Synnefo

# Copyright 2011-2012 GRNET S.A. All rights reserved.

#

# Redistribution and use in source and binary forms, with or

# without modification, are permitted provided that the following

# conditions are met:

#

#   1. Redistributions of source code must retain the above

#      copyright notice, this list of conditions and the following

#      disclaimer.

#

#   2. Redistributions in binary form must reproduce the above

#      copyright notice, this list of conditions and the following

#      disclaimer in the documentation and/or other materials

#      provided with the distribution.

#

# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR

# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF

# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED

# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN

# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

# POSSIBILITY OF SUCH DAMAGE.

#

# The views and conclusions contained in the software and

# documentation are those of the authors and should not be

# interpreted as representing official policies, either expressed

# or implied, of GRNET S.A.

from time import time

from sqlalchemy import Table, Integer, BigInteger, DECIMAL, Column, String, MetaData, ForeignKey

from sqlalchemy.types import Text

from sqlalchemy.schema import Index, Sequence

from sqlalchemy.sql import func, and_, or_, not_, null, select, bindparam, text, exists

from sqlalchemy.ext.compiler import compiles

from sqlalchemy.engine.reflection import Inspector

from sqlalchemy.exc import NoSuchTableError

from dbworker import DBWorker

from pithos.backends.filter import parse_filters

ROOTNODE = 0

(SERIAL, NODE, HASH, SIZE, TYPE, SOURCE, MTIME, MUSER, UUID, CHECKSUM,

 CLUSTER) = range(11)

(MATCH_PREFIX, MATCH_EXACT) = range(2)

inf = float('inf')

def strnextling(prefix):

    """Return the first unicode string

       greater than but not starting with given prefix.

       strnextling('hello') -> 'hellp'

    """

    if not prefix:

        ## all strings start with the null string,

        ## therefore we have to approximate strnextling('')

        ## with the last unicode character supported by python

        ## 0x10ffff for wide (32-bit unicode) python builds

        ## 0x00ffff for narrow (16-bit unicode) python builds

        ## We will not autodetect. 0xffff is safe enough.

        return unichr(0xffff)

    s = prefix[:-1]

    c = ord(prefix[-1])

    if c >= 0xffff:

        raise RuntimeError

    s += unichr(c + 1)

    return s

def strprevling(prefix):

    """Return an approximation of the last unicode string

       less than but not starting with given prefix.

       strprevling(u'hello') -> u'helln\\xffff'

    """

    if not prefix:

        ## There is no prevling for the null string

        return prefix

    s = prefix[:-1]

    c = ord(prefix[-1])

    if c > 0:

        s += unichr(c - 1) + unichr(0xffff)

    return s

_propnames = {

    'serial': 0,

    'node': 1,

    'hash': 2,

    'size': 3,

    'type': 4,

    'source': 5,

    'mtime': 6,

    'muser': 7,

    'uuid': 8,

    'checksum': 9,

    'cluster': 10

}

def create_tables(engine):

    metadata = MetaData()

    #create nodes table

    columns = []

    columns.append(Column('node', Integer, primary_key=True))

    columns.append(Column('parent', Integer,

                          ForeignKey('nodes.node',

                                     ondelete='CASCADE',

                                     onupdate='CASCADE'),

                          autoincrement=False))

    columns.append(Column('latest_version', Integer))

    columns.append(Column('path', String(2048), default='', nullable=False))

    nodes = Table('nodes', metadata, *columns, mysql_engine='InnoDB')

    Index('idx_nodes_path', nodes.c.path, unique=True)

    Index('idx_nodes_parent', nodes.c.parent)

    #create policy table

    columns = []

    columns.append(Column('node', Integer,

                          ForeignKey('nodes.node',

                                     ondelete='CASCADE',

                                     onupdate='CASCADE'),

                          primary_key=True))

    columns.append(Column('key', String(128), primary_key=True))

    columns.append(Column('value', String(256)))

    policy = Table('policy', metadata, *columns, mysql_engine='InnoDB')

