from __future__ import absolute_import
import abc
import logging
import re
from kafka.vendor import six
from kafka.errors import IllegalStateError
from kafka.protocol.offset import OffsetResetStrategy
from kafka.structs import OffsetAndMetadata
log = logging.getLogger(__name__)
class SubscriptionState(object):
"""
A class for tracking the topics, partitions, and offsets for the consumer.
A partition is "assigned" either directly with assign_from_user() (manual
assignment) or with assign_from_subscribed() (automatic assignment from
subscription).
Once assigned, the partition is not considered "fetchable" until its initial
position has been set with seek(). Fetchable partitions track a fetch
position which is used to set the offset of the next fetch, and a consumed
position which is the last offset that has been returned to the user. You
can suspend fetching from a partition through pause() without affecting the
fetched/consumed offsets. The partition will remain unfetchable until the
resume() is used. You can also query the pause state independently with
is_paused().
Note that pause state as well as fetch/consumed positions are not preserved
when partition assignment is changed whether directly by the user or
through a group rebalance.
This class also maintains a cache of the latest commit position for each of
the assigned partitions. This is updated through committed() and can be used
to set the initial fetch position (e.g. Fetcher._reset_offset() ).
"""
_SUBSCRIPTION_EXCEPTION_MESSAGE = (
"You must choose only one way to configure your consumer:"
" (1) subscribe to specific topics by name,"
" (2) subscribe to topics matching a regex pattern,"
" (3) assign itself specific topic-partitions.")
# Taken from: https://github.com/apache/kafka/blob/39eb31feaeebfb184d98cc5d94da9148c2319d81/clients/src/main/java/org/apache/kafka/common/internals/Topic.java#L29
_MAX_NAME_LENGTH = 249
_TOPIC_LEGAL_CHARS = re.compile('^[a-zA-Z0-9._-]+$')
def __init__(self, offset_reset_strategy='earliest'):
"""Initialize a SubscriptionState instance
Keyword Arguments:
offset_reset_strategy: 'earliest' or 'latest', otherwise
exception will be raised when fetching an offset that is no
longer available. Default: 'earliest'
"""
try:
offset_reset_strategy = getattr(OffsetResetStrategy,
offset_reset_strategy.upper())
except AttributeError:
log.warning('Unrecognized offset_reset_strategy, using NONE')
offset_reset_strategy = OffsetResetStrategy.NONE
self._default_offset_reset_strategy = offset_reset_strategy
self.subscription = None # set() or None
self.subscribed_pattern = None # regex str or None
self._group_subscription = set()
self._user_assignment = set()
self.assignment = dict()
self.listener = None
# initialize to true for the consumers to fetch offset upon starting up
self.needs_fetch_committed_offsets = True
def subscribe(self, topics=(), pattern=None, listener=None):
"""Subscribe to a list of topics, or a topic regex pattern.
Partitions will be dynamically assigned via a group coordinator.
Topic subscriptions are not incremental: this list will replace the
current assignment (if there is one).
This method is incompatible with assign_from_user()
Arguments:
topics (list): List of topics for subscription.
pattern (str): Pattern to match available topics. You must provide
either topics or pattern, but not both.
listener (ConsumerRebalanceListener): Optionally include listener
callback, which will be called before and after each rebalance
operation.
As part of group management, the consumer will keep track of the
list of consumers that belong to a particular group and will
trigger a rebalance operation if one of the following events
trigger:
* Number of partitions change for any of the subscribed topics
* Topic is created or deleted
* An existing member of the consumer group dies
* A new member is added to the consumer group
When any of these events are triggered, the provided listener
will be invoked first to indicate that the consumer's assignment
has been revoked, and then again when the new assignment has
been received. Note that this listener will immediately override
any listener set in a previous call to subscribe. It is
guaranteed, however, that the partitions revoked/assigned
through this interface are from topics subscribed in this call.
"""
if self._user_assignment or (topics and pattern):
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
assert topics or pattern, 'Must provide topics or pattern'
if pattern:
log.info('Subscribing to pattern: /%s/', pattern)
self.subscription = set()
self.subscribed_pattern = re.compile(pattern)
else:
self.change_subscription(topics)
if listener and not isinstance(listener, ConsumerRebalanceListener):
raise TypeError('listener must be a ConsumerRebalanceListener')
self.listener = listener
def _ensure_valid_topic_name(self, topic):
""" Ensures that the topic name is valid according to the kafka source. """
# See Kafka Source:
# https://github.com/apache/kafka/blob/39eb31feaeebfb184d98cc5d94da9148c2319d81/clients/src/main/java/org/apache/kafka/common/internals/Topic.java
if topic is None:
raise TypeError('All topics must not be None')
if not isinstance(topic, six.string_types):
raise TypeError('All topics must be strings')
if len(topic) == 0:
raise ValueError('All topics must be non-empty strings')
if topic == '.' or topic == '..':
raise ValueError('Topic name cannot be "." or ".."')
if len(topic) > self._MAX_NAME_LENGTH:
raise ValueError('Topic name is illegal, it can\'t be longer than {0} characters, topic: "{1}"'.format(self._MAX_NAME_LENGTH, topic))
if not self._TOPIC_LEGAL_CHARS.match(topic):
raise ValueError('Topic name "{0}" is illegal, it contains a character other than ASCII alphanumerics, ".", "_" and "-"'.format(topic))
def change_subscription(self, topics):
"""Change the topic subscription.
Arguments:
topics (list of str): topics for subscription
Raises:
IllegalStateErrror: if assign_from_user has been used already
TypeError: if a topic is None or a non-str
ValueError: if a topic is an empty string or
- a topic name is '.' or '..' or
- a topic name does not consist of ASCII-characters/'-'/'_'/'.'
"""
if self._user_assignment:
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
if isinstance(topics, six.string_types):
topics = [topics]
if self.subscription == set(topics):
log.warning("subscription unchanged by change_subscription(%s)",
topics)
return
for t in topics:
self._ensure_valid_topic_name(t)
log.info('Updating subscribed topics to: %s', topics)
self.subscription = set(topics)
self._group_subscription.update(topics)
# Remove any assigned partitions which are no longer subscribed to
for tp in set(self.assignment.keys()):
if tp.topic not in self.subscription:
del self.assignment[tp]
def group_subscribe(self, topics):
"""Add topics to the current group subscription.
This is used by the group leader to ensure that it receives metadata
updates for all topics that any member of the group is subscribed to.
Arguments:
topics (list of str): topics to add to the group subscription
"""
if self._user_assignment:
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
self._group_subscription.update(topics)
def reset_group_subscription(self):
"""Reset the group's subscription to only contain topics subscribed by this consumer."""
if self._user_assignment:
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
assert self.subscription is not None, 'Subscription required'
self._group_subscription.intersection_update(self.subscription)
def assign_from_user(self, partitions):
"""Manually assign a list of TopicPartitions to this consumer.
This interface does not allow for incremental assignment and will
replace the previous assignment (if there was one).
Manual topic assignment through this method does not use the consumer's
group management functionality. As such, there will be no rebalance
operation triggered when group membership or cluster and topic metadata
change. Note that it is not possible to use both manual partition
assignment with assign() and group assignment with subscribe().
Arguments:
partitions (list of TopicPartition): assignment for this instance.
Raises:
IllegalStateError: if consumer has already called subscribe()
"""
if self.subscription is not None:
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
if self._user_assignment != set(partitions):
self._user_assignment = set(partitions)
for partition in partitions:
if partition not in self.assignment:
self._add_assigned_partition(partition)
for tp in set(self.assignment.keys()) - self._user_assignment:
del self.assignment[tp]
self.needs_fetch_committed_offsets = True
def assign_from_subscribed(self, assignments):
"""Update the assignment to the specified partitions
This method is called by the coordinator to dynamically assign
partitions based on the consumer's topic subscription. This is different
from assign_from_user() which directly sets the assignment from a
user-supplied TopicPartition list.
