Implementation:Lance format Lance Java IndexDescription

Knowledge Sources	Lance
Domains	Java_SDK, Indexing
Last Updated	2026-02-08 19:33 GMT

Overview

Description

IndexDescription is a final Java class in the org.lance.index package that provides a high-level description of an index, aggregating metadata across all segments. It mirrors the Rust IndexDescription trait and is returned from Dataset.describeIndices. The class holds the index name, field IDs, the underlying protobuf type URL, a human-readable index type identifier, the approximate number of rows indexed, per-segment Index metadata, and an optional JSON representation of index-specific details.

Usage

IndexDescription objects are returned by the Lance Java SDK when calling dataset describe-indices APIs. They give callers a comprehensive view of each index including its type, coverage, and implementation-specific details. All required fields are validated with Objects.requireNonNull in the constructor.

Code Reference

Source Location

java/src/main/java/org/lance/index/IndexDescription.java

Signature

public final class IndexDescription {
    public IndexDescription(
        String name,
        List<Integer> fieldIds,
        String typeUrl,
        String indexType,
        long rowsIndexed,
        List<Index> metadata,
        String detailsJson);

    public String getName();
    public List<Integer> getFieldIds();
    public String getTypeUrl();
    public String getIndexType();
    public long getRowsIndexed();
    public List<Index> getMetadata();
    public String getDetailsJson();
}

Import

import org.lance.index.IndexDescription;

I/O Contract

Constructor Inputs

Parameter	Type	Required	Description
name	String	Yes	Logical name of the index
fieldIds	List<Integer>	Yes	Field IDs the index is built on
typeUrl	String	Yes	Underlying protobuf type URL for index details
indexType	String	Yes	Human-readable index type (e.g., BTREE, INVERTED, IVF_PQ)
rowsIndexed	long	Yes	Approximate number of rows covered
metadata	List<Index>	Yes	Per-segment Index metadata objects
detailsJson	String	No	JSON representation of index-specific details (may be null)

Accessor Outputs

Method	Return Type	Description
getName()	String	The logical index name
getFieldIds()	List<Integer>	Field IDs covered by the index
getTypeUrl()	String	Protobuf type URL for details
getIndexType()	String	Human-readable index type identifier
getRowsIndexed()	long	Approximate rows indexed
getMetadata()	List<Index>	Per-segment metadata
getDetailsJson()	String	JSON details string (may be null)

Usage Examples

import org.lance.index.IndexDescription;
import org.lance.index.Index;

// IndexDescription is typically returned from dataset APIs
// Example: inspecting an IndexDescription
IndexDescription desc = dataset.describeIndices(criteria).get(0);

System.out.println("Index: " + desc.getName());
System.out.println("Type: " + desc.getIndexType());
System.out.println("Rows indexed: " + desc.getRowsIndexed());
System.out.println("Fields: " + desc.getFieldIds());

// Iterate per-segment metadata
for (Index seg : desc.getMetadata()) {
    System.out.println("  Segment UUID: " + seg.uuid());
    System.out.println("  Version: " + seg.indexVersion());
}

// Access raw JSON details if available
if (desc.getDetailsJson() != null) {
    System.out.println("Details: " + desc.getDetailsJson());
}

Related Pages

• Index - Per-segment index metadata contained in the description
• IndexCriteria - Criteria used to filter which index descriptions are returned
• IndexType - Enum of index type identifiers