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KAFKA-17076: retain last batch in each round of cleaning (#17193) #20535

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Nov 24, 2025
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KAFKA-17076: retain last batch in each round of cleaning (#17193) #20535

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545fd78
KAFKA-17076: retain last batch in each round of cleaning (#17193)
vincent81jiang Sep 25, 2024
8b1ef6c
Merge branch '3.9' into cp-KAFKA-17076
CalvinConfluent Nov 21, 2025
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16 changes: 12 additions & 4 deletions core/src/main/scala/kafka/log/LogCleaner.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -624,7 +624,7 @@ private[log] class Cleaner(val id: Int,
val groupedSegments = groupSegmentsBySize(log.logSegments(0, endOffset), log.config.segmentSize,
log.config.maxIndexSize, cleanable.firstUncleanableOffset)
for (group <- groupedSegments)
cleanSegments(log, group, offsetMap, currentTime, stats, transactionMetadata, legacyDeleteHorizonMs)
cleanSegments(log, group, offsetMap, currentTime, stats, transactionMetadata, legacyDeleteHorizonMs, upperBoundOffset)

// record buffer utilization
stats.bufferUtilization = offsetMap.utilization
Expand All @@ -645,14 +645,16 @@ private[log] class Cleaner(val id: Int,
* @param transactionMetadata State of ongoing transactions which is carried between the cleaning
* of the grouped segments
* @param legacyDeleteHorizonMs The delete horizon used for tombstones whose version is less than 2
* @param upperBoundOffsetOfCleaningRound The upper bound offset of this round of cleaning
*/
private[log] def cleanSegments(log: UnifiedLog,
segments: Seq[LogSegment],
map: OffsetMap,
currentTime: Long,
stats: CleanerStats,
transactionMetadata: CleanedTransactionMetadata,
legacyDeleteHorizonMs: Long): Unit = {
legacyDeleteHorizonMs: Long,
upperBoundOffsetOfCleaningRound: Long): Unit = {
// create a new segment with a suffix appended to the name of the log and indexes
val cleaned = UnifiedLog.createNewCleanedSegment(log.dir, log.config, segments.head.baseOffset)
transactionMetadata.cleanedIndex = Some(cleaned.txnIndex)
Expand Down Expand Up @@ -682,7 +684,7 @@ private[log] class Cleaner(val id: Int,

try {
cleanInto(log.topicPartition, currentSegment.log, cleaned, map, retainLegacyDeletesAndTxnMarkers, log.config.deleteRetentionMs,
log.config.maxMessageSize, transactionMetadata, lastOffsetOfActiveProducers, stats, currentTime = currentTime)
log.config.maxMessageSize, transactionMetadata, lastOffsetOfActiveProducers, upperBoundOffsetOfCleaningRound, stats, currentTime = currentTime)
} catch {
case e: LogSegmentOffsetOverflowException =>
// Split the current segment. It's also safest to abort the current cleaning process, so that we retry from
Expand Down Expand Up @@ -728,6 +730,7 @@ private[log] class Cleaner(val id: Int,
* @param maxLogMessageSize The maximum message size of the corresponding topic
* @param transactionMetadata The state of ongoing transactions which is carried between the cleaning of the grouped segments
* @param lastRecordsOfActiveProducers The active producers and its last data offset
* @param upperBoundOffsetOfCleaningRound Next offset of the last batch in the source segment
* @param stats Collector for cleaning statistics
* @param currentTime The time at which the clean was initiated
*/
Expand All @@ -740,6 +743,7 @@ private[log] class Cleaner(val id: Int,
maxLogMessageSize: Int,
transactionMetadata: CleanedTransactionMetadata,
lastRecordsOfActiveProducers: mutable.Map[Long, LastRecord],
upperBoundOffsetOfCleaningRound: Long,
stats: CleanerStats,
currentTime: Long): Unit = {
val logCleanerFilter: RecordFilter = new RecordFilter(currentTime, deleteRetentionMs) {
Expand Down Expand Up @@ -774,7 +778,11 @@ private[log] class Cleaner(val id: Int,
val batchRetention: BatchRetention =
if (batch.hasProducerId && isBatchLastRecordOfProducer)
BatchRetention.RETAIN_EMPTY
else if (discardBatchRecords)
else if (batch.nextOffset == upperBoundOffsetOfCleaningRound) {
// retain the last batch of the cleaning round, even if it's empty, so that last offset information
// is not lost after cleaning.
BatchRetention.RETAIN_EMPTY
} else if (discardBatchRecords)
BatchRetention.DELETE
else
BatchRetention.DELETE_EMPTY
Expand Down
67 changes: 50 additions & 17 deletions core/src/test/scala/unit/kafka/log/LogCleanerTest.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -168,7 +168,7 @@ class LogCleanerTest extends Logging {
val stats = new CleanerStats()
val expectedBytesRead = segments.map(_.size).sum
val shouldRemain = LogTestUtils.keysInLog(log).filterNot(keys.contains)
cleaner.cleanSegments(log, segments, map, 0L, stats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, segments, map, 0L, stats, new CleanedTransactionMetadata, -1, segments.last.readNextOffset)
assertEquals(shouldRemain, LogTestUtils.keysInLog(log))
assertEquals(expectedBytesRead, stats.bytesRead)
}
Expand Down Expand Up @@ -256,7 +256,7 @@ class LogCleanerTest extends Logging {
val segments = log.logSegments(0, log.activeSegment.baseOffset).toSeq
val stats = new CleanerStats()
cleaner.buildOffsetMap(log, 0, log.activeSegment.baseOffset, offsetMap, stats)
cleaner.cleanSegments(log, segments, offsetMap, 0L, stats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, segments, offsetMap, 0L, stats, new CleanedTransactionMetadata, -1, segments.last.readNextOffset)

