Add comprehensive migration documentation section

Create consolidated migration guides covering:
- Overview page with migration path comparison table
- PostgreSