retainAckedMessages property
Indicates whether to retain acknowledged messages.
If true, then messages are not expunged from the subscription's backlog,
even if they are acknowledged, until they fall out of the
message_retention_duration window. This must be true if you would like
to [Seek to a
timestamp](https://cloud.google.com/pubsub/docs/replay-overview#seek_to_a_time)
in the past to replay previously-acknowledged messages.
Optional.
Implementation
core.bool? retainAckedMessages;