dnishimura commented on a change in pull request #1027: SAMZA-2046: Startpoint 
fan out implementation
URL: https://github.com/apache/samza/pull/1027#discussion_r284073610
 
 

 ##########
 File path: 
samza-core/src/main/java/org/apache/samza/startpoint/StartpointManager.java
 ##########
 @@ -20,87 +20,115 @@
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
+import java.io.IOException;
 import java.time.Duration;
 import java.time.Instant;
-import java.util.HashSet;
-import java.util.Objects;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Set;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.collections4.MapUtils;
+import org.apache.commons.lang3.ArrayUtils;
 import org.apache.samza.SamzaException;
-import org.apache.samza.config.Config;
 import org.apache.samza.container.TaskName;
 import 
org.apache.samza.coordinator.metadatastore.NamespaceAwareCoordinatorStreamStore;
-import org.apache.samza.job.model.ContainerModel;
-import org.apache.samza.job.model.JobModel;
-import org.apache.samza.job.model.TaskModel;
 import org.apache.samza.metadatastore.MetadataStore;
-import org.apache.samza.metadatastore.MetadataStoreFactory;
-import org.apache.samza.metrics.MetricsRegistry;
-import org.apache.samza.serializers.JsonSerdeV2;
 import org.apache.samza.system.SystemStreamPartition;
+import org.codehaus.jackson.map.ObjectMapper;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 
 /**
- * The StartpointManager reads and writes {@link Startpoint} to the {@link 
MetadataStore} defined by
- * the configuration task.startpoint.metadata.store.factory.
- *
- * Startpoints are keyed in the MetadataStore by two different formats:
- * 1) Only by {@link SystemStreamPartition}
- * 2) A combination of {@link SystemStreamPartition} and {@link TaskName}
+ * The StartpointManager reads and writes {@link Startpoint} to the provided 
{@link MetadataStore}
  *
  * The intention for the StartpointManager is to maintain a strong contract 
between the caller
  * and how Startpoints are stored in the underlying MetadataStore.
+ *
+ * Startpoints are written in the MetadataStore using keys of two different 
formats:
+ * 1) {@link SystemStreamPartition} only
+ * 2) A combination of {@link SystemStreamPartition} and {@link TaskName}
+ *
+ * Startpoints are then fanned out to a fan out namespace in the MetadataStore 
by the
+ * {@link org.apache.samza.clustermanager.ClusterBasedJobCoordinator} or the 
standalone
+ * {@link org.apache.samza.coordinator.JobCoordinator} upon startup and the
+ * {@link org.apache.samza.checkpoint.OffsetManager} gets the fan outs to set 
the starting offsets per task and per
+ * {@link SystemStreamPartition}. The fan outs are deleted once the offsets 
are committed to the checkpoint.
+ *
+ * The read, write and delete methods are intended for external callers.
+ * The fan out methods are intended to be used within a job coordinator.
  */
 public class StartpointManager {
-  private static final Logger LOG = 
LoggerFactory.getLogger(StartpointManager.class);
-  public static final String NAMESPACE = "samza-startpoint-v1";
+  public static final Integer VERSION = 1;
 
 Review comment:
   No, will make it private.

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