contrib/perf-utils/discovery-helper.sh

discovery-helper: use reflink copy if available

A reflink copy will copy the files "as usual" but keep using the same data block
underneath. This is only supported by "copy on write" file system like btrfs or
zfs.

This will achieve similar performance that the existing hardlink clone that
Mercurial performs with the same initial space saving. However, it will behave
better on revlogs start being touch by strip. Instead of duplicating all data in
the touched revlogs, only the block actually affected by the strip will be
duplicated. This save a lot of space when building many variants of large
repositories.

The --reflink=always flag make sure the `cp` call fails if reflink copies are
not supported. Falling back to local clone.

#!/bin/bash
#
# produces two repositories with different common and missing subsets
#
#   $ discovery-helper.sh REPO NBHEADS DEPT
#
# The Goal is to produce two repositories with some common part and some
# exclusive part on each side. Provide a source repository REPO, it will
# produce two repositories REPO-left and REPO-right.
#
# Each repository will be missing some revisions exclusive to NBHEADS of the
# repo topological heads. These heads and revisions exclusive to them (up to
# DEPTH depth) are stripped.
#
# The "left" repository will use the NBHEADS first heads (sorted by
# description). The "right" use the last NBHEADS one.
#
# To find out how many topological heads a repo has, use:
#
#   $ hg heads -t -T '{rev}\n' | wc -l
#
# Example:
#
#  The `pypy-2018-09-01` repository has 192 heads. To produce two repositories
#  with 92 common heads and ~50 exclusive heads on each side.
#
#    $ ./discovery-helper.sh pypy-2018-08-01 50 10

set -euo pipefail

printusage () {
     echo "usage: `basename $0` REPO NBHEADS DEPTH [left|right]" >&2
}

if [ $# -lt 3 ]; then
    printusage
    exit 64
fi

repo="$1"
shift

nbheads="$1"
shift

depth="$1"
shift

doleft=1
doright=1
if [ $# -gt 1 ]; then
    printusage
    exit 64
elif [ $# -eq 1 ]; then
    if [ "$1" == "left" ]; then
        doleft=1
        doright=0
    elif [ "$1" == "right" ]; then
        doleft=0
        doright=1
    else
        printusage
        exit 64
    fi
fi

leftrepo="${repo}-${nbheads}h-${depth}d-left"
rightrepo="${repo}-${nbheads}h-${depth}d-right"

left="first(sort(heads(all()), 'desc'), $nbheads)"
right="last(sort(heads(all()), 'desc'), $nbheads)"

leftsubset="ancestors($left, $depth) and only($left, heads(all() - $left))"
rightsubset="ancestors($right, $depth) and only($right, heads(all() - $right))"

echo '### creating left/right repositories with missing changesets:'
if [ $doleft -eq 1 ]; then
    echo '# left  revset:' '"'${leftsubset}'"'
fi
if [ $doright -eq 1 ]; then
    echo '# right revset:' '"'${rightsubset}'"'
fi

buildone() {
    side="$1"
    dest="$2"
    revset="$3"
    echo "### building $side repository: $dest"
    if [ -e "$dest" ]; then
        echo "destination repo already exists: $dest" >&2
        exit 1
    fi
    echo '# cloning'
    if ! cp --recursive --reflink=always ${repo} ${dest}; then
        hg clone --noupdate "${repo}" "${dest}"
    fi
    echo '# stripping' '"'${revset}'"'
    hg -R "${dest}" --config extensions.strip= strip --rev "$revset" --no-backup
}

if [ $doleft -eq 1 ]; then
    buildone left "$leftrepo" "$leftsubset"
fi

if [ $doright -eq 1 ]; then
    buildone right "$rightrepo" "$rightsubset"
fi