contrib/buildrpm

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/bash -e
#
# Build a Mercurial RPM from the current repo
#
# Tested on
# - Fedora 20
# - CentOS 5
# - centOS 6

. $(dirname $0)/packagelib.sh

BUILD=1
RPMBUILDDIR="$PWD/rpmbuild"
while [ "$1" ]; do
    case "$1" in
    --prepare )
        shift
        BUILD=
        ;;
    --withpython | --with-python)
        shift
        PYTHONVER=2.7.10
        PYTHONMD5=d7547558fd673bd9d38e2108c6b42521
        ;;
    --rpmbuilddir )
        shift
        RPMBUILDDIR="$1"
        shift
        ;;
    * )
        echo "Invalid parameter $1!" 1>&2
        exit 1
        ;;
    esac
done

cd "`dirname $0`/.."

specfile=$PWD/contrib/mercurial.spec
if [ ! -f $specfile ]; then
    echo "Cannot find $specfile!" 1>&2
    exit 1
fi

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

gethgversion

# TODO: handle distance/node set, and type set

if [ -z "$type" ] ; then
   release=1
else
    release=0.9_$type
fi

if [ -n "$distance" ] ; then
    release=$release+$distance_$node
fi

if [ "$PYTHONVER" ]; then
    release=$release+$PYTHONVER
    RPMPYTHONVER=$PYTHONVER
else
    RPMPYTHONVER=%{nil}
fi

mkdir -p $RPMBUILDDIR/{SOURCES,BUILD,SRPMS,RPMS}
$HG archive -t tgz $RPMBUILDDIR/SOURCES/mercurial-$version-$release.tar.gz
if [ "$PYTHONVER" ]; then
(
    mkdir -p build
    cd build
    PYTHON_SRCFILE=Python-$PYTHONVER.tgz
    [ -f $PYTHON_SRCFILE ] || curl -Lo $PYTHON_SRCFILE http://www.python.org/ftp/python/$PYTHONVER/$PYTHON_SRCFILE
    if [ "$PYTHONMD5" ]; then
        echo "$PYTHONMD5 $PYTHON_SRCFILE" | md5sum -w -c
    fi
    ln -f $PYTHON_SRCFILE $RPMBUILDDIR/SOURCES/$PYTHON_SRCFILE

    DOCUTILSVER=`sed -ne "s/^%global docutilsname docutils-//p" $specfile`
    DOCUTILS_SRCFILE=docutils-$DOCUTILSVER.tar.gz
    [ -f $DOCUTILS_SRCFILE ] || curl -Lo $DOCUTILS_SRCFILE http://downloads.sourceforge.net/project/docutils/docutils/$DOCUTILSVER/$DOCUTILS_SRCFILE
    DOCUTILSMD5=`sed -ne "s/^%global docutilsmd5 //p" $specfile`
    if [ "$DOCUTILSMD5" ]; then
        echo "$DOCUTILSMD5 $DOCUTILS_SRCFILE" | md5sum -w -c
    fi
    ln -f $DOCUTILS_SRCFILE $RPMBUILDDIR/SOURCES/$DOCUTILS_SRCFILE
)
fi

mkdir -p $RPMBUILDDIR/SPECS
rpmspec=$RPMBUILDDIR/SPECS/mercurial.spec

sed -e "s,^Version:.*,Version: $version," \
    -e "s,^Release:.*,Release: $release," \
    $specfile > $rpmspec

echo >> $rpmspec
echo "%changelog" >> $rpmspec

if echo $version | grep '+' > /dev/null 2>&1; then
    latesttag="`echo $version | sed -e 's/+.*//'`"
    $HG log -r .:"$latesttag" -fM \
        --template '{date|hgdate}\t{author}\t{desc|firstline}\n' | python -c '
import sys, time

def datestr(date, format):
    return time.strftime(format, time.gmtime(float(date[0]) - date[1]))

changelog = []
for l in sys.stdin.readlines():
    tok = l.split("\t")
    hgdate = tuple(int(v) for v in tok[0].split())
    changelog.append((datestr(hgdate, "%F"), tok[1], hgdate, tok[2]))
prevtitle = ""
for l in sorted(changelog, reverse=True):
    title = "* %s %s" % (datestr(l[2], "%a %b %d %Y"), l[1])
    if prevtitle != title:
        prevtitle = title
        print
        print title
    print "- %s" % l[3].strip()
' >> $rpmspec

else

    $HG log \
         --template '{date|hgdate}\t{author}\t{desc|firstline}\n' \
         .hgtags | python -c '
import sys, time

def datestr(date, format):
    return time.strftime(format, time.gmtime(float(date[0]) - date[1]))

for l in sys.stdin.readlines():
    tok = l.split("\t")
    hgdate = tuple(int(v) for v in tok[0].split())
    print "* %s %s\n- %s" % (datestr(hgdate, "%a %b %d %Y"), tok[1], tok[2])
' >> $rpmspec

fi

sed -i \
    -e "s/^%define withpython.*$/%define withpython $RPMPYTHONVER/" \
    $rpmspec

if [ "$BUILD" ]; then
    rpmbuild --define "_topdir $RPMBUILDDIR" -ba $rpmspec --clean
    if [ $? = 0 ]; then
        echo
        echo "Built packages for $version-$release:"
        find $RPMBUILDDIR/*RPMS/ -type f -newer $rpmspec
    fi
else
    echo "Prepared sources for $version-$release $rpmspec are in $RPMBUILDDIR/SOURCES/ - use like:"
    echo "rpmbuild --define '_topdir $RPMBUILDDIR' -ba $rpmspec --clean"
fi