The client gets an exception similar to:
ReplyError: ERR XReadGroup is cancelled. Pending Entries List limit per consumer is about to be reached. Limit: 1000, Current PEL size: 90, Requested Read: 20, Key: mstream, Group: group1, Consumer: consumer1.
Pending Entries List of the stream for the consumer is full. For each consumer in a consumer group, there is a pending entries list. This list keeps the messages that are delivered to a consumer but not yet acknowledged via XACK. This list is populated via XREADGROUP.
Acknowledge the consumed messages via XACK from the list of the associated group and consumer.