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# Copyright 2008 Google 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.
#
from google.appengine.api import memcache
from google.appengine.ext import db
import random
class GeneralCounterShardConfig(db.Model):
"""Tracks the number of shards for each named counter."""
name = db.StringProperty(required=True)
num_shards = db.IntegerProperty(required=True, default=20)
class GeneralCounterShard(db.Model):
"""Shards for each named counter"""
name = db.StringProperty(required=True)
count = db.IntegerProperty(required=True, default=0)
def get_count(name):
"""Retrieve the value for a given sharded counter.
Parameters:
name - The name of the counter
"""
total = memcache.get(name)
if total is None:
total = 0
for counter in GeneralCounterShard.all().filter('name = ', name):
total += counter.count
memcache.add(name, total, 60)
return total
def increment(name):
"""Increment the value for a given sharded counter.
Parameters:
name - The name of the counter
"""
config = GeneralCounterShardConfig.get_or_insert(name, name=name)
def txn():
index = random.randint(0, config.num_shards - 1)
shard_name = name + str(index)
counter = GeneralCounterShard.get_by_key_name(shard_name)
if counter is None:
counter = GeneralCounterShard(key_name=shard_name, name=name)
counter.count += 1
counter.put()
db.run_in_transaction(txn)
# does nothing if the key does not exist
memcache.incr(name)
def increase_shards(name, num):
"""Increase the number of shards for a given sharded counter.
Will never decrease the number of shards.
Parameters:
name - The name of the counter
num - How many shards to use
"""
config = GeneralCounterShardConfig.get_or_insert(name, name=name)
def txn():
if config.num_shards < num:
config.num_shards = num
config.put()
db.run_in_transaction(txn)
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