[jira] [Resolved] (KAFKA-21152) LogCompactionTester should read until the end offsets instead of stopping at an empty poll

["Chia-Ping Tsai (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-21152?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Chia-Ping Tsai resolved KAFKA-21152.
------------------------------------
    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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