Arguments:
assignments (list of TopicPartition): partitions to assign to this
consumer instance.
"""
if not self.partitions_auto_assigned():
raise IllegalStateError(self._SUBSCRIPTION_EXCEPTION_MESSAGE)
for tp in assignments:
if tp.topic not in self.subscription:
raise ValueError("Assigned partition %s for non-subscribed topic." % (tp,))
# after rebalancing, we always reinitialize the assignment state
self.assignment.clear()
for tp in assignments:
self._add_assigned_partition(tp)
self.needs_fetch_committed_offsets = True
log.info("Updated partition assignment: %s", assignments)
def unsubscribe(self):
"""Clear all topic subscriptions and partition assignments"""
self.subscription = None
self._user_assignment.clear()
self.assignment.clear()
self.subscribed_pattern = None
def group_subscription(self):
"""Get the topic subscription for the group.
For the leader, this will include the union of all member subscriptions.
For followers, it is the member's subscription only.
This is used when querying topic metadata to detect metadata changes
that would require rebalancing (the leader fetches metadata for all
topics in the group so that it can do partition assignment).
Returns:
set: topics
"""
return self._group_subscription
def seek(self, partition, offset):
"""Manually specify the fetch offset for a TopicPartition.
Overrides the fetch offsets that the consumer will use on the next
poll(). If this API is invoked for the same partition more than once,
the latest offset will be used on the next poll(). Note that you may
lose data if this API is arbitrarily used in the middle of consumption,
to reset the fetch offsets.
Arguments:
partition (TopicPartition): partition for seek operation
offset (int): message offset in partition
"""
self.assignment[partition].seek(offset)
def assigned_partitions(self):
"""Return set of TopicPartitions in current assignment."""
return set(self.assignment.keys())
def paused_partitions(self):
"""Return current set of paused TopicPartitions."""
return set(partition for partition in self.assignment
if self.is_paused(partition))
def fetchable_partitions(self):
"""Return set of TopicPartitions that should be Fetched."""
fetchable = set()
for partition, state in six.iteritems(self.assignment):
if state.is_fetchable():
fetchable.add(partition)
return fetchable
def partitions_auto_assigned(self):
"""Return True unless user supplied partitions manually."""
return self.subscription is not None
def all_consumed_offsets(self):
"""Returns consumed offsets as {TopicPartition: OffsetAndMetadata}"""
all_consumed = {}
for partition, state in six.iteritems(self.assignment):
if state.has_valid_position:
all_consumed[partition] = OffsetAndMetadata(state.position, '')
return all_consumed
def need_offset_reset(self, partition, offset_reset_strategy=None):
"""Mark partition for offset reset using specified or default strategy.
Arguments:
partition (TopicPartition): partition to mark
offset_reset_strategy (OffsetResetStrategy, optional)
"""
if offset_reset_strategy is None:
offset_reset_strategy = self._default_offset_reset_strategy
self.assignment[partition].await_reset(offset_reset_strategy)
def has_default_offset_reset_policy(self):
"""Return True if default offset reset policy is Earliest or Latest"""
return self._default_offset_reset_strategy != OffsetResetStrategy.NONE
def is_offset_reset_needed(self, partition):
return self.assignment[partition].awaiting_reset
def has_all_fetch_positions(self):
for state in self.assignment.values():
if not state.has_valid_position:
return False
return True
def missing_fetch_positions(self):
missing = set()
for partition, state in six.iteritems(self.assignment):
if not state.has_valid_position:
missing.add(partition)
return missing
def is_assigned(self, partition):
return partition in self.assignment
def is_paused(self, partition):
return partition in self.assignment and self.assignment[partition].paused
def is_fetchable(self, partition):
return partition in self.assignment and self.assignment[partition].is_fetchable()
def pause(self, partition):
self.assignment[partition].pause()
def resume(self, partition):
self.assignment[partition].resume()
def _add_assigned_partition(self, partition):
self.assignment[partition] = TopicPartitionState()
class TopicPartitionState(object):
def __init__(self):
self.committed = None # last committed position
self.has_valid_position = False # whether we have valid position
self.paused = False # whether this partition has been paused by the user
self.awaiting_reset = False # whether we are awaiting reset
self.reset_strategy = None # the reset strategy if awaitingReset is set