    #create statistics table

    columns = []

    columns.append(Column('node', Integer,

                          ForeignKey('nodes.node',

                                     ondelete='CASCADE',

                                     onupdate='CASCADE'),

                          primary_key=True))

    columns.append(Column('population', Integer, nullable=False, default=0))

    columns.append(Column('size', BigInteger, nullable=False, default=0))

    columns.append(Column('mtime', DECIMAL(precision=16, scale=6)))

    columns.append(Column('cluster', Integer, nullable=False, default=0,

                          primary_key=True, autoincrement=False))

    statistics = Table('statistics', metadata, *columns, mysql_engine='InnoDB')

    #create versions table

    columns = []

    columns.append(Column('serial', Integer, primary_key=True))

    columns.append(Column('node', Integer,

                          ForeignKey('nodes.node',

                                     ondelete='CASCADE',

                                     onupdate='CASCADE')))

    columns.append(Column('hash', String(256)))

    columns.append(Column('size', BigInteger, nullable=False, default=0))

    columns.append(Column('type', String(256), nullable=False, default=''))

    columns.append(Column('source', Integer))

    columns.append(Column('mtime', DECIMAL(precision=16, scale=6)))

    columns.append(Column('muser', String(256), nullable=False, default=''))

    columns.append(Column('uuid', String(64), nullable=False, default=''))

    columns.append(Column('checksum', String(256), nullable=False, default=''))

    columns.append(Column('cluster', Integer, nullable=False, default=0))

    versions = Table('versions', metadata, *columns, mysql_engine='InnoDB')

    Index('idx_versions_node_mtime', versions.c.node, versions.c.mtime)

    Index('idx_versions_node_uuid', versions.c.uuid)

    #create attributes table

    columns = []

    columns.append(Column('serial', Integer,

                          ForeignKey('versions.serial',

                                     ondelete='CASCADE',

                                     onupdate='CASCADE'),

                          primary_key=True))

    columns.append(Column('domain', String(256), primary_key=True))

    columns.append(Column('key', String(128), primary_key=True))

    columns.append(Column('value', String(256)))

    attributes = Table('attributes', metadata, *columns, mysql_engine='InnoDB')

    metadata.create_all(engine)

    return metadata.sorted_tables

class Node(DBWorker):

    """Nodes store path organization and have multiple versions.

       Versions store object history and have multiple attributes.

       Attributes store metadata.

    """

    # TODO: Provide an interface for included and excluded clusters.

    def __init__(self, **params):

        DBWorker.__init__(self, **params)

        try:

            metadata = MetaData(self.engine)

            self.nodes = Table('nodes', metadata, autoload=True)

            self.policy = Table('policy', metadata, autoload=True)

            self.statistics = Table('statistics', metadata, autoload=True)

            self.versions = Table('versions', metadata, autoload=True)

            self.attributes = Table('attributes', metadata, autoload=True)

        except NoSuchTableError:

            tables = create_tables(self.engine)

            map(lambda t: self.__setattr__(t.name, t), tables)

        s = self.nodes.select().where(and_(self.nodes.c.node == ROOTNODE,

                                           self.nodes.c.parent == ROOTNODE))

        rp = self.conn.execute(s)

        r = rp.fetchone()

        rp.close()

        if not r:

            s = self.nodes.insert(

            ).values(node=ROOTNODE, parent=ROOTNODE, path='')

            self.conn.execute(s)

    def node_create(self, parent, path):

        """Create a new node from the given properties.

           Return the node identifier of the new node.

        """

        #TODO catch IntegrityError?

        s = self.nodes.insert().values(parent=parent, path=path)

        r = self.conn.execute(s)

        inserted_primary_key = r.inserted_primary_key[0]

        r.close()

        return inserted_primary_key

    def node_lookup(self, path):

        """Lookup the current node of the given path.

           Return None if the path is not found.

        """

        # Use LIKE for comparison to avoid MySQL problems with trailing spaces.

        s = select([self.nodes.c.node], self.nodes.c.path.like(

            self.escape_like(path), escape='\\'))

        r = self.conn.execute(s)

        row = r.fetchone()

        r.close()

        if row:

            return row[0]

        return None

    def node_lookup_bulk(self, paths):

        """Lookup the current nodes for the given paths.

           Return () if the path is not found.

        """

        if not paths:

            return ()

        # Use LIKE for comparison to avoid MySQL problems with trailing spaces.

        s = select([self.nodes.c.node], self.nodes.c.path.in_(paths))

        r = self.conn.execute(s)

        rows = r.fetchall()

        r.close()

        return [row[0] for row in rows]

    def node_get_properties(self, node):

        """Return the node's (parent, path).

