SegmentMetadataQuery: Retain segment id when merging, if possible.

This is helpful on realtime nodes, where two analyses from two different hydrants
are merged together but they are actually from the same segment.

processing/src/main/java/io/druid/query/metadata/SegmentMetadataQueryQueryToolChest.java

@@ -329,8 +329,16 @@ public class SegmentMetadataQueryQueryToolChest extends QueryToolChest<SegmentAn
       }
     }
 
+    final String mergedId;
+
+    if (arg1.getId() != null && arg2.getId() != null && arg1.getId().equals(arg2.getId())) {
+      mergedId = arg1.getId();
+    } else {
+      mergedId = "merged";
+    }
+
     return new SegmentAnalysis(
-        "merged",
+        mergedId,
         newIntervals,
         columns,
         arg1.getSize() + arg2.getSize(),

processing/src/test/java/io/druid/query/metadata/SegmentMetadataQueryTest.java

@@ -75,23 +75,27 @@ public class SegmentMetadataQueryTest
 
   @SuppressWarnings("unchecked")
   public static QueryRunner makeMMappedQueryRunner(
+      String segmentId,
       QueryRunnerFactory factory
   )
   {
     return QueryRunnerTestHelper.makeQueryRunner(
         factory,
-        new QueryableIndexSegment(QueryRunnerTestHelper.segmentId, TestIndex.getMMappedTestIndex())
+        segmentId,
+        new QueryableIndexSegment(segmentId, TestIndex.getMMappedTestIndex())
     );
   }
 
   @SuppressWarnings("unchecked")
   public static QueryRunner makeIncrementalIndexQueryRunner(
+      String segmentId,
       QueryRunnerFactory factory
   )
   {
     return QueryRunnerTestHelper.makeQueryRunner(
         factory,
-        new IncrementalIndexSegment(TestIndex.getIncrementalTestIndex(), QueryRunnerTestHelper.segmentId)
+        segmentId,
+        new IncrementalIndexSegment(TestIndex.getIncrementalTestIndex(), segmentId)
     );
   }
 
@@ -99,30 +103,36 @@ public class SegmentMetadataQueryTest
   private final QueryRunner runner2;
   private final boolean mmap1;
   private final boolean mmap2;
+  private final boolean differentIds;
   private final SegmentMetadataQuery testQuery;
   private final SegmentAnalysis expectedSegmentAnalysis1;
   private final SegmentAnalysis expectedSegmentAnalysis2;
 
-  @Parameterized.Parameters(name = "mmap1 = {0}, mmap2 = {1}")
+  @Parameterized.Parameters(name = "mmap1 = {0}, mmap2 = {1}, differentIds = {2}")
   public static Collection<Object[]> constructorFeeder()
   {
     return ImmutableList.of(
-        new Object[]{true, true},
-        new Object[]{true, false},
-        new Object[]{false, true},
-        new Object[]{false, false}
+        new Object[]{true, true, false},
+        new Object[]{true, false, false},
+        new Object[]{false, true, false},
+        new Object[]{false, false, false},
+        new Object[]{false, false, true}
     );
   }
 
   public SegmentMetadataQueryTest(
       boolean mmap1,
-      boolean mmap2
+      boolean mmap2,
+      boolean differentIds
   )
   {
-    this.runner1 = mmap1 ? makeMMappedQueryRunner(FACTORY) : makeIncrementalIndexQueryRunner(FACTORY);
-    this.runner2 = mmap2 ? makeMMappedQueryRunner(FACTORY) : makeIncrementalIndexQueryRunner(FACTORY);
+    final String id1 = differentIds ? "testSegment1" : "testSegment";
+    final String id2 = differentIds ? "testSegment2" : "testSegment";
+    this.runner1 = mmap1 ? makeMMappedQueryRunner(id1, FACTORY) : makeIncrementalIndexQueryRunner(id1, FACTORY);
+    this.runner2 = mmap2 ? makeMMappedQueryRunner(id2, FACTORY) : makeIncrementalIndexQueryRunner(id2, FACTORY);
     this.mmap1 = mmap1;
     this.mmap2 = mmap2;
+    this.differentIds = differentIds;
     testQuery = Druids.newSegmentMetadataQueryBuilder()
                       .dataSource("testing")
                       .intervals("2013/2014")
@@ -132,7 +142,7 @@ public class SegmentMetadataQueryTest
                       .build();
 
     expectedSegmentAnalysis1 = new SegmentAnalysis(
-        "testSegment",
+        id1,
         ImmutableList.of(
             new Interval("2011-01-12T00:00:00.000Z/2011-04-15T00:00:00.001Z")
         ),
@@ -166,7 +176,7 @@ public class SegmentMetadataQueryTest
         null
     );
     expectedSegmentAnalysis2 = new SegmentAnalysis(
-        "testSegment",
+        id2,
         ImmutableList.of(
             new Interval("2011-01-12T00:00:00.000Z/2011-04-15T00:00:00.001Z")
         ),
@@ -217,7 +227,7 @@ public class SegmentMetadataQueryTest
   public void testSegmentMetadataQueryWithHasMultipleValuesMerge()
   {
     SegmentAnalysis mergedSegmentAnalysis = new SegmentAnalysis(
-        "merged",
+        differentIds ? "merged" : "testSegment",
         null,
         ImmutableMap.of(
             "placement",
@@ -279,7 +289,7 @@ public class SegmentMetadataQueryTest
   public void testSegmentMetadataQueryWithComplexColumnMerge()
   {
     SegmentAnalysis mergedSegmentAnalysis = new SegmentAnalysis(
-        "merged",
+        differentIds ? "merged" : "testSegment",
         null,
         ImmutableMap.of(
             "placement",
@@ -341,7 +351,7 @@ public class SegmentMetadataQueryTest
   public void testSegmentMetadataQueryWithDefaultAnalysisMerge()
   {
     SegmentAnalysis mergedSegmentAnalysis = new SegmentAnalysis(
-        "merged",
+        differentIds ? "merged" : "testSegment",
         ImmutableList.of(expectedSegmentAnalysis1.getIntervals().get(0)),
         ImmutableMap.of(
             "__time",
@@ -405,7 +415,7 @@ public class SegmentMetadataQueryTest
   public void testSegmentMetadataQueryWithNoAnalysisTypesMerge()
   {
     SegmentAnalysis mergedSegmentAnalysis = new SegmentAnalysis(
-        "merged",
+        differentIds ? "merged" : "testSegment",
         null,
         ImmutableMap.of(
             "placement",
@@ -463,7 +473,7 @@ public class SegmentMetadataQueryTest
       expectedAggregators.put(agg.getName(), agg.getCombiningFactory());
     }
     SegmentAnalysis mergedSegmentAnalysis = new SegmentAnalysis(
-        "merged",
+        differentIds ? "merged" : "testSegment",
         null,
         ImmutableMap.of(
             "placement",