self._position = None # offset exposed to the user
self.highwater = None
self.drop_pending_message_set = False
# The last message offset hint available from a message batch with
# magic=2 which includes deleted compacted messages
self.last_offset_from_message_batch = None
def _set_position(self, offset):
assert self.has_valid_position, 'Valid position required'
self._position = offset
def _get_position(self):
return self._position
position = property(_get_position, _set_position, None, "last position")
def await_reset(self, strategy):
self.awaiting_reset = True
self.reset_strategy = strategy
self._position = None
self.last_offset_from_message_batch = None
self.has_valid_position = False
def seek(self, offset):
self._position = offset
self.awaiting_reset = False
self.reset_strategy = None
self.has_valid_position = True
self.drop_pending_message_set = True
self.last_offset_from_message_batch = None
def pause(self):
self.paused = True
def resume(self):
self.paused = False
def is_fetchable(self):
return not self.paused and self.has_valid_position
[docs]class ConsumerRebalanceListener(object):
"""
A callback interface that the user can implement to trigger custom actions
when the set of partitions assigned to the consumer changes.
This is applicable when the consumer is having Kafka auto-manage group
membership. If the consumer's directly assign partitions, those
partitions will never be reassigned and this callback is not applicable.
When Kafka is managing the group membership, a partition re-assignment will
be triggered any time the members of the group changes or the subscription
of the members changes. This can occur when processes die, new process
instances are added or old instances come back to life after failure.
Rebalances can also be triggered by changes affecting the subscribed
topics (e.g. when then number of partitions is administratively adjusted).
There are many uses for this functionality. One common use is saving offsets
in a custom store. By saving offsets in the on_partitions_revoked(), call we
can ensure that any time partition assignment changes the offset gets saved.
Another use is flushing out any kind of cache of intermediate results the
consumer may be keeping. For example, consider a case where the consumer is
subscribed to a topic containing user page views, and the goal is to count
the number of page views per users for each five minute window. Let's say
the topic is partitioned by the user id so that all events for a particular
user will go to a single consumer instance. The consumer can keep in memory
a running tally of actions per user and only flush these out to a remote
data store when its cache gets too big. However if a partition is reassigned
it may want to automatically trigger a flush of this cache, before the new
owner takes over consumption.
This callback will execute in the user thread as part of the Consumer.poll()
whenever partition assignment changes.
It is guaranteed that all consumer processes will invoke
on_partitions_revoked() prior to any process invoking
on_partitions_assigned(). So if offsets or other state is saved in the
on_partitions_revoked() call, it should be saved by the time the process
taking over that partition has their on_partitions_assigned() callback
called to load the state.
"""
__metaclass__ = abc.ABCMeta
[docs] @abc.abstractmethod
def on_partitions_revoked(self, revoked):
"""
A callback method the user can implement to provide handling of offset
commits to a customized store on the start of a rebalance operation.
This method will be called before a rebalance operation starts and
after the consumer stops fetching data. It is recommended that offsets
should be committed in this callback to either Kafka or a custom offset
store to prevent duplicate data.
NOTE: This method is only called before rebalances. It is not called
prior to KafkaConsumer.close()
Arguments:
revoked (list of TopicPartition): the partitions that were assigned
to the consumer on the last rebalance
"""
pass
[docs] @abc.abstractmethod
def on_partitions_assigned(self, assigned):
"""
A callback method the user can implement to provide handling of
customized offsets on completion of a successful partition
re-assignment. This method will be called after an offset re-assignment
completes and before the consumer starts fetching data.
It is guaranteed that all the processes in a consumer group will execute
their on_partitions_revoked() callback before any instance executes its
on_partitions_assigned() callback.
Arguments:
assigned (list of TopicPartition): the partitions assigned to the
consumer (may include partitions that were previously assigned)
"""
pass