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Last active Dec 14, 2015
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Using API's on Google App Engine

Demo and code

Missing presentable (non-internal) implementation atm. Maybe on later Pyvo's:

>>> from __future__ import demo
... ImportError: n/a atm

Hints

  1. Run sync on background. Use either:
  • Task Push Queues

    • Use deferred Tasks for simple implementation to start with.

    • Runs up to 10 minutes, then raises google.appengine.runtime import DeadlineExceededError.

      • Wrap the task, catch the exception and reschedule it with current state (fast).
      • Keep separated from built-in on-error retries.
  • Dynamic Backends

  1. Raise urlfetch default deadline (5s):
  • On GAE instance decorate google.appengine.api.urlfetch.fetch()

    • insert custom deadline either as a 6th positional argument, or a keyword one
  • Alternate (official) path would be to hook urlfetch calls,

    apiproxy_stub_map.apiproxy.GetPreCallHooks().Append('urlfetch default deadline', hook_method, 'urlfetch')
    

    but request.set_deadline() has no effect here at GAE instances (works on GAE SDK dev server).

  1. Avoid application instances being killed and restarted because of RAM exhaustion.
  • Disable ndb caching, if you use ndb to store the retrieved objects:

    ndb.put_multi(changes, use_cache=False, use_memcache=False)
    
  • Disable Google Data lib debug logs:

    client.http_client.debug = False
    
  • Limit batch sizes if you receive errors:

    • Happened on 128MB instances with syncing batches of 999 document changes, lowering to 500 solved that, we even pushed that down to 250 on live site.

    • It can even help you to optimize the performance. Do the tests.

      • Size: 999 items, Request: 7-10 sec, Storing: 30-45 sec
      • Size: 250 items, Request: 1 sec, Storing: 5 sec
  1. Limits:
  • Urlfetch free quota: 657k / day

    • Witch batch size 250 it's 164m synced items daily.
    • When performing at 40 items per second and one task instance, you need to set the queue to process 47 tasks in parallel to run at max troughput.
    • With paid apps you get default limit: 45m / day
  1. Use ETags if synchronizing possibly updated objects, like Google Apps user profiles via Contacts API
  • Store ETag with saved objects. On synchronization add new objects and update those with newer ETag.
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