thanos-io/thanos · error

not implemented

Error message

not implemented

What it means

AggrChunk.Appender() unconditionally returns this sentinel error because aggregate (downsampled) chunks are read-only: they are built once during downsampling and support only iteration/Get, not sample appends. It fires whenever any code path (e.g. a compaction or head writer) tries to obtain a chunkenc.Appender for an AggrChunk.

Solutions

1. Do not call Appender() on AggrChunk; it is intentionally unsupported.
2. Build a new AggrChunk from source chunks instead of appending to an existing one.
3. Route write paths to raw chunks and keep AggrChunk read-only.

When it happens

Trigger: Thrown at pkg/compact/downsample/aggr.go:49 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/ba124ba7bf7e84e7. Report an issue: GitHub.

Appendix: source

Thrown at pkg/compact/downsample/aggr.go:49

			b = append(b, buf[:n]...)
			continue
		}
		l := len(c.Bytes())
		n := binary.PutUvarint(buf[:], uint64(l))
		b = append(b, buf[:n]...)
		b = append(b, byte(c.Encoding()))
		b = append(b, c.Bytes()...)
	}
	chk := AggrChunk(b)
	return &chk
}

func (c AggrChunk) Bytes() []byte {
	return []byte(c)
}

func (c AggrChunk) Appender() (chunkenc.Appender, error) {
	return nil, errors.New("not implemented")
}

func (c AggrChunk) Iterator(_ chunkenc.Iterator) chunkenc.Iterator {
	return chunkenc.NewNopIterator()
}

func (c AggrChunk) NumSamples() int {
	x, err := c.Get(AggrCount)
	if err != nil {
		return 0
	}
	return x.NumSamples()
}

// ErrAggrNotExist is returned if a requested aggregation is not present in an AggrChunk.
var ErrAggrNotExist = errors.New("aggregate does not exist")

func (c AggrChunk) Encoding() chunkenc.Encoding {

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