linux@xxxxxxxxxxx wrote:
Git packs so well that it's very common for the unpacked source to be much
larger than the history in .git. The linux-kernel archive is a prime example.
I've also started using git-svn (awesome tool, BTW) and have discovered
the impressive disk space costs associated with SVN's tags/ directories
if I actually want to download the full history.
If you have multiple cloned repositories on one system, git can share
the history, but the working directory problem is exacerbated.
(Disk is cheap, but the RAM to cache it is limited.)
This got me thinking...
Wouldn't it be nice if there were a way to tell git-update-index and
git-checkout index that certain directories are not in the working
directory, but don't worry. Just pretend they exist and match the index.
I think that update-index is able to do (some of) this already:
$ man git-update-index
SYNOPSIS
git-update-index
[--cacheinfo <mode> <object> <file>]*
--cacheinfo <mode> <object> <path>
Directly insert the specified info into the index.
USING --CACHEINFO OR --INFO-ONLY
--cacheinfo is used to register a file that is not in the current
working directory. This is useful for minimum-checkout merging.
To pretend you have a file with mode and sha1 at path, say:
$ git-update-index --cacheinfo mode sha1 path
--info-only is used to register files without placing them in the
object database. This is useful for status-only repositories.
Both --cacheinfo and --info-only behave similarly: the index is
updated
but the object database isn't. --cacheinfo is useful when the
object is
in the database but the file isn't available locally. --info-only is
useful when the file is available, but you do not wish to update the
object database.
At any rate, it looks like some of the infrastructure is existing
already, even if the complete solution doesn't exist.
I *guess* it might even be as simple as maintaining a list of
"uncheckedout files with mode and sha" in the .git directory, and
merging that with what has actually been checked out when updating the
index.
i.e.
$ git checkout master:src/drivers
Get the <tree> object for master. Step through each entry. If the
requested path falls under the entry, recurse into it, checking out the
required files, otherwise write the <tree/file> info into
.git/partialcheckout.
Hack, hack, hack in src/drivers.
When you want to check what part of the tree is dirty, check if
.git/partialcheckouts exists. If it does, read through each entry,
comparing them to the index. Then, for the entries that are not in
partialcheckout, but are in the index, actually go to the filesystem to
check stat for each file.
Not quite sure how to handle something like:
$ git checkout master:src/drivers/scsi
$ git checkout master:src/drivers/usb
I guess one would have to trim entries from .git/partialcheckout as they
are actually fully checked out.
Rogan
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