KAFKA-19280: Fix NoSuchElementException in UnifiedLog#19717
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Thanks for the PR (and catching the issue!). Looks good overall, just left a couple of suggestions
| LogOffsetMetadata highWatermarkMetadata = fetchHighWatermarkMetadata(); | ||
| if (firstUnstableOffsetMetadata.isPresent() && firstUnstableOffsetMetadata.get().messageOffset < highWatermarkMetadata.messageOffset) { | ||
| LogOffsetMetadata lom = firstUnstableOffsetMetadata.get(); | ||
| Optional<LogOffsetMetadata> firstUnstableOffsetMetadataCopy = firstUnstableOffsetMetadata; |
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Should we add a comment or update the comment just above?
| public long lastStableOffset() { | ||
| if (firstUnstableOffsetMetadata.isPresent() && firstUnstableOffsetMetadata.get().messageOffset < highWatermark()) { | ||
| return firstUnstableOffsetMetadata.get().messageOffset; | ||
| Optional<LogOffsetMetadata> firstUnstableOffsetMetadataCopy = firstUnstableOffsetMetadata; |
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Maybe worth adding a comment. There are a few places in this class where we say we cache a value to avoid concurrency issues.
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Thanks for the review @mimaison. Ready for re-review |
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I opened #22609 to address this. The details are in the PR; happy to adjust based on what you'd prefer. |
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In FETCH requests and TXN_OFFSET_COMMIT requests, on current trunk we
run into a race condition inside UnifiedLog, causing a
NoSuchElementExceptioninUnifiedLog.fetchLastStableOffsetMetadata(UnifiedLog.java:651).The cause is that the line a performing an
isPresentcheck on avolatile Optional before accessing it in
get, leaving the door open toa race condition when the optional changes between
isPresentandget. This change takes a copy of the volatile variable first.Reviewers: Mickael Maison mickael.maison@gmail.com, wilmerdooley wilmer@snovon.com