Hello Jonathan, At the very high-level, KSQL statements is compiled into a Kafka Streams topology for execution. And the concept "state stores" are for Kafka Streams, not for KSQL, where inside the topology for those processor nodes that need stateful processing, like Joins, one or more state stores would be associated with the nodes.
Back to your example, this KSQL statement will be compiled into a Kafka Streams that roughly looks like this: ---------- Kafka topic that defines stream "topics" --> source node --> join node (queries the "users-state" store, as generated below) --> sink node --> Kafka topic that defines stream "orders_enriched" Kafka topic that defines table "users" --> source node --> materialization node (associated with a state store, let's name it "users-state") ---------- That is, one state store will be used to materialize the table changelog stream for "users", where the other stream's record will query on. In Kafka Streams, you can query a state store following the interactive query mechanism: https://kafka.apache.org/documentation/streams/developer-guide/interactive-queries.html It is not supported in KSQL yet. Guozhang On Wed, Jul 11, 2018 at 1:41 AM, Jonathan Roy < jonathan....@caldera.com.invalid> wrote: > Hi Kafka users, > > I am very new to Kafka and more globally to stream processing, and am > trying to understand some of the concepts used by Kafka. From what I > understand, a key-value state store is created on each processor node that > performs stateful operations such as aggregations or joins. Let’s take an > example. I have an ‘orders’ stream and a ‘users’ table, and I want to > enrich the orders events with the corresponding users information, using > the KSQL CLI: > > CREATE STREAM orders_enriched AS SELECT o.id <http://o.id/>, o.article, > o.quantity, o.userId, u.name, u.address, u.email FROM orders o LEFT JOIN > users u ON o.userId = u.id <http://u.id/>; > > Where is located the state store in this case? What will it contain > exactly? Is it possible to query it from another node? > > Thanks beforehand for your help! > > Jonathan -- -- Guozhang
