Your expectation and understanding how GlobalKTables work is correct. If you can reproduce the issue in an IDE, set a breakpoint in `GlobalStreamThread#pollAndUpdate()` to see if data is fetched from the brokers.
-Matthias On 6/26/19 7:09 AM, Imre Gábor wrote: > Hi, > > I am new to Kafka and observed a strange behavior. (I am using Kafka through > the spring-kafka library) > > I think I misunderstand something about the "liveness" of the data in a > global table. > I thought if I define and materialize a GlobalKTable at the startup of my > application, and messages arrive later to the underlying topic, the data in > the store are automatically updated. > i.e. if I have a method that queries the store of the table, it will see the > most up-to-date data. (With a bit of latency of course.) > However, it seems not to be the case: > > > 1. My application defines a GlobalKTable over a topic, materialized > with a name and serializers passed. > > 2. I have a business logic method that calls store() method with the > name of this global table, and tries to get a value by key. > > 3. Next, I wrote a test case, that starts the application, and I send a > message with a producer to the appropriate topic, and I expect I can get it > by its key from the global table's store. > > However, it returns null. I can see the message in the topic so it is surely > delivered. > > 4. If I iterate through the store via store.all() before calling > store.get(key), the KeyValue is there with the appropriate key! However, > store.get(key) still returns null. > > 5. I implemented hashCode and equals for my key class appropriately, so > it cannot be the problem > > 6. Also, it is a not about a small latency, because if I wait about a > minute, still cannot get the data. > > 7. If I modify my test case so that I do not send a test message > (because there is one in the topic already), and rerun the test (which starts > the application and defined the global table), > > the value is correctly found by key. (I guess the message from the topic is > read when the table is created.) > > Do you have any idea what am I missing? > > Best regards > > Gabor >
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