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https://issues.apache.org/jira/browse/KAFKA-21152?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chia-Ping Tsai resolved KAFKA-21152.
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Fix Version/s: 4.5.0
Resolution: Fixed
> LogCompactionTester should read until the end offsets instead of stopping at
> an empty poll
> ------------------------------------------------------------------------------------------
>
> Key: KAFKA-21152
> URL: https://issues.apache.org/jira/browse/KAFKA-21152
> Project: Kafka
> Issue Type: Bug
> Components: system tests, tools
> Reporter: Eric Chang
> Assignee: Eric Chang
> Priority: Minor
> Labels: flaky-test
> Fix For: 4.5.0
>
> Attachments: build948-trimmed.log
>
>
> h3. What happened
> {{LogCompactionTest.test_log_compaction}} is flaky. In the 4.4.0-rc1 system
> test run (zstd level 10, ISOLATED_KRAFT), the tester read only 7498 of about
> 191k rows and the validation failed. The same case passed 5 out of 5 times on
> rerun. The trimmed logs are attached.
> The cause is in the tester, not in the broker or the consumer.
> {{LogCompactionTester.consumeMessages()}}
> ({{tools/src/main/java/org/apache/kafka/tools/LogCompactionTester.java}})
> stops at the first empty {{poll()}}:
> {code:java}
> while (true) {
> ConsumerRecords<String, String> consumerRecords =
> consumer.poll(Duration.ofSeconds(20));
> if (consumerRecords.isEmpty()) return consumedFilePath;
> ...
> }
> {code}
> Since KAFKA-12980 (3.2.0), {{poll()}} can return no records even when more
> data remains. So {{consumeMessages()}} sometimes stops early, the consumed
> file is incomplete, and {{validateOutput()}} fails. This is not a 4.4
> regression: the consumer behavior exists since 3.2.0, and the tester code is
> even older.
> h3. Details
> Why {{poll()}} returns no records: after compaction, a batch keeps its
> {{lastOffset}} even when its last records are removed. If one {{poll()}}
> returns exactly {{max.poll.records}} records and the last one is the last
> retained record of a fetch, the next {{poll()}} only moves the position to
> {{lastOffset + 1}} and returns right away with no records. In the failed run,
> the tester stopped at a batch with {{lastOffset}} 649433 whose last retained
> record is 649426. The consumer behavior is expected (KAFKA-14865 tracks it).
> This ticket only fixes the tester.
> Simple repro (offsets 5..9 compacted away; {{fetch.max.bytes=1}} for one
> batch per fetch, {{max.poll.records=5}}):
> {noformat}
> poll#1 count=5 position=5 endOffset=16 (offsets 0..4)
> poll#2 count=0 position=10 endOffset=16 (skips removed offsets 5..9: empty,
> but not at the end)
> poll#3 count=5 position=15 endOffset=16 (offsets 10..14)
> {noformat}
> Fix: in {{consumeMessages()}}, get the end offsets before consuming, and poll
> until the position of every partition reaches its end offset. Give up only
> when a poll returns no records and moves no position.
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