- Ensure that rollback instant is always created before the next commit instant.

This especially affects IncrementalPull for MOR tables since we can end up pulling in
  log blocks for uncommitted data
- Ensure that generated commit instants are 1 second apart

hudi-client/src/main/java/org/apache/hudi/HoodieWriteClient.java

@@ -135,7 +135,7 @@ public class HoodieWriteClient<T extends HoodieRecordPayload> extends AbstractHo
   }
 
   public static SparkConf registerClasses(SparkConf conf) {
-    conf.registerKryoClasses(new Class[] {HoodieWriteConfig.class, HoodieRecord.class, HoodieKey.class});
+    conf.registerKryoClasses(new Class[]{HoodieWriteConfig.class, HoodieRecord.class, HoodieKey.class});
     return conf;
   }
 
@@ -953,16 +953,26 @@ public class HoodieWriteClient<T extends HoodieRecordPayload> extends AbstractHo
    * Provides a new commit time for a write operation (insert/update)
    */
   public String startCommit() {
-    String commitTime = HoodieActiveTimeline.createNewCommitTime();
+    // NOTE : Need to ensure that rollback is done before a new commit is started
-    startCommitWithTime(commitTime);
-    return commitTime;
-  }
-
-  public void startCommitWithTime(String instantTime) {
     if (rollbackInFlight) {
       // Only rollback inflight commit/delta-commits. Do not touch compaction commits
       rollbackInflightCommits();
     }
+    String commitTime = HoodieActiveTimeline.createNewCommitTime();
+    startCommit(commitTime);
+    return commitTime;
+  }
+
+  public void startCommitWithTime(String instantTime) {
+    // NOTE : Need to ensure that rollback is done before a new commit is started
+    if (rollbackInFlight) {
+      // Only rollback inflight commit/delta-commits. Do not touch compaction commits
+      rollbackInflightCommits();
+    }
+    startCommit(instantTime);
+  }
+
+  private void startCommit(String instantTime) {
     logger.info("Generate a new instant time " + instantTime);
     HoodieTableMetaClient metaClient = createMetaClient(true);
     // if there are pending compactions, their instantTime must not be greater than that of this instant time
@@ -978,7 +988,6 @@ public class HoodieWriteClient<T extends HoodieRecordPayload> extends AbstractHo
     activeTimeline.createInflight(new HoodieInstant(true, commitActionType, instantTime));
   }
 
-
   /**
    * Schedules a new compaction instant
    */

hudi-common/src/main/java/org/apache/hudi/common/table/timeline/HoodieActiveTimeline.java

@@ -28,6 +28,7 @@ import java.util.Arrays;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 import java.util.stream.Stream;
 import org.apache.hadoop.fs.FSDataInputStream;
@@ -66,12 +67,21 @@ public class HoodieActiveTimeline extends HoodieDefaultTimeline {
 
   private static final transient Logger log = LogManager.getLogger(HoodieActiveTimeline.class);
   protected HoodieTableMetaClient metaClient;
+  private static AtomicReference<String> lastInstantTime = new AtomicReference<>(String.valueOf(Integer.MIN_VALUE));
 
   /**
    * Returns next commit time in the {@link #COMMIT_FORMATTER} format.
+   * Ensures each commit time is atleast 1 second apart since we create COMMIT times at second granularity
    */
   public static String createNewCommitTime() {
-    return HoodieActiveTimeline.COMMIT_FORMATTER.format(new Date());
+    lastInstantTime.updateAndGet((oldVal) -> {
+      String newCommitTime = null;
+      do {
+        newCommitTime = HoodieActiveTimeline.COMMIT_FORMATTER.format(new Date());
+      } while (HoodieTimeline.compareTimestamps(newCommitTime, oldVal, LESSER_OR_EQUAL));
+      return newCommitTime;
+    });
+    return lastInstantTime.get();
   }
 
   protected HoodieActiveTimeline(HoodieTableMetaClient metaClient, Set<String> includedExtensions) {
@@ -99,7 +109,8 @@ public class HoodieActiveTimeline extends HoodieDefaultTimeline {
    *
    * @deprecated
    */
-  public HoodieActiveTimeline() {}
+  public HoodieActiveTimeline() {
+  }
 
   /**
    * This method is only used when this object is deserialized in a spark executor.
@@ -112,7 +123,6 @@ public class HoodieActiveTimeline extends HoodieDefaultTimeline {
 
   /**
    * Get all instants (commits, delta commits) that produce new data, in the active timeline *
-   *
    */
   public HoodieTimeline getCommitsTimeline() {
     return getTimelineOfActions(Sets.newHashSet(COMMIT_ACTION, DELTA_COMMIT_ACTION));
@@ -258,7 +268,9 @@ public class HoodieActiveTimeline extends HoodieDefaultTimeline {
     return readDataFromPath(detailPath);
   }
 
-  /** BEGIN - COMPACTION RELATED META-DATA MANAGEMENT **/
+  /**
+   * BEGIN - COMPACTION RELATED META-DATA MANAGEMENT
+   **/
 
   public Option<byte[]> getInstantAuxiliaryDetails(HoodieInstant instant) {
     Path detailPath = new Path(metaClient.getMetaAuxiliaryPath(), instant.getFileName());