fix(compaction): batch filename collision causes up to 84% data loss - #358
#358Merged
xe-nvdk merged 1 commit intoMar 27, 2026
mainBasekick-Labs/arc:mainfrom
fix/compaction-batch-filename-collisionBasekick-Labs/arc:fix/compaction-batch-filename-collisionCopy head branch name to clipboard
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fix(compaction): batch filename collision causes up to 84% data loss#358xe-nvdk merged 1 commit intomainBasekick-Labs/arc:mainfrom fix/compaction-batch-filename-collisionBasekick-Labs/arc:fix/compaction-batch-filename-collisionCopy head branch name to clipboard
xe-nvdk merged 1 commit into
mainBasekick-Labs/arc:mainfrom
fix/compaction-batch-filename-collisionBasekick-Labs/arc:fix/compaction-batch-filename-collisionCopy head branch name to clipboard
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Code Review
This pull request addresses a critical data loss bug where compaction batches would overwrite each other due to filename collisions caused by second-precision timestamps. The fix introduces nanosecond precision to ensure unique filenames. Feedback suggests refining the filename format by using a single nanosecond-precision timestamp string instead of appending a raw Unix nanosecond value, which improves readability and maintains the existing filename structure.
…357) When partitions had >30 files, SplitCandidateIntoBatches created sequential batches of 30. Each batch generated output filenames with second-precision timestamps, causing all batches within the same second to produce identical filenames. Each batch overwrote the previous, destroying up to 84% of data. Fixed by adding UnixNano to compacted filenames for guaranteed uniqueness: system_20260327_020510_1774577110783053268_compacted.parquet Also updated extractNewestFileTime to handle both old format (measurement_YYYYMMDD_HHMMSS_compacted) and new format with nanos (measurement_YYYYMMDD_HHMMSS_nanos_compacted). Closes #357 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
SplitCandidateIntoBatchescreates sequential batches of 30. Each batch generated output filenames with second-precision timestamps (YYYYMMDD_HHMMSS), causing all batches to produce identical filenames. Each batch overwrote the previous — only the last batch survived.max_buffer_age_ms=500which produces ~120 files/hour.YYYYMMDD_HHMMSSprefix forextractNewestFileTimecompatibility.Closes #357
Test plan
go build ./cmd/... ./internal/...— cleango test ./internal/compaction/...— pass