sharded-counters/simplecounter.py

   1 # Copyright 2008 Google Inc.
   2 #
   3 # Licensed under the Apache License, Version 2.0 (the "License");
   4 # you may not use this file except in compliance with the License.
   5 # You may obtain a copy of the License at
   6 #
   7 #     http://www.apache.org/licenses/LICENSE-2.0
   8 #
   9 # Unless required by applicable law or agreed to in writing, software
  10 # distributed under the License is distributed on an "AS IS" BASIS,
  11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 # See the License for the specific language governing permissions and
  13 # limitations under the License.
  14 #
  15
  16 from google.appengine.ext import db
  17 import random
  18
  19 class SimpleCounterShard(db.Model):
  20   """Shards for the counter"""
  21   count = db.IntegerProperty(required=True, default=0)
  22
  23 NUM_SHARDS = 20
  24
  25 def get_count():
  26   """Retrieve the value for a given sharded counter."""
  27   total = 0
  28   for counter in SimpleCounterShard.all():
  29     total += counter.count
  30   return total
  31
  32 def increment():
  33   """Increment the value for a given sharded counter."""
  34   def txn():
  35     index = random.randint(0, NUM_SHARDS - 1)
  36     shard_name = "shard" + str(index)
  37     counter = SimpleCounterShard.get_by_key_name(shard_name)
  38     if counter is None:
  39       counter = SimpleCounterShard(key_name=shard_name)
  40     counter.count += 1
  41     counter.put()
  42   db.run_in_transaction(txn)
  43
  44