ERR XReadGroup is cancelled

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Symptom

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.

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Diagnosis

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.

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Solution

Acknowledge the consumed messages via XACK from the list of the associated group and consumer.