git/Documentation/git-multi-pack-index.txt
Taylor Blau 5d3cd09a80 midx: reject empty --preferred-pack's
The soon-to-be-implemented multi-pack bitmap treats object in the first
bit position specially by assuming that all objects in the pack it was
selected from are also represented from that pack in the MIDX. In other
words, the pack from which the first object was selected must also have
all of its other objects selected from that same pack in the MIDX in
case of any duplicates.

But this assumption relies on the fact that there is at least one object
in that pack to begin with; otherwise the object in the first bit
position isn't from a preferred pack, in which case we can no longer
assume that all objects in that pack were also selected from the same
pack.

Guard this assumption by checking the number of objects in the given
preferred pack, and failing if the given pack is empty.

To make sure we can safely perform this check, open any packs which are
contained in an existing MIDX via prepare_midx_pack(). The same is done
for new packs via the add_pack_to_midx() callback, but packs picked up
from a previous MIDX will not yet have these opened.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-09-01 10:58:43 -07:00

106 lines
3.2 KiB
Text

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]
[--preferred-pack=<pack>] <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. The following options are available for
the `write` sub-command:
+
--
--preferred-pack=<pack>::
Optionally specify the tie-breaking pack used when
multiple packs contain the same object. `<pack>` must
contain at least one object. If not given, ties are
broken in favor of the pack with the lowest mtime.
--
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