- goal of best practices: use less quota so pay less money and google have less load :-)
- free preview will always be free:
- 500Mb storage
- 2Gb bandwidth
- currently don’t allow you to pay for App Engine, but committed to charging for additional capacity by end of year
- CPU: 10-12 cents/hr
- Storage: 15-18 cents/hr
- etc.
- if double free preview, can expect about $40 / month
- currently support Python, but others will be coming
- they know but they’re not telling
- looking to provide large upload/download support, but not sure how yet
- current limit is 1Mb for file and response size
- currently no SLA
- working with Cloud Status to monitor — http://www.cloudstatus.com/
- Google don’t put adverts on app engine apps
- they will make more money on search :-)
- They also don’t look at your data
storing data
- keys are limited to 500 bytes
- can’t change the ID or key_name
- transactional read & write with get() and put()
counters
- Bigtable doesn’t know size of tables — that would be O(N)
Model.count()is a big transaction- could create an entity that maintains the count
- frequent updates can cause high contention
- fundamental limitation of distributed systems
- instead, create sharded counters
- randomly break counters into shards using a counter config to hold references to all shards
- when want to count, ask counter config to add them all together
- use
get_or_insert()to fetch or create atomically
memcache
- when you add things to memcache, you define the staleness that you’re happy with
- use memcache to reduce storage and processing requirements
Q & A
can use urlfetch to request data from your own servers
- all app engine requests must complete in 10secs
- and urlfetch must complete faster (4secs?)
- you get an HTTP error that you can handle if the request times out
Is there a profiling tool for app engine or Bigtable?
- not aware of anything
- difficult to see return on implementing memcache
What logging is there?
- there is a log; it logs requests and you can write to it
SLA…?
- the quota will be calculated using a moving average, not a total for the month
- however, the aim is that if you get slashdotted you’ll stay up
Parallel processes?
- don’t allow threading
- don’t allow direct file write access
- have limited file read access
- can’t access direct network sockets
- however, there is a mapreduce implementation for app engine written by a Googler — http://code.google.com/p/httpmr/?
email restrictions?
- can send from any developer of app or from a logged in user
- restricted to sending one per second
when will Django 1.0 will be included?
- some people have uploaded django 1.0 themselves
- django 1.0 includes a C library, so this must be worked around at the moment
three big languages internally in Google: Python, Java & C++
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