KAFKA-6659: Improve error message if state store is not found

[perkss]

Update the exception message thrown to state about the state store not found and suggest checking store has been connected to the processor.

[perkss]

@mjsax please take a look. Thanks

[mjsax]

\cc @bbejeck @vvcephei

[mjsax]

\cc @astubbs

[astubbs]

The problem with this new message is that most DSL users won’t know what it means. Would be food to somehow cover both bases?

[perkss]

@astubbs I could change the text from explicit you to just "Please check the store has been connected to the processor." I think this would make it more generic or we use the terminology about adding state store?

[mjsax]

Maybe we can be more explicit. Something like this:

"Processor " + currentNode().name() + " has no access to StateStore " + name + " as the store is not connected to the processor."
+ " If you add stores manually via '.addStateStore()' make sure to connect the added store to the processor by providing the processor name to '.addStateStore()' or connect them via '.connectProcessorAndStateStores()'."
+ " DSL users need to provide the store name to '.process()', '.transform()', or '.transformValues()' to connect the store to the corresponding operator."
+ " If you don't add stores manually, please file a bug report at https://issues.apache.org/jira/projects/KAFKA."

[perkss]

@astubbs what do you think of @mjsax suggestion?

[mjsax]

LGTM.

Call for second review: @astubbs @guozhangwang @bbejeck @vvcephei

[bbejeck]

Thanks for the patch, LGTM

[mjsax]

If there are no further comments, I'll merge this soon.

[mjsax]

Merged to trunk.

Thanks for the patch @perkss !

[perkss]

@mjsax @bbejeck thank you!