To avoid any confusion about terminology used, the number of clients that can be attached and subscribed to a channel is unlimited. See the channel pub/sub documentation for more info on attaching and subscribing without limits.
This article addresses limits in regards to the number of members that can be present on a channel. See the presence documentation for more info on using presence, and find out why presence limits exist on channels. For a complete list of all limits that may apply to your account, please see connection, message or rate limits on an account.
In order to understand what happens if you exceed the number of members present on a channel, it's easier if we talk through a likely scenario:
- You have a free account which has a hard limit of 50 members present on a channel.
- 25 users each establish a connection, attach to a channel, register their presence, and also listen for presence events i.e. when users enter or leave a channel. At this point, you have 25 members present on the channel (so have 25 left).
- Another 200 new people then attach to the channel, but don't register for presence, but they want to know who is present so subscribe for presence events too. At this point, you still only have 25 members present, and the 200 listeners do not count towards your allocation of 50 on a channel.
- 30 more users then attach and attempt to register their presence. The first 25 will succeed in attaching and entering the channel. The next person will attach to the channel, but when they attempt to enter, their enter operation will fail and they will be presented with an error message indicating the limit of 50 members has been met.
Therefore, you should bear in mind that when we apply our channel presence limits, the limit is applied only when users enter the channel, and the outcome is binary i.e. they are permitted to be present or rejected. At no point are the presence events discarded or lost if the limit is hit. Also, the number of subscribers for presence has no bearing on the limits for a channel.