git/Documentation/config/pack.txt
Derrick Stolee de3a864114 config: set pack.useSparse=true by default
The pack.useSparse config option was introduced by 3d036eb0
(pack-objects: create pack.useSparse setting, 2019-01-19) and was
first available in v2.21.0. When enabled, the pack-objects process
during 'git push' will use a sparse tree walk when deciding which
trees and blobs to send to the remote. The algorithm was introduced
by d5d2e93 (revision: implement sparse algorithm, 2019-01-16) and
has been in production use by VFS for Git since around that time.
The features.experimental config option also enabled pack.useSparse,
so hopefully that has also increased exposure.

It is worth noting that pack.useSparse has a possibility of
sending more objects across a push, but requires a special
arrangement of exact _copies_ across directories. There is a test
in t5322-pack-objects-sparse.sh that demonstrates this possibility.
This test uses the --sparse option to "git pack-objects" but we
can make it implied by the config value to demonstrate that the
default value has changed.

While updating that test, I noticed that the documentation did not
include an option for --no-sparse, which is now more important than
it was before.

Since the downside is unlikely but the upside is significant, set
the default value of pack.useSparse to true. Remove it from the
set of options implied by features.experimental.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-03-20 14:22:31 -07:00

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pack.window::
The size of the window used by linkgit:git-pack-objects[1] when no
window size is given on the command line. Defaults to 10.
pack.depth::
The maximum delta depth used by linkgit:git-pack-objects[1] when no
maximum depth is given on the command line. Defaults to 50.
Maximum value is 4095.
pack.windowMemory::
The maximum size of memory that is consumed by each thread
in linkgit:git-pack-objects[1] for pack window memory when
no limit is given on the command line. The value can be
suffixed with "k", "m", or "g". When left unconfigured (or
set explicitly to 0), there will be no limit.
pack.compression::
An integer -1..9, indicating the compression level for objects
in a pack file. -1 is the zlib default. 0 means no
compression, and 1..9 are various speed/size tradeoffs, 9 being
slowest. If not set, defaults to core.compression. If that is
not set, defaults to -1, the zlib default, which is "a default
compromise between speed and compression (currently equivalent
to level 6)."
+
Note that changing the compression level will not automatically recompress
all existing objects. You can force recompression by passing the -F option
to linkgit:git-repack[1].
pack.allowPackReuse::
When true, and when reachability bitmaps are enabled,
pack-objects will try to send parts of the bitmapped packfile
verbatim. This can reduce memory and CPU usage to serve fetches,
but might result in sending a slightly larger pack. Defaults to
true.
pack.island::
An extended regular expression configuring a set of delta
islands. See "DELTA ISLANDS" in linkgit:git-pack-objects[1]
for details.
pack.islandCore::
Specify an island name which gets to have its objects be
packed first. This creates a kind of pseudo-pack at the front
of one pack, so that the objects from the specified island are
hopefully faster to copy into any pack that should be served
to a user requesting these objects. In practice this means
that the island specified should likely correspond to what is
the most commonly cloned in the repo. See also "DELTA ISLANDS"
in linkgit:git-pack-objects[1].
pack.deltaCacheSize::
The maximum memory in bytes used for caching deltas in
linkgit:git-pack-objects[1] before writing them out to a pack.
This cache is used to speed up the writing object phase by not
having to recompute the final delta result once the best match
for all objects is found. Repacking large repositories on machines
which are tight with memory might be badly impacted by this though,
especially if this cache pushes the system into swapping.
A value of 0 means no limit. The smallest size of 1 byte may be
used to virtually disable this cache. Defaults to 256 MiB.
pack.deltaCacheLimit::
The maximum size of a delta, that is cached in
linkgit:git-pack-objects[1]. This cache is used to speed up the
writing object phase by not having to recompute the final delta
result once the best match for all objects is found.
Defaults to 1000. Maximum value is 65535.
pack.threads::
Specifies the number of threads to spawn when searching for best
delta matches. This requires that linkgit:git-pack-objects[1]
be compiled with pthreads otherwise this option is ignored with a
warning. This is meant to reduce packing time on multiprocessor
machines. The required amount of memory for the delta search window
is however multiplied by the number of threads.
Specifying 0 will cause Git to auto-detect the number of CPU's
and set the number of threads accordingly.
pack.indexVersion::
Specify the default pack index version. Valid values are 1 for
legacy pack index used by Git versions prior to 1.5.2, and 2 for
the new pack index with capabilities for packs larger than 4 GB
as well as proper protection against the repacking of corrupted
packs. Version 2 is the default. Note that version 2 is enforced
and this config option ignored whenever the corresponding pack is
larger than 2 GB.
+
If you have an old Git that does not understand the version 2 `*.idx` file,
cloning or fetching over a non native protocol (e.g. "http")
that will copy both `*.pack` file and corresponding `*.idx` file from the
other side may give you a repository that cannot be accessed with your
older version of Git. If the `*.pack` file is smaller than 2 GB, however,
you can use linkgit:git-index-pack[1] on the *.pack file to regenerate
the `*.idx` file.
pack.packSizeLimit::
The maximum size of a pack. This setting only affects
packing to a file when repacking, i.e. the git:// protocol
is unaffected. It can be overridden by the `--max-pack-size`
option of linkgit:git-repack[1]. Reaching this limit results
in the creation of multiple packfiles; which in turn prevents
bitmaps from being created.
The minimum size allowed is limited to 1 MiB.
The default is unlimited.
Common unit suffixes of 'k', 'm', or 'g' are
supported.
pack.useBitmaps::
When true, git will use pack bitmaps (if available) when packing
to stdout (e.g., during the server side of a fetch). Defaults to
true. You should not generally need to turn this off unless
you are debugging pack bitmaps.
pack.useSparse::
When true, git will default to using the '--sparse' option in
'git pack-objects' when the '--revs' option is present. This
algorithm only walks trees that appear in paths that introduce new
objects. This can have significant performance benefits when
computing a pack to send a small change. However, it is possible
that extra objects are added to the pack-file if the included
commits contain certain types of direct renames. Default is
`true`.
pack.writeBitmaps (deprecated)::
This is a deprecated synonym for `repack.writeBitmaps`.
pack.writeBitmapHashCache::
When true, git will include a "hash cache" section in the bitmap
index (if one is written). This cache can be used to feed git's
delta heuristics, potentially leading to better deltas between
bitmapped and non-bitmapped objects (e.g., when serving a fetch
between an older, bitmapped pack and objects that have been
pushed since the last gc). The downside is that it consumes 4
bytes per object of disk space. Defaults to true.