'-ERR max number of clients reached' should be treated as bad connection

[dlee-libo]

When the Redis reaches its max clients, it will send back this error: '-ERR max number of clients reached' and close the connection immediately. So this connection can not be reused anyhow.

Expected Behavior

the connection should be treated as a bad connection and closed.

Current Behavior

the current implementation won't treat the connection as a bad connection and will put it back into the pool. Even though later send command read reply loop will detect the connection is closed(usually through a connection reset by peer error when read reply). But we can detect this earlier actually.

Possible Solution

We can modify the isBadConn function a little bit to detect such an error earlier.

[SoulPancake]

@dlee-libo What I can see here is for this error too we have a retry logic, maybe that's why it's not closed?

[wrfly]

@SoulPancake Hi, I don't get it why it should retry since "max number of clients reached", no more connections would be created.

[ndyakov]

Hello @wrfly, let's assume a client disconnects. Then the command can be executed. Closing this.

[wrfly]

@ndyakov it's also possiable that all the clients are trying to "reconnect" to the server, which will make the situation worse.

[ndyakov]

@wrfly I agree, this will however be handled by the max number of retries, don't you think?

[wrfly]

@ndyakov Yes, the "max number of retries" will technically handle the issue, but it doesn't truly resolve the root cause—especially during peak hours when the volume of incoming requests spikes. I recall we encountered a similar problem before, and we addressed it by increasing the "max number of connections" on the server side.

[ndyakov]

@wrfly increasing the max number of connections on the server, or reducing the max in the pool, both can be used, based on the user needs and the traffic they have to handle.