def _lookup(lookup_arg, key, hint):
"""Given a table name and a key return the servers of the Group where the
shard of this table can be found
:param lookup_arg: table name for "LOCAL" lookups
Shard Mapping ID for "GLOBAL" lookups.
:param key: The key value that needs to be looked up
:param hint: A hint indicates if the query is LOCAL or GLOBAL
:return: The servers of the Group that contains the range in which the
key belongs.
"""
VALID_HINTS = ('LOCAL', 'GLOBAL')
hint = hint.upper()
if hint not in VALID_HINTS:
raise _errors.ShardingError(INVALID_SHARDING_HINT)
group = None
#Perform the lookup for the group contaning the lookup data.
if hint == "GLOBAL":
#Fetch the shard mapping object. In the case of GLOBAL lookups
#the shard mapping ID is passed directly. In the case of "LOCAL"
#lookups it is the table name that is passed.
shard_mapping = ShardMapping.fetch_by_id(lookup_arg)
if shard_mapping is None:
raise _errors.ShardingError(
SHARD_MAPPING_NOT_FOUND % (lookup_arg, )
)
#GLOBAL lookups. There can be only one global group, hence using
#shard_mapping[0] is safe.
group = Group.fetch(shard_mapping[0].global_group)
else:
shard_mapping = ShardMapping.fetch(lookup_arg)
if shard_mapping is None:
raise _errors.ShardingError(TABLE_NAME_NOT_FOUND % (lookup_arg, ))
sharding_specification =\
SHARDING_SPECIFICATION_HANDLER[shard_mapping.type_name].\
lookup(key, shard_mapping.shard_mapping_id, shard_mapping.type_name)
if sharding_specification is None:
raise _errors.ShardingError(INVALID_SHARDING_KEY % (key, ))
shard = Shards.fetch(str(sharding_specification.shard_id))
if shard.state == "DISABLED":
raise _errors.ShardingError(SHARD_NOT_ENABLED)
#group cannot be None since there is a foreign key on the group_id.
#An exception will be thrown nevertheless.
group = Group.fetch(shard.group_id)
if group is None:
raise _errors.ShardingError(SHARD_LOCATION_NOT_FOUND)
ret = []
#An empty list will be returned if the registered group has not
#servers.
for server in group.servers():
ret.append([str(server.uuid), server.address,
group.master == server.uuid])
return ret
def verify_and_fetch_shard(shard_id):
"""Find out if the shard_id exists and return the sharding specification for
it. If it does not exist throw an exception.
:param shard_id: The ID for the shard whose specification needs to be
fetched.
:return: The sharding specification class representing the shard ID.
:raises: ShardingError if the shard ID is not found.
"""
#Here the underlying sharding specification might be a RANGE
#or a HASH. The type of sharding specification is obtained from the
#shard mapping.
range_sharding_spec = RangeShardingSpecification.fetch(shard_id)
if range_sharding_spec is None:
raise _errors.ShardingError(SHARD_NOT_FOUND % (shard_id, ))
#Fetch the shard mappings and use them to find the type of sharding
#scheme.
shard_mappings = ShardMapping.fetch_by_id(
range_sharding_spec.shard_mapping_id
)
if shard_mappings is None:
raise _errors.ShardingError(
SHARD_MAPPING_NOT_FOUND % (
range_sharding_spec.shard_mapping_id,
)
)
#Fetch the shard mapping definition. There is only one shard mapping
#definition associated with all of the shard mappings.
shard_mapping_defn = ShardMapping.fetch_shard_mapping_defn(
range_sharding_spec.shard_mapping_id
)
if shard_mapping_defn is None:
raise _errors.ShardingError(
SHARD_MAPPING_DEFN_NOT_FOUND % (
range_sharding_spec.shard_mapping_id,
)
)
shard = Shards.fetch(shard_id)
if shard is None:
raise _errors.ShardingError(SHARD_NOT_FOUND % (shard_id, ))
#Both of the shard_mappings retrieved will be of the same sharding
#type. Hence it is safe to use one of them to retireve the sharding type.
if shard_mappings[0].type_name == "HASH":
return HashShardingSpecification.fetch(shard_id), \
shard, shard_mappings, shard_mapping_defn
else:
return range_sharding_spec, shard, shard_mappings, shard_mapping_defn
def _lookup(lookup_arg, key, hint):
"""Given a table name and a key return the servers of the Group where the
shard of this table can be found
:param lookup_arg: table name for "LOCAL" lookups
Shard Mapping ID for "GLOBAL" lookups.
