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#!/bin/bash
# Example script to deltify an entire GIT repository based on the commit list.
# The most recent version of a file is the reference and previous versions
# are made delta against the best earlier version available. And so on for
# successive versions going back in time. This way the increasing delta
# overhead is pushed towards older versions of any given file.
#
# The -d argument allows to provide a limit on the delta chain depth.
# If 0 is passed then everything is undeltafied. Limiting the delta
# depth is meaningful for subsequent access performance to old revisions.
# A value of 16 might be a good compromize between performance and good
# space saving. Current default is unbounded.
#
# The --max-behind=30 argument is passed to git-mkdelta so to keep
# combinations and memory usage bounded a bit. If you have lots of memory
# and CPU power you may remove it (or set to 0) to let git-mkdelta find the
# best delta match regardless of the number of revisions for a given file.
# You can also make the value smaller to make it faster and less
# memory hungry. A value of 5 ought to still give pretty good results.
# When set to 0 or ommitted then look behind is unbounded. Note that
# git-mkdelta might die with a segmentation fault in that case if it
# runs out of memory. Note that the GIT repository will still be consistent
# even if git-mkdelta dies unexpectedly.
set -e
max_depth=
[ "$1" == "-d" ] && max_depth="--max-depth=$2" && shift 2
overlap=30
max_behind="--max-behind=$overlap"
function process_list() {
if [ "$list" ]; then
echo "Processing $curr_file"
echo "$list" | xargs git-mkdelta $max_depth $max_behind -v
fi
}
rev_list=""
curr_file=""
git-rev-list HEAD |
while true; do
# Let's batch revisions into groups of 1000 to give it a chance to
# scale with repositories containing long revision lists. We also
# overlap with the previous batch the size of mkdelta's look behind
# value in order to account for the processing discontinuity.
rev_list="$(echo -e -n "$rev_list" | tail --lines=$overlap)"
for i in $(seq 1000); do
read rev || break
rev_list="$rev_list$rev\n"
done
echo -e -n "$rev_list" |
git-diff-tree -r -t --stdin |
awk '/^:/ { if ($5 == "M") printf "%s %s\n%s %s\n", $4, $6, $3, $6 }' |
LC_ALL=C sort -s -k 2 | uniq |
while read sha1 file; do
if [ "$file" == "$curr_file" ]; then
list="$list $sha1"
else
process_list
curr_file="$file"
list="$sha1"
fi
done
[ "$rev" ] || break
done
process_list
curr_file="root directory"
list="$(
git-rev-list HEAD |
while read commit; do
git-cat-file commit $commit |
sed -n 's/tree //p;Q'
done
)"
process_list
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