vvcephei commented on a change in pull request #11582:
URL: https://github.com/apache/kafka/pull/11582#discussion_r771517463



##########
File path: 
streams/src/main/java/org/apache/kafka/streams/state/internals/StoreQueryUtils.java
##########
@@ -16,18 +16,78 @@
  */
 package org.apache.kafka.streams.state.internals;
 
+import org.apache.kafka.common.utils.Bytes;
 import org.apache.kafka.streams.processor.StateStore;
 import org.apache.kafka.streams.processor.StateStoreContext;
 import org.apache.kafka.streams.processor.api.RecordMetadata;
+import org.apache.kafka.streams.query.FailureReason;
+import org.apache.kafka.streams.query.KeyQuery;
 import org.apache.kafka.streams.query.Position;
 import org.apache.kafka.streams.query.PositionBound;
 import org.apache.kafka.streams.query.Query;
 import org.apache.kafka.streams.query.QueryResult;
+import org.apache.kafka.streams.state.KeyValueStore;
 
+import java.io.PrintWriter;
+import java.io.StringWriter;
 import java.util.Map;
 
+import static org.apache.kafka.common.utils.Utils.mkEntry;
+import static org.apache.kafka.common.utils.Utils.mkMap;
+
 public final class StoreQueryUtils {
 
+    /**
+     * a utility interface to facilitate stores' query dispatch logic,
+     * allowing them to generically store query execution logic as the values
+     * in a map.
+     */
+    @FunctionalInterface
+    public interface QueryHandler {
+        QueryResult<?> apply(
+            final Query<?> query,
+            final PositionBound positionBound,
+            final boolean collectExecutionInfo,
+            final StateStore store
+        );
+    }
+
+
+    @SuppressWarnings("unchecked")
+    private static final Map<Class<?>, QueryHandler> QUERY_HANDLER_MAP =
+        mkMap(
+            mkEntry(
+                PingQuery.class,

Review comment:
       Actually, the PingQuery isn't in the KIP at all. I added it (as an 
internal API) so that I could verify the stores work properly in the absence of 
any actual queries (because I implemented the framework before any real 
queries, to control the scope of the PR).
   
   Now that we have real queries, I don't think we need to keep Ping around. 
I'll remove it.




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