async def _get_routing_table(self):
""" Update the routing table from the first router able to provide
valid routing information.
"""
# copied because it can be modified
existing_routers = list(self._routing_table.routers)
has_tried_initial_routers = False
if self._missing_writer:
has_tried_initial_routers = True
rt = await self._get_routing_table_from(self._initial_routers)
if rt:
return rt
rt = await self._get_routing_table_from(*existing_routers)
if rt:
return rt
if not has_tried_initial_routers and self._initial_routers not in existing_routers:
rt = await self._get_routing_table_from(self._initial_routers)
if rt:
return rt
# None of the routers have been successful, so just fail
log.error("Unable to retrieve routing information")
raise Neo4jAvailabilityError("Unable to retrieve routing information")
async def _select_pool(self, readonly=False):
""" Selects the pool with the fewest in-use connections.
"""
await self._ensure_routing_table_is_fresh(readonly=readonly)
if readonly:
addresses = self._routing_table.readers
else:
addresses = self._routing_table.writers
pools = [pool for address, pool in self._pools.items() if address in addresses]
pools_by_usage = {}
for pool in pools:
pools_by_usage.setdefault(pool.in_use, []).append(pool)
if not pools_by_usage:
raise Neo4jAvailabilityError("No {} service currently "
"available".format("read" if readonly else "write"))
return choice(pools_by_usage[min(pools_by_usage)])
def _select_address(self, access_mode=None):
from neo4j import READ_ACCESS
""" Selects the address with the fewest in-use connections.
"""
self.ensure_routing_table_is_fresh(access_mode)
if access_mode == READ_ACCESS:
addresses = self.routing_table.readers
else:
addresses = self.routing_table.writers
addresses_by_usage = {}
for address in addresses:
addresses_by_usage.setdefault(
self.in_use_connection_count(address), []).append(address)
if not addresses_by_usage:
raise Neo4jAvailabilityError(
"No {} service currently available".format(
"read" if access_mode == READ_ACCESS else "write"))
return choice(addresses_by_usage[min(addresses_by_usage)])
def on_write_failure(self, address):
raise Neo4jAvailabilityError(
"No write service available for pool {}".format(self))