           Return None if the node is not found.

        """

        s = select([self.nodes.c.parent, self.nodes.c.path])

        s = s.where(self.nodes.c.node == node)

        r = self.conn.execute(s)

        l = r.fetchone()

        r.close()

        return l

    def node_get_versions(self, node, keys=(), propnames=_propnames):

        """Return the properties of all versions at node.

           If keys is empty, return all properties in the order

           (serial, node, hash, size, type, source, mtime, muser, uuid, checksum, cluster).

        """

        s = select([self.versions.c.serial,

                    self.versions.c.node,

                    self.versions.c.hash,

                    self.versions.c.size,

                    self.versions.c.type,

                    self.versions.c.source,

                    self.versions.c.mtime,

                    self.versions.c.muser,

                    self.versions.c.uuid,

                    self.versions.c.checksum,

                    self.versions.c.cluster], self.versions.c.node == node)

        s = s.order_by(self.versions.c.serial)

        r = self.conn.execute(s)

        rows = r.fetchall()

        r.close()

        if not rows:

            return rows

        if not keys:

            return rows

        return [[p[propnames[k]] for k in keys if k in propnames] for p in rows]

    def node_count_children(self, node):

        """Return node's child count."""

        s = select([func.count(self.nodes.c.node)])

        s = s.where(and_(self.nodes.c.parent == node,

                         self.nodes.c.node != ROOTNODE))

        r = self.conn.execute(s)

        row = r.fetchone()

        r.close()

        return row[0]

    def node_purge_children(self, parent, before=inf, cluster=0):

        """Delete all versions with the specified

           parent and cluster, and return

           the hashes and size of versions deleted.

           Clears out nodes with no remaining versions.

        """

        #update statistics

        c1 = select([self.nodes.c.node],

                    self.nodes.c.parent == parent)

        where_clause = and_(self.versions.c.node.in_(c1),

                            self.versions.c.cluster == cluster)

        s = select([func.count(self.versions.c.serial),

                    func.sum(self.versions.c.size)])

        s = s.where(where_clause)

        if before != inf:

            s = s.where(self.versions.c.mtime <= before)

        r = self.conn.execute(s)

        row = r.fetchone()

        r.close()

        if not row:

            return (), 0

        nr, size = row[0], -row[1] if row[1] else 0

        mtime = time()

        self.statistics_update(parent, -nr, size, mtime, cluster)

        self.statistics_update_ancestors(parent, -nr, size, mtime, cluster)

        s = select([self.versions.c.hash, self.versions.c.serial])

        s = s.where(where_clause)

        r = self.conn.execute(s)

        hashes = []

        serials = []

        for row in r.fetchall():

            hashes += [row[0]]

            serials += [row[1]]

        r.close()

        #delete versions

        s = self.versions.delete().where(where_clause)

        r = self.conn.execute(s)

        r.close()

        #delete nodes

        s = select([self.nodes.c.node],

                   and_(self.nodes.c.parent == parent,

                        select([func.count(self.versions.c.serial)],

                               self.versions.c.node == self.nodes.c.node).as_scalar() == 0))

        rp = self.conn.execute(s)

        nodes = [r[0] for r in rp.fetchall()]

        rp.close()

        if nodes:

            s = self.nodes.delete().where(self.nodes.c.node.in_(nodes))

            self.conn.execute(s).close()

        return hashes, size, serials

    def node_purge(self, node, before=inf, cluster=0):

        """Delete all versions with the specified

           node and cluster, and return

           the hashes and size of versions deleted.

           Clears out the node if it has no remaining versions.

