{"record":{"id":"64e4c4c29a3924d6","repo":"thanos-io/thanos","slug":"cannot-populate-chunk-d","errorCode":null,"errorMessage":"cannot populate chunk %d","messagePattern":"cannot populate chunk (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/compactv2/chunk_series_set.go","lineNumber":120,"sourceCode":"func (e errChunkIterator) Err() error               { return e.err }\n\ntype errChunk struct{ err errChunkIterator }\n\nfunc (e errChunk) Bytes() []byte                                { return nil }\nfunc (e errChunk) Encoding() chunkenc.Encoding                  { return chunkenc.EncXOR }\nfunc (e errChunk) Appender() (chunkenc.Appender, error)         { return nil, e.err.err }\nfunc (e errChunk) Iterator(chunkenc.Iterator) chunkenc.Iterator { return e.err }\nfunc (e errChunk) NumSamples() int                              { return 0 }\nfunc (e errChunk) Compact()                                     {}\nfunc (e errChunk) Reset(stream []byte)                          {}\n\nfunc (l *lazyPopulatableChunk) populate() {\n\t// TODO(bwplotka): In most cases we don't need to parse anything, just copy. Extend reader/writer for this.\n\tvar err error\n\t// Ignore iterable as it should be nil.\n\tl.populated, _, err = l.cr.ChunkOrIterable(*l.m)\n\tif err != nil {\n\t\tl.m.Chunk = errChunk{err: errChunkIterator{err: errors.Wrapf(err, \"cannot populate chunk %d\", l.m.Ref)}}\n\t\treturn\n\t}\n\n\tl.m.Chunk = l.populated\n}\n\nfunc (l *lazyPopulatableChunk) Bytes() []byte {\n\tif l.populated == nil {\n\t\tl.populate()\n\t}\n\treturn l.populated.Bytes()\n}\n\nfunc (l *lazyPopulatableChunk) Encoding() chunkenc.Encoding {\n\tif l.populated == nil {\n\t\tl.populate()\n\t}\n\treturn l.populated.Encoding()","sourceCodeStart":102,"sourceCodeEnd":138,"githubUrl":"https://github.com/thanos-io/thanos/blob/35b8b991177def87ed52dcf10f9b6d87f07282c8/pkg/compactv2/chunk_series_set.go#L102-L138","documentation":"lazyPopulatableChunk.populate loads the actual chunk bytes via ChunkOrIterable for a chunk meta; on failure the chunk is replaced with an errChunk holding the wrapped error. The error surfaces later as a chunk iterator error when the data is read, referencing the chunk's Ref. It's a deferred failure: population happens lazily during compaction materialization.","triggerScenarios":"Calling populate (transitively via Bytes/Encoding/Iterator/NumSamples) on a chunk whose ChunkOrIterable call fails — typically reading the chunk from the source block's chunk files fails: bad offset in chunk meta, truncated/corrupt chunk segment file, IO error.","commonSituations":"Truncated chunks files from interrupted uploads to object storage, disk corruption, chunk refs pointing at a different (incompatible) block after manual block manipulation, version-mismatched block format.","solutions":["Inspect the inner error from the errChunk iterator: treat corruption by deleting/repairing the offending source block.","Verify chunk file integrity (chunk checksums) and re-sync the block from a healthy replica.","Ensure the compactor reads blocks that are fully uploaded (check upload completion markers; avoid compacting partial blocks).","Retry compaction after storage issues resolve; if persistent, exclude the bad block via ignore-blocks or re-upload it."],"exampleFix":"// the library defers the error into an errChunk iterator:\nl.m.Chunk = errChunk{err: errChunkIterator{err: errors.Wrapf(err, \"cannot populate chunk %d\", l.m.Ref)}}\n// caller should surface it instead of silently dropping samples:\nit := chk.Chunk.Iterator(nil)\nfor it.Next() != chunkenc.ValNone {\n    if it.Err() != nil {\n        return errors.Wrapf(it.Err(), \"reading chunk %d\", chk.Ref)\n    }\n}","handlingStrategy":"try-catch","validationCode":"// check chunk data availability before compacting the block\nif err := validateChunkFiles(blockDir); err != nil {\n    return fmt.Errorf(\"block %s has corrupt chunk data: %w\", blockDir, err)\n}","typeGuard":"func chunkIsReadable(m chunks.Meta, cr *blockChunkReader) error {\n    _, _, err := cr.ChunkOrIterable(m)\n    return err\n}","tryCatchPattern":"defer func() {\n    if rec := recover(); rec != nil { _ = rec }\n}()\nit := chk.Chunk.Iterator(nil)\nfor it.Next() != chunkenc.ValNone {\n    if err := it.Err(); err != nil {\n        return errors.Wrapf(err, \"chunk %d unreadable\", chk.Ref)\n    }\n}","preventionTips":["Ensure blocks are fully uploaded before compacting (check upload markers)","Verify checksums of chunk segment files during block sync","Restore corrupt blocks from replication before compacting","Monitor disk health on compactor nodes"],"tags":["go","tsdb","chunk","corruption"],"backgroundTag":"database-query-failed","analyzedSha":"35b8b991177def87ed52dcf10f9b6d87f07282c8","analyzedAt":"2026-09-07T01:49:59.689Z","contentChangedAt":"2026-09-07T01:49:59.689Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}