Synnefo » Pithos

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

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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

from sqlalchemy.ext.compiler import compiles

from sqlalchemy.engine.reflection import Inspector

from dbworker import DBWorker

from pithos.lib.filter import parse_filters, OPERATORS

ROOTNODE  = 0

( SERIAL, NODE, HASH, SIZE, SOURCE, MTIME, MUSER, UUID, CLUSTER ) = range(9)

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,

    'source'    : 4,

    'mtime'     : 5,

    'muser'     : 6,

    'uuid'      : 7,

    'cluster'   : 8

}

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))

        path_length = 2048

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

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

        #create policy table

        columns=[]

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

                              ForeignKey('nodes.node',

                                         ondelete='CASCADE',

                                         onupdate='CASCADE'),

                              primary_key=True))

        columns.append(Column('key', String(255), primary_key=True))

        columns.append(Column('value', String(255)))

        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(255)))

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

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

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

        columns.append(Column('muser', String(255), nullable=False, default=''))

        columns.append(Column('uuid', String(64), 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(255), primary_key=True))

        columns.append(Column('key', String(255), primary_key=True))

        columns.append(Column('value', String(255)))

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

        metadata.create_all(self.engine)

        # the following code creates an index of specific length

        # this can be accompliced in sqlalchemy >= 0.7.3

        # providing mysql_length option during index creation

        insp = Inspector.from_engine(self.engine)

        indexes = [elem['name'] for elem in insp.get_indexes('nodes')]

        if 'idx_nodes_path' not in indexes:

            explicit_length = '(%s)' %path_length if self.engine.name == 'mysql' else ''

            s = text('CREATE INDEX idx_nodes_path ON nodes (path%s)' %explicit_length)

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

        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_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, source, mtime, muser, uuid, cluster).

        """

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

                    self.versions.c.node,

                    self.versions.c.hash,

                    self.versions.c.size,

                    self.versions.c.source,

                    self.versions.c.mtime,

                    self.versions.c.muser,

                    self.versions.c.uuid,

                    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 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 ()

        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

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

        """Delete all versions with the specified

           node and cluster, and return

           the hashes 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 ()

        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

    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.source,

                    self.versions.c.mtime,

                    self.versions.c.muser,

                    self.versions.c.uuid,

                    self.versions.c.cluster])

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

                            self.versions.c.node == node)

        if before != inf:

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

        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)])

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

        if before != inf:

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

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

        s = s.where(and_(v.c.serial == c1.where(self.versions.c.node == v.c.node),

                         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).

        # XXX: 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)])

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

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

        if before != inf:

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

        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 version_create(self, node, hash, size, source, muser, uuid, 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, source=source,

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

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

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

        return serial, mtime

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

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

           Return a list with its properties:

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

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

        """

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

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

                    v.c.size, v.c.source, v.c.mtime,

                    v.c.muser, v.c.uuid, v.c.cluster])

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

            self.versions.c.node == node)

        if before != inf:

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

        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_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, source, mtime, muser, uuid, cluster).

        """

        v = self.versions.alias()

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

                    v.c.size, v.c.source, v.c.mtime,

                    v.c.muser, v.c.uuid, 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_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()

        return hash

    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()

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

        if before != inf:

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

        s = s.where(v.c.serial == filtered.where(self.versions.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(a.c.serial == v.c.serial)

        s = s.where(a.c.domain == domain)

        s = s.where(n.c.node == v.c.node)

        conj = []

        for x in pathq:

            conj.append(n.c.path.like(self.escape_like(x) + '%', escape='\\'))

        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=[]):

        """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