Source code for cassandra.pool

# Copyright 2013-2015 DataStax, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
Connection pooling and host management.
"""

import logging
import socket
import time
from threading import Lock, RLock, Condition
import weakref
try:
    from weakref import WeakSet
except ImportError:
    from cassandra.util import WeakSet  # NOQA

from cassandra import AuthenticationFailed
from cassandra.connection import ConnectionException
from cassandra.policies import HostDistance

log = logging.getLogger(__name__)


[docs]class NoConnectionsAvailable(Exception): """ All existing connections to a given host are busy, or there are no open connections. """ pass
[docs]class Host(object): """ Represents a single Cassandra node. """ address = None """ The IP address or hostname of the node. """ conviction_policy = None """ A :class:`~.ConvictionPolicy` instance for determining when this node should be marked up or down. """ is_up = None """ :const:`True` if the node is considered up, :const:`False` if it is considered down, and :const:`None` if it is not known if the node is up or down. """ _datacenter = None _rack = None _reconnection_handler = None lock = None _currently_handling_node_up = False def __init__(self, inet_address, conviction_policy_factory, datacenter=None, rack=None): if inet_address is None: raise ValueError("inet_address may not be None") if conviction_policy_factory is None: raise ValueError("conviction_policy_factory may not be None") self.address = inet_address self.conviction_policy = conviction_policy_factory(self) self.set_location_info(datacenter, rack) self.lock = RLock() @property def datacenter(self): """ The datacenter the node is in. """ return self._datacenter @property def rack(self): """ The rack the node is in. """ return self._rack def set_location_info(self, datacenter, rack): """ Sets the datacenter and rack for this node. Intended for internal use (by the control connection, which periodically checks the ring topology) only. """ self._datacenter = datacenter self._rack = rack def set_up(self): if not self.is_up: log.debug("Host %s is now marked up", self.address) self.conviction_policy.reset() self.is_up = True def set_down(self): self.is_up = False def signal_connection_failure(self, connection_exc): return self.conviction_policy.add_failure(connection_exc) def is_currently_reconnecting(self): return self._reconnection_handler is not None def get_and_set_reconnection_handler(self, new_handler): """ Atomically replaces the reconnection handler for this host. Intended for internal use only. """ with self.lock: old = self._reconnection_handler self._reconnection_handler = new_handler return old def __eq__(self, other): return self.address == other.address def __hash__(self): return hash(self.address) def __lt__(self, other): return self.address < other.address def __str__(self): return str(self.address) def __repr__(self): dc = (" %s" % (self._datacenter,)) if self._datacenter else "" return "<%s: %s%s>" % (self.__class__.__name__, self.address, dc)
class _ReconnectionHandler(object): """ Abstract class for attempting reconnections with a given schedule and scheduler. """ _cancelled = False def __init__(self, scheduler, schedule, callback, *callback_args, **callback_kwargs): self.scheduler = scheduler self.schedule = schedule self.callback = callback self.callback_args = callback_args self.callback_kwargs = callback_kwargs def start(self): if self._cancelled: log.debug("Reconnection handler was cancelled before starting") return first_delay = next(self.schedule) self.scheduler.schedule(first_delay, self.run) def run(self): if self._cancelled: return conn = None try: conn = self.try_reconnect() except Exception as exc: try: next_delay = next(self.schedule) except StopIteration: # the schedule has been exhausted next_delay = None # call on_exception for logging purposes even if next_delay is None if self.on_exception(exc, next_delay): if next_delay is None: log.warning( "Will not continue to retry reconnection attempts " "due to an exhausted retry schedule") else: self.scheduler.schedule(next_delay, self.run) else: if not self._cancelled: self.on_reconnection(conn) self.callback(*(self.callback_args), **(self.callback_kwargs)) finally: if conn: conn.close() def cancel(self): self._cancelled = True def try_reconnect(self): """ Subclasses must implement this method. It should attempt to open a new Connection and return it; if a failure occurs, an Exception should be raised. """ raise NotImplementedError() def on_reconnection(self, connection): """ Called when a new Connection is successfully opened. Nothing is done by default. """ pass def on_exception(self, exc, next_delay): """ Called when an Exception is raised when trying to connect. `exc` is the Exception that was raised and `next_delay` is the number of seconds (as a float) that the handler will wait before attempting to connect again. Subclasses should return :const:`False` if no more attempts to connection should be made, :const:`True` otherwise. The default behavior is to always retry unless the error is an :exc:`.AuthenticationFailed` instance. """ if isinstance(exc, AuthenticationFailed): return False else: return True class _HostReconnectionHandler(_ReconnectionHandler): def __init__(self, host, connection_factory, is_host_addition, on_add, on_up, *args, **kwargs): _ReconnectionHandler.