SELECTs from engine=Kafka

Question

What will happen, if we would run SELECT query from working Kafka table with MV attached? Would data showed in SELECT query appear later in MV destination table?

Answer

  1. Most likely SELECT query would show nothing.
  2. If you lucky enough and something would show up, those rows wouldn’t appear in MV destination table.

So it’s not recommended to run SELECT queries on working Kafka tables.

In case of debug it’s possible to use another Kafka table with different consumer_group, so it wouldn’t affect your main pipeline.

Last modified 2021.08.12 : General corrections and updates. (5969b688)