satishd commented on code in PR #13561:
URL: https://github.com/apache/kafka/pull/13561#discussion_r1296731885


##########
core/src/main/java/kafka/log/remote/RemoteLogManager.java:
##########
@@ -696,11 +704,327 @@ public void run() {
             }
         }
 
+        public void handleLogStartOffsetUpdate(TopicPartition topicPartition, 
long remoteLogStartOffset) {
+            if (isLeader()) {
+                logger.debug("Updating {} with remoteLogStartOffset: {}", 
topicPartition, remoteLogStartOffset);
+                updateRemoteLogStartOffset.accept(topicPartition, 
remoteLogStartOffset);
+            }
+        }
+
+        class RemoteLogRetentionHandler {
+
+            private final Optional<RetentionSizeData> retentionSizeData;
+            private final Optional<RetentionTimeData> retentionTimeData;
+
+            private long remainingBreachedSize;
+
+            private OptionalLong logStartOffset = OptionalLong.empty();
+
+            public RemoteLogRetentionHandler(Optional<RetentionSizeData> 
retentionSizeData, Optional<RetentionTimeData> retentionTimeData) {
+                this.retentionSizeData = retentionSizeData;
+                this.retentionTimeData = retentionTimeData;
+                remainingBreachedSize = retentionSizeData.map(sizeData -> 
sizeData.remainingBreachedSize).orElse(0L);
+            }
+
+            private boolean 
deleteRetentionSizeBreachedSegments(RemoteLogSegmentMetadata metadata) throws 
RemoteStorageException, ExecutionException, InterruptedException {
+                if (!retentionSizeData.isPresent()) {
+                    return false;
+                }
+
+                boolean isSegmentDeleted = deleteRemoteLogSegment(metadata, x 
-> {
+                    // Assumption that segments contain size >= 0
+                    if (remainingBreachedSize > 0) {
+                        long remainingBytes = remainingBreachedSize - 
x.segmentSizeInBytes();
+                        if (remainingBytes >= 0) {
+                            remainingBreachedSize = remainingBytes;
+                            return true;
+                        }
+                    }
+
+                    return false;
+                });
+                if (isSegmentDeleted) {
+                    logStartOffset = OptionalLong.of(metadata.endOffset() + 1);
+                    logger.info("Deleted remote log segment {} due to 
retention size {} breach. Log size after deletion will be {}.",
+                            metadata.remoteLogSegmentId(), 
retentionSizeData.get().retentionSize, remainingBreachedSize + 
retentionSizeData.get().retentionSize);
+                }
+                return isSegmentDeleted;
+            }
+
+            public boolean 
deleteRetentionTimeBreachedSegments(RemoteLogSegmentMetadata metadata)
+                    throws RemoteStorageException, ExecutionException, 
InterruptedException {
+                if (!retentionTimeData.isPresent()) {
+                    return false;
+                }
+
+                boolean isSegmentDeleted = deleteRemoteLogSegment(metadata,
+                        x -> x.maxTimestampMs() <= 
retentionTimeData.get().cleanupUntilMs);
+                if (isSegmentDeleted) {
+                    remainingBreachedSize = Math.max(0, remainingBreachedSize 
- metadata.segmentSizeInBytes());
+                    // It is fine to have logStartOffset as 
`metadata.endOffset() + 1` as the segment offset intervals
+                    // are ascending with in an epoch.
+                    logStartOffset = OptionalLong.of(metadata.endOffset() + 1);
+                    logger.info("Deleted remote log segment {} due to 
retention time {}ms breach based on the largest record timestamp in the 
segment",
+                            metadata.remoteLogSegmentId(), 
retentionTimeData.get().retentionMs);
+                }
+                return isSegmentDeleted;
+            }
+
+            private boolean 
deleteLogStartOffsetBreachedSegments(RemoteLogSegmentMetadata metadata, long 
startOffset)
+                    throws RemoteStorageException, ExecutionException, 
InterruptedException {
+                boolean isSegmentDeleted = deleteRemoteLogSegment(metadata, x 