        """

        #update statistics

        s = select([func.count(self.versions.c.serial),

                    func.sum(self.versions.c.size)])

        where_clause = and_(self.versions.c.node == node,

                            self.versions.c.cluster == cluster)

        s = s.where(where_clause)

        if before != inf:

            s = s.where(self.versions.c.mtime <= before)

        r = self.conn.execute(s)

        row = r.fetchone()

        nr, size = row[0], row[1]

        r.close()

        if not nr:

            return (), 0

        mtime = time()

        self.statistics_update_ancestors(node, -nr, -size, mtime, cluster)

        s = select([self.versions.c.hash, self.versions.c.serial])

        s = s.where(where_clause)

        r = self.conn.execute(s)

        hashes = []

        serials = []

        for row in r.fetchall():

            hashes += [row[0]]

            serials += [row[1]]

        r.close()

        #delete versions

        s = self.versions.delete().where(where_clause)

        r = self.conn.execute(s)

        r.close()

        #delete nodes

        s = select([self.nodes.c.node],

                   and_(self.nodes.c.node == node,

                        select([func.count(self.versions.c.serial)],

                               self.versions.c.node == self.nodes.c.node).as_scalar() == 0))

        r = self.conn.execute(s)

        nodes = r.fetchall()

        r.close()

        if nodes:

            s = self.nodes.delete().where(self.nodes.c.node.in_(nodes))

            self.conn.execute(s).close()

        return hashes, size, serials

    def node_remove(self, node):

        """Remove the node specified.

           Return false if the node has children or is not found.

        """

        if self.node_count_children(node):

            return False

        mtime = time()

        s = select([func.count(self.versions.c.serial),

                    func.sum(self.versions.c.size),

                    self.versions.c.cluster])

        s = s.where(self.versions.c.node == node)

        s = s.group_by(self.versions.c.cluster)

        r = self.conn.execute(s)

        for population, size, cluster in r.fetchall():

            self.statistics_update_ancestors(

                node, -population, -size, mtime, cluster)

        r.close()

        s = self.nodes.delete().where(self.nodes.c.node == node)

        self.conn.execute(s).close()

        return True

    def policy_get(self, node):

        s = select([self.policy.c.key, self.policy.c.value],

                   self.policy.c.node == node)

        r = self.conn.execute(s)

        d = dict(r.fetchall())

        r.close()

        return d

    def policy_set(self, node, policy):

        #insert or replace

        for k, v in policy.iteritems():

            s = self.policy.update().where(and_(self.policy.c.node == node,

                                                self.policy.c.key == k))

            s = s.values(value=v)

            rp = self.conn.execute(s)

            rp.close()

            if rp.rowcount == 0:

                s = self.policy.insert()

                values = {'node': node, 'key': k, 'value': v}

                r = self.conn.execute(s, values)

                r.close()

    def statistics_get(self, node, cluster=0):

        """Return population, total size and last mtime

           for all versions under node that belong to the cluster.

        """

        s = select([self.statistics.c.population,

                    self.statistics.c.size,

                    self.statistics.c.mtime])

        s = s.where(and_(self.statistics.c.node == node,

                         self.statistics.c.cluster == cluster))

        r = self.conn.execute(s)

        row = r.fetchone()

        r.close()

        return row

    def statistics_update(self, node, population, size, mtime, cluster=0):

        """Update the statistics of the given node.

           Statistics keep track the population, total

           size of objects and mtime in the node's namespace.

           May be zero or positive or negative numbers.

        """

        s = select([self.statistics.c.population, self.statistics.c.size],

                   and_(self.statistics.c.node == node,

                        self.statistics.c.cluster == cluster))

        rp = self.conn.execute(s)

        r = rp.fetchone()

        rp.close()

        if not r:

            prepopulation, presize = (0, 0)

        else:

            prepopulation, presize = r

        population += prepopulation

        size += presize

        #insert or replace

        #TODO better upsert

        u = self.statistics.update().where(and_(self.statistics.c.node == node,

                                           self.statistics.c.cluster == cluster))

        u = u.values(population=population, size=size, mtime=mtime)

        rp = self.conn.execute(u)

        rp.close()

        if rp.rowcount == 0:

            ins = self.statistics.insert()

            ins = ins.values(node=node, population=population, size=size,

                             mtime=mtime, cluster=cluster)

            self.conn.execute(ins).close()

    def statistics_update_ancestors(self, node, population, size, mtime, cluster=0):

        """Update the statistics of the given node's parent.

           Then recursively update all parents up to the root.

           Population is not recursive.

        """

        while True:

            if node == ROOTNODE:

                break

            props = self.node_get_properties(node)

            if props is None:

                break

            parent, path = props

            self.statistics_update(parent, population, size, mtime, cluster)

            node = parent

            population = 0  # Population isn't recursive

    def statistics_latest(self, node, before=inf, except_cluster=0):

        """Return population, total size and last mtime

           for all latest versions under node that

           do not belong to the cluster.

