Boredom comes to those Boredom comes to those who waitwho waitAsynchronous calls to Datastore PlusAsynchronous calls to Datastore Plus

What you should knowWhat you should know

•toplevels/taskletstoplevels/tasklets

•futuresfutures

•yield (you are going to build lots of generators)yield (you are going to build lots of generators)

•you'll use yield instead of return (most of the time) you'll use yield instead of return (most of the time)

•don't think about threadsdon't think about threads

•..._async..._async

•the query API changesthe query API changes

•an insanely great use for comparator overridesan insanely great use for comparator overrides

How it used to be doneHow it used to be done

class Fact(model.Model):class Fact(model.Model): text = model.TextProperty()    text = model.TextProperty()            rating = model.FloatProperty(default = 400.)rating = model.FloatProperty(default = 400.) random_index = model.ComputedProperty(    random_index = model.ComputedProperty(   

                lambda self : random.randint(0,lambda self : random.randint(0,                         sys.maxint))sys.maxint))

(...)(...)

for i in range(10):for i in range(10): Fact(text = 'Fact %d' % i).put()    Fact(text = 'Fact %d' % i).put()   

Digression: _ah/statsDigression: _ah/stats

•A good way to understand the performance of your appsA good way to understand the performance of your apps

•If you are doing something wrong, it'll become obviousIf you are doing something wrong, it'll become obvious

Easy to enable on app.yaml:Easy to enable on app.yaml:

builtins:builtins:(...)(...)- appstats: on- appstats: on

How the first example How the first example behaves locallybehaves locally

… … and on the serverand on the server

The asynchronous wayThe asynchronous way

futures = []futures = []for i in range(10):for i in range(10): futures.append(Fact(text = 'Fact %d' % \    futures.append(Fact(text = 'Fact %d' % \   

                i).put_async())i).put_async())[ f.get_result() for f in futures ][ f.get_result() for f in futures ]

  

Gives the opportunity to aggregate puts into one large datastore Gives the opportunity to aggregate puts into one large datastore operation (and we don't have to worry about it)operation (and we don't have to worry about it)

_ah/stats_ah/stats

On the serverOn the server

Better: toplevel/taskletBetter: toplevel/tasklet

@context.toplevel@context.toplevel

(decorating something – usually a request handler – that will call the following tasklet)(decorating something – usually a request handler – that will call the following tasklet)

  

@tasklets.tasklet@tasklets.tasklet

def init_facts()def init_facts()

    futures = []futures = [] for i in range(10):  for i in range(10):  futures.append(Fact(text = 'Fact %d' % \    futures.append(Fact(text = 'Fact %d' % \   

            i).put_async())i).put_async()) yield futures  yield futures 

  

Yield allows the toplevel event loop to manage other generators making asynchronous callsYield allows the toplevel event loop to manage other generators making asynchronous calls

… … even bettereven better

@context.toplevel@context.toplevel

(decorating your handler)(decorating your handler)

@tasklets.tasklet@tasklets.tasklet

def init_facts()def init_facts()

Futures = []Futures = []

for i in range(10):for i in range(10):

futures.append(Fact(text = 'Fact %d' \futures.append(Fact(text = 'Fact %d' \

% i).put_async())% i).put_async())

raise tasklets.Return(futures)raise tasklets.Return(futures)

Because it's considered polite to raise things when a generator has nothing else to generateBecause it's considered polite to raise things when a generator has nothing else to generate

ab -n 10000 -c 50 (synchronous)ab -n 10000 -c 50 (synchronous)

Connection Times (ms)Connection Times (ms) min mean[+/-sd] median max    min mean[+/-sd] median max    Connect: 140 159 69.1 145 976Connect: 140 159 69.1 145 976Processing: 338 7408 5452.2 6231 46247  Processing: 338 7408 5452.2 6231 46247  Waiting: 338 7407 5452.2 6230 46247  Waiting: 338 7407 5452.2 6230 46247  Total: Total: 482 7567 5442.4 6377 46401  482 7567 5442.4 6377 46401  

Percentage of the requests served within a certain time (ms)Percentage of the requests served within a certain time (ms)     50% 6377  50% 6377   66% 8540     66% 8540     75% 10131    75% 10131    80% 11068    80% 11068    90% 13419    90% 13419    95% 16077    95% 16077    98% 23883    98% 23883    99% 30173    99% 30173   100% 46401 (longest request)   100% 46401 (longest request)   

ab -n 10000 -c 50 (asynchronous)ab -n 10000 -c 50 (asynchronous)

Connection Times (ms)Connection Times (ms) min mean[+/-sd] median max  min mean[+/-sd] median max  Connect: 140 669 1375.6 151 21193Connect: 140 669 1375.6 151 21193Processing: 189 338 300.0 256 15320Processing: 189 338 300.0 256 15320Waiting: 189 335 243.7 255 4143Waiting: 189 335 243.7 255 4143Total: Total: 332 1007 1407.6 438 21450332 1007 1407.6 438 21450

Percentage of the requests served within a certain time (ms)Percentage of the requests served within a certain time (ms) 50% 438      50% 438      66% 565      66% 565          75% 732   75% 732    80% 1272     80% 1272     90% 3372     90% 3372     95% 3456     95% 3456     98% 3762     98% 3762     99% 9366     99% 9366    100% 21450 (longest request)   100% 21450 (longest request)   

What's the difference?What's the difference?

WrongWrong

for f in Fact.query():for f in Fact.query():

f.rating = random.normalvariate(400, 20)f.rating = random.normalvariate(400, 20)

f.put() f.put()

Why?Why?

Right: map_asyncRight: map_async

@tasklets.tasklet@tasklets.taskletdef randomize_rating(f):def randomize_rating(f): f.rating = random.normalvariate(400, 20)  f.rating = random.normalvariate(400, 20)  raise tasklets.Return(f.put_async())  raise tasklets.Return(f.put_async()) 

@context.toplevel@context.topleveldef randomize_all():def randomize_all(): Fact.query().map_async(randomize_rating)  Fact.query().map_async(randomize_rating) 

Right: map_asyncRight: map_async

What else should I know?What else should I know?

•context and its event loopcontext and its event loop

•cachescaches

•new datatypesnew datatypes

•new names for old typesnew names for old types

•repeated = True repeated = True

•StructuredProperty, LocalStructuredPropertyStructuredProperty, LocalStructuredProperty

•compresscompress

•shorter response times and more efficient instance usageshorter response times and more efficient instance usage

Where do I find it?Where do I find it?

•official buildsofficial builds

•http://code.google.com/p/appengine-ndb-experiment/downloads/listhttp://code.google.com/p/appengine-ndb-experiment/downloads/list

•"Bleeding" edge "Bleeding" edge

•hg clone https://code.google.com/p/appengine-ndb-experiment/hg clone https://code.google.com/p/appengine-ndb-experiment/

•version 0.7 released yesterdayversion 0.7 released yesterday

To know moreTo know more

•documentation:documentation:

http://code.google.com/p/appengine-ndb-experiment/http://code.google.com/p/appengine-ndb-experiment/

•Google group:Google group:

http://groups.google.com/group/appengine-ndb-discuss/http://groups.google.com/group/appengine-ndb-discuss/

ThanksThanks

Thanks to the fine people who hang out on the appengine-ndb-discuss Thanks to the fine people who hang out on the appengine-ndb-discuss group, in special to Guido and Vladimir, whose suggestions pointed me on group, in special to Guido and Vladimir, whose suggestions pointed me on the right direction.the right direction.