:param key: The key value that needs to be looked up
:param hint: A hint indicates if the query is LOCAL or GLOBAL
:return: The servers of the Group that contains the range in which the
key belongs.
"""
VALID_HINTS = ('LOCAL', 'GLOBAL')
hint = hint.upper()
if hint not in VALID_HINTS:
raise _errors.ShardingError(INVALID_SHARDING_HINT)
group = None
#Perform the lookup for the group contaning the lookup data.
if hint == "GLOBAL":
#Fetch the shard mapping object. In the case of GLOBAL lookups
#the shard mapping ID is passed directly. In the case of "LOCAL"
#lookups it is the table name that is passed.
shard_mapping = ShardMapping.fetch_by_id(lookup_arg)
if shard_mapping is None:
raise _errors.ShardingError(SHARD_MAPPING_NOT_FOUND %
(lookup_arg, ))
#GLOBAL lookups. There can be only one global group, hence using
#shard_mapping[0] is safe.
group_id = shard_mapping[0].global_group
else:
shard_mapping = ShardMapping.fetch(lookup_arg)
if shard_mapping is None:
raise _errors.ShardingError(TABLE_NAME_NOT_FOUND % (lookup_arg, ))
sharding_specification = \
SHARDING_SPECIFICATION_HANDLER[shard_mapping.type_name].\
lookup(key, shard_mapping.shard_mapping_id, shard_mapping.type_name)
if sharding_specification is None:
raise _errors.ShardingError(INVALID_SHARDING_KEY % (key, ))
shard = Shards.fetch(str(sharding_specification.shard_id))
if shard.state == "DISABLED":
raise _errors.ShardingError(SHARD_NOT_ENABLED)
#group cannot be None since there is a foreign key on the group_id.
#An exception will be thrown nevertheless.
group_id = shard.group_id
return ServerLookups().execute(group_id=group_id)
def verify_and_fetch_shard(shard_id):
"""Find out if the shard_id exists and return the sharding specification for
it. If it does not exist throw an exception.
:param shard_id: The ID for the shard whose specification needs to be
fetched.
:return: The sharding specification class representing the shard ID.
:raises: ShardingError if the shard ID is not found.
"""
#Here the underlying sharding specification might be a RANGE
#or a HASH. The type of sharding specification is obtained from the
#shard mapping.
range_sharding_spec = RangeShardingSpecification.fetch(shard_id)
if range_sharding_spec is None:
raise _errors.ShardingError(SHARD_NOT_FOUND % (shard_id, ))
#Fetch the shard mappings and use them to find the type of sharding
#scheme.
shard_mappings = ShardMapping.fetch_by_id(
range_sharding_spec.shard_mapping_id)
if shard_mappings is None:
raise _errors.ShardingError(SHARD_MAPPING_NOT_FOUND %
(range_sharding_spec.shard_mapping_id, ))
#Fetch the shard mapping definition. There is only one shard mapping
#definition associated with all of the shard mappings.
shard_mapping_defn = ShardMapping.fetch_shard_mapping_defn(
range_sharding_spec.shard_mapping_id)
if shard_mapping_defn is None:
raise _errors.ShardingError(SHARD_MAPPING_DEFN_NOT_FOUND %
(range_sharding_spec.shard_mapping_id, ))
shard = Shards.fetch(shard_id)
if shard is None:
raise _errors.ShardingError(SHARD_NOT_FOUND % (shard_id, ))
#Both of the shard_mappings retrieved will be of the same sharding
#type. Hence it is safe to use one of them to retireve the sharding type.
if shard_mappings[0].type_name == "HASH":
return HashShardingSpecification.fetch(shard_id), \
shard, shard_mappings, shard_mapping_defn
else:
return range_sharding_spec, shard, shard_mappings, shard_mapping_defn
