fixes for bySegment queries and caching

- prevent bySegment queries from getting cached
- avoid computing cache keys if not populating or using cache
- avoid computing cache data when not populating cache

server/src/main/java/io/druid/client/CachingClusteredClient.java

@@ -151,6 +151,7 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
     contextBuilder.put("priority", priority);
 
     if (populateCache) {
+      // prevent down-stream nodes from caching results as well if we are populating the cache
       contextBuilder.put(CacheConfig.POPULATE_CACHE, false);
       contextBuilder.put("bySegment", true);
     }
@@ -186,14 +187,17 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
     }
 
     final byte[] queryCacheKey;
-    if (strategy != null) {
+
+    if ( (populateCache || useCache) // implies strategy != null
+        && !isBySegment ) // explicit bySegment queries are never cached
+    {
       queryCacheKey = strategy.computeCacheKey(query);
     } else {
       queryCacheKey = null;
     }
 
     if (queryCacheKey != null) {
-      // cache keys must preserve segment ordering, in order for shards to always be combined in the same order
+      // cachKeys map must preserve segment ordering, in order for shards to always be combined in the same order
       Map<Pair<ServerSelector, SegmentDescriptor>, Cache.NamedKey> cacheKeys = Maps.newLinkedHashMap();
       for (Pair<ServerSelector, SegmentDescriptor> segment : segments) {
         final Cache.NamedKey segmentCacheKey = CacheUtil.computeSegmentCacheKey(
@@ -223,6 +227,7 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
           segments.remove(segment);
           cachedResults.add(Pair.of(segmentQueryInterval, cachedValue));
         } else if (populateCache) {
+          // otherwise, if populating cache, add segment to list of segments to cache
           final String segmentIdentifier = segment.lhs.getSegment().getIdentifier();
           cachePopulatorMap.put(
               String.format("%s_%s", segmentIdentifier, segmentQueryInterval),
@@ -326,13 +331,15 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
               }
 
               final MultipleSpecificSegmentSpec segmentSpec = new MultipleSpecificSegmentSpec(descriptors);
-              List<Interval> intervals = segmentSpec.getIntervals();
+              final List<Interval> intervals = segmentSpec.getIntervals();
 
               final Sequence<T> resultSeqToAdd;
               if (!server.isAssignable() || !populateCache || isBySegment) { // Direct server queryable
                 if (!isBySegment) {
                   resultSeqToAdd = clientQueryable.run(query.withQuerySegmentSpec(segmentSpec), responseContext);
                 } else {
+                  // bySegment queries need to be de-serialized, see DirectDruidClient.run()
+
                   @SuppressWarnings("unchecked")
                   final Query<Result<BySegmentResultValueClass<T>>> bySegmentQuery = (Query<Result<BySegmentResultValueClass<T>>>) query;
 
@@ -386,6 +393,9 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                           public Sequence<T> apply(Result<BySegmentResultValueClass<T>> input)
                           {
                             final BySegmentResultValueClass<T> value = input.getValue();
+                            final CachePopulator cachePopulator = cachePopulatorMap.get(
+                                String.format("%s_%s", value.getSegmentId(), value.getInterval())
+                            );
 
                             final List<Object> cacheData = Lists.newLinkedList();
 
@@ -398,18 +408,21 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                                           @Override
                                           public T apply(final T input)
                                           {
-                                            cacheFutures.add(
-                                                backgroundExecutorService.submit(
-                                                    new Runnable()
-                                                    {
-                                                      @Override
-                                                      public void run()
+                                            if(cachePopulator != null) {
+                                              // only compute cache data if populating cache
+                                              cacheFutures.add(
+                                                  backgroundExecutorService.submit(
+                                                      new Runnable()
                                                       {
-                                                        cacheData.add(cacheFn.apply(input));
+                                                        @Override
+                                                        public void run()
+                                                        {
+                                                          cacheData.add(cacheFn.apply(input));
+                                                        }
                                                       }
-                                                    }
-                                                )
-                                            );
+                                                  )
+                                              );
+                                            }
                                             return input;
                                           }
                                         }
@@ -426,9 +439,6 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                                   @Override
                                   public void run()
                                   {
-                                    CachePopulator cachePopulator = cachePopulatorMap.get(
-                                        String.format("%s_%s", value.getSegmentId(), value.getInterval())
-                                    );
                                     if (cachePopulator != null) {
                                       try {
                                         Futures.allAsList(cacheFutures).get();

server/src/main/java/io/druid/client/cache/CacheConfig.java

@@ -54,6 +54,7 @@ public class CacheConfig
   {
     return useCache;
   }
+
   public int getNumBackgroundThreads(){
     return numBackgroundThreads;
   }