[KAFKA-6686] Allow reading topic as KStream and GlobalKTable

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: streams
• Assignee: Unassigned
• Reporter: Matthias J. Sax
• Created: 19/Mar/18 16:24
• Updated: 08/Mar/19 12:52

Description

Users often want to read topic multiple times, eg, as a stream and a table. For KSteam/KTable this is possible by reading the data as a KTable, disable caching on the KTable, and get a stream via toStream(). This pattern does not work for KStream/GlobalKTable though.

However, there is no need to raise an exception

Exception in thread “main” org.apache.kafka.streams.errors.TopologyException: Invalid topology: Topic source has already been registered by another source.

for this case, because the GlobalKTable is consumer by a different consumer (in contrast to KStream/KTable case for which KStream and KTable use a shared consumer). This fix should also allow to add a topic to a Topology twice; ie, one as regular and once as global-store topic.

Issue Links

• relates to: KAFKA-6687 Allow to read a topic multiple times