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fix(compactor): correct misleading help text for cortex_compactor_garbage_collected_blocks_total#7673

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Goutham-Annem:fix/3610-compactor-gc-metric-help
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fix(compactor): correct misleading help text for cortex_compactor_garbage_collected_blocks_total#7673
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Goutham-Annem:fix/3610-compactor-gc-metric-help

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What this PR does:

The metric cortex_compactor_garbage_collected_blocks_total had an
identical help string to cortex_compactor_blocks_marked_for_deletion_total
("Total number of blocks marked for deletion by compactor."), which was
confusing and misleading. The two metrics track different things:

  • cortex_compactor_garbage_collected_blocks_total — counts blocks that the
    Thanos syncer's GC pass has actually garbage-collected (i.e., deleted after
    previously being marked). Sourced from Thanos pkg/compact/compact.go.
  • cortex_compactor_blocks_marked_for_deletion_total — counts blocks that
    Cortex's own logic has explicitly marked for deletion.

This PR corrects the help text to accurately describe what the metric
measures: "Total number of blocks garbage collected (deleted after being marked) by the compactor syncer." The test expectation is updated to match.

Which issue(s) this PR fixes:
Fixes #3610

Checklist

  • Tests updated (test expectation string updated to match new help text)
  • CHANGELOG.md updated
  • Documentation added (N/A — metric help text is self-documenting)

Note: This PR was developed with AI assistance (Claude Code).

@dosubot dosubot Bot added component/compactor type/chore Something that needs to be done; not a bug or a feature type/observability To help know what is going on inside Cortex labels Jul 5, 2026
…bage_collected_blocks_total

The metric counted blocks garbage collected by the Thanos syncer (i.e.,
blocks deleted after being marked), not all blocks marked for deletion.
Its help string was identical to cortex_compactor_blocks_marked_for_deletion_total,
which caused confusion for operators monitoring compaction activity.

Fixes cortexproject#3610

Signed-off-by: Goutham Annem <gouthemannem@gmail.com>
@Goutham-Annem Goutham-Annem force-pushed the fix/3610-compactor-gc-metric-help branch from 563daa8 to 868d7ee Compare July 10, 2026 10:41
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component/compactor size/XS type/chore Something that needs to be done; not a bug or a feature type/observability To help know what is going on inside Cortex

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Two metrics have the same help value

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