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#!/usr/bin/env python
# Copyright 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.
# This script shows an example "request init listener" which can be registered to track certain request metrics
# for a session. In this case we're just accumulating total request and error counts, as well as some statistics
# about the encoded request size. Note that the counts would be available using the internal 'metrics' tracking --
# this is just demonstrating a way to track a few custom attributes.
from cassandra.cluster import Cluster
from greplin import scales
import pprint
pp = pprint.PrettyPrinter(indent=2)
class RequestAnalyzer(object):
"""
Class used to track request and error counts for a Session.
Also computes statistics on encoded request size.
"""
requests = scales.PmfStat('request size')
errors = scales.IntStat('errors')
def __init__(self, session):
scales.init(self, '/cassandra')
# each instance will be registered with a session, and receive a callback for each request generated
session.add_request_init_listener(self.on_request)
def on_request(self, rf):
# This callback is invoked each time a request is created, on the thread creating the request.
# We can use this to count events, or add callbacks
rf.add_callbacks(self.on_success, self.on_error, callback_args=(rf,), errback_args=(rf,))
def on_success(self, _, response_future):
# future callback on a successful request; just record the size
self.requests.addValue(response_future.request_encoded_size)
def on_error(self, _, response_future):
# future callback for failed; record size and increment errors
self.requests.addValue(response_future.request_encoded_size)
self.errors += 1
def __str__(self):
# just extracting request count from the size stats (which are recorded on all requests)
request_sizes = dict(self.requests)
count = request_sizes.pop('count')
return "%d requests (%d errors)\nRequest size statistics:\n%s" % (count, self.errors, pp.pformat(request_sizes))
# connect a session
session = Cluster().connect()
# attach a listener to this session
ra = RequestAnalyzer(session)
session.execute("SELECT release_version FROM system.local")
session.execute("SELECT release_version FROM system.local")
print(ra)
# 2 requests (0 errors)
# Request size statistics:
# { '75percentile': 74,
# '95percentile': 74,
# '98percentile': 74,
# '999percentile': 74,
# '99percentile': 74,
# 'max': 74,
# 'mean': 74.0,
# 'median': 74.0,
# 'min': 74,
# 'stddev': 0.0}
try:
# intentional error to show that count increase
session.execute("syntax err")
except Exception as e:
pass
print()
print(ra) # note: the counts are updated, but the stats are not because scales only updates every 20s
# 3 requests (1 errors)
# Request size statistics:
# { '75percentile': 74,
# '95percentile': 74,
# '98percentile': 74,
# '999percentile': 74,
# '99percentile': 74,
# 'max': 74,
# 'mean': 74.0,
# 'median': 74.0,
# 'min': 74,
# 'stddev': 0.0}
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