Python redis subscribe can not get all datas?

I am using python to get datas from redis and then parser it to kafka. It works well in most situations.

But when I use python to simulate build the data to redis, or there was a fast put-in datas in queuen, I can't get all the data.

Here is my code about redis producer to simulate build 20000 datas to redis:

rc = redis.Redis(host='127.0.0.1', port=6379)
rc.ping()
ps = rc.pubsub()
ps.subscribe('bdwaf')
r_str = "--8198b507-A--\n[22/Jun/2017:14:13:19 +0800]ucTcxcMcicAcAcAcicAcAcAm 192.168.1.189 50054 127.0.0.1 80\n"
for i in range(0, 20000):
    rc.publish('bdwaf', r_str)

and the redis consumer also the kafka producer is:

rc = redis.Redis(host='localhost', port=6379)
rc.ping()
ps = rc.pubsub()
ps.subscribe('bdwaf')
num = 0
for item in ps.listen():
     if item['type'] == 'message':
         num += 1
         a.parser(item['data'])
         print num

It only prints out like 4000 datas.

If I comment the a.parser(item['data']), it can print out all datas num.

Or wirte sleep(0.001) in the redis producer, it can print out all datas num too.

What is wrong with my code?

I assume you are using redis-py.

The documentation refers to listen as older version of the lib... Maybe you should use another method for message reading. For example with a callback

p = r.pubsub()

def my_handler(message):
    print 'MY HANDLER: ', message['data']
    if item['type'] == 'message':
         num += 1
         a.parser(item['data'])
         print num

p.subscribe('bdwaf', my_handler)
# read the subscribe confirmation message
p.get_message()

Edit:

It is possible that your redis server is running out of memory when you publish 20000 messages at once. Try increasing redis memory in redis.conf file