Doc: Add a page explaining migration from other table formats to iceberg

docs/delta-lake-migration.md

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+---
+title: "Delta Lake Migration"
+url: delta-lake-migration
+aliases:
+    - "java/delta-lake-migration"
+menu:
+    main:
+        parent: "API"
+        weight: 400
+---
+<!--
+ - Licensed to the Apache Software Foundation (ASF) under one or more
+ - contributor license agreements.  See the NOTICE file distributed with
+ - this work for additional information regarding copyright ownership.
+ - The ASF licenses this file to You under the Apache License, Version 2.0
+ - (the "License"); you may not use this file except in compliance with
+ - the License.  You may obtain a copy of the License at
+ -
+ -   http://www.apache.org/licenses/LICENSE-2.0
+ -
+ - Unless required by applicable law or agreed to in writing, software
+ - distributed under the License is distributed on an "AS IS" BASIS,
+ - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ - See the License for the specific language governing permissions and
+ - limitations under the License.
+ -->
+# Delta Lake Table Migration
+Iceberg supports converting Delta Lake tables to Iceberg tables through the `iceberg-delta-lake` module
+by using [Delta Standalone](https://docs.delta.io/latest/delta-standalone.html) to read logs of Delta lake tables.
+
+
+## Enabling Migration from Delta Lake to Iceberg
+The `iceberg-delta-lake` module is not bundled with Spark and Flink engine runtimes. Users need to manually include this module in their environment to enable the conversion.
+Also, users need to provide [Delta Standalone](https://github.com/delta-io/connectors/releases/tag/v0.6.0) and [Delta Storage](https://repo1.maven.org/maven2/io/delta/delta-storage/2.2.0/)
+because they are what `iceberg-delta-lake` uses to read Delta Lake tables.
+
+## 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
+
+Please refer to [Delta Lake Table Protocol Versioning](https://docs.delta.io/latest/versioning.html) for more details about Delta Lake protocol versions.
+
+For delta lake table contains `TimestampType` columns, please make sure to set table property `read.parquet.vectorization.enabled` to `false` since the vectorized reader doesn't support `INT96` yet.
+Such support is under development in the [PR#6962](https://github.com/apache/iceberg/pull/6962)
+
+## API
+The `iceberg-delta-lake` module provides an interface named `DeltaLakeToIcebergMigrationActionsProvider`, which contains actions that helps converting 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
+```java
+DeltaLakeToIcebergMigrationActionsProvider defaultActions = DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
+```
+
+### `snapshotDeltaLakeTable`
+The action reads the Delta Lake table's most recent snapshot and converts it 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 is default to be the same as that
+of the source Delta Lake Table. Users can also specify a different location for the snapshot table.
+
+{{< hint info >}}
+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 effect 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.
+{{< /hint >}}
+
+#### Arguments
+The delta table's location is required to be provided when initializing the action.
+
+| Argument Name | Required? | Type | Description |
+|---------------|-----------|------|-------------|
+|`sourceTableLocation` | Yes | String | The location of the source Delta Lake table | 
+
+#### Configurations
+The configurations can be gave via method chaining
+
+| Method Name | Arguments      | Required? | Type                                       | Description                                                                                                  |
+|---------------------------|----------------|-----------|--------------------------------------------|--------------------------------------------------------------------------------------------------------------|
+| `as`                      | `identifier`   | Yes       | org.apache.iceberg.catalog.TableIdentifier | The identifier of the Iceberg table to be created.                                                           |
+| `icebergCatalog`          | `catalog`      | Yes       | org.apache.iceberg.catalog.Catalog         | The Iceberg catalog for the Iceberg table to be created                                                      |
+| `deltaLakeConfiguration`  | `conf`         | Yes       | org.apache.hadoop.conf.Configuration       | The Hadoop Configuration to access Delta Lake Table's log and datafiles                                      |
+| `tableLocation`           | `location`     | No        | String                                     | The location of the Iceberg table to be created. Defaults to the same location as the given Delta Lake table |
+| `tableProperty`           | `name`,`value` | No        | String, String                             | A property entry to add to the Iceberg table to be created                                                   |
+| `tableProperties`         | `properties`   | No        | Map<String, String>                        | Properties to add to the the Iceberg table to be created                                                     |
+
+#### 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 |
+
+#### Examples
+Snapshot a Delta Lake table located at `s3://my-bucket/delta-table` to an Iceberg table named `my_table` in the `my_db` database in the `my_catalog` catalog.
+```java
+DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
+    .snapshotDeltaLakeTable("s3://my-bucket/delta-table")
+    .as("my_db.my_table")
+    .icebergCatalog("my_catalog")
+    .deltaLakeConfiguration(new Configuration())
+    .execute();
+```
+Snapshot a Delta Lake table located at `s3://my-bucket/delta-table` to an Iceberg table named `my_table` in the `my_db` database in the `my_catalog` catalog at a manually
+specified location `s3://my-bucket/snapshot-loc`. Also, add a table property `my_property` with value `my_value` to the Iceberg table.
+```java
+DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
+    .snapshotDeltaLakeTable("s3://my-bucket/delta-table")
+    .as("my_db.my_table")
+    .icebergCatalog("my_catalog")
+    .deltaLakeConfiguration(new Configuration())
+    .tableLocation("s3://my-bucket/snapshot-loc")
+    .tableProperty("my_property", "my_value")
+    .execute();
+```

