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We have two different repacking strategies in Git:
- The "gc" strategy uses git-gc(1).
- The "incremental" strategy uses multi-pack indices and `git
multi-pack-index repack` to merge together smaller packfiles as
determined by a specific batch size.
The former strategy is our old and trusted default, whereas the latter
has historically been used for our scheduled maintenance. But both
strategies have their shortcomings:
- The "gc" strategy performs regular all-into-one repacks. Furthermore
it is rather inflexible, as it is not easily possible for a user to
enable or disable specific subtasks.
- The "incremental" strategy is not a full replacement for the "gc"
strategy as it doesn't know to prune stale data.
So today, we don't have a strategy that is well-suited for large repos
while being a full replacement for the "gc" strategy.
Introduce a new "geometric" strategy that aims to fill this gap. This
strategy invokes all the usual cleanup tasks that git-gc(1) does like
pruning reflogs and rerere caches as well as stale worktrees. But where
it differs from both the "gc" and "incremental" strategy is that it uses
our geometric repacking infrastructure exposed by git-repack(1) to
repack packfiles. The advantage of geometric repacking is that we only
need to perform an all-into-one repack when the object count in a repo
has grown significantly.
One downside of this strategy is that pruning of unreferenced objects is
not going to happen regularly anymore. Every geometric repack knows to
soak up all loose objects regardless of their reachability, and merging
two or more packs doesn't consider reachability, either. Consequently,
the number of unreachable objects will grow over time.
This is remedied by doing an all-into-one repack instead of a geometric
repack whenever we determine that the geometric repack would end up
merging all packfiles anyway. This all-into-one repack then performs our
usual reachability checks and writes unreachable objects into a cruft
pack. As cruft packs won't ever be merged during geometric repacks we
can thus phase out these objects over time.
Of course, this still means that we retain unreachable objects for far
longer than with the "gc" strategy. But the maintenance strategy is
intended especially for large repositories, where the basic assumption
is that the set of unreachable objects will be significantly dwarfed by
the number of reachable objects.
If this assumption is ever proven to be too disadvantageous we could for
example introduce a time-based strategy: if the largest packfile has not
been touched for longer than $T, we perform an all-into-one repack. But
for now, such a mechanism is deferred into the future as it is not clear
yet whether it is needed in the first place.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Acked-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
136 lines
6.8 KiB
Plaintext
136 lines
6.8 KiB
Plaintext
maintenance.auto::
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This boolean config option controls whether some commands run
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`git maintenance run --auto` after doing their normal work. Defaults
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to true.
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maintenance.autoDetach::
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Many Git commands trigger automatic maintenance after they have
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written data into the repository. This boolean config option
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controls whether this automatic maintenance shall happen in the
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foreground or whether the maintenance process shall detach and
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continue to run in the background.
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+
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If unset, the value of `gc.autoDetach` is used as a fallback. Defaults
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to true if both are unset, meaning that the maintenance process will
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detach.
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maintenance.strategy::
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This string config option provides a way to specify one of a few
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recommended strategies for repository maintenance. This affects
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which tasks are run during `git maintenance run`, provided no
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`--task=<task>` arguments are provided. This setting impacts manual
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maintenance, auto-maintenance as well as scheduled maintenance. The
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tasks that run may be different depending on the maintenance type.
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+
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The maintenance strategy can be further tweaked by setting
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`maintenance.<task>.enabled` and `maintenance.<task>.schedule`. If set, these
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values are used instead of the defaults provided by `maintenance.strategy`.
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+
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The possible strategies are:
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+
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* `none`: This strategy implies no tasks are run at all. This is the default
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strategy for scheduled maintenance.
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* `gc`: This strategy runs the `gc` task. This is the default strategy for
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manual maintenance.
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* `geometric`: This strategy performs geometric repacking of packfiles and
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keeps auxiliary data structures up-to-date. The strategy expires data in the
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reflog and removes worktrees that cannot be located anymore. When the
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geometric repacking strategy would decide to do an all-into-one repack, then
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the strategy generates a cruft pack for all unreachable objects. Objects that
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are already part of a cruft pack will be expired.
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+
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This repacking strategy is a full replacement for the `gc` strategy and is
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recommended for large repositories.