__init__(self, *args, **kwargs) self.is_host_addition = is_host_addition self.on_add = on_add self.on_up = on_up self.host = host self.connection_factory = connection_factory def try_reconnect(self): return self.connection_factory() def on_reconnection(self, connection): log.info("Successful reconnection to %s, marking node up if it isn't already", self.host) if self.is_host_addition: self.on_add(self.host) else: self.on_up(self.host) def on_exception(self, exc, next_delay): if isinstance(exc, AuthenticationFailed): return False else: log.warning("Error attempting to reconnect to %s, scheduling retry in %s seconds: %s", self.host, next_delay, exc) log.debug("Reconnection error details", exc_info=True) return True class HostConnection(object): """ When using v3 of the native protocol, this is used instead of a connection pool per host (HostConnectionPool) due to the increased in-flight capacity of individual connections. """ host = None host_distance = None is_shutdown = False _session = None _connection = None _lock = None def __init__(self, host, host_distance, session): self.host = host self.host_distance = host_distance self._session = weakref.proxy(session) self._lock = Lock() if host_distance == HostDistance.IGNORED: log.debug("Not opening connection to ignored host %s", self.host) return elif host_distance == HostDistance.REMOTE and not session.cluster.connect_to_remote_hosts: log.debug("Not opening connection to remote host %s", self.host) return log.debug("Initializing connection for host %s", self.host) self._connection = session.cluster.connection_factory(host.address) if session.keyspace: self._connection.set_keyspace_blocking(session.keyspace) log.debug("Finished initializing connection for host %s", self.host) def borrow_connection(self, timeout): if self.is_shutdown: raise ConnectionException( "Pool for %s is shutdown" % (self.host,), self.host) conn = self._connection if not conn: raise NoConnectionsAvailable() with conn.lock: if conn.in_flight < conn.max_request_id: conn.in_flight += 1 return conn, conn.get_request_id() raise NoConnectionsAvailable("All request IDs are currently in use") def return_connection(self, connection): with connection.lock: connection.in_flight -= 1 if connection.is_defunct or connection.is_closed: log.debug("Defunct or closed connection (%s) returned to pool, potentially " "marking host %s as down", id(connection), self.host) is_down = self._session.cluster.signal_connection_failure( self.host, connection.last_error, is_host_addition=False) if is_down: self.shutdown() else: self._connection = None with self._lock: if self._is_replacing: return self._is_replacing = True self._session.submit(self._replace, connection) def _replace(self, connection): log.debug("Replacing connection (%s) to %s", id(connection), self.host) conn = self._session.cluster.connection_factory(self.host.address) if self._session.keyspace: conn.set_keyspace_blocking(self._session.keyspace) self._connection = conn with self._lock: self._is_replacing = False def shutdown(self): with self._lock: if self.is_shutdown: return else: self.is_shutdown = True if self._connection: self._connection.close() def _set_keyspace_for_all_conns(self, keyspace, callback): if self.is_shutdown or not self._connection: return def connection_finished_setting_keyspace(conn, error): self.return_connection(conn) errors = [] if not error else [error] callback(self, errors) self._connection.set_keyspace_async(keyspace, connection_finished_setting_keyspace) def get_connections(self): c = self._connection return [c] if c else [] def get_state(self): connection = self._connection open_count = 1 if connection and not (connection.is_closed or connection.is_defunct) else 0 in_flights = [connection.in_flight] if connection else [] return {'shutdown': self.is_shutdown, 'open_count': open_count, 'in_flights': in_flights} @property def open_count(self): connection = self._connection return 1 if connection and not (connection.is_closed or connection.is_defunct) else 0 _MAX_SIMULTANEOUS_CREATION = 1 _MIN_TRASH_INTERVAL = 10 class HostConnectionPool(object): """ Used to pool connections to a host for v1 and v2 native protocol. """ host = None host_distance = None is_shutdown = False open_count = 0 _scheduled_for_creation = 0 _next_trash_allowed_at = 0 def __init__(self, host, host_distance, session): self.host = host self.host_distance = host_distance self._session = weakref.proxy(session) self._lock = RLock() self._conn_available_condition = Condition() log.debug("Initializing new connection pool for host %s", self.host) core_conns = session.cluster.get_core_connections_per_host(host_distance) self._connections = [session.cluster.connection_factory(host.address) for i in range(core_conns)] if session.keyspace: for conn in self._connections: conn.set_keyspace_blocking(session.keyspace) self._trash = set() self._next_trash_allowed_at = time.time() self.open_count = core_conns log.debug("Finished initializing new connection pool for host %s", self.host) def borrow_connection(self, timeout): if self.is_shutdown: raise ConnectionException( "Pool for %s is shutdown" % (self.host,), self.host) conns = self._connections if not conns: # handled specially just for simpler code log.debug("Detected empty pool, opening core conns to %s", self.host) core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance) with self._lock: # we check the length of self._connections again # along with self._scheduled_for_creation while holding the lock # in case multiple threads hit this condition at the same time to_create = core_conns - (len(self._connections) + self._scheduled_for_creation) for i in range(to_create): self._scheduled_for_creation += 1 self._session.submit(self._create_new_connection) # in_flight is incremented by wait_for_conn conn = self._wait_for_conn(timeout) return conn else: # note: it would be nice to push changes to these config settings # to pools instead of doing a new lookup on every # borrow_connection() call max_reqs = self._session.cluster.get_max_requests_per_connection(self.host_distance) max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance) least_busy = min(conns, key=lambda c: c.in_flight) request_id = None # to avoid another thread closing this connection while # trashing it (through the return_connection process), hold # the connection lock from this point until we've incremented # its in_flight count need_to_wait = False with least_busy.lock: if least_busy.in_flight < least_busy.max_request_id: least_busy.in_flight += 1 request_id = least_busy.get_request_id() else: # once we release the lock, wait for another connection need_to_wait = True if need_to_wait: # wait_for_conn will increment in_flight on the conn least_busy, request_id = self._wait_for_conn(timeout) # if we have too many requests on this connection but we still # have space to open a new connection against this host, go ahead # and schedule the creation of a new connection if least_busy.in_flight >= max_reqs and len(self._connections) < max_conns: self._maybe_spawn_new_connection() return least_busy, request_id def _maybe_spawn_new_connection(self): with self._lock: if self._scheduled_for_creation >= _MAX_SIMULTANEOUS_CREATION: return if self.open_count >= self._session.cluster.get_max_connections_per_host(self.host_distance): return self._scheduled_for_creation += 1 log.debug("Submitting task for creation of new Connection to %s", self.host) self._session.submit(self._create_new_connection) def _create_new_connection(self): try: self._add_conn_if_under_max() except (ConnectionException, socket.error) as exc: log.warning("Failed to create new connection to %s: %s", self.host, exc) except Exception: log.exception("Unexpectedly failed to create new connection") finally: with self._lock: self._scheduled_for_creation -= 1 def _add_conn_if_under_max(self): max_conns = self._session.cluster.get_max_connections_per_host(self.host_distance) with self._lock: if self.is_shutdown: return False if self.open_count >= max_conns: return False self.open_count += 1 log.debug("Going to open new connection to host %s", self.host) try: conn = self._session.cluster.connection_factory(self.host.address) if self._session.keyspace: conn.set_keyspace_blocking(self._session.keyspace) self._next_trash_allowed_at = time.time() + _MIN_TRASH_INTERVAL with self._lock: new_connections = self._connections[:] + [conn] self._connections = new_connections log.debug("Added new connection (%s) to pool for host %s, signaling availablility", id(conn), self.host) self._signal_available_conn() return True except (ConnectionException, socket.error) as exc: log.warning("Failed to add new connection to pool for host %s: %s", self.host, exc) with self._lock: self.open_count -= 1 if self._session.cluster.signal_connection_failure(self.host, exc, is_host_addition=False): self.shutdown() return False except AuthenticationFailed: with self._lock: self.open_count -= 1 return False def _await_available_conn(self, timeout): with self._conn_available_condition: self._conn_available_condition.wait(timeout) def _signal_available_conn(self): with self._conn_available_condition: self._conn_available_condition.notify() def _signal_all_available_conn(self): with self._conn_available_condition: self._conn_available_condition.notify_all() def _wait_for_conn(self, timeout): start = time.time() remaining = timeout while remaining > 0: # wait on our condition for the possibility that a connection # is useable self._await_available_conn(remaining) # self.shutdown() may trigger the above Condition if self.is_shutdown: raise ConnectionException("Pool is shutdown") conns = self._connections if conns: least_busy = min(conns, key=lambda c: c.in_flight) with least_busy.lock: if least_busy.in_flight < least_busy.max_request_id: least_busy.in_flight += 1 return least_busy, least_busy.get_request_id() remaining = timeout - (time.time() - start) raise NoConnectionsAvailable() def return_connection(self, connection): with connection.lock: connection.in_flight -= 1 in_flight = connection.in_flight if connection.is_defunct or connection.is_closed: log.debug("Defunct or closed connection (%s) returned to pool, potentially " "marking host %s as down", id(connection), self.host) is_down = self._session.cluster.signal_connection_failure( self.host, connection.last_error, is_host_addition=False) if is_down: self.shutdown() else: self._replace(connection) else: if connection in self._trash: with connection.lock: if connection.in_flight == 0: with self._lock: if connection in self._trash: self._trash.remove(connection) log.debug("Closing trashed connection (%s) to %s", id(connection), self.host) connection.close() return core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance) min_reqs = self._session.cluster.get_min_requests_per_connection(self.host_distance) # we can use in_flight here without holding the connection lock # because the fact that in_flight dipped below the min at some # point is enough to start the trashing procedure if len(self._connections) > core_conns and in_flight <= min_reqs and \ time.time() >= self._next_trash_allowed_at: self._maybe_trash_connection(connection) else: self._signal_available_conn() def _maybe_trash_connection(self, connection): core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance) did_trash = False with self._lock: if connection not in self._connections: return if self.open_count > core_conns: did_trash = True self.open_count -= 1 new_connections = self._connections[:] new_connections.remove(connection) self._connections = new_connections with connection.lock: if connection.in_flight == 0: log.debug("Skipping trash and closing unused connection (%s) to %s", id(connection), self.host) connection.close() # skip adding it to the trash if we're already closing it return self._trash.add(connection) if did_trash: self._next_trash_allowed_at = time.time() + _MIN_TRASH_INTERVAL log.debug("Trashed connection (%s) to %s", id(connection), self.host) def _replace(self, connection): should_replace = False with self._lock: if connection in self._connections: new_connections = self._connections[:] new_connections.remove(connection) self._connections = new_connections self.open_count -= 1 should_replace = True if should_replace: log.debug("Replacing connection (%s) to %s", id(connection), self.host) def close_and_replace(): connection.close() self._add_conn_if_under_max() self._session.submit(close_and_replace) else: # just close it log.debug("Closing connection (%s) to %s", id(connection), self.host) connection.close() def shutdown(self): with self._lock: if self.is_shutdown: return else: self.is_shutdown = True self._signal_all_available_conn() for conn in self._connections: conn.close() self.open_count -= 1 for conn in self._trash: conn.close() def ensure_core_connections(self): if self.is_shutdown: return core_conns = self._session.cluster.get_core_connections_per_host(self.host_distance) with self._lock: to_create = core_conns - (len(self._connections) + self._scheduled_for_creation) for i in range(to_create): self._scheduled_for_creation += 1 self._session.submit(self._create_new_connection) def _set_keyspace_for_all_conns(self, keyspace, callback): """ Asynchronously sets the keyspace for all connections. When all connections have been set, `callback` will be called with two arguments: this pool, and a list of any errors that occurred. """ remaining_callbacks = set(self._connections) errors = [] if not remaining_callbacks: callback(self, errors) return def connection_finished_setting_keyspace(conn, error): self.return_connection(conn) remaining_callbacks.remove(conn) if error: errors.append(error) if not remaining_callbacks: callback(self, errors) for conn in self._connections: conn.set_keyspace_async(keyspace, connection_finished_setting_keyspace) def get_connections(self): return self._connections def get_state(self): in_flights = [c.in_flight for c in self._connections] return {'shutdown': self.is_shutdown, 'open_count': self.open_count, 'in_flights': in_flights}