process, move them to the
repack-midx.c compilation unit instead of the general repack.c one.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Instead of storing the list of MIDX pack names separately, let's inline
it into the existing_packs struct, further reducing the number of
parameters we have to pass around.
This amounts to adding a new string_list to the existing_packs struct,
and populating it via `existing_packs_collect()`. This is fairly
straightforward to do, since we are already looping over all packs, all
we need to do is:
if (p->multi_pack_index)
string_list_append(&existing->midx_packs, pack_basename(p));
Note, however, that this check *must* come before other conditions where
we discard and do not keep track of a pack, including the condition "if
(!p->pack_local)" immediately below. This is because the existing
routine which collects MIDX pack names does so blindly, and does not
discard, for example, non-local packs.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a MIDX, 'git repack' takes a snapshot of the repository's
references and writes the result out to a file, which it then passes to
'git multi-pack-index write' via the '--refs-snapshot'.
This is done in order to make bitmap selections with respect to what we
are packing, thus avoiding a race where an incoming reference update
causes us to try and write a bitmap for a commit not present in the
MIDX.
Extract this functionality out into a new repack-midx.c compilation
unit, and expose the necessary functions via the repack.h API.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that the pack_geometry API is fully factored and isolated from the
rest of the builtin, declare it within repack.h and move its
implementation to "repack-geometry.c" as a separate component.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have properly factored the portion of the builtin which is
responsible for repacking promisor objects, we can move that function
(and associated dependencies) out of the builtin entirely.
Similar to previous extractions, this function is declared in repack.h,
but implemented in a separate repack-promisor.c file. This is done to
separate promisor-specific repacking functionality from generic repack
utilities (like "existing_packs", and "generated_pack" APIs).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have factored the "generated_pack" API, we can move it to
repack.ch, further slimming down builtin/repack.c.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The repack builtin defines an API for keeping track of which packs
were found in the repository at the beginning of the repack operation.
This is used to classify what state a pack was in (kept, non-kept, or
cruft), and is also used to mark which packs to delete (or keep) at the
end of a repack operation.
Now that the prerequisite refactoring is complete, this API is isolated
enough that it can be moved out to repack.[ch] and removed from the
builtin entirely.
As a result, some of its functions become static within repack.c,
cleaning up the visible API.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Extract "remove_redundant_pack()" as generic repack-related
functionality by moving its implementation to the repack.[ch]
compilation unit.
This is a prerequisite to moving the "existing_packs" API, which is one
of the callers of this function. (The remaining caller in the pack
geometry code will eventually move to its own compilation unit as well,
and will likewise rely on this function.)
While moving it over, prefix the function name with "repack_" to
indicate that it belongs to the repack-subsystem.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that the 'prepare_pack_objects' function no longer refers to
external, static variables, move it out to repack.h as generic
functionality.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The static variable 'delta_base_offset' determines whether or not we
pass the "--delta-base-offset" command-line argument when spawning
pack-objects as a child process. Its introduction dates back to when
repack was rewritten in C, all the way back in a1bbc6c017 (repack:
rewrite the shell script in C, 2013-09-15).
'struct pack_objects_args' was introduced much later on in 4571324b99
(builtin/repack.c: allow configuring cruft pack generation, 2022-05-20),
but did not move the 'delta_base_offset' variable.
Since the 'delta_base_offset' is a property of an individual
pack-objects command, re-introduce that variable as a member of 'struct
pack_objects_args', which will enable further code movement in the
subsequent commits.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Over the years, builtin/repack.c has turned into a grab-bag of
functionality powering the 'git repack' builtin. Among its many
capabilities, it:
- can build and spawn 'git pack-objects' commands, which in turn
generate new packs
- has infrastructure to manage the set of existing packs in a
repository
- has infrastructure to split a sequence of packs into a geometric
progression based on object size
- can manage both generating and combining cruft packs together
- can write new MIDXs
to name a few.
As a result, this builtin has accumulated a lot of code, making adding
new functionality difficult. In the future, 'repack' will learn how to
manage a chain of incremental MIDXs, adding yet more functionality into
the builtin.
As a prerequisite step, let's first move some of the functionality in
the builtin into its own repack.[ch].
This will be done over the course of many steps, since there are many
individual components, some of which will end up in other, yet-to-exist
compilation units of their own. Some of the code movement here is also
non-trivial, so performing it in individual steps will make it easier to
verify.
Let's start by migrating 'struct pack_objects_args' (and the related
corresponding pack_objects_args_release() function) into repack.h, and
teach both the Makefile and Meson how to build the new compilation unit.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