        """

        # The node.

        props = self.node_get_properties(node)

        if props is None:

            return None

        parent, path = props

        # The latest version.

        s = select([self.versions.c.serial,

                    self.versions.c.node,

                    self.versions.c.hash,

                    self.versions.c.size,

                    self.versions.c.type,

                    self.versions.c.source,

                    self.versions.c.mtime,

                    self.versions.c.muser,

                    self.versions.c.uuid,

                    self.versions.c.checksum,

                    self.versions.c.cluster])

        if before != inf:

            filtered = select([func.max(self.versions.c.serial)],

                              self.versions.c.node == node)

            filtered = filtered.where(self.versions.c.mtime < before)

        else:

            filtered = select([self.nodes.c.latest_version],

                              self.versions.c.node == node)

        s = s.where(and_(self.versions.c.cluster != except_cluster,

                         self.versions.c.serial == filtered))

        r = self.conn.execute(s)

        props = r.fetchone()

        r.close()

        if not props:

            return None

        mtime = props[MTIME]

        # First level, just under node (get population).

        v = self.versions.alias('v')

        s = select([func.count(v.c.serial),

                    func.sum(v.c.size),

                    func.max(v.c.mtime)])

        if before != inf:

            c1 = select([func.max(self.versions.c.serial)])

            c1 = c1.where(self.versions.c.mtime < before)

            c1.where(self.versions.c.node == v.c.node)

        else:

            c1 = select([self.nodes.c.latest_version])

            c1.where(self.nodes.c.node == v.c.node)

        c2 = select([self.nodes.c.node], self.nodes.c.parent == node)

        s = s.where(and_(v.c.serial == c1,

                         v.c.cluster != except_cluster,

                         v.c.node.in_(c2)))

        rp = self.conn.execute(s)

        r = rp.fetchone()

        rp.close()

        if not r:

            return None

        count = r[0]

        mtime = max(mtime, r[2])

        if count == 0:

            return (0, 0, mtime)

        # All children (get size and mtime).

        # This is why the full path is stored.

        s = select([func.count(v.c.serial),

                    func.sum(v.c.size),

                    func.max(v.c.mtime)])

        if before != inf:

            c1 = select([func.max(self.versions.c.serial)],

                        self.versions.c.node == v.c.node)

            c1 = c1.where(self.versions.c.mtime < before)

        else:

            c1 = select([self.nodes.c.serial],

                        self.nodes.c.node == v.c.node)

        c2 = select([self.nodes.c.node], self.nodes.c.path.like(

            self.escape_like(path) + '%', escape='\\'))

        s = s.where(and_(v.c.serial == c1,

                         v.c.cluster != except_cluster,

                         v.c.node.in_(c2)))

        rp = self.conn.execute(s)

        r = rp.fetchone()

        rp.close()

        if not r:

            return None

        size = r[1] - props[SIZE]

        mtime = max(mtime, r[2])

        return (count, size, mtime)

    def nodes_set_latest_version(self, node, serial):

        s = self.nodes.update().where(self.nodes.c.node == node)

        s = s.values(latest_version=serial)

        self.conn.execute(s).close()

    def version_create(self, node, hash, size, type, source, muser, uuid, checksum, cluster=0):

        """Create a new version from the given properties.

           Return the (serial, mtime) of the new version.

        """

        mtime = time()

        s = self.versions.insert(

        ).values(node=node, hash=hash, size=size, type=type, source=source,

                 mtime=mtime, muser=muser, uuid=uuid, checksum=checksum, cluster=cluster)

        serial = self.conn.execute(s).inserted_primary_key[0]

        self.statistics_update_ancestors(node, 1, size, mtime, cluster)

        self.nodes_set_latest_version(node, serial)

        return serial, mtime

    def version_lookup(self, node, before=inf, cluster=0, all_props=True):

        """Lookup the current version of the given node.

           Return a list with its properties:

           (serial, node, hash, size, type, source, mtime,

            muser, uuid, checksum, cluster)

           or None if the current version is not found in the given cluster.

