Add javadoc and test for Granularity configs in Compaction / Auto Compaction

integration-tests/src/test/java/org/apache/druid/tests/indexer/ITCompactionTaskTest.java

@@ -110,15 +110,29 @@ public void testCompactionWithQueryGranularityInGranularitySpec() throws Excepti
       checkQueryGranularity(SEGMENT_METADATA_QUERY_RESOURCE, GranularityType.SECOND.name(), 4);
       String queryResponseTemplate = getQueryResponseTemplate(INDEX_QUERIES_RESOURCE);
       queryHelper.testQueriesFromString(queryResponseTemplate);
-      // QueryGranularity was SECOND, now we will change it to HOUR
+      // QueryGranularity was SECOND, now we will change it to HOUR (QueryGranularity changed to coarser)
       compactData(COMPACTION_TASK_WITH_GRANULARITY_SPEC, null, GranularityType.HOUR);
 
-      // The original 4 segments should be compacted into 2 new segments
+      // The original 4 segments should be compacted into 2 new segments since data only has 2 days and the compaction
+      // segmentGranularity is DAY
       checkNumberOfSegments(2);
       queryResponseTemplate = getQueryResponseTemplate(INDEX_QUERIES_HOUR_RESOURCE);
       queryHelper.testQueriesFromString(queryResponseTemplate);
       checkQueryGranularity(SEGMENT_METADATA_QUERY_RESOURCE, GranularityType.HOUR.name(), 2);
       checkCompactionIntervals(expectedIntervalAfterCompaction);
+
+      // QueryGranularity was HOUR, now we will change it to MINUTE (QueryGranularity changed to finer)
+      compactData(COMPACTION_TASK_WITH_GRANULARITY_SPEC, null, GranularityType.MINUTE);
+
+      // There will be no change in number of segments as compaction segmentGranularity is the same and data interval
+      // is the same. Since QueryGranularity is changed to finer qranularity, the data will remains the same. (data
+      // will just be bucketed to a finer qranularity but roll up will not be different
+      // i.e. 2020-10-29T05:00 will just be bucketed to 2020-10-29T05:00:00)
+      checkNumberOfSegments(2);
+      queryResponseTemplate = getQueryResponseTemplate(INDEX_QUERIES_HOUR_RESOURCE);
+      queryHelper.testQueriesFromString(queryResponseTemplate);
+      checkQueryGranularity(SEGMENT_METADATA_QUERY_RESOURCE, GranularityType.MINUTE.name(), 2);
+      checkCompactionIntervals(expectedIntervalAfterCompaction);
     }
   }
 

server/src/main/java/org/apache/druid/client/indexing/ClientCompactionTaskGranularitySpec.java

@@ -22,9 +22,20 @@
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.druid.java.util.common.granularity.Granularity;
+import org.apache.druid.segment.indexing.granularity.GranularitySpec;
 
 import java.util.Objects;
 
+/**
+ * Spec containing Granularity configs for Compaction Task.
+ * This class mimics JSON field names for fields supported in compaction task with
+ * the corresponding fields in {@link GranularitySpec}.
+ * This is done for end-user ease of use. Basically, end-user will use the same syntax / JSON structure to set
+ * Granularity configs for Compaction task as they would for any other ingestion task.
+ * Note that this class is not the same as {@link GranularitySpec}. This class simply holds Granularity configs
+ * and use it to generate index task specs (Compaction task internally creates index task).
+ * This class does not do bucketing, group events or knows how to partition data.
+ */
 public class ClientCompactionTaskGranularitySpec
 {
   private final Granularity segmentGranularity;

server/src/main/java/org/apache/druid/segment/realtime/appenderator/AppenderatorImpl.java

@@ -333,11 +333,11 @@ public AppenderatorAddResult add(
         // persistAll clears rowsCurrentlyInMemory, no need to update it.
         log.info("Flushing in-memory data to disk because %s.", String.join(",", persistReasons));
 
-        long bytesPersisted = 0L;
+        long bytesToBePersisted = 0L;
         for (Map.Entry<SegmentIdWithShardSpec, Sink> entry : sinks.entrySet()) {
           final Sink sinkEntry = entry.getValue();
           if (sinkEntry != null) {
-            bytesPersisted += sinkEntry.getBytesInMemory();
+            bytesToBePersisted += sinkEntry.getBytesInMemory();
             if (sinkEntry.swappable()) {
               // After swapping the sink, we use memory mapped segment instead. However, the memory mapped segment still consumes memory.
               // These memory mapped segments are held in memory throughout the ingestion phase and permanently add to the bytesCurrentlyInMemory
@@ -347,7 +347,7 @@ public AppenderatorAddResult add(
           }
         }
 
-        if (!skipBytesInMemoryOverheadCheck && bytesCurrentlyInMemory.get() - bytesPersisted > maxBytesTuningConfig) {
+        if (!skipBytesInMemoryOverheadCheck && bytesCurrentlyInMemory.get() - bytesToBePersisted > maxBytesTuningConfig) {
           // We are still over maxBytesTuningConfig even after persisting.
           // This means that we ran out of all available memory to ingest (due to overheads created as part of ingestion)
           final String alertMessage = StringUtils.format(

server/src/main/java/org/apache/druid/server/coordinator/UserCompactionTaskGranularityConfig.java

@@ -22,9 +22,19 @@
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import org.apache.druid.java.util.common.granularity.Granularity;
+import org.apache.druid.segment.indexing.granularity.GranularitySpec;
 
 import java.util.Objects;
 
+/**
+ * Spec containing Granularity configs for Auto Compaction.
+ * This class mimics JSON field names for fields supported in auto compaction with
+ * the corresponding fields in {@link GranularitySpec}.
+ * This is done for end-user ease of use. Basically, end-user will use the same syntax / JSON structure to set
+ * Granularity configs for Auto Compaction as they would for any other ingestion task.
+ * Note that this class is not the same as {@link GranularitySpec}. This class simply holds Granularity configs
+ * and pass it to compaction task spec. This class does not do bucketing, group events or knows how to partition data.
+ */
 public class UserCompactionTaskGranularityConfig
 {
   private final Granularity segmentGranularity;