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git/t/t5700-clone-reference.sh
Junio C Hamano 3d5c418ff5 git-clone: aggressively optimize local clone behaviour.
This changes the behaviour of cloning from a repository on the
local machine, by defaulting to "-l" (use hardlinks to share
files under .git/objects) and making "-l" a no-op.  A new
option, --no-hardlinks, is also added to cause file-level copy
of files under .git/objects while still avoiding the normal
"pack to pipe, then receive and index pack" network transfer
overhead.  The old behaviour of local cloning without -l nor -s
is availble by specifying the source repository with the newly
introduced file:///path/to/repo.git/ syntax (i.e. "same as
network" cloning).

 * With --no-hardlinks (i.e. have all .git/objects/ copied via
   cpio) would not catch the source repository corruption, and
   also risks corrupted recipient repository if an
   alpha-particle hits memory cell while indexing and resolving
   deltas.  As long as the recipient is created uncorrupted, you
   have a good back-up.

 * same-as-network is expensive, but it would catch the breakage
   of the source repository.  It still risks corrupted recipient
   repository due to hardware failure.  As long as the recipient
   is created uncorrupted, you have a good back-up.

 * The new default on the same filesystem, as long as the source
   repository is healthy, it is very likely that the recipient
   would be, too.  Also it is very cheap.  You do not get any
   back-up benefit, though.

None of the method is resilient against the source repository
corruption, so let's discount that from the comparison.  Then
the difference with and without --no-hardlinks matters primarily
if you value the back-up benefit or not.  If you want to use the
cloned repository as a back-up, then it is cheaper to do a clone
with --no-hardlinks and two git-fsck (source before clone,
recipient after clone) than same-as-network clone, especially as
you are likely to do a git-fsck on the recipient if you are so
paranoid anyway.

Which leads me to believe that being able to use file:/// is
probably a good idea, if only for testability, but probably of
little practical value.  We default to hardlinked clone for
everyday use, and paranoids can use --no-hardlinks as a way to
make a back-up.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-08-01 23:42:36 -07:00

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#!/bin/sh
#
# Copyright (C) 2006 Martin Waitz <tali@admingilde.org>
#
test_description='test clone --reference'
. ./test-lib.sh
base_dir=`pwd`
test_expect_success 'preparing first repository' \
'test_create_repo A && cd A &&
echo first > file1 &&
git add file1 &&
git commit -m initial'
cd "$base_dir"
test_expect_success 'preparing second repository' \
'git clone A B && cd B &&
echo second > file2 &&
git add file2 &&
git commit -m addition &&
git repack -a -d &&
git prune'
cd "$base_dir"
test_expect_success 'cloning with reference (-l -s)' \
'git clone -l -s --reference B A C'
cd "$base_dir"
test_expect_success 'existence of info/alternates' \
'test `wc -l <C/.git/objects/info/alternates` = 2'
cd "$base_dir"
test_expect_success 'pulling from reference' \
'cd C &&
git pull ../B'
cd "$base_dir"
test_expect_success 'that reference gets used' \
'cd C &&
echo "0 objects, 0 kilobytes" > expected &&
git count-objects > current &&
diff expected current'
cd "$base_dir"
test_expect_success 'cloning with reference (no -l -s)' \
'git clone --reference B file://`pwd`/A D'
cd "$base_dir"
test_expect_success 'existence of info/alternates' \
'test `wc -l <D/.git/objects/info/alternates` = 1'
cd "$base_dir"
test_expect_success 'pulling from reference' \
'cd D && git pull ../B'
cd "$base_dir"
test_expect_success 'that reference gets used' \
'cd D && echo "0 objects, 0 kilobytes" > expected &&
git count-objects > current &&
diff expected current'
cd "$base_dir"
test_expect_success 'updating origin' \
'cd A &&
echo third > file3 &&
git add file3 &&
git commit -m update &&
git repack -a -d &&
git prune'
cd "$base_dir"
test_expect_success 'pulling changes from origin' \
'cd C &&
git pull origin'
cd "$base_dir"
# the 2 local objects are commit and tree from the merge
test_expect_success 'that alternate to origin gets used' \
'cd C &&
echo "2 objects" > expected &&
git count-objects | cut -d, -f1 > current &&
diff expected current'
cd "$base_dir"
test_expect_success 'pulling changes from origin' \
'cd D &&
git pull origin'
cd "$base_dir"
# the 5 local objects are expected; file3 blob, commit in A to add it
# and its tree, and 2 are our tree and the merge commit.
test_expect_success 'check objects expected to exist locally' \
'cd D &&
echo "5 objects" > expected &&
git count-objects | cut -d, -f1 > current &&
diff expected current'
cd "$base_dir"
test_done