[Twisted-Python] Twisted tips for designing highly concurrent twisted REST API

Waqar Khan wk80333 at gmail.com
Wed Jun 26 00:48:24 MDT 2019


Hello folks,
  I recently stumbled upon twisted and was wondering if it could suit my
needs. On one hand, I want to use python but on another hand there are all
these scalability concerns with this language so, I though I would pick the
brains of the community. So.. a flask based app would look something like
this.

similar_types = ['foo', 'bar', 'baz']


def long_computation(rec_type):
     # some long computation
     return recs

@app.route('/fetch_similar_users/<user_id>'
def fetch_similar_users(user_id)
        r = json.loads(requests.get('url/to/fetch/%s'%user_id).text)
        recs = {}
        for stype in similar_types:
             recs[stype] = long_computation(rec_type)
       return recs



Now, I tried to "twistify" but it failed.

@defer.inlinecallbacks

def long_computation(rec_type):
     # some long computation
     *defer.returnValue(recs)*

@defer.inlinecallbacks
def fetch_data(user_id):
        r = yieldjson.loads(requests.get('url/to/fetch/%s'%user_id).text)
     defer.returnValue(r)


@defer.inlinecallbacks
def fetch_recs(user_id):
       data = yield fetch_data(user_id)
        recs = {}
       for stype in similar_types:
            d = defer.ToThread(fetch_data, *(stype))
           rec = yield d
           recs[stype] = rec
     defer.returnValue(recs)



I wrapped all the above in twisted render_Get method.. but then I did a
load test with locust (https://docs.locust.io/en/latest/what-is-locust.html)
framework.
It choked. As the time progressed, the response time increased.
I am guessing, things are still blocking.

Can you please help me look into the right place. Why exactly am I seeing
increase in response time as the time progresses. I am guessing things are
still working in "blocking" fashion but i thought the above should run
things in async.
Thanks
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