docs/table-migration.md

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+---
+title: "Table Migration"
+url: table-migration
+weight: 1300
+menu: main
+---
+<!--
+ - Licensed to the Apache Software Foundation (ASF) under one or more
+ - contributor license agreements.  See the NOTICE file distributed with
+ - this work for additional information regarding copyright ownership.
+ - The ASF licenses this file to You under the Apache License, Version 2.0
+ - (the "License"); you may not use this file except in compliance with
+ - the License.  You may obtain a copy of the License at
+ -
+ -   http://www.apache.org/licenses/LICENSE-2.0
+ -
+ - Unless required by applicable law or agreed to in writing, software
+ - distributed under the License is distributed on an "AS IS" BASIS,
+ - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ - See the License for the specific language governing permissions and
+ - limitations under the License.
+ -->
+# Table Migration
+Apache Iceberg supports converting existing tables in other formats to Iceberg tables. This section introduces the general concept of table migration, its approaches, and existing implementations in Iceberg.
+
+## Migration Approaches
+There are two main approaches to perform table migration: CTAS (Create Table As Select) and in-place migration.
+
+### Create-Table-As-Select Migration
+CTAS migration involves creating a new Iceberg table and copying data from the existing table to the new one. This method is preferred when you want to completely cut ties with your old table, ensuring the new table is independent and fully managed by Iceberg.
+However, CTAS migration may require more time to complete and might not be suitable for production use cases where downtime is not acceptable.
+![CTAS Migration](../../../img/iceberg-CTAS.png)
+### In-Place Migration
+In-place migration retains the existing data files but adds Iceberg metadata on top of them. This approach is faster and does not require copying data, making it more suitable for production use cases.
+![In-Place Migration](../../../img/iceberg-In-place.png)
+## In-Place Migration Actions
+Apache Iceberg primarily supports the in-place migration approach, which includes three important actions:
+
+1. Snapshot Table
+2. Migrate Table
+3. Add Files
+
+### Snapshot Table
+The Snapshot Table action creates a new iceberg table with the same schema and partitioning as the source table, leaving the source table unchanged during and after the action.
+
+**Step 1:** Create a new Iceberg table with the same metadata (schema, partition spec, etc.) as the source table
+![Snapshot Table Step 1](../../../img/iceberg-snapshotaction-step1.png)
+
+**Step 2:** Commit all data files across all partitions to the new Iceberg table. The source table remains unchanged.
+![Snapshot Table Step 2](../../../img/iceberg-snapshotaction-step2.png)
+### Migrate Table
+The Migrate Table action also creates a new Iceberg table with the same schema and partitioning as the source table. However, during the action execution, it locks and drops the source table from the catalog.
+Consequently, Migrate Table requires all readers and writers working on the source table to be stopped before the action is performed.
+
+**Step 1:** Stop all readers and writers interacting with the source table
+![Migrate Table Step 1](../../../img/iceberg-migrateaction-step1.png)
+
+**Step 2:** Create a new Iceberg table with the same metadata (schema, partition spec, etc.) as the source table. Rename the source table for a backup in case of failure and rollback.
+![Migrate Table Step 2](../../../img/iceberg-migrateaction-step2.png)
+
+**Step 3:** Commit all data files across all partitions to the new Iceberg table. Drop the source table.
+![Migrate Table Step 3](../../../img/iceberg-migrateaction-step3.png)
+### Add Files
+After the initial step (either Snapshot Table or Migrate Table), it is common to find some data files that have not been migrated. These files often originate from concurrent writers who continue writing to the source table during or after the migration process.
+In practice, these files can be new data files in Hive tables or new snapshots (versions) of Delta Lake tables. The Add Files action is essential for incorporating these files into the Iceberg table.
+
+## In-Place Migration Completion
+Once all data files have been migrated and there are no more concurrent writers writing to the source table, the migration process is complete.
+Readers and writers can now switch to the new Iceberg table for their operations.
+
+## Migration Implementation: From Hive/Spark to Iceberg
+Apache Hive and Apache Spark are two popular data warehouse systems used for big data processing and analysis.
+However, both systems do not natively support time travel or rollback to previous snapshots.
+When migrating data to an Iceberg table, which provides versioning and transactional updates, only the most recent data files need to be migrated.
+
+Iceberg supports all three migration actions: Snapshot Table, Migrate Table, and Add Files for migrating from Hive or Spark tables to Iceberg tables. Since Hive or Spark tables do not maintain snapshots,
+the migration process essentially involves creating a new Iceberg table with the existing schema and committing all data files across all partitions to the new Iceberg table.
+After the initial migration, any new data files are added to the new Iceberg table using the Add Files action.
+
+For more details on how to perform the migration on Hive/Spark tables, please refer to the [Table Migration via Spark Procedures](../spark-procedures/#table-migration) page.
+
+## Migration Implementation: From Delta Lake to Iceberg
+Delta Lake is a popular data storage system that 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.
+
+Currently, Iceberg only supports the Snapshot Table action for migrating from Delta Lake to Iceberg tables. Since Delta Lake tables maintain snapshots, all available snapshots 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 snapshots and subsequently added to the new Iceberg table using the Add Snapshot action. The Add Snapshot action, a variant of the Add File action, is still under development.
+
+For more details on how to perform the migration on Delta Lake tables, please refer to the [Delta Lake Migration](../delta-lake-migration/#delta-lake-table-migration) page.