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* `incremental`: This setting optimizes for performing small maintenance
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activities that do not delete any data. This does not schedule the `gc`
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task, but runs the `prefetch` and `commit-graph` tasks hourly, the
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`loose-objects` and `incremental-repack` tasks daily, and the `pack-refs`
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task weekly. Manual repository maintenance uses the `gc` task.
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maintenance.<task>.enabled::
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This boolean config option controls whether the maintenance task
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with name `<task>` is run when no `--task` option is specified to
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`git maintenance run`. These config values are ignored if a
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`--task` option exists. By default, only `maintenance.gc.enabled`
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is true.
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maintenance.<task>.schedule::
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This config option controls whether or not the given `<task>` runs
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during a `git maintenance run --schedule=<frequency>` command. The
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value must be one of "hourly", "daily", or "weekly".
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maintenance.commit-graph.auto::
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This integer config option controls how often the `commit-graph` task
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should be run as part of `git maintenance run --auto`. If zero, then
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the `commit-graph` task will not run with the `--auto` option. A
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negative value will force the task to run every time. Otherwise, a
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positive value implies the command should run when the number of
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reachable commits that are not in the commit-graph file is at least
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the value of `maintenance.commit-graph.auto`. The default value is
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100.
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maintenance.loose-objects.auto::
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This integer config option controls how often the `loose-objects` task
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should be run as part of `git maintenance run --auto`. If zero, then
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the `loose-objects` task will not run with the `--auto` option. A
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negative value will force the task to run every time. Otherwise, a
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positive value implies the command should run when the number of
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loose objects is at least the value of `maintenance.loose-objects.auto`.
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The default value is 100.
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maintenance.loose-objects.batchSize::
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This integer config option controls the maximum number of loose objects
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written into a packfile during the `loose-objects` task. The default is
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fifty thousand. Use value `0` to indicate no limit.
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maintenance.incremental-repack.auto::
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This integer config option controls how often the `incremental-repack`
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task should be run as part of `git maintenance run --auto`. If zero,
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then the `incremental-repack` task will not run with the `--auto`
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option. A negative value will force the task to run every time.
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Otherwise, a positive value implies the command should run when the
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number of pack-files not in the multi-pack-index is at least the value
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of `maintenance.incremental-repack.auto`. The default value is 10.
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maintenance.geometric-repack.auto::
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This integer config option controls how often the `geometric-repack`
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task should be run as part of `git maintenance run --auto`. If zero,
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then the `geometric-repack` task will not run with the `--auto`
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option. A negative value will force the task to run every time.
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Otherwise, a positive value implies the command should run either when
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there are packfiles that need to be merged together to retain the
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geometric progression, or when there are at least this many loose
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objects that would be written into a new packfile. The default value is
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100.
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maintenance.geometric-repack.splitFactor::
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This integer config option controls the factor used for the geometric
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sequence. See the `--geometric=` option in linkgit:git-repack[1] for
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more details. Defaults to `2`.
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maintenance.reflog-expire.auto::
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This integer config option controls how often the `reflog-expire` task
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should be run as part of `git maintenance run --auto`. If zero, then
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the `reflog-expire` task will not run with the `--auto` option. A
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negative value will force the task to run every time. Otherwise, a
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positive value implies the command should run when the number of
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expired reflog entries in the "HEAD" reflog is at least the value of
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`maintenance.loose-objects.auto`. The default value is 100.
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maintenance.rerere-gc.auto::
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This integer config option controls how often the `rerere-gc` task
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should be run as part of `git maintenance run --auto`. If zero, then
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the `rerere-gc` task will not run with the `--auto` option. A negative
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value will force the task to run every time. Otherwise, any positive
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value implies the command will run when the "rr-cache" directory exists
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and has at least one entry, regardless of whether it is stale or not.
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This heuristic may be refined in the future. The default value is 1.
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maintenance.worktree-prune.auto::
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This integer config option controls how often the `worktree-prune` task
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should be run as part of `git maintenance run --auto`. If zero, then
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the `worktree-prune` task will not run with the `--auto` option. A
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negative value will force the task to run every time. Otherwise, a
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positive value implies the command should run when the number of
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prunable worktrees exceeds the value. The default value is 1.
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