MemPalace/mempalace · error · BackendMismatchError

palace at {palace_path!r} contains multiple backend artifact

Error message

palace at {palace_path!r} contains multiple backend artifacts: {', '.join(detected_backends)}

What it means

Error "palace at {palace_path!r} contains multiple backend artifacts: {', '.join(detected_backends)}" thrown in MemPalace/mempalace.

Source

Thrown at mempalace/palace.py:400

    4. Detected existing palace artifacts.
    5. ``chroma``.

    If artifacts for a different backend are already present, raise
    ``BackendMismatchError`` so normal write paths cannot silently mix storage
    formats in one palace directory.
    """
    explicit = explicit or os.environ.get(_EXPLICIT_BACKEND_ENV)
    selected = resolve_backend_for_palace(
        explicit=explicit.strip().lower() if explicit else None,
        config_value=_config_backend_value(palace_path),
        env_value=_env_backend_value(),
        palace_path=palace_path,
        default="chroma",
    )
    get_backend_class(selected)
    detected_backends = detect_backends_for_path(palace_path)
    if len(detected_backends) > 1:
        raise BackendMismatchError(
            f"palace at {palace_path!r} contains multiple backend artifacts: "
            f"{', '.join(detected_backends)}"
        )
    detected = detected_backends[0] if detected_backends else None
    if detected and detected != selected:
        raise BackendMismatchError(
            f"palace at {palace_path!r} contains {detected!r} backend artifacts, "
            f"but {selected!r} was selected"
        )
    return selected


_MULTI_PROCESS_WRITER_BACKENDS = frozenset({"pgvector", "qdrant"})


def backend_requires_single_writer(backend_name: str) -> bool:
    """Return whether a backend needs one process-lifetime writer owner.

View on GitHub (pinned to 06cb6987f0)

Solutions

1. Remove the artifacts of the unused backend, or select the backend explicitly

When it happens

Trigger: Thrown at mempalace/palace.py:400 when the library encounters an invalid state.

Common situations: Multiple backend artifact sets were found in one palace directory.

AI-assisted analysis of MemPalace/mempalace@06cb6987f0 (2026-08-15). Data as JSON: /api/errors/37fc97fb740b47a8. Report an issue: GitHub.