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The git-gc(1) command has been introduced in the early days of Git in
30f610b7b0 (Create 'git gc' to perform common maintenance operations.,
2006-12-27) as the main repository maintenance utility. And while the
tool has of course evolved since then to cover new parts, the basic
strategy it uses has never really changed much.
It is safe to say that since 2006 the Git ecosystem has changed quite a
bit. Repositories tend to be much larger nowadays than they have been
almost 20 years ago, and large parts of the industry went crazy for
monorepos (for various wildly different definitions of "monorepo"). So
the maintenance strategy we used back then may not be the best fit
nowadays anymore.
Arguably, most of the maintenance tasks that git-gc(1) does are still
perfectly fine today: repacking references, expiring various data
structures and things like tend to not cause huge problems. But the big
exception is the way we repack objects.
git-gc(1) by default uses a split strategy: it performs incremental
repacks by default, and then whenever we have too many packs we perform
a large all-into-one repack. This all-into-one repack is what is causing
problems nowadays, as it is an operation that is quite expensive. While
it is wasteful in small- and medium-sized repositories, in large repos
it may even be prohibitively expensive.
We have eventually introduced git-maintenance(1) that was slated as a
replacement for git-gc(1). In contrast to git-gc(1), it is much more
flexible as it is structured around configurable tasks and strategies.
So while its default "gc" strategy still uses git-gc(1) under the hood,
it allows us to iterate.
A second strategy it knows about is the "incremental" strategy, which we
configure when registering a repository for scheduled maintenance. This
strategy isn't really a full replacement for git-gc(1) though, as it
doesn't know to expire unused data structures. In Git 2.52 we have thus
introduced a new "geometric" strategy that is a proper replacement for
the old git-gc(1).
In contrast to the incremental/all-into-one split used by git-gc(1), the
new "geometric" strategy maintains a geometric progression of packfiles,
which significantly reduces the number of all-into-one repacks that we
have to perform in large repositories. It is thus a much better fit for
large repositories than git-gc(1).
Note that the "geometric" strategy isn't perfect though: while we
perform way less all-into-one repacks compared to git-gc(1), we still
have to perform them eventually. But for the largest repositories out
there this may not be an option either, as client machines might not be
powerful enough to perform such a repack in the first place. These cases
would thus still be covered by the "incremental" strategy.
Switch the default strategy away from "gc" to "geometric", but retain
the "incremental" strategy configured when registering background
maintenance with `git maintenance register`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
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.
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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. This is the default strategy for manual
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maintenance.
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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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