suvodeep-pyne commented on code in PR #19740:
URL: https://github.com/apache/pinot/pull/19740#discussion_r4321267273


##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/realtime/PinotLLCRealtimeSegmentManager.java:
##########
@@ -806,11 +820,63 @@ private SegmentZKMetadata 
updateSegmentZKMetadataToCommitting(String realtimeTab
     return segmentZKMetadata;
   }
 
+  /// Returns `true` if a pauseless commit start can resume an earlier attempt 
that moved the segment to COMMITTING
+  /// with the same end offset, but did not complete, e.g. because the 
IdealState update failed or the controller
+  /// stopped. Steps 2 and 3 are idempotent for the same segment and end 
offset: the resumed attempt uses the new
+  /// segment created by an earlier attempt if any (see 
findNewSegmentOfEarlierAttempt), new segment ZK metadata is only
+  /// created if absent, and the IdealState update is skipped when it is 
already applied. Once the max segment
+  /// completion time is exceeded, RealtimeSegmentValidationManager repairs 
the segment instead.
+  private boolean isCommitStartResumable(String realtimeTableName,
+      CommittingSegmentDescriptor committingSegmentDescriptor) {
+    String segmentName = committingSegmentDescriptor.getSegmentName();
+    SegmentZKMetadata segmentZKMetadata = 
getSegmentZKMetadata(realtimeTableName, segmentName);
+    if (segmentZKMetadata.getStatus() != Status.COMMITTING) {
+      return false;
+    }
+    String endOffset = segmentZKMetadata.getEndOffset();
+    if (!committingSegmentDescriptor.getNextOffset().equals(endOffset)) {
+      LOGGER.warn("Cannot resume commit start for segment: {} with end offset: 
{}, segment is COMMITTING with end "
+          + "offset: {}", segmentName, 
committingSegmentDescriptor.getNextOffset(), endOffset);
+      return false;
+    }
+    if (isExceededMaxSegmentCompletionTime(realtimeTableName, segmentName, 
getCurrentTimeMs())) {
+      LOGGER.warn("Cannot resume commit start for segment: {} after the max 
segment completion time", segmentName);
+      return false;
+    }
+    LOGGER.info("Resuming commit start for segment: {} which is COMMITTING 
with end offset: {}", segmentName,
+        endOffset);
+    return true;
+  }
+
+  /// Returns the new segment created by an earlier attempt of a resumed 
commit start, or `null` if there is none.
+  ///
+  /// The new segment is named after its creation time with minute 
granularity, and is created between step 1 of the
+  /// first attempt (the modification time of the committing segment ZK 
metadata) and now, which is bounded by the max
+  /// segment completion time. Probes the names for every minute in between, 
with one minute of slack on both ends for
+  /// clock differences between controllers and ZK.
+  @Nullable
+  private String findNewSegmentOfEarlierAttempt(String realtimeTableName, 
LLCSegmentName committingLLCSegment) {
+    Stat stat = new Stat();
+    getSegmentZKMetadata(realtimeTableName, 
committingLLCSegment.getSegmentName(), stat);
+    long oneMinuteMs = TimeUnit.MINUTES.toMillis(1);
+    long startTimeMs = Math.floorDiv(stat.getMtime(), oneMinuteMs) * 
oneMinuteMs - oneMinuteMs;

Review Comment:
   Added a note on this invariant to the Javadoc of 
`findNewSegmentOfEarlierAttempt` in 40ea6e1470.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/realtime/PinotLLCRealtimeSegmentManager.java:
##########
@@ -1398,6 +1564,11 @@ private Map<Integer, SegmentZKMetadata> 
getLatestSegmentZKMetadataMap(String rea
         } else {
           if (llcSegmentName.getSequenceNumber() > 
latestLLCSegmentName.getSequenceNumber()) {
             return llcSegmentName;
+          } else if (llcSegmentName.getSequenceNumber() == 
latestLLCSegmentName.getSequenceNumber()) {
+            LOGGER.warn("Found segments: {} and {} with the same sequence 
number in partition: {} of table: {}",
+                latestLLCSegmentName.getSegmentName(), segmentName, 
partitionId, realtimeTableName);
+            return 
!instanceStatesMap.containsKey(latestLLCSegmentName.getSegmentName())

