Delta Lake Migration

Migrate Delta Lake tables to Iceberg format with full history preservation

Delta Lake is a table format that supports Parquet file format and provides time travel and versioning features. When migrating data from Delta Lake to Iceberg, it is common to migrate all snapshots to maintain the history of the data.

Overview

Currently, Iceberg supports the Snapshot Table action for migrating from Delta Lake to Iceberg tables.

Since Delta Lake tables maintain transactions, all available transactions will be committed to the new Iceberg table as transactions in order.

For Delta Lake tables, any additional data files added after the initial migration will be included in their corresponding transactions and subsequently added to the new Iceberg table using the Add Transaction action.

The Add Transaction action, a variant of the Add File action, is still under development.

Enabling Migration from Delta Lake to Iceberg

The iceberg-delta-lake module is not bundled with Spark and Flink engine runtimes. To enable migration from Delta Lake features, the minimum required dependencies are:

• iceberg-delta-lake-1.2.1.jar
• delta-standalone_2.13-0.6.0.jar
• delta-storage-2.2.0.jar

Compatibilities

The module is built and tested with Delta Standalone 0.6.0 and supports Delta Lake tables with the following protocol version:

• minReaderVersion: 1
• minWriterVersion: 2

Refer to Delta Lake Table Protocol Versioning for more details about Delta Lake protocol versions.

API

The iceberg-delta-lake module provides an interface named DeltaLakeToIcebergMigrationActionsProvider, which contains actions that help convert from Delta Lake to Iceberg.

The supported actions are:

• snapshotDeltaLakeTable: Snapshot an existing Delta Lake table to an Iceberg table

Default Implementation

The iceberg-delta-lake module also provides a default implementation of the interface which can be accessed by:

DeltaLakeToIcebergMigrationActionsProvider defaultActions = 
    DeltaLakeToIcebergMigrationActionsProvider.defaultActions();

Snapshot Delta Lake Table to Iceberg

The action snapshotDeltaLakeTable reads the Delta Lake table’s transactions and converts them to a new Iceberg table with the same schema and partitioning in one Iceberg transaction. The original Delta Lake table remains unchanged.

The newly created table can be changed or written to without affecting the source table, but the snapshot uses the original table’s data files. Existing data files are added to the Iceberg table’s metadata and can be read using a name-to-id mapping created from the original table schema.

When inserts or overwrites run on the snapshot, new files are placed in the snapshot table’s location. The location defaults to be the same as that of the source Delta Lake Table. Users can also specify a different location for the snapshot table.

Because tables created by snapshotDeltaLakeTable are not the sole owners of their data files, they are prohibited from actions like expire_snapshots which would physically delete data files. Iceberg deletes, which only affect metadata, are still allowed.

In addition, any operations which affect the original data files will disrupt the snapshot’s integrity. DELETE statements executed against the original Delta Lake table will remove original data files and the snapshotDeltaLakeTable table will no longer be able to access them.

Usage

Required Input	Configured By	Description
Source Table Location	Argument sourceTableLocation	The location of the source Delta Lake table
New Iceberg Table Identifier	Configuration API as	The identifier specifies the namespace and table name for the new Iceberg table
Iceberg Catalog	Configuration API icebergCatalog	The catalog used to create the new Iceberg table
Hadoop Configuration	Configuration API deltaLakeConfiguration	The Hadoop Configuration used to read the source Delta Lake table

For detailed usage and other optional configurations, please refer to the SnapshotDeltaLakeTable API.

Output

Output Name	Type	Description
imported_files_count	long	Number of files added to the new table

Added Table Properties

The following table properties are added to the Iceberg table to be created by default:

Property Name	Value	Description
snapshot_source	delta	Indicates that the table is snapshot from a Delta Lake table
original_location	location of the Delta Lake table	The absolute path to the location of the original Delta Lake table
schema.name-mapping.default	JSON name mapping derived from the schema	The name mapping string used to read Delta Lake table’s data files

Example

Here’s a complete example of migrating a Delta Lake table to Iceberg:

import org.apache.iceberg.catalog.TableIdentifier;
import org.apache.iceberg.catalog.Catalog;
import org.apache.hadoop.conf.Configuration;
import org.apache.iceberg.delta.DeltaLakeToIcebergMigrationActionsProvider;

String sourceDeltaLakeTableLocation = "s3://my-bucket/delta-table";
String destTableLocation = "s3://my-bucket/iceberg-table";
TableIdentifier destTableIdentifier = TableIdentifier.of("my_db", "my_table");

// Iceberg Catalog fetched from engines like Spark or created via CatalogUtil.loadCatalog
Catalog icebergCatalog = ...;

// Hadoop Configuration fetched from engines like Spark 
// and have proper file system configuration to access the Delta Lake table
Configuration hadoopConf = ...;
    
DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
    .snapshotDeltaLakeTable(sourceDeltaLakeTableLocation)
    .as(destTableIdentifier)
    .icebergCatalog(icebergCatalog)
    .tableLocation(destTableLocation)
    .deltaLakeConfiguration(hadoopConf)
    .tableProperty("my_property", "my_value")
    .execute();

Migration Workflow

1. Add required dependencies

   Ensure the iceberg-delta-lake module and Delta Standalone dependencies are available in your classpath.

2. Verify Delta Lake compatibility

   Check that your Delta Lake table uses a compatible protocol version:

   • minReaderVersion: 1
   • minWriterVersion: 2
3. Prepare catalog and configuration

   Set up your Iceberg catalog and Hadoop configuration with proper credentials and access to both source and destination locations.

4. Execute snapshot

   Run the snapshotDeltaLakeTable action with the appropriate configuration:

   DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
       .snapshotDeltaLakeTable(sourceDeltaLakeTableLocation)
       .as(destTableIdentifier)
       .icebergCatalog(icebergCatalog)
       .tableLocation(destTableLocation)
       .deltaLakeConfiguration(hadoopConf)
       .execute();
   
5. Verify migration

   Query the new Iceberg table to verify:

   • Row counts match
   • Schema is correct
   • Historical snapshots are preserved
   • Data is readable
6. Update applications

   Switch read and write workloads to the new Iceberg table.

Best Practices

Preserve transaction history

The snapshot action preserves all Delta Lake transactions as Iceberg snapshots, maintaining full lineage and time-travel capabilities.

Plan for storage isolation

Consider specifying a different tableLocation for the Iceberg table to achieve full storage isolation from the Delta Lake table.

Avoid destructive operations on source

Do not run VACUUM or DELETE operations on the source Delta Lake table after migration, as this will break the Iceberg table’s ability to read the data files.

Monitor migration performance

Large Delta Lake tables with extensive transaction history may take longer to migrate. Monitor the process and plan accordingly.

Test with a subset first

Before migrating production tables, test the migration process on a smaller table or subset of data to validate the workflow.

Limitations

• Tables created via snapshotDeltaLakeTable cannot run expire_snapshots or other operations that physically delete data files
• Only Delta Lake tables with protocol versions minReaderVersion: 1 and minWriterVersion: 2 are supported
• The Add Transaction action for incremental updates is still under development