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
+menu:
+  main:
+    parent: "Migration"
+    weight: 300
+---
+<!--
+ - 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
+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.
+
+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](https://repo1.maven.org/maven2/org/apache/iceberg/iceberg-delta-lake/1.2.1/iceberg-delta-lake-1.2.1.jar)
+- [delta-standalone-0.6.0](https://repo1.maven.org/maven2/io/delta/delta-standalone_2.13/0.6.0/delta-standalone_2.13-0.6.0.jar)
+- [delta-storage-2.2.0](https://repo1.maven.org/maven2/io/delta/delta-storage/2.2.0/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
+
+Please refer to [Delta Lake Table Protocol Versioning](https://docs.delta.io/latest/versioning.html) for more details about Delta Lake protocol versions.
+
+### 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()
+```
+
+## 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 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 >}}
+
+#### Usage
+| Required Input               | Configured By                                                                                                                                                                                             | Description                                                                     |
+|------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------|
+| Source Table Location        | Argument [`sourceTableLocation`](https://iceberg.apache.org/javadoc/latest/org/apache/iceberg/delta/DeltaLakeToIcebergMigrationActionsProvider.html#snapshotDeltaLakeTable(java.lang.String))             | The location of the source Delta Lake table                                     | 
+| New Iceberg Table Identifier | Configuration API [`as`](https://iceberg.apache.org/javadoc/latest/org/apache/iceberg/delta/SnapshotDeltaLakeTable.html#as(org.apache.iceberg.catalog.TableIdentifier))                                   | The identifier specifies the namespace and table name for the new iceberg table |
+| Iceberg Catalog              | Configuration API [`icebergCatalog`](https://iceberg.apache.org/javadoc/latest/org/apache/iceberg/delta/SnapshotDeltaLakeTable.html#icebergCatalog(org.apache.iceberg.catalog.Catalog))                   | The catalog used to create the new iceberg table                                |
+| Hadoop Configuration         | Configuration API [`deltaLakeConfiguration`](https://iceberg.apache.org/javadoc/latest/org/apache/iceberg/delta/SnapshotDeltaLakeTable.html#deltaLakeConfiguration(org.apache.hadoop.conf.Configuration)) | The Hadoop Configuration used to read the source Delta Lake table.              |
+
+For detailed usage and other optional configurations, please refer to the [SnapshotDeltaLakeTable API](https://iceberg.apache.org/javadoc/latest/org/apache/iceberg/delta/SnapshotDeltaLakeTable.html)
+
+#### 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
+```java
+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");
+Catalog icebergCatalog = ...; // Iceberg Catalog fetched from engines like Spark or created via CatalogUtil.loadCatalog
+Configuration hadoopConf = ...; // Hadoop Configuration fetched from engines like Spark and have proper file system configuration to access the Delta Lake table.
+
+DeltaLakeToIcebergMigrationActionsProvider.defaultActions()
+    .snapshotDeltaLakeTable(sourceDeltaLakeTableLocation)
+    .as(destTableIdentifier)
+    .icebergCatalog(icebergCatalog)
+    .tableLocation(destTableLocation)
+    .deltaLakeConfiguration(hadoopConf)
+    .tableProperty("my_property", "my_value")
+    .execute();
+```

docs/hive-migration.md

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+---
+title: "Hive Migration"
+url: hive-migration
+menu:
+  main:
+    parent: "Migration"
+    weight: 200
+---
+<!--
+ - 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.
+ -->
+
+# Hive Table Migration
+Apache Hive supports ORC, Parquet, and Avro file formats that could be migrated to Iceberg.
+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 tables to Iceberg tables. Since Hive 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.
+
+## Enabling Migration from Hive to Iceberg
+The Hive table migration actions are supported by the Spark Integration module via Spark Procedures. 
+The procedures are bundled in the Spark runtime jar, which is available in the [Iceberg Release Downloads](https://iceberg.apache.org/releases/#downloads).
+
+## Snapshot Hive Table to Iceberg
+To snapshot a Hive table, users can run the following Spark SQL:
+```sql
+CALL catalog_name.system.snapshot('db.source', 'db.dest')
+```
+See [Spark Procedure: snapshot](../spark-procedures/#snapshot) for more details.
+
+## Migrate Hive Table To Iceberg
+To migrate a Hive table to Iceberg, users can run the following Spark SQL:
+```sql
+CALL catalog_name.system.migrate('db.sample')
+```
+See [Spark Procedure: migrate](../spark-procedures/#migrate) for more details.
+
+## Add Files From Delta Lake Table to Iceberg
+To add data files from a Hive table to a given Iceberg table, users can run the following Spark SQL:
+```sql
+CALL spark_catalog.system.add_files(
+table => 'db.tbl',
+source_table => 'db.src_tbl'
+)
+```
+See [Spark Procedure: add_files](../spark-procedures/#add_files) for more details.

docs/table-migration.md

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+---
+title: "Overview"
+url: table-migration
+menu:
+  main:
+    parent: "Migration"
+    weight: 100
+---
+<!--
+ - 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 methods for executing table migration: full data migration and in-place metadata migration.
+
+Full data migration involves copying all data files from the source table to the new Iceberg table. This method makes the new table fully isolated from the source table, but is slower and doubles the space.
+In practice, users can use operations like [Create-Table-As-Select](../spark-ddl/#create-table--as-select), [INSERT](../spark-writes/#insert-into), and Change-Data-Capture pipelines to perform such migration.
+
+In-place metadata migration preserves the existing data files while incorporating Iceberg metadata on top of them.
+This method is not only faster but also eliminates the need for data duplication. However, the new table and the source table are not fully isolated. In other words, if any processes vacuum data files from the source table, the new table will also be affected.
+
+In this doc, we will describe more about in-place metadata migration.
+
+![In-Place Metadata Migration](../../../img/iceberg-in-place-metadata-migration.png)
+
+Apache Iceberg supports the in-place metadata migration approach, which includes three important actions: **Snapshot Table**, **Migrate Table**, and **Add Files**.
+
+## Snapshot Table
+The Snapshot Table action creates a new iceberg table with a different name and with the same schema and partitioning as the source table, leaving the source table unchanged during and after the action.
+
+- Create a new Iceberg table with the same metadata (schema, partition spec, etc.) as the source table and a different name. Readers and Writers on the source table can continue to work.
+
+![Snapshot Table Step 1](../../../img/iceberg-snapshotaction-step1.png)
+
+- Commit all data files across all partitions to the new Iceberg table. The source table remains unchanged. Readers can be switched to the new Iceberg table.
+
+![Snapshot Table Step 2](../../../img/iceberg-snapshotaction-step2.png)
+
+- Eventually, all writers can be switched to the new Iceberg table. Once all writers are transitioned to the new Iceberg table, the migration process will be considered complete.
+
+## 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 modifications working on the source table to be stopped before the action is performed.
+
+Stop all writers interacting with the source table. Readers that also support Iceberg may continue reading.
+
+![Migrate Table Step 1](../../../img/iceberg-migrateaction-step1.png)
+
+- Create a new Iceberg table with the same identifier and 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)
+
+- Commit all data files across all partitions to the new Iceberg table. Drop the source table. Writers can start writing to the new Iceberg 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.
+
+# Migrating From Different Table Formats
+* [From Hive to Iceberg](../hive-migration)
+* [From Delta Lake to Iceberg](../delta-lake-migration)