我在这里提供的解决方案我最终使用GAE中的mapreduce(没有缩小阶段)。如果我从头开始,我可能会使用由Drew Sears提供的解决方案。
它工作在GAE的Python 1.5.0
在应用。YAML我添加了MapReduce的处理程序:
- url: /mapreduce(/.*)?
script: $PYTHON_LIB/google/appengine/ext/mapreduce/main.py
和我的mapreduce的代码处理程序(我使用的URL/mapred_update收集由MapReduce的产生的结果):
- url: /mapred_.*
script: mapred.py
创建mapreduce.yaml用于加工车实体:
mapreduce:
- name: Color_Counter
params:
- name: done_callback
value: /mapred_update
mapper:
input_reader: google.appengine.ext.mapreduce.input_readers.DatastoreInputReader
handler: mapred.process
params:
- name: entity_kind
default: models.Car
说明:done_callback是mapreduce完成其操作后调用的url。 mapred.process是一个处理单个实体和更新计数器(它在mapred.py文件中定义)的函数。型号汽车在models.py
mapred.py定义:
from models import CarsByColor
from google.appengine.ext import db
from google.appengine.ext.mapreduce import operation as op
from google.appengine.ext.mapreduce.model import MapreduceState
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app
def process(entity):
"""Process individual Car"""
color = entity.color
if color:
yield op.counters.Increment('car_color_%s' % color)
class UpdateCounters(webapp.RequestHandler):
"""Create stats models CarsByColor based on the data
gathered by mapreduce counters"""
def post(self):
"""Called after mapreduce operation are finished"""
# Finished mapreduce job id is passed in request headers
job_id = self.request.headers['Mapreduce-Id']
state = MapreduceState.get_by_job_id(job_id)
to_put = []
counters = state.counters_map.counters
# Remove counter not needed for stats
del counters['mapper_calls']
for counter in counters.keys():
stat = CarsByColor.get_by_key_name(counter)
if not stat:
stat = CarsByColor(key_name=counter,
name=counter)
stat.value = counters[counter]
to_put.append(stat)
db.put(to_put)
self.response.headers['Content-Type'] = 'text/plain'
self.response.out.write('Updated.')
application = webapp.WSGIApplication(
[('/mapred_update', UpdateCounters)],
debug=True)
def main():
run_wsgi_app(application)
if __name__ == "__main__":
main()
有CarsByColor模式的改变定义相比,略有问题的。
您可以从url:http://yourapp/mapreduce/手动启动mapreduce作业,并希望从cron(我还没有测试过cron)。