[GitHub] [kafka] guozhangwang commented on a change in pull request #9293: POC: Allow bypassing the cache layer in IQ

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guozhangwang commented on a change in pull request #9293:
URL: https://github.com/apache/kafka/pull/9293#discussion_r728524198



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File path: streams/src/main/java/org/apache/kafka/streams/state/internals/MeteredKeyValueStore.java
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@@ -46,43 +46,90 @@
  * @param <K>
  * @param <V>
  */
-public class MeteredKeyValueStore<K, V>
-    extends WrappedStateStore<KeyValueStore<Bytes, byte[]>, K, V>
+public class MeteredKeyValueStore<K, V, OwnType extends MeteredKeyValueStore<K, V, OwnType>>

Review comment:
       I had a slight (? well, maybe not so slight) different idea, which assumes that we only want to have the control at the whole app level, rather than a per-store level at IQ APIs only: suppose we just have, e.g. a config on Streams that enables bypass or not for IQ, then upon calling the get/range/etc APIs at the cached layer:
   
   1) Whether the current thread is a stream thread, if yes, never bypass the cache.
   2) If not, depend on the config to decide whether bypass the cache.
   
   Doing so we then would not need the unwrap/rewrap and the template types as well. The question then goes back to: whether we would need bypassing at the per-store or global level? Personally I think it's not necessary for a finer-grained control, mainly because that in the long run with the new IQ API and the caller likely to have a totally different way to handle consistency / staleness, i.e. we would deprecate `staleStore` per store or global configs in the long run anyways, and the API calls itself is associated with a token to indicate whether allow staleness or bypass cache.




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