maytasm commented on code in PR #18568:
URL: https://github.com/apache/druid/pull/18568#discussion_r2395965656


##########
processing/src/main/java/org/apache/druid/query/scan/ScanQueryQueryToolChest.java:
##########
@@ -191,6 +198,76 @@ public Sequence<Object[]> resultsAsArrays(final ScanQuery 
query, final Sequence<
     );
   }
 
+  @Override
+  public CacheStrategy<ScanResultValue, ScanResultValue, ScanQuery> 
getCacheStrategy(
+      final ScanQuery query,
+      @Nullable final ObjectMapper objectMapper
+  )
+  {
+    return new CacheStrategy<>()
+    {
+      @Override
+      public boolean isCacheable(ScanQuery query, boolean willMergeRunners, 
boolean segmentLevel)
+      {
+        // Currently, there is no bijective mapping from ScanResultValue to 
Result<BySegmentResultValueClass<ScanResultValue>>.
+        // This means queries will fail if:
+        //   - A query is issued with bySegment:true
+        //   - Segment-level cache is enabled on the broker (in which case it 
sends bySegment queries to data nodes).
+        return !query.context().isBySegment() && (!segmentLevel || 
willMergeRunners);
+      }
+
+      @Override
+      public byte[] computeCacheKey(ScanQuery query)
+      {
+        CacheKeyBuilder builder = new CacheKeyBuilder(SCAN_QUERY)
+            .appendByte(CACHE_STRATEGY_VERSION)
+            .appendCacheable(query.getDataSource())
+            .appendCacheable(query.getVirtualColumns())
+            .appendString(query.getResultFormat().toString())
+            .appendLong(query.getScanRowsOffset())
+            .appendLong(query.getScanRowsLimit())
+            .appendCacheable(query.getFilter())
+            .appendStrings(query.getColumns() != null ? query.getColumns() : 
List.of())
+            .appendString(query.getTimeOrder().toString());
+
+        List<OrderBy> orderBys = query.getOrderBys();
+        if (orderBys != null) {
+          for (OrderBy orderBy : orderBys) {
+            builder.appendString(orderBy.getColumnName())
+                   .appendString(orderBy.getOrder().toString());
+          }
+        }
+
+        return builder.build();
+      }
+
+      @Override
+      public byte[] computeResultLevelCacheKey(ScanQuery query)
+      {
+        // Use the same key as segment-level cache no result-level 
transformations like aggregations
+        return computeCacheKey(query);
+      }
+
+      @Override
+      public TypeReference<ScanResultValue> getCacheObjectClazz()
+      {
+        return TYPE_REFERENCE;
+      }
+
+      @Override
+      public Function<ScanResultValue, ScanResultValue> 
prepareForCache(boolean isResultLevelCache)

Review Comment:
   Why are the cache for other queryType converting to Object?



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