kamalcph commented on code in PR #14004:
URL: https://github.com/apache/kafka/pull/14004#discussion_r1268420993
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storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogLeaderEpochState.java:
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@@ -100,17 +100,29 @@ void
handleSegmentWithCopySegmentStartedState(RemoteLogSegmentId remoteLogSegmen
void handleSegmentWithCopySegmentFinishedState(Long startOffset,
RemoteLogSegmentId remoteLogSegmentId,
Long leaderEpochEndOffset) {
+ // If there are duplicate segments uploaded due to leader-election,
then mark them as unreferenced.
+ // Duplicate segments can be uploaded when the previous leader had
tier-lags and the next leader uploads the
+ // segment for the same leader-epoch which is a super-set of
previously uploaded segments.
+ // (eg)
+ // case-1: Duplicate segment
+ // L0 uploaded segment S0 with offsets 0-100 and L1 uploaded
segment S1 with offsets 0-200.
+ // We will mark the segment S0 as duplicate and add it to
unreferencedSegmentIds.
+ // case-2: Overlapping segments
+ // L0 uploaded segment S0 with offsets 10-90 and L1 uploaded
segment S1 with offsets 5-100, S2-101-200,
+ // and so on. When the consumer request for segment with offset
95, it should get the segment S1 and not S0.
+ Map.Entry<Long, RemoteLogSegmentId> lastEntry = offsetToId.lastEntry();
+ while (lastEntry != null && lastEntry.getKey() >= startOffset &&
highestLogOffset <= leaderEpochEndOffset) {
Review Comment:
> But are the any drawbacks by removing highestLogOffset <=
leaderEpochEndOffset from the while? What kind of problem we can face and why
having this check is more safe rather than remove it?
Assume there are multiple back-to-back unclean leader elections happened and
only **one replica** is available at any point of time. Both B1 and B2 may not
be aware of all the leader-epochs. If the consumer reads the data from the
beginning of the topic, then we should be able to serve the respective remote
log segments for the (epoch, start_offset) present in both B1 and B2.
This patch only mark the segment as unreferenced if the current segment is a
superset of all the previously uploaded segments for the same epoch which means
the message is same across the segments.
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