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from itertools import izip_longest, repeat
import logging
from threading import Lock
from kafka.common import (
ErrorMapping, FetchRequest,
OffsetRequest, OffsetFetchRequest, OffsetCommitRequest
)
from kafka.util import (
ReentrantTimer
)
log = logging.getLogger("kafka")
AUTO_COMMIT_MSG_COUNT = 100
AUTO_COMMIT_INTERVAL = 5000
class SimpleConsumer(object):
"""
A simple consumer implementation that consumes all partitions for a topic
client: a connected KafkaClient
group: a name for this consumer, used for offset storage and must be unique
topic: the topic to consume
auto_commit: default True. Whether or not to auto commit the offsets
auto_commit_every_n: default 100. How many messages to consume before a commit
auto_commit_every_t: default 5000. How much time (in milliseconds) to wait before commit
Auto commit details:
If both auto_commit_every_n and auto_commit_every_t are set, they will reset one another
when one is triggered. These triggers simply call the commit method on this class. A
manual call to commit will also reset these triggers
"""
def __init__(self, client, group, topic, auto_commit=True,
auto_commit_every_n=AUTO_COMMIT_MSG_COUNT,
auto_commit_every_t=AUTO_COMMIT_INTERVAL):
self.client = client
self.topic = topic
self.group = group
self.client._load_metadata_for_topics(topic)
self.offsets = {}
# Variables for handling offset commits
self.commit_lock = Lock()
self.commit_timer = None
self.count_since_commit = 0
self.auto_commit = auto_commit
self.auto_commit_every_n = auto_commit_every_n
self.auto_commit_every_t = auto_commit_every_t
# Set up the auto-commit timer
if auto_commit is True and auto_commit_every_t is not None:
self.commit_timer = ReentrantTimer(auto_commit_every_t,
self._timed_commit)
self.commit_timer.start()
def get_or_init_offset_callback(resp):
if resp.error == ErrorMapping.NO_ERROR:
return resp.offset
elif resp.error == ErrorMapping.UNKNOWN_TOPIC_OR_PARTITON:
return 0
else:
raise Exception("OffsetFetchRequest for topic=%s, partition=%d failed with errorcode=%s" % (
resp.topic, resp.partition, resp.error))
# Uncomment for 0.8.1
#
#for partition in self.client.topic_partitions[topic]:
# req = OffsetFetchRequest(topic, partition)
# (offset,) = self.client.send_offset_fetch_request(group, [req],
# callback=get_or_init_offset_callback, fail_on_error=False)
# self.offsets[partition] = offset
for partition in self.client.topic_partitions[topic]:
self.offsets[partition] = 0
def seek(self, offset, whence):
"""
Alter the current offset in the consumer, similar to fseek
offset: how much to modify the offset
whence: where to modify it from
0 is relative to the earliest available offset (head)
1 is relative to the current offset
2 is relative to the latest known offset (tail)
"""
if whence == 1: # relative to current position
for partition, _offset in self.offsets.items():
self.offsets[partition] = _offset + offset
elif whence in (0, 2): # relative to beginning or end
# divide the request offset by number of partitions, distribute the remained evenly
(delta, rem) = divmod(offset, len(self.offsets))
deltas = {}
for partition, r in izip_longest(self.offsets.keys(), repeat(1, rem), fillvalue=0):
deltas[partition] = delta + r
reqs = []
for partition in self.offsets.keys():
if whence == 0:
reqs.append(OffsetRequest(self.topic, partition, -2, 1))
elif whence == 2:
reqs.append(OffsetRequest(self.topic, partition, -1, 1))
else:
pass
resps = self.client.send_offset_request(reqs)
for resp in resps:
self.offsets[resp.partition] = resp.offsets[0] + deltas[resp.partition]
else:
raise ValueError("Unexpected value for `whence`, %d" % whence)
def pending(self, partitions=[]):
"""
Gets the pending message count
partitions: list of partitions to check for, default is to check all
"""
if len(partitions) == 0:
partitions = self.offsets.keys()
total = 0
reqs = []
for partition in partitions:
reqs.append(OffsetRequest(self.topic, partition, -1, 1))
resps = self.client.send_offset_request(reqs)
for resp in resps:
partition = resp.partition
pending = resp.offsets[0]
offset = self.offsets[partition]
total += pending - offset - (1 if offset > 0 else 0)
return total
def _timed_commit(self):
"""
Commit offsets as part of timer
"""
self.commit(include_current_offset=False)
# Once the commit is done, start the timer again
self.commit_timer.start()
def commit(self, partitions=[], include_current_offset=True):
"""
Commit offsets for this consumer
partitions: list of partitions to commit, default is to commit all of them
"""
# short circuit if nothing happened
if self.count_since_commit == 0:
return
with self.commit_lock:
reqs = []
if len(partitions) == 0: # commit all partitions
partitions = self.offsets.keys()
for partition in partitions:
if include_current_offset is True:
offset = self.offsets[partition] + 1
else:
offset = self.offsets[partition]
log.debug("Commit offset %d in SimpleConsumer: "
"group=%s, topic=%s, partition=%s" %
(offset, self.group, self.topic, partition))
reqs.append(OffsetCommitRequest(self.topic, partition,
offset, None))
resps = self.client.send_offset_commit_request(self.group, reqs)
for resp in resps:
assert resp.error == 0
self.count_since_commit = 0
def __iter__(self):
"""
Create an iterate per partition. Iterate through them calling next() until they are
all exhausted.
"""
iters = {}
for partition, offset in self.offsets.items():
iters[partition] = self.__iter_partition__(partition, offset)
if len(iters) == 0:
return
while True:
if len(iters) == 0:
break
for partition, it in iters.items():
try:
yield it.next()
except StopIteration:
log.debug("Done iterating over partition %s" % partition)
del iters[partition]
continue # skip auto-commit since we didn't yield anything
# auto commit logic
self.count_since_commit += 1
if self.auto_commit is True:
if self.auto_commit_every_n is not None and self.count_since_commit > self.auto_commit_every_n:
if self.commit_timer is not None:
self.commit_timer.stop()
self.commit()
self.commit_timer.start()
else:
self.commit()
def __iter_partition__(self, partition, offset):
"""
Iterate over the messages in a partition. Create a FetchRequest to get back
a batch of messages, yield them one at a time. After a batch is exhausted,
start a new batch unless we've reached the end of ths partition.
"""
while True:
req = FetchRequest(self.topic, partition, offset, 1024) # TODO configure fetch size
(resp,) = self.client.send_fetch_request([req])
assert resp.topic == self.topic
assert resp.partition == partition
next_offset = None
for message in resp.messages:
next_offset = message.offset
self.offsets[partition] = message.offset
yield message
if next_offset is None:
break
else:
offset = next_offset + 1
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