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       # 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 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
+      }
       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)
               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))
               self.nodes = Table('nodes', metadata, *columns, mysql_engine='InnoDB')
               Index('idx_nodes_path', self.nodes.c.path, unique=True)
               Index('idx_nodes_parent', self.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)))
               self.policies = 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))
               self.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))
               self.versions = Table('versions', metadata, *columns, mysql_engine='InnoDB')
               Index('idx_versions_node_mtime', self.versions.c.node, self.versions.c.mtime)
               Index('idx_versions_node_uuid', self.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)))
               self.attributes = Table('attributes', metadata, *columns, mysql_engine='InnoDB')
               metadata.create_all(self.engine)
               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)
                   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.
               """
               # 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])
               s = s.where(where_clause)
               r = self.conn.execute(s)
               hashes = [row[0] for row in r.fetchall()]
               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()
               s = self.nodes.delete().where(self.nodes.c.node.in_(nodes))
               self.conn.execute(s).close()
               return hashes, size
           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])
               s = s.where(where_clause)
               r = self.conn.execute(s)
               hashes = [r[0] for r in r.fetchall()]
               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()
               s = self.nodes.delete().where(self.nodes.c.node.in_(nodes))
               self.conn.execute(s).close()
               return hashes, size
           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.policies.c.key, self.policies.c.value],
                   self.policies.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.policies.update().where(and_(self.policies.c.node == node,
                                                         self.policies.c.key == k))
                   s = s.values(value = v)
                   rp = self.conn.execute(s)
                   rp.close()
                   if rp.rowcount == 0:
                       s = self.policies.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(v.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.
               """
               if keys:
                   attrs = self.attributes.alias()
                   s = select([attrs.c.key, attrs.c.value])
                   s = s.where(and_(attrs.c.key.in_(keys),
                                    attrs.c.serial == serial,
                                    attrs.c.domain == domain))
               else:
                   attrs = self.attributes.alias()
                   s = select([attrs.c.key, attrs.c.value])
                   s = s.where(and_(attrs.c.serial == serial,
                                    attrs.c.domain == domain))
               r = self.conn.execute(s)
               l = r.fetchall()
               r.close()
               return l
           def attribute_set(self, serial, domain, items):
               """Set the attributes of the version specified by serial.
                  Receive attributes as an iterable of (key, value) pairs.
               """
               #insert or replace
               #TODO better upsert
               for k, v in items:
                   s = self.attributes.update()
                   s = s.where(and_(self.attributes.c.serial == serial,
                                    self.attributes.c.domain == domain,
                                    self.attributes.c.key == k))
                   s = s.values(value = v)
                   rp = self.conn.execute(s)
                   rp.close()
                   if rp.rowcount == 0:
                       s = self.attributes.insert()
                       s = s.values(serial=serial, domain=domain, key=k, value=v)
                       self.conn.execute(s).close()
           def attribute_del(self, serial, domain, keys=()):
               """Delete attributes of the version specified by serial.
                  If keys is empty, delete all attributes.
                  Otherwise delete those specified.
               """
               if keys:
                   #TODO more efficient way to do this?
                   for key in keys:
                       s = self.attributes.delete()
                       s = s.where(and_(self.attributes.c.serial == serial,
                                        self.attributes.c.domain == domain,
                                        self.attributes.c.key == key))
                       self.conn.execute(s).close()
               else:
                   s = self.attributes.delete()
                   s = s.where(and_(self.attributes.c.serial == serial,
                                    self.attributes.c.domain == domain))
                   self.conn.execute(s).close()
           def attribute_copy(self, source, dest):
               s = select([dest, self.attributes.c.domain, self.attributes.c.key, self.attributes.c.value],
                   self.attributes.c.serial == source)
               rp = self.conn.execute(s)
               attributes = rp.fetchall()
               rp.close()
               for dest, domain, k, v in attributes:
                   #insert or replace
                   s = self.attributes.update().where(and_(
                       self.attributes.c.serial == dest,
                       self.attributes.c.domain == domain,
                       self.attributes.c.key == k))
                   rp = self.conn.execute(s, value=v)
                   rp.close()
                   if rp.rowcount == 0:
                       s = self.attributes.insert()
                       values = {'serial':dest, 'domain':domain, 'key':k, 'value':v}
                       self.conn.execute(s, values).close()
           def latest_attribute_keys(self, parent, domain, before=inf, except_cluster=0, pathq=[]):
               """Return a list with all keys pairs defined
                  for all latest versions under parent that
                  do not belong to the cluster.
               """
               # TODO: Use another table to store before=inf results.
               a = self.attributes.alias('a')
               v = self.versions.alias('v')
               n = self.nodes.alias('n')
               s = select([a.c.key]).distinct()
               if before != inf:
                   filtered = select([func.max(self.versions.c.serial)])
                   filtered = filtered.where(self.versions.c.mtime < before)
                   filtered = filtered.where(self.versions.c.node == v.c.node)
               else:
                   filtered = select([self.nodes.c.latest_version])
                   filtered = filtered.where(self.nodes.c.node == v.c.node)
               s = s.where(v.c.serial == filtered)
               s = s.where(v.c.cluster != except_cluster)
               s = s.where(v.c.node.in_(select([self.nodes.c.node],
                   self.nodes.c.parent == parent)))
               s = s.where(a.c.serial == v.c.serial)
               s = s.where(a.c.domain == domain)
               s = s.where(n.c.node == v.c.node)
               conj = []
               for path, match in pathq:
                   if match == MATCH_PREFIX:
                       conj.append(n.c.path.like(self.escape_like(path) + '%', escape='\\'))
                   elif match == MATCH_EXACT:
                       conj.append(n.c.path == path)
               if conj:
                   s = s.where(or_(*conj))
               rp = self.conn.execute(s)
               rows = rp.fetchall()
               rp.close()
               return [r[0] for r in rows]
           def latest_version_list(self, parent, prefix='', delimiter=None,
                                   start='', limit=10000, before=inf,
                                   except_cluster=0, pathq=[], domain=None,
                                   filterq=[], sizeq=None, all_props=False):
               """Return a (list of (path, serial) tuples, list of common prefixes)
                  for the current versions of the paths with the given parent,
                  matching the following criteria.
