fix ordering for partitions with same start time, fixes #796

Partitions with same start time may produce results out of order,
           especially in the presence of data gaps.

Results for those segments must be re-ordered prior to being merged

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

@@ -25,7 +25,6 @@ import com.google.common.base.Function;
 import com.google.common.base.Supplier;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.Iterables;
 import com.google.common.collect.Iterators;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
@@ -261,14 +260,22 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
                 Ordering.natural().onResultOf(Pair.<DateTime, Sequence<T>>lhsFn())
             );
 
-            final Sequence<Sequence<T>> seq = Sequences.simple(
+            final List<Sequence<T>> orderedSequences = Lists.newLinkedList();
-                Iterables.transform(listOfSequences, Pair.<DateTime, Sequence<T>>rhsFn())
+            DateTime unorderedStart = null;
-            );
+            List<Sequence<T>> unordered = Lists.newLinkedList();
-            if (strategy == null) {
+            for (Pair<DateTime, Sequence<T>> sequencePair : listOfSequences) {
-              return toolChest.mergeSequences(seq);
+              if (unorderedStart != null && unorderedStart.getMillis() != sequencePair.lhs.getMillis()) {
-            } else {
+                orderedSequences.add(toolChest.mergeSequencesUnordered(Sequences.simple(unordered)));
-              return strategy.mergeSequences(seq);
+                unordered = Lists.newLinkedList();
+              }
+              unorderedStart = sequencePair.lhs;
+              unordered.add(sequencePair.rhs);
             }
+            if(!unordered.isEmpty()) {
+              orderedSequences.add(toolChest.mergeSequencesUnordered(Sequences.simple(unordered)));
+            }
+
+            return toolChest.mergeSequences(Sequences.simple(orderedSequences));
           }
 
           private void addSequencesFromCache(ArrayList<Pair<DateTime, Sequence<T>>> listOfSequences)
@@ -332,7 +339,9 @@ public class CachingClusteredClient<T> implements QueryRunner<T>
               if (!server.isAssignable() || !populateCache || isBySegment) {
                 resultSeqToAdd = clientQueryable.run(query.withQuerySegmentSpec(segmentSpec));
               } else {
-                resultSeqToAdd = toolChest.mergeSequences(
+                // this could be more efficient, since we only need to reorder results
+                // for batches of segments with the same segment start time.
+                resultSeqToAdd = toolChest.mergeSequencesUnordered(
                     Sequences.map(
                         clientQueryable.run(rewrittenQuery.withQuerySegmentSpec(segmentSpec)),
                         new Function<Object, Sequence<T>>()

server/src/test/java/io/druid/client/CachingClusteredClientTest.java

@@ -309,6 +309,63 @@ public class CachingClusteredClientTest
     );
   }
 
+  @Test
+  public void testTimeseriesMergingOutOfOrderPartitions() throws Exception
+  {
+    final Druids.TimeseriesQueryBuilder builder = Druids.newTimeseriesQueryBuilder()
+                                                        .dataSource(DATA_SOURCE)
+                                                        .intervals(SEG_SPEC)
+                                                        .filters(DIM_FILTER)
+                                                        .granularity(GRANULARITY)
+                                                        .aggregators(AGGS)
+                                                        .postAggregators(POST_AGGS)
+                                                        .context(CONTEXT);
+
+    QueryRunner runner = new FinalizeResultsQueryRunner(client, new TimeseriesQueryQueryToolChest(new QueryConfig()));
+
+    testQueryCaching(
+        runner,
+        builder.build(),
+        new Interval("2011-01-05/2011-01-10"),
+        makeTimeResults(
+            new DateTime("2011-01-05T02"), 80, 100,
+            new DateTime("2011-01-06T02"), 420, 520,
+            new DateTime("2011-01-07T02"), 12, 2194,
+            new DateTime("2011-01-08T02"), 59, 201,
+            new DateTime("2011-01-09T02"), 181, 52
+        ),
+        new Interval("2011-01-05/2011-01-10"),
+        makeTimeResults(
+            new DateTime("2011-01-05T00"), 85, 102,
+            new DateTime("2011-01-06T00"), 412, 521,
+            new DateTime("2011-01-07T00"), 122, 21894,
+            new DateTime("2011-01-08T00"), 5, 20,
+            new DateTime("2011-01-09T00"), 18, 521
+        )
+    );
+
+    TestHelper.assertExpectedResults(
+        makeRenamedTimeResults(
+            new DateTime("2011-01-05T00"), 85, 102,
+            new DateTime("2011-01-05T02"), 80, 100,
+            new DateTime("2011-01-06T00"), 412, 521,
+            new DateTime("2011-01-06T02"), 420, 520,
+            new DateTime("2011-01-07T00"), 122, 21894,
+            new DateTime("2011-01-07T02"), 12, 2194,
+            new DateTime("2011-01-08T00"), 5, 20,
+            new DateTime("2011-01-08T02"), 59, 201,
+            new DateTime("2011-01-09T00"), 18, 521,
+            new DateTime("2011-01-09T02"), 181, 52
+        ),
+        runner.run(
+            builder.intervals("2011-01-05/2011-01-10")
+                   .aggregators(RENAMED_AGGS)
+                   .postAggregators(RENAMED_POST_AGGS)
+                   .build()
+        )
+    );
+  }
+
   @Test
   @SuppressWarnings("unchecked")
   public void testTimeseriesCachingTimeZone() throws Exception