Source<EventEnvelope,NotUsed> eventsByTag(java.lang.String tag, Offset offset)
The consumer can keep track of its current position in the event stream by storing the
offset and restart the query from a given
offset after a crash/restart.
The exact meaning of the
offset depends on the journal and must be documented by the
read journal plugin. It may be a sequential id number that uniquely identifies the
position of each event within the event stream. Distributed data stores cannot easily
support those semantics and they may use a weaker meaning. For example it may be a
timestamp (taken when the event was created or stored). Timestamps are not unique and
not strictly ordered, since clocks on different machines may not be synchronized.
The returned event stream should be ordered by
offset if possible, but this can also be
difficult to fulfill for a distributed data store. The order must be documented by the
read journal plugin.
The stream is not completed when it reaches the end of the currently stored events,
but it continues to push new events when new events are persisted.
Corresponding query that is completed when it reaches the end of the currently
stored events is provided by