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https://issues.apache.org/jira/browse/CASSSIDECAR-484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18097601#comment-18097601
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Yafeng Lu commented on CASSSIDECAR-484:
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Could anyone take a look of this PR? thanks!
cc: [~jberragan] [~ycai] [~frankgh] [~bernardo.botella]
> Fix the spurious oldest segment age in CdcRawDirectorySpaceCleaner
> ------------------------------------------------------------------
>
> Key: CASSSIDECAR-484
> URL: https://issues.apache.org/jira/browse/CASSSIDECAR-484
> Project: Sidecar for Apache Cassandra
> Issue Type: Improvement
> Reporter: Yafeng Lu
> Priority: Major
> Time Spent: 10m
> Remaining Estimate: 0h
>
> {{CdcRawDirectorySpaceCleaner}} re-reads segment metadata via
> {{File.lastModified()}} well after the initial {{listFiles()}} scan. If
> Cassandra (or any other actor) reclaims a segment in the interim, the
> {{File.lastModified()}} will return {{{}0{}}}, and {{nowInMillis - 0}}
> collapses to wall-clock milliseconds. This produced three subtle failure
> modes on a hot cluster:
> # {{oldestSegmentAge}} gauge reported a nonsensical ~50-year age. Because
> {{segmentFiles}} is sorted ascending by {{segmentId}} and Cassandra reclaims
> oldest-first, the race hits precisely the file whose age is being reported.
> # Critical/low CDC-buffer alerts ({{{}criticalCdcRawSpace{}}},
> {{{}lowCdcRawSpace{}}}) were silently suppressed. With {{ageMillis}}
> collapsed to ~10¹² ms, both {{< criticalMillis}} and {{< lowMillis}}
> conditions were always false.
> # {{deletedSegment}} metric was over-attributed to the cleaner. When
> Cassandra reclaimed a segment first, the cleaner still called
> {{deleteSegment(...)}} (a no-op via {{{}Files.deleteIfExists{}}}), logged a
> misleading "Deleting Cdc segment lastModified=0" line, and bumped the metric
> with the cached file size.
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