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core.fsync: documentation and user-friendly aggregate options 

This commit adds aggregate options for the core.fsync setting that are
more user-friendly. These options are specified in terms of 'levels of
safety', indicating which Git operations are considered to be sync
points for durability.

The new documentation is also included here in its entirety for ease of
review.

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Neeraj Singh 2022-03-15 12:12:45 -07:00 committed by Junio C Hamano
parent ba95e96d4c
commit b9f5d0358d
3 changed files with 65 additions and 3 deletions
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40
Documentation/config/core.txt
View File

@ -547,6 +547,46 @@ core.whitespace::
is relevant for `indent-with-non-tab` and when Git fixes `tab-in-indent`
errors. The default tab width is 8. Allowed values are 1 to 63.
core.fsync::
A comma-separated list of components of the repository that
should be hardened via the core.fsyncMethod when created or
modified. You can disable hardening of any component by
prefixing it with a '-'. Items that are not hardened may be
lost in the event of an unclean system shutdown. Unless you
have special requirements, it is recommended that you leave
this option empty or pick one of `committed`, `added`,
or `all`.
+
When this configuration is encountered, the set of components starts with
the platform default value, disabled components are removed, and additional
components are added. `none` resets the state so that the platform default
is ignored.
+
The empty string resets the fsync configuration to the platform
default. The default on most platforms is equivalent to
`core.fsync=committed,-loose-object`, which has good performance,
but risks losing recent work in the event of an unclean system shutdown.
+
* `none` clears the set of fsynced components.
* `loose-object` hardens objects added to the repo in loose-object form.
* `pack` hardens objects added to the repo in packfile form.
* `pack-metadata` hardens packfile bitmaps and indexes.
* `commit-graph` hardens the commit graph file.
* `index` hardens the index when it is modified.
* `objects` is an aggregate option that is equivalent to
`loose-object,pack`.
* `derived-metadata` is an aggregate option that is equivalent to
`pack-metadata,commit-graph`.
* `committed` is an aggregate option that is currently equivalent to
`objects`. This mode sacrifices some performance to ensure that work
that is committed to the repository with `git commit` or similar commands
is hardened.
* `added` is an aggregate option that is currently equivalent to
`committed,index`. This mode sacrifices additional performance to
ensure that the results of commands like `git add` and similar operations
are hardened.
* `all` is an aggregate option that syncs all individual components above.
core.fsyncMethod::
A value indicating the strategy Git will use to harden repository data
using fsync and related primitives.

23
cache.h
View File

@ -1007,9 +1007,26 @@ enum fsync_component {
FSYNC_COMPONENT_INDEX = 1 << 4,
};
#define FSYNC_COMPONENTS_DEFAULT (FSYNC_COMPONENT_PACK | \
FSYNC_COMPONENT_PACK_METADATA | \
FSYNC_COMPONENT_COMMIT_GRAPH)
#define FSYNC_COMPONENTS_OBJECTS (FSYNC_COMPONENT_LOOSE_OBJECT | \
FSYNC_COMPONENT_PACK)
#define FSYNC_COMPONENTS_DERIVED_METADATA (FSYNC_COMPONENT_PACK_METADATA | \
FSYNC_COMPONENT_COMMIT_GRAPH)
#define FSYNC_COMPONENTS_DEFAULT (FSYNC_COMPONENTS_OBJECTS | \
FSYNC_COMPONENTS_DERIVED_METADATA | \
~FSYNC_COMPONENT_LOOSE_OBJECT)
#define FSYNC_COMPONENTS_COMMITTED (FSYNC_COMPONENTS_OBJECTS)
#define FSYNC_COMPONENTS_ADDED (FSYNC_COMPONENTS_COMMITTED | \
FSYNC_COMPONENT_INDEX)
#define FSYNC_COMPONENTS_ALL (FSYNC_COMPONENT_LOOSE_OBJECT | \
FSYNC_COMPONENT_PACK | \
FSYNC_COMPONENT_PACK_METADATA | \
FSYNC_COMPONENT_COMMIT_GRAPH | \
FSYNC_COMPONENT_INDEX)
/*
* A bitmask indicating which components of the repo should be fsynced.

5
config.c
View File

@ -1332,6 +1332,11 @@ static const struct fsync_component_name {
{ "pack-metadata", FSYNC_COMPONENT_PACK_METADATA },
{ "commit-graph", FSYNC_COMPONENT_COMMIT_GRAPH },
{ "index", FSYNC_COMPONENT_INDEX },
{ "objects", FSYNC_COMPONENTS_OBJECTS },
{ "derived-metadata", FSYNC_COMPONENTS_DERIVED_METADATA },
{ "committed", FSYNC_COMPONENTS_COMMITTED },
{ "added", FSYNC_COMPONENTS_ADDED },
{ "all", FSYNC_COMPONENTS_ALL },
};
static enum fsync_component parse_fsync_components(const char *var, const char *string)