thanos-io/thanos · error

failed to finalize the block

Error message

failed to finalize the block %s

What it means

Wraps the finalization step for a compacted result block — writing Thanos metadata via metadata.InjectThanos and finalizing files on disk after the index passed health checks. Failure here means the block exists on disk but is not upload-ready, so the compaction attempt is retried.

Solutions

1. Check write permissions on the block dir
2. Inspect the wrapped metadata error
3. Re-run compaction for this group

When it happens

Trigger: Thrown at pkg/compact/compact.go:1342 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/1cab77581c7ba93d. Report an issue: GitHub.

Appendix: source

Thrown at pkg/compact/compact.go:1342

			return false, nil, halt(errors.Wrapf(err, "invalid result block %s", bdir))
		}

		thanosMeta := metadata.Thanos{
			Labels:       cg.labels.Map(),
			Downsample:   metadata.ThanosDownsample{Resolution: cg.resolution},
			Source:       metadata.CompactorSource,
			SegmentFiles: block.GetSegmentFiles(bdir),
			Extensions:   cg.Extensions(),
		}
		if stats.ChunkMaxSize > 0 {
			thanosMeta.IndexStats.ChunkMaxSize = stats.ChunkMaxSize
		}
		if stats.SeriesMaxSize > 0 {
			thanosMeta.IndexStats.SeriesMaxSize = stats.SeriesMaxSize
		}
		newMeta, err = metadata.InjectThanos(cg.logger, bdir, thanosMeta, nil)
		if err != nil {
			return false, nil, errors.Wrapf(err, "failed to finalize the block %s", bdir)
		}
		// Ensure the output block is not overlapping with anything else,
		// unless vertical compaction is enabled.
		if !cg.enableVerticalCompaction {
			if err := cg.areBlocksOverlapping(newMeta, toCompact...); err != nil {
				return false, nil, halt(errors.Wrapf(err, "resulted compacted block %s overlaps with something", bdir))
			}
		}

		begin = time.Now()

		err = tracing.DoInSpanWithErr(ctx, "compaction_block_upload", func(ctx context.Context) error {
			return block.Upload(ctx, cg.logger, cg.bkt, bdir, cg.hashFunc, objstore.WithUploadConcurrency(cg.blockFilesConcurrency))
		})
		if err != nil {
			return false, nil, retry(errors.Wrapf(err, "upload of %s failed", compID))
		}
		level.Info(cg.logger).Log("msg", "uploaded block", "result_block", compID, "duration", time.Since(begin), "duration_ms", time.Since(begin).Milliseconds())

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