contrib/builddeb

revlog: add an experimental option to mitigated delta issues (issue5480)

The general delta heuristic to select a delta do not scale with the number of
branch. The delta base is frequently too far away to be able to reuse a chain
according to the "distance" criteria. This leads to insertion of larger delta (or
even full text) that themselves push the bases for the next delta further away
leading to more large deltas and full texts. This full text and frequent
recomputation throw Mercurial performance in disarray.

For example of a slightly large repository

  280 000 files (2 150 000 versions)
  430 000 changesets (10 000 topological heads)

Number below compares repository with and without the distance criteria:

manifest size:
    with:    21.4 GB
    without:  0.3 GB

store size:
    with:    28.7 GB
    without   7.4 GB

bundle last 15 00 revisions:
    with:    800 seconds
             971 MB
    without:  50 seconds
              73 MB

unbundle time (of the last 15K revisions):
    with:    1150 seconds (~19 minutes)
    without:   35 seconds

Similar issues has been observed in other repositories.


Adding a new option or "feature" on stable is uncommon. However, given that this
issues is making Mercurial practically unusable, I'm exceptionally targeting
this patch for stable.

What is actually needed is a full rework of the delta building and reading
logic. However, that will be a longer process and churn not suitable for stable.

In the meantime, we introduces a quick and dirty mitigation of this in the
'experimental' config space. The new option introduces a way to set the maximum
amount of memory usable to store a diff in memory. This extend the ability for
Mercurial to create chains without removing all safe guard regarding memory
access. The option should be phased out when core has a more proper solution
available.

Setting the limit to '0' remove all limits, setting it to '-1' use the default
limit (textsize x 4).

#!/bin/sh -e
#
# Build a Mercurial debian package from the current repo
#
# Tested on Jessie (stable as of original script authoring.)

. $(dirname $0)/packagelib.sh

BUILD=1
CLEANUP=1
DISTID=`(lsb_release -is 2> /dev/null | tr '[:upper:]' '[:lower:]') || echo debian`
CODENAME=`lsb_release -cs 2> /dev/null || echo unknown`
DEBFLAGS=-b
while [ "$1" ]; do
    case "$1" in
    --distid )
        shift
        DISTID="$1"
        shift
        ;;
    --codename )
        shift
        CODENAME="$1"
        shift
        ;;
    --cleanup )
        shift
        BUILD=
        ;;
    --build )
        shift
        CLEANUP=
        ;;
    --source-only )
        shift
        DEBFLAGS=-S
        ;;
    * )
        echo "Invalid parameter $1!" 1>&2
        exit 1
        ;;
    esac
done

trap "if [ '$CLEANUP' ] ; then rm -r '$PWD/debian' ; fi" EXIT

set -u

if [ ! -d .hg ]; then
    echo 'You are not inside a Mercurial repository!' 1>&2
    exit 1
fi

gethgversion
debver="$version"
if [ -n "$type" ] ; then
    debver="$debver~$type"
fi
if [ -n "$distance" ] ; then
    debver="$debver+$distance-$CODENAME-$node"
elif [ "$DEBFLAGS" = "-S" ] ; then
    # for building a ppa (--source-only) for a release (distance == 0), we need
    # to version the distroseries so that we can upload to launchpad
    debver="$debver~${CODENAME}1"
fi

control=debian/control
changelog=debian/changelog

if [ "$BUILD" ]; then
    if [ -d debian ] ; then
        echo "Error! debian control directory already exists!"
        exit 1
    fi

    cp -r $PWD/contrib/debian debian

    sed -i.tmp "s/__VERSION__/$debver/" $changelog
    sed -i.tmp "s/__DATE__/$(date --rfc-2822)/" $changelog
    sed -i.tmp "s/__CODENAME__/$CODENAME/" $changelog
    rm $changelog.tmp

    # remove the node from the version string
    SRCFILE="mercurial_$(echo $debver | sed "s,-$node,,").orig.tar.gz"
    "$PWD/hg" archive $SRCFILE
    mv $SRCFILE ..
    debuild -us -uc -i -I $DEBFLAGS
    if [ $? != 0 ]; then
        echo 'debuild failed!'
        exit 1
    fi

fi
if [ "$CLEANUP" ] ; then
    echo
    OUTPUTDIR=${OUTPUTDIR:=packages/$DISTID-$CODENAME}
    mkdir -p "$OUTPUTDIR"
    find ../mercurial*.deb ../mercurial_*.build ../mercurial_*.changes \
          ../mercurial*.dsc ../mercurial*.gz \
          -type f -newer $control -print0 2>/dev/null | \
      xargs -Inarf -0 mv narf "$OUTPUTDIR"
    echo "Built packages for $debver:"
    find "$OUTPUTDIR" -type f -newer $control -name '*.deb'
fi