Review Comment:
   Added a sentence to the Javadoc in 40ea6e1470: if none of them is in the 
IdealState, whichever is listed first is the latest one.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/realtime/PinotLLCRealtimeSegmentManager.java:
##########
@@ -1517,6 +1695,20 @@ IdealState updateIdealStateOnSegmentCompletion(String 
realtimeTableName, String
         false);
   }
 
+  /// Returns `true` if the IdealState already reflects the completion of the 
committing segment, i.e. all its replicas
+  /// are ONLINE, and the new consuming segment (if one is expected) is 
present.
+  @VisibleForTesting
+  static boolean isSegmentCompletionApplied(IdealState idealState, String 
committingSegmentName,
+      @Nullable String newSegmentName) {
+    Map<String, String> committingSegmentInstanceStateMap = 
idealState.getInstanceStateMap(committingSegmentName);
+    if (committingSegmentInstanceStateMap == null || 
committingSegmentInstanceStateMap.isEmpty()
+        || 
!committingSegmentInstanceStateMap.values().stream().allMatch(SegmentStateModel.ONLINE::equals))
 {

Review Comment:
   Right, that is intended. It keeps the existing behavior for a committing 
segment that is not ONLINE on every replica.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/realtime/PinotLLCRealtimeSegmentManager.java:
##########
@@ -806,11 +820,63 @@ private SegmentZKMetadata 
updateSegmentZKMetadataToCommitting(String realtimeTab
     return segmentZKMetadata;
   }
 
+  /// Returns `true` if a pauseless commit start can resume an earlier attempt 
that moved the segment to COMMITTING
+  /// with the same end offset, but did not complete, e.g. because the 
IdealState update failed or the controller
+  /// stopped. Steps 2 and 3 are idempotent for the same segment and end 
offset: the resumed attempt uses the new
+  /// segment created by an earlier attempt if any (see 
findNewSegmentOfEarlierAttempt), new segment ZK metadata is only
+  /// created if absent, and the IdealState update is skipped when it is 
already applied. Once the max segment
+  /// completion time is exceeded, RealtimeSegmentValidationManager repairs 
the segment instead.
+  private boolean isCommitStartResumable(String realtimeTableName,
+      CommittingSegmentDescriptor committingSegmentDescriptor) {
+    String segmentName = committingSegmentDescriptor.getSegmentName();
+    SegmentZKMetadata segmentZKMetadata = 
getSegmentZKMetadata(realtimeTableName, segmentName);
+    if (segmentZKMetadata.getStatus() != Status.COMMITTING) {
+      return false;
+    }
+    String endOffset = segmentZKMetadata.getEndOffset();
+    if (!committingSegmentDescriptor.getNextOffset().equals(endOffset)) {
+      LOGGER.warn("Cannot resume commit start for segment: {} with end offset: 
{}, segment is COMMITTING with end "
+          + "offset: {}", segmentName, 
committingSegmentDescriptor.getNextOffset(), endOffset);
+      return false;
+    }
+    if (isExceededMaxSegmentCompletionTime(realtimeTableName, segmentName, 
getCurrentTimeMs())) {
+      LOGGER.warn("Cannot resume commit start for segment: {} after the max 
segment completion time", segmentName);
+      return false;
+    }
+    LOGGER.info("Resuming commit start for segment: {} which is COMMITTING 
with end offset: {}", segmentName,
+        endOffset);
+    return true;
+  }
+
+  /// Returns the new segment created by an earlier attempt of a resumed 
commit start, or `null` if there is none.
+  ///
+  /// The new segment is named after its creation time with minute 
granularity, and is created between step 1 of the
+  /// first attempt (the modification time of the committing segment ZK 
metadata) and now, which is bounded by the max
+  /// segment completion time. Probes the names for every minute in between, 
with one minute of slack on both ends for
+  /// clock differences between controllers and ZK.
+  @Nullable
+  private String findNewSegmentOfEarlierAttempt(String realtimeTableName, 
LLCSegmentName committingLLCSegment) {

