git-commit-vandalism/Documentation/git-multi-pack-index.txt
Derrick Stolee 1eb22c7dd8 multi-pack-index: repack batches below --batch-size
The --batch-size=<size> option of 'git multi-pack-index repack' is
intended to limit the amount of work done by the repack. In the case of
a large repository, this command should repack a number of small
pack-files but leave the large pack-files alone. Most often, the
repository has one large pack-file from a 'git clone' operation and
number of smaller pack-files from incremental 'git fetch' operations.

The issue with '--batch-size' is that it also _prevents_ the repack from
happening if the expected size of the resulting pack-file is too small.
This was intended as a way to avoid frequent churn of small pack-files,
but it has mostly caused confusion when a repository is of "medium"
size. That is, not enormous like the Windows OS repository, but also not
so small that this incremental repack isn't valuable.

The solution presented here is to collect pack-files for repack if their
expected size is smaller than the batch-size parameter until either the
total expected size exceeds the batch-size or all pack-files are
considered. If there are at least two pack-files, then these are
combined to a new pack-file whose size should not be too much larger
than the batch-size.

This new strategy should succeed in keeping the number of pack-files
small in these "medium" size repositories. The concern about churn is
likely not interesting, as the real control over that is the frequency
in which the repack command is run.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-08-11 14:05:26 -07:00

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git-multi-pack-index(1)
=======================
NAME
----
git-multi-pack-index - Write and verify multi-pack-indexes
SYNOPSIS
--------
[verse]
'git multi-pack-index' [--object-dir=<dir>] [--[no-]progress] <subcommand>
DESCRIPTION
-----------
Write or verify a multi-pack-index (MIDX) file.
OPTIONS
-------
--object-dir=<dir>::
Use given directory for the location of Git objects. We check
`<dir>/packs/multi-pack-index` for the current MIDX file, and
`<dir>/packs` for the pack-files to index.
--[no-]progress::
Turn progress on/off explicitly. If neither is specified, progress is
shown if standard error is connected to a terminal.
The following subcommands are available:
write::
Write a new MIDX file.
verify::
Verify the contents of the MIDX file.
expire::
Delete the pack-files that are tracked by the MIDX file, but
have no objects referenced by the MIDX. Rewrite the MIDX file
afterward to remove all references to these pack-files.
repack::
Create a new pack-file containing objects in small pack-files
referenced by the multi-pack-index. If the size given by the
`--batch-size=<size>` argument is zero, then create a pack
containing all objects referenced by the multi-pack-index. For
a non-zero batch size, Select the pack-files by examining packs
from oldest-to-newest, computing the "expected size" by counting
the number of objects in the pack referenced by the
multi-pack-index, then divide by the total number of objects in
the pack and multiply by the pack size. We select packs with
expected size below the batch size until the set of packs have
total expected size at least the batch size, or all pack-files
are considered. If only one pack-file is selected, then do
nothing. If a new pack-file is created, rewrite the
multi-pack-index to reference the new pack-file. A later run of
'git multi-pack-index expire' will delete the pack-files that
were part of this batch.
+
If `repack.packKeptObjects` is `false`, then any pack-files with an
associated `.keep` file will not be selected for the batch to repack.
EXAMPLES
--------
* Write a MIDX file for the packfiles in the current .git folder.
+
-----------------------------------------------
$ git multi-pack-index write
-----------------------------------------------
* Write a MIDX file for the packfiles in an alternate object store.
+
-----------------------------------------------
$ git multi-pack-index --object-dir <alt> write
-----------------------------------------------
* Verify the MIDX file for the packfiles in the current .git folder.
+
-----------------------------------------------
$ git multi-pack-index verify
-----------------------------------------------
SEE ALSO
--------
See link:technical/multi-pack-index.html[The Multi-Pack-Index Design
Document] and link:technical/pack-format.html[The Multi-Pack-Index
Format] for more information on the multi-pack-index feature.
GIT
---
Part of the linkgit:git[1] suite