prestodb/presto · error · PrestoException

LANCE_ERROR

LANCE_ERROR

Error message

lance.root must be set when using lance.impl=dir

What it means

Configuration guard in LanceNamespaceHolder: the catalog was configured with lance.impl=dir (directory-backed namespace) but no lance.root property was supplied, so there is no root directory under which to resolve namespaces and datasets.

Source

Thrown at presto-lance/src/main/java/com/facebook/presto/lance/LanceNamespaceHolder.java:131

        // Parse namespace properties from catalog config
        String impl = config.getImpl();
        Map<String, String> properties = new HashMap<>();
        Map<String, String> storageOpts = new HashMap<>();
        for (Map.Entry<String, String> entry : namespaceProperties.entrySet()) {
            String key = entry.getKey();
            if (key.startsWith("lance.")) {
                String strippedKey = key.substring(6);
                properties.put(strippedKey, entry.getValue());
                if (strippedKey.startsWith("storage.")) {
                    storageOpts.put(strippedKey.substring(8), entry.getValue());
                }
            }
        }
        this.namespaceStorageOptions = ImmutableMap.copyOf(storageOpts);

        // Validate that 'root' is set for directory namespace
        if ("dir".equals(impl) && !properties.containsKey("root")) {
            throw new PrestoException(LanceErrorCode.LANCE_ERROR,
                    "lance.root must be set when using lance.impl=dir");
        }

        // For DirectoryNamespace, ensure default settings are applied
        if ("dir".equals(impl)) {
            properties.putIfAbsent("manifest_enabled", "true");
            properties.putIfAbsent("dir_listing_enabled", "true");
        }

        // Initialize namespace
        this.namespace = LanceNamespace.connect(impl, properties, allocator);

        // Initialize namespace level handling
        this.singleLevelNs = config.isSingleLevelNs();
        String parent = config.getParent();
        if (parent != null && !parent.isEmpty()) {
            // Parent uses '$' as delimiter to avoid conflicts with common path separators ('/' and '.')
            // and namespace-level separators. Example: "org$warehouse" -> ["org", "warehouse"]

View on GitHub (pinned to 55bb57d202)

Solutions

1. Set lance.root in the catalog properties to the directory that holds the Lance datasets
2. Or switch lance.impl to a managed-namespace implementation that does not require a local root

When it happens

Trigger: Thrown at presto-lance/src/main/java/com/facebook/presto/lance/LanceNamespaceHolder.java:131 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/b9030cbb54b03a33. Report an issue: GitHub.