Review Comment:
   It is one extra ZK read on the resume path only, which runs after a failed 
commit start. Passing the `Stat` through would add a parameter to 
`createNewSegmentMetadata`, which the regular commit path shares, so I kept the 
read local.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/realtime/PinotLLCRealtimeSegmentManager.java:
##########
@@ -806,11 +820,63 @@ private SegmentZKMetadata 
updateSegmentZKMetadataToCommitting(String realtimeTab
     return segmentZKMetadata;
   }
 
+  /// Returns `true` if a pauseless commit start can resume an earlier attempt 
that moved the segment to COMMITTING
+  /// with the same end offset, but did not complete, e.g. because the 
IdealState update failed or the controller
+  /// stopped. Steps 2 and 3 are idempotent for the same segment and end 
offset: the resumed attempt uses the new
+  /// segment created by an earlier attempt if any (see 
findNewSegmentOfEarlierAttempt), new segment ZK metadata is only
+  /// created if absent, and the IdealState update is skipped when it is 
already applied. Once the max segment
+  /// completion time is exceeded, RealtimeSegmentValidationManager repairs 
the segment instead.
+  private boolean isCommitStartResumable(String realtimeTableName,
+      CommittingSegmentDescriptor committingSegmentDescriptor) {
+    String segmentName = committingSegmentDescriptor.getSegmentName();
+    SegmentZKMetadata segmentZKMetadata = 
getSegmentZKMetadata(realtimeTableName, segmentName);
+    if (segmentZKMetadata.getStatus() != Status.COMMITTING) {
+      return false;
+    }
+    String endOffset = segmentZKMetadata.getEndOffset();
+    if (!committingSegmentDescriptor.getNextOffset().equals(endOffset)) {
+      LOGGER.warn("Cannot resume commit start for segment: {} with end offset: 
{}, segment is COMMITTING with end "
+          + "offset: {}", segmentName, 
committingSegmentDescriptor.getNextOffset(), endOffset);
+      return false;
+    }
+    if (isExceededMaxSegmentCompletionTime(realtimeTableName, segmentName, 
getCurrentTimeMs())) {
+      LOGGER.warn("Cannot resume commit start for segment: {} after the max 
segment completion time", segmentName);
+      return false;
+    }
+    LOGGER.info("Resuming commit start for segment: {} which is COMMITTING 
with end offset: {}", segmentName,
+        endOffset);
+    return true;
+  }
+
+  /// Returns the new segment created by an earlier attempt of a resumed 
commit start, or `null` if there is none.
+  ///
+  /// The new segment is named after its creation time with minute 
granularity, and is created between step 1 of the
+  /// first attempt (the modification time of the committing segment ZK 
metadata) and now, which is bounded by the max
+  /// segment completion time. Probes the names for every minute in between, 
with one minute of slack on both ends for
+  /// clock differences between controllers and ZK.
+  @Nullable
+  private String findNewSegmentOfEarlierAttempt(String realtimeTableName, 
LLCSegmentName committingLLCSegment) {
+    Stat stat = new Stat();
+    getSegmentZKMetadata(realtimeTableName, 
committingLLCSegment.getSegmentName(), stat);

Review Comment:
   Same as https://github.com/apache/pinot/pull/19740#discussion_r4278274406: 
it is a single read on the resume-only path, so I kept it local rather than 
adding a parameter to the shared `createNewSegmentMetadata`.



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