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Joey Hess 2013-10-18 15:11:17 -04:00
parent 50684ea7bf
commit 30ca7805d6
1 changed files with 28 additions and 14 deletions
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doc/design/assistant/disaster_recovery.mdwn
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@ -86,15 +86,29 @@ Run `git fsck` and parse output to find bad objects, and determine
from its output if they are a commit, a tree, or a blob.
Check if there's a remote. If so, and if the bad objects are all
present on it, can simply get all bad objects from it, and inject them
back into .git/objects to recover.
How to best re-get bad objects from a remote? May need to re-clone from
the remote, and rsync .git/objects from the clone.
present on it, can simply get all bad objects from the remote,
and inject them back into .git/objects to recover:
Otherwise, find commits in each local branch that are broken by
all found bad objects. Some of this can be parsed from git fsck
output, but for eg bad blobs, the commits need to be walked to
walk the trees, to find trees that refer to the blobs.
1. If the local repository contains packs, the packs may be corrupt.
So, start by using `git unpack-objects` to unpack all
packs it can handle (which may include parts of corrupt packs)
back to loose objects. And delete all packs.
2. Delete all loose corrupt objects.
3. Make a new (bare) clone from the remote. Use `--reference` pointing
at the broken repository, to avoid re-downloading objects that
are present in it. (git does not seem to provide an easy way to just
fetch specific missing objects from a remote; `git fetch-pack` only
operates on refs... but this clone method should be pretty efficient)
4. Unpack any packs in the clone, so we can operate on loose objects.
5. Copy each missing object from the new clone's .git/objects to the
repository.
6. If each bad object was able to be repaired this way, we're done!
(If not, can reuse the clone for getting objects from the next remote.)
If some missing objects cannot be recovered from remotes, find commits in each
local branch that are broken by all remaining missing objects. Some of this can
be parsed from git fsck output, but for eg blobs, the commits need to
be walked to walk the trees, to find trees that refer to the blobs.
For each branch that is affected, look in the reflog and/or `git log
$branch` to find the last good change that predates all broken commits. (If
@ -103,17 +117,17 @@ anything useful, but the reflog can be used to find past refs for the
branch -- have to first delete the .git/HEAD file if it points to the
broken ref.)
Reset the branch to the last good change. This will leave git showing any
changes made since then as staged in the index and uncommitted. Or if
the index is missing/corrupt, any files in the tree will show as modified
and uncommitted. User (or git-annex assistant) can then commit as
appropriate.
Reset the branch to the last good change. For the head branch, this will
leave git showing any changes made since then as staged in the index and
uncommitted. Or if the index is missing/corrupt, any files in the tree will
show as modified and uncommitted. User (or git-annex assistant) can then
commit as appropriate.
(Special handling for git-annex branch: Commit .git/annex/index over
top of the reset git-annex branch, and then run a `git annex fsck --fast`
to fix up any object location info.)
Also should check all remote tracking branches. If such a branch refers
to a bad object, it is sufficient to remove the tracking
to a missing object, it is sufficient to remove the tracking
branch and then `git fetch` from the remote, which will re-download missing
objects from it and reinstate the tracking branch.