multi process with websocket have more 8,000 time wait

[xingdongzhe]

aioredis #803

and today I use Redis monitor command, found that so much to execute ZREMRANGEBYSCORE and ZRANGE

[xingdongzhe]

I fix issue with unix socket

[carltongibson]

Can you explain a little more? Thanks.

[xingdongzhe]

I use python3.6+django2.1+channel_redsi to make a chat project, channe_redis's configration are default.
when I use 16 processes, each process have 4 threads, each thread loop for 100 times to push message to frontend，that I found that there are more than 8000 time_wait connection at 127.0.0.1:6379. And i use redis monitor command found that they all are ZREMRANGEBYSCORE and ZRANGE, i think these two command are from group_send when i look deep into the channel_redis code.

anything else should i tell?

[xingdongzhe]

But when I change configuration host (localhost, 6379) to unix sock, there are only thirty time_wait connection

[carltongibson]

@xingdongzhe Very interesting thanks.

[carltongibson]

Possibly relevant to #83.

[harmv]

I managed to find out what was the root cause here. (Not sure how to fix though).

dango-channels (async_to_sycn() more specifically) does not work nice together with the connection pooling of channels_redis (#117)

Many callers of group_send() are synchronous. Django-channels/channels_redis document says you should wrap your call in async_to_sync().

Although that seems to work. (functionally that works...) it breaks the connection pooling implemented in channels_redis.

aioredis (1.3.1)/channels_redis implements connection pooling. ( on top of aioredis.create_redis_pool()) but that implementation uses a pool per event loop.
And ..... if you use async_to_sync(), a new event loop is spawed for every invocation of async_to_sync().... So when the group_send() is done... the even loop is destroyed, and so is the connection pool -> closing the socket to Redis.

This leaves you with one closed Redis socket, lingering in TIME_WAIT per invocation of group_send().....

This workaround worked for me:

# Don't use async_to_sync(), as you'll end up with thousands of TIME_WAIT sockets
loop = asyncio.get_event_loop()
task = loop.create_task(self.channel_layer.group_send(
              "chat",
              {
                  "type": "chat.message",
                  "text": text_data,
              }
          ))
loop.run_until_complete(task)

Instead of

# THIS LEAVES TIME_WAIT sockets 
async_to_sync(self.channel_layer.group_send)(
            "chat",
            {
                "type": "chat.message",
                "text": text_data,
            },
        )

Versions

python 3.7.13

channels==3.0.4
aioredis==1.3.1
channels-redis==3.4.0
django-redis==5.2.0