                  The property tuple for a version is returned if all
                  of these conditions are true:
                       a. parent matches
                       b. path > start
                       c. path starts with prefix (and paths in pathq)
                       d. version is the max up to before
                       e. version is not in cluster
                       f. the path does not have the delimiter occuring
                          after the prefix, or ends with the delimiter
                       g. serial matches the attribute filter query.
                          A filter query is a comma-separated list of
                          terms in one of these three forms:
                          key
                              an attribute with this key must exist
                          !key
                              an attribute with this key must not exist
                          key ?op value
                              the attribute with this key satisfies the value
                              where ?op is one of ==, != <=, >=, <, >.
                       h. the size is in the range set by sizeq
                  The list of common prefixes includes the prefixes
                  matching up to the first delimiter after prefix,
                  and are reported only once, as "virtual directories".
                  The delimiter is included in the prefixes.
                  If arguments are None, then the corresponding matching rule
                  will always match.
                  Limit applies to the first list of tuples returned.
                  If all_props is True, return all properties after path, not just serial.
               """
               if not start or start < prefix:
                   start = strprevling(prefix)
               nextling = strnextling(prefix)
               v = self.versions.alias('v')
               n = self.nodes.alias('n')
               if not all_props:
                   s = select([n.c.path, v.c.serial]).distinct()
               else:
                   s = select([n.c.path,
                               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]).distinct()
               if before != inf:
                   filtered = select([func.max(self.versions.c.serial)])
                   filtered = filtered.where(self.versions.c.mtime < before)
               else:
                   filtered = select([self.nodes.c.latest_version])
               s = s.where(v.c.serial == filtered.where(self.nodes.c.node == v.c.node))
               s = s.where(v.c.cluster != except_cluster)
               s = s.where(v.c.node.in_(select([self.nodes.c.node],
                   self.nodes.c.parent == parent)))
               s = s.where(n.c.node == v.c.node)
               s = s.where(and_(n.c.path > bindparam('start'), n.c.path < nextling))
               conj = []
               for path, match in pathq:
                   if match == MATCH_PREFIX:
                       conj.append(n.c.path.like(self.escape_like(path) + '%', escape='\\'))
                   elif match == MATCH_EXACT:
                       conj.append(n.c.path == path)
               if conj:
                   s = s.where(or_(*conj))
               if sizeq and len(sizeq) == 2:
                   if sizeq[0]:
                       s = s.where(v.c.size >= sizeq[0])
                   if sizeq[1]:
                       s = s.where(v.c.size < sizeq[1])
               if domain and filterq:
                   a = self.attributes.alias('a')
                   included, excluded, opers = parse_filters(filterq)
                   if included:
                       subs = select([1])
                       subs = subs.where(a.c.serial == v.c.serial).correlate(v)
                       subs = subs.where(a.c.domain == domain)
                       subs = subs.where(or_(*[a.c.key.op('=')(x) for x in included]))
                       s = s.where(exists(subs))
                   if excluded:
                       subs = select([1])
                       subs = subs.where(a.c.serial == v.c.serial).correlate(v)
                       subs = subs.where(a.c.domain == domain)
                       subs = subs.where(or_(*[a.c.key.op('=')(x) for x in excluded]))
                       s = s.where(not_(exists(subs)))
                   if opers:
                       for k, o, val in opers:
                           subs = select([1])
                           subs = subs.where(a.c.serial == v.c.serial).correlate(v)
                           subs = subs.where(a.c.domain == domain)
                           subs = subs.where(and_(a.c.key.op('=')(k), a.c.value.op(o)(val)))
                           s = s.where(exists(subs))
               s = s.order_by(n.c.path)
               if not delimiter:
                   s = s.limit(limit)
                   rp = self.conn.execute(s, start=start)
                   r = rp.fetchall()
                   rp.close()
                   return r, ()
               pfz = len(prefix)
               dz = len(delimiter)
               count = 0
               prefixes = []
               pappend = prefixes.append
               matches = []
               mappend = matches.append
               rp = self.conn.execute(s, start=start)
               while True:
                   props = rp.fetchone()
                   if props is None:
                       break
                   path = props[0]
                   serial = props[1]
                   idx = path.find(delimiter, pfz)
                   if idx < 0:
                       mappend(props)
                       count += 1
                       if count >= limit:
                           break
                       continue
                   if idx + dz == len(path):
                       mappend(props)
                       count += 1
                       continue # Get one more, in case there is a path.
                   pf = path[:idx + dz]
                   pappend(pf)
                   if count >= limit:
                       break
                   rp = self.conn.execute(s, start=strnextling(pf)) # New start.
               rp.close()
               return matches, prefixes
           def latest_uuid(self, uuid):
               """Return a (path, serial) tuple, for the latest version of the given uuid."""
               v = self.versions.alias('v')
               n = self.nodes.alias('n')
               s = select([n.c.path, v.c.serial])
               filtered = select([func.max(self.versions.c.serial)])
               s = s.where(v.c.serial == filtered.where(self.versions.c.uuid == uuid))
               s = s.where(n.c.node == v.c.node)
               r = self.conn.execute(s)
               l = r.fetchone()
               r.close()
               return l