// Validate based on the file name that log segment file is renamed exactly once for async deletion
assertEquals(expectedFileName, firstLogFile.file().getPath)
Expand Down Expand Up @@ -423,7 +423,7 @@ class LogCleanerTest extends Logging {
val segments = log.logSegments(0, log.activeSegment.baseOffset).toSeq
val stats = new CleanerStats(time)
cleaner.buildOffsetMap(log, dirtyOffset, log.activeSegment.baseOffset, offsetMap, stats)
cleaner.cleanSegments(log, segments, offsetMap, time.milliseconds(), stats, new CleanedTransactionMetadata, Long.MaxValue)
cleaner.cleanSegments(log, segments, offsetMap, time.milliseconds(), stats, new CleanedTransactionMetadata, Long.MaxValue, segments.last.readNextOffset)
dirtyOffset = offsetMap.latestOffset + 1
}

Expand Down Expand Up @@ -925,7 +925,7 @@ class LogCleanerTest extends Logging {

// clean the log
val stats = new CleanerStats()
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), map, 0L, stats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), map, 0L, stats, new CleanedTransactionMetadata, -1, log.logSegments.asScala.head.readNextOffset)
val shouldRemain = LogTestUtils.keysInLog(log).filterNot(keys.contains)
assertEquals(shouldRemain, LogTestUtils.keysInLog(log))
}
Expand All @@ -938,7 +938,7 @@ class LogCleanerTest extends Logging {
val (log, offsetMap) = createLogWithMessagesLargerThanMaxSize(largeMessageSize = 1024 * 1024)

val cleaner = makeCleaner(Int.MaxValue, maxMessageSize=1024)
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1, log.logSegments.asScala.head.readNextOffset)
val shouldRemain = LogTestUtils.keysInLog(log).filter(k => !offsetMap.map.containsKey(k.toString))
assertEquals(shouldRemain, LogTestUtils.keysInLog(log))
}
Expand All @@ -957,7 +957,7 @@ class LogCleanerTest extends Logging {

val cleaner = makeCleaner(Int.MaxValue, maxMessageSize=1024)
assertThrows(classOf[CorruptRecordException], () =>
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1, log.logSegments.asScala.head.readNextOffset)
)
}

Expand All @@ -974,7 +974,7 @@ class LogCleanerTest extends Logging {

val cleaner = makeCleaner(Int.MaxValue, maxMessageSize=1024)
assertThrows(classOf[CorruptRecordException], () =>
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, Seq(log.logSegments.asScala.head), offsetMap, 0L, new CleanerStats, new CleanedTransactionMetadata, -1, log.logSegments.asScala.head.readNextOffset)
)
}

Expand Down Expand Up @@ -1356,12 +1356,42 @@ class LogCleanerTest extends Logging {
val keys = LogTestUtils.keysInLog(log)
val map = new FakeOffsetMap(Int.MaxValue)
keys.foreach(k => map.put(key(k), Long.MaxValue))
val segments = log.logSegments.asScala.take(3).toSeq
assertThrows(classOf[LogCleaningAbortedException], () =>
cleaner.cleanSegments(log, log.logSegments.asScala.take(3).toSeq, map, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
cleaner.cleanSegments(log, segments, map, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1, segments.last.readNextOffset)
)
}