-> startOffset > x.endOffset());
+                if (isSegmentDeleted && retentionSizeData.isPresent()) {
+                    remainingBreachedSize = Math.max(0, remainingBreachedSize 
- metadata.segmentSizeInBytes());
+                    logger.info("Deleted remote log segment {} due to log 
start offset {} breach", metadata.remoteLogSegmentId(), startOffset);
+                }
+
+                return isSegmentDeleted;
+            }
+
+            // It removes the segments beyond the current leader's earliest 
epoch. Those segments are considered as
+            // unreferenced because they are not part of the current leader 
epoch lineage.
+            private boolean 
deleteLogSegmentsDueToLeaderEpochCacheTruncation(EpochEntry earliestEpochEntry, 
RemoteLogSegmentMetadata metadata) throws RemoteStorageException, 
ExecutionException, InterruptedException {
+                boolean isSegmentDeleted = deleteRemoteLogSegment(metadata, x 
->
+                        
x.segmentLeaderEpochs().keySet().stream().allMatch(epoch -> epoch < 
earliestEpochEntry.epoch));
+                if (isSegmentDeleted) {
+                    logger.info("Deleted remote log segment {} due to leader 
epoch cache truncation. Current earliest epoch: {}, segmentEndOffset: {} and 
segmentEpochs: {}",
+                            metadata.remoteLogSegmentId(), earliestEpochEntry, 
metadata.endOffset(), metadata.segmentLeaderEpochs().keySet());
+                }
+
+                // No need to update the log-start-offset as these 
epochs/offsets are earlier to that value.
+                return isSegmentDeleted;
+            }
+
+            private boolean deleteRemoteLogSegment(RemoteLogSegmentMetadata 
segmentMetadata, Predicate<RemoteLogSegmentMetadata> predicate)
+                    throws RemoteStorageException, ExecutionException, 
InterruptedException {
+                if (predicate.test(segmentMetadata)) {
+                    logger.info("Deleting remote log segment {}", 
segmentMetadata.remoteLogSegmentId());
+                    // Publish delete segment started event.
+                    remoteLogMetadataManager.updateRemoteLogSegmentMetadata(
+                            new 
RemoteLogSegmentMetadataUpdate(segmentMetadata.remoteLogSegmentId(), 
time.milliseconds(),
+                                    segmentMetadata.customMetadata(), 
RemoteLogSegmentState.DELETE_SEGMENT_STARTED, brokerId)).get();
+
+                    // Delete the segment in remote storage.
+                    
remoteLogStorageManager.deleteLogSegmentData(segmentMetadata);
+
+                    // Publish delete segment finished event.
+                    remoteLogMetadataManager.updateRemoteLogSegmentMetadata(
+                            new 
RemoteLogSegmentMetadataUpdate(segmentMetadata.remoteLogSegmentId(), 
time.milliseconds(),
+                                    segmentMetadata.customMetadata(), 
RemoteLogSegmentState.DELETE_SEGMENT_FINISHED, brokerId)).get();
+                    logger.info("Deleted remote log segment {}", 
segmentMetadata.remoteLogSegmentId());
+                    return true;
+                }
+
+                return false;
+            }
+
+        }
+
+        private void cleanupExpiredRemoteLogSegments() throws 
RemoteStorageException, ExecutionException, InterruptedException {
+            if (isCancelled() || !isLeader()) {
+                logger.info("Returning from remote log segments cleanup as the 
task state is changed");
+                return;
+            }
+
+            // Cleanup remote log segments and update the log start offset if 
applicable.
+            final Iterator<RemoteLogSegmentMetadata> segmentMetadataIter = 
remoteLogMetadataManager.listRemoteLogSegments(topicIdPartition);
+            if (!segmentMetadataIter.hasNext()) {
+                logger.debug("No remote log segments available on remote 
storage for partition: {}", topicIdPartition);
+                return;
+            }
+
+            final Optional<UnifiedLog> logOptional = 
fetchLog.apply(topicIdPartition.topicPartition());
+            if (!logOptional.isPresent()) {
+                logger.debug("No UnifiedLog instance available for partition: 