        """

        v = self.versions.alias('v')

        if not all_props:

            s = select([v.c.serial])

        else:

            s = select([v.c.serial, v.c.node, v.c.hash,

                        v.c.size, v.c.type, v.c.source,

                        v.c.mtime, v.c.muser, v.c.uuid,

                        v.c.checksum, v.c.cluster])

        if before != inf:

            c = select([func.max(self.versions.c.serial)],

                       self.versions.c.node == node)

            c = c.where(self.versions.c.mtime < before)

        else:

            c = select([self.nodes.c.latest_version],

                       self.nodes.c.node == node)

        s = s.where(and_(v.c.serial == c,

                         v.c.cluster == cluster))

        r = self.conn.execute(s)

        props = r.fetchone()

        r.close()

        if props:

            return props

        return None

    def version_lookup_bulk(self, nodes, before=inf, cluster=0, all_props=True):

        """Lookup the current versions of the given nodes.

           Return a list with their properties:

           (serial, node, hash, size, type, source, mtime, muser, uuid, checksum, cluster).

        """

        if not nodes:

            return ()

        v = self.versions.alias('v')

        if not all_props:

            s = select([v.c.serial])

        else:

            s = select([v.c.serial, v.c.node, v.c.hash,

                        v.c.size, v.c.type, v.c.source,

                        v.c.mtime, v.c.muser, v.c.uuid,

                        v.c.checksum, v.c.cluster])

        if before != inf:

            c = select([func.max(self.versions.c.serial)],

                       self.versions.c.node.in_(nodes))

            c = c.where(self.versions.c.mtime < before)

            c = c.group_by(self.versions.c.node)

        else:

            c = select([self.nodes.c.latest_version],

                       self.nodes.c.node.in_(nodes))

        s = s.where(and_(v.c.serial.in_(c),

                         v.c.cluster == cluster))

        s = s.order_by(v.c.node)

        r = self.conn.execute(s)

        rproxy = r.fetchall()

        r.close()

        return (tuple(row.values()) for row in rproxy)

    def version_get_properties(self, serial, keys=(), propnames=_propnames):

        """Return a sequence of values for the properties of

           the version specified by serial and the keys, in the order given.

           If keys is empty, return all properties in the order

           (serial, node, hash, size, type, source, mtime, muser, uuid, checksum, cluster).

        """

        v = self.versions.alias()

        s = select([v.c.serial, v.c.node, v.c.hash,

                    v.c.size, v.c.type, v.c.source,

                    v.c.mtime, v.c.muser, v.c.uuid,

                    v.c.checksum, v.c.cluster], v.c.serial == serial)

        rp = self.conn.execute(s)

        r = rp.fetchone()

        rp.close()

        if r is None:

            return r

        if not keys:

            return r

        return [r[propnames[k]] for k in keys if k in propnames]

    def version_put_property(self, serial, key, value):

        """Set value for the property of version specified by key."""

        if key not in _propnames:

            return

        s = self.versions.update()

        s = s.where(self.versions.c.serial == serial)

        s = s.values(**{key: value})

        self.conn.execute(s).close()

    def version_recluster(self, serial, cluster):

        """Move the version into another cluster."""

        props = self.version_get_properties(serial)

        if not props:

            return

        node = props[NODE]

        size = props[SIZE]

        oldcluster = props[CLUSTER]

        if cluster == oldcluster:

            return

        mtime = time()

        self.statistics_update_ancestors(node, -1, -size, mtime, oldcluster)

        self.statistics_update_ancestors(node, 1, size, mtime, cluster)

        s = self.versions.update()

        s = s.where(self.versions.c.serial == serial)

        s = s.values(cluster=cluster)

        self.conn.execute(s).close()

    def version_remove(self, serial):

        """Remove the serial specified."""

        props = self.version_get_properties(serial)

        if not props:

            return

        node = props[NODE]

        hash = props[HASH]

        size = props[SIZE]

        cluster = props[CLUSTER]

        mtime = time()

        self.statistics_update_ancestors(node, -1, -size, mtime, cluster)

        s = self.versions.delete().where(self.versions.c.serial == serial)

        self.conn.execute(s).close()

        props = self.version_lookup(node, cluster=cluster, all_props=False)

        if props:

            self.nodes_set_latest_version(node, serial)

        return hash, size

    def attribute_get(self, serial, domain, keys=()):

        """Return a list of (key, value) pairs of the version specified by serial.

           If keys is empty, return all attributes.

           Othwerise, return only those specified.

        """