Implementation:Lance format Lance Java RewriteOp

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

Overview

Description

The Rewrite class is an immutable operation for reorganizing data within a Lance dataset without changing its logical content. It implements the Operation interface and is the primary mechanism for data compaction and reordering. Because the operation modifies the physical addresses of existing rows, any vector or scalar indices that cover the rewritten fragments must be remapped.

The operation contains three components: a list of RewriteGroup objects (each mapping old fragments to new fragments), a list of RewrittenIndex objects (tracking index remapping), and an optional Index for fragment reuse optimization. All lists default to empty when not set.

Usage

Use Rewrite for compaction operations that consolidate small fragments into larger ones, remove deleted row tombstones, or physically reorder data for improved scan performance. After a rewrite, affected indices are remapped using the rewrittenIndices list.

Code Reference

Source Location

java/src/main/java/org/lance/operation/Rewrite.java

Signature

public class Rewrite implements Operation {
    public static Builder builder();
    public List<RewriteGroup> groups();
    public List<RewrittenIndex> rewrittenIndices();
    public Optional<Index> fragReuseIndex();
    public String name();  // returns "Rewrite"
}

Import

import org.lance.operation.Rewrite;

I/O Contract

Inputs

Parameter	Type	Required	Description
groups	List<RewriteGroup>	No	Groups mapping old fragments to new fragments (defaults to empty)
rewrittenIndices	List<RewrittenIndex>	No	Index remapping entries for affected indices (defaults to empty)
fragReuseIndex	Index	No	Optional index for fragment reuse optimization

Outputs

Return	Type	Description
groups()	List<RewriteGroup>	The rewrite groups mapping old to new fragments
rewrittenIndices()	List<RewrittenIndex>	Index remapping entries
fragReuseIndex()	Optional<Index>	The fragment reuse index, if present
name()	String	Returns "Rewrite" for JNI dispatch

Usage Examples

// Compact fragments: merge old fragments into new, larger fragments
RewriteGroup group = new RewriteGroup(oldFragments, newFragments);

Rewrite rewriteOp = Rewrite.builder()
    .groups(List.of(group))
    .rewrittenIndices(List.of(remappedIndex))
    .build();

String opName = rewriteOp.name(); // "Rewrite"
List<RewriteGroup> groups = rewriteOp.groups();

Related Pages

• Implementation:Lance_format_Lance_Java_CreateIndexOp -- Creates or replaces indices (may follow a rewrite)
• Implementation:Lance_format_Lance_Java_AppendOp -- Appends data (may cause fragmentation that rewrite consolidates)
• Implementation:Lance_format_Lance_Java_DataReplacementOp -- Replaces column data within fragments