{}", topicIdPartition);
+                return;
+            }
+
+            final UnifiedLog log = logOptional.get();
+            final Option<LeaderEpochFileCache> leaderEpochCacheOption = 
log.leaderEpochCache();
+            if (leaderEpochCacheOption.isEmpty()) {
+                logger.debug("No leader epoch cache available for partition: 
{}", topicIdPartition);
+                return;
+            }
+
+            final Set<Integer> epochsSet = new HashSet<>();
+            // Good to have an API from RLMM to get all the remote leader 
epochs of all the segments of a partition
+            // instead of going through all the segments and building it here.
+            while (segmentMetadataIter.hasNext()) {
+                RemoteLogSegmentMetadata segmentMetadata = 
segmentMetadataIter.next();
+                
epochsSet.addAll(segmentMetadata.segmentLeaderEpochs().keySet());
+            }
+
+            // All the leader epochs in sorted order that exists in remote 
storage
+            final List<Integer> remoteLeaderEpochs = new 
ArrayList<>(epochsSet);
+            Collections.sort(remoteLeaderEpochs);
+
+            LeaderEpochFileCache leaderEpochCache = 
leaderEpochCacheOption.get();
+            NavigableMap<Integer, Long> epochWithOffsets = 
leaderEpochCache.epochWithOffsets();
+            Optional<EpochEntry> earliestEpochEntryOptional = 
leaderEpochCache.earliestEntry();
+
+            Optional<RetentionSizeData> retentionSizeData = 
buildRetentionSizeData(log.config().retentionSize,
+                    log.onlyLocalLogSegmentsSize(), log.logEndOffset(), 
epochWithOffsets);
+            Optional<RetentionTimeData> retentionTimeData = 
buildRetentionTimeData(log.config().retentionMs);
+
+            RemoteLogRetentionHandler remoteLogRetentionHandler = new 
RemoteLogRetentionHandler(retentionSizeData, retentionTimeData);
+            Iterator<Integer> epochIterator = 
epochWithOffsets.navigableKeySet().iterator();
+            boolean isSegmentDeleted = true;
+            while (isSegmentDeleted && epochIterator.hasNext()) {
+                Integer epoch = epochIterator.next();
+                Iterator<RemoteLogSegmentMetadata> segmentsIterator = 
remoteLogMetadataManager.listRemoteLogSegments(topicIdPartition, epoch);
+                while (isSegmentDeleted && segmentsIterator.hasNext()) {
+                    if (isCancelled() || !isLeader()) {
+                        logger.info("Returning from remote log segments 
cleanup for the remaining segments as the task state is changed.");
+                        return;
+                    }
+                    RemoteLogSegmentMetadata metadata = 
segmentsIterator.next();
+
+                    // check whether the segment contains the required epoch 
range with in the current leader epoch lineage.
+                    if (isRemoteSegmentWithinLeaderEpochs(metadata, 
log.logEndOffset(), epochWithOffsets)) {
+                        isSegmentDeleted =
+                                
remoteLogRetentionHandler.deleteRetentionTimeBreachedSegments(metadata) ||
+                                        
remoteLogRetentionHandler.deleteRetentionSizeBreachedSegments(metadata) ||
+                                        
remoteLogRetentionHandler.deleteLogStartOffsetBreachedSegments(metadata, 
log.logStartOffset());
+                    }
+                }
+            }
+
+            // Remove the remote log segments whose segment-leader-epochs are 
less than the earliest-epoch known

Review Comment:
   >One way to solve is it is to delete the data that we know for sure is ready 
for deletion, e.g. if we have 10MB of data in remote store for non-active 
lineage and retention size is 2MB, then we can safely delete the rest of the 
8MB. This is because even if this leadership chain becomes active, it will 
adhere to retention size.
   
   It is hard or impossible to find the non-active lineage deterministically as 
the failed host can have any subset of the non active lineage. Determining 
which epoch/segments can be marked for deletion under such circumstances is not 
feasible. 



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