@Test
def testCleanSegmentsRetainingLastEmptyBatch(): Unit = {
val cleaner = makeCleaner(Int.MaxValue)
val logProps = new Properties()
logProps.put(TopicConfig.SEGMENT_BYTES_CONFIG, 1024: java.lang.Integer)

val log = makeLog(config = LogConfig.fromProps(logConfig.originals, logProps))

// append messages to the log until we have four segments
while (log.numberOfSegments < 4)
log.appendAsLeader(record(log.logEndOffset.toInt, log.logEndOffset.toInt), leaderEpoch = 0)
val keysFound = LogTestUtils.keysInLog(log)
assertEquals(0L until log.logEndOffset, keysFound)

// pretend all keys are deleted
val map = new FakeOffsetMap(Int.MaxValue)
keysFound.foreach(k => map.put(key(k), Long.MaxValue))

// clean the log
val segments = log.logSegments.asScala.take(3).toSeq
val stats = new CleanerStats()
cleaner.cleanSegments(log, segments, map, 0L, stats, new CleanedTransactionMetadata, -1, segments.last.readNextOffset)
assertEquals(2, log.logSegments.size)
assertEquals(1, log.logSegments.asScala.head.log.batches.asScala.size, "one batch should be retained in the cleaned segment")
val retainedBatch = log.logSegments.asScala.head.log.batches.asScala.head
assertEquals(log.logSegments.asScala.last.baseOffset - 1, retainedBatch.lastOffset, "the retained batch should be the last batch")
assertFalse(retainedBatch.iterator.hasNext, "the retained batch should be an empty batch")
}

/**
* Validate the logic for grouping log segments together for cleaning
*/
Expand Down Expand Up @@ -1618,16 +1648,17 @@ class LogCleanerTest extends Logging {
// Try to clean segment with offset overflow. This will trigger log split and the cleaning itself must abort.
assertThrows(classOf[LogCleaningAbortedException], () =>
cleaner.cleanSegments(log, Seq(segmentWithOverflow), offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, segmentWithOverflow.readNextOffset)
)
assertEquals(numSegmentsInitial + 1, log.logSegments.size)
assertEquals(allKeys, LogTestUtils.keysInLog(log))
assertFalse(LogTestUtils.hasOffsetOverflow(log))

// Clean each segment now that split is complete.
val upperBoundOffset = log.logSegments.asScala.last.readNextOffset
for (segmentToClean <- log.logSegments.asScala)
cleaner.cleanSegments(log, List(segmentToClean), offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
assertEquals(expectedKeysAfterCleaning, LogTestUtils.keysInLog(log))
assertFalse(LogTestUtils.hasOffsetOverflow(log))
log.close()
Expand Down Expand Up @@ -1666,9 +1697,11 @@ class LogCleanerTest extends Logging {
for (k <- 1 until messageCount by 2)
offsetMap.put(key(k), Long.MaxValue)

val upperBoundOffset = log.activeSegment.baseOffset

// clean the log
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
var cleanedKeys = LogTestUtils.keysInLog(log)
Expand All @@ -1684,7 +1717,7 @@ class LogCleanerTest extends Logging {

// clean again
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
cleanedKeys = LogTestUtils.keysInLog(log)
Expand All @@ -1701,7 +1734,7 @@ class LogCleanerTest extends Logging {

// clean again
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
cleanedKeys = LogTestUtils.keysInLog(log)
Expand All @@ -1723,7 +1756,7 @@ class LogCleanerTest extends Logging {
for (k <- 1 until messageCount by 2)
offsetMap.put(key(k), Long.MaxValue)
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
cleanedKeys = LogTestUtils.keysInLog(log)
Expand All @@ -1741,7 +1774,7 @@ class LogCleanerTest extends Logging {
for (k <- 1 until messageCount by 2)
offsetMap.put(key(k), Long.MaxValue)
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
cleanedKeys = LogTestUtils.keysInLog(log)
Expand All @@ -1759,7 +1792,7 @@ class LogCleanerTest extends Logging {
for (k <- 1 until messageCount by 2)
offsetMap.put(key(k), Long.MaxValue)
cleaner.cleanSegments(log, log.logSegments.asScala.take(9).toSeq, offsetMap, 0L, new CleanerStats(),
new CleanedTransactionMetadata, -1)
new CleanedTransactionMetadata, -1, upperBoundOffset)
// clear scheduler so that async deletes don't run
time.scheduler.clear()
cleanedKeys = LogTestUtils.keysInLog(log)
Expand Down