Optimization: Dumping JSON from a Streaming API to Mongo

问题

Background: I have a python module set up to grab JSON objects from a streaming API and store them (bulk insert of 25 at a time) in MongoDB using pymongo. For comparison, I also have a bash command to curl from the same streaming API and pipe it to mongoimport. Both these approaches store data in separate collections.

Periodically, I monitor the count() of the collections to check how they fare.

So far, I see the python module lagging by about 1000 JSON objects behind the curl | mongoimport approach.

Problem: How can I optimize my python module to be ~ in sync with the curl | mongoimport?

I cannot use tweetstream since I am not using the Twitter API but a 3rd party streaming service.

Could someone please help me out here?

Python module:

class StreamReader:
    def __init__(self):
        try:
            self.buff = ""
            self.tweet = ""
            self.chunk_count = 0
            self.tweet_list = []
            self.string_buffer = cStringIO.StringIO()
            self.mongo = pymongo.Connection(DB_HOST)
            self.db = self.mongo[DB_NAME]
            self.raw_tweets = self.db["raw_tweets_gnip"]
            self.conn = pycurl.Curl()
            self.conn.setopt(pycurl.ENCODING, 'gzip')
            self.conn.setopt(pycurl.URL, STREAM_URL)
            self.conn.setopt(pycurl.USERPWD, AUTH)
            self.conn.setopt(pycurl.WRITEFUNCTION, self.handle_data)
            self.conn.perform()
        except Exception as ex:
            print "error ocurred : %s" % str(ex)

    def handle_data(self, data):
        try:
            self.string_buffer = cStringIO.StringIO(data)
            for line in self.string_buffer:
                try:
                    self.tweet = json.loads(line)
                except Exception as json_ex:
                    print "JSON Exception occurred: %s" % str(json_ex)
                    continue

                if self.tweet:
                    try:
                        self.tweet_list.append(self.tweet)
                        self.chunk_count += 1
                        if self.chunk_count % 1000 == 0
                            self.raw_tweets.insert(self.tweet_list)
                            self.chunk_count = 0
                            self.tweet_list = []

                    except Exception as insert_ex:
                        print "Error inserting tweet: %s" % str(insert_ex)
                        continue
        except Exception as ex:
            print "Exception occurred: %s" % str(ex)
            print repr(self.buff)

    def __del__(self):
        self.string_buffer.close()

Thanks for reading.

回答1:

Originally there was a bug in your code.

                if self.chunk_count % 50 == 0
                    self.raw_tweets.insert(self.tweet_list)
                    self.chunk_count = 0

You reset the chunk_count but you don't reset the tweet_list. So second time through you try to insert 100 items (50 new ones plus 50 that were already sent to DB the time before). You've fixed this, but still see a difference in performance.

The whole batch size thing turns out to be a red herring. I tried using a large file of json and loading it via python vs. loading it via mongoimport and Python was always faster (even in safe mode - see below).

Taking a closer look at your code, I realized the problem is with the fact that the streaming API is actually handing you data in chunks. You are expected to just take those chunks and put them into the database (that's what mongoimport is doing). The extra work your python is doing to split up the stream, add it to a list and then periodically send batches to Mongo is probably the difference between what I see and what you see.

Try this snippet for your handle_data()

def handle_data(self, data):
    try:
        string_buffer = StringIO(data)
        tweets = json.load(string_buffer)
    except Exception as ex:
        print "Exception occurred: %s" % str(ex)
    try:
        self.raw_tweets.insert(tweets)
    except Exception as ex:
        print "Exception occurred: %s" % str(ex)

One thing to note is that your python inserts are not running in "safe mode" - you should change that by adding an argument safe=True to your insert statement. You will then get an exception on any insert that fails and your try/catch will print the error exposing the problem.

It doesn't cost much in performance either - I'm currently running a test and after about five minutes, the sizes of two collections are 14120 14113.

回答2:

Got rid of the StringIO library. As the WRITEFUNCTION callback handle_data, in this case, gets invoked for every line, just load the JSON directly. Sometimes, however, there could be two JSON objects contained in data. I am sorry, I can't post the curl command that I use as it contains our credentials. But, as I said, this is a general issue applicable to any streaming API.

def handle_data(self, buf): 
    try:
        self.tweet = json.loads(buf)
    except Exception as json_ex:
        self.data_list = buf.split('\r\n')
        for data in self.data_list:
            self.tweet_list.append(json.loads(data))    

来源：https://stackoverflow.com/questions/10855518/optimization-dumping-json-from-a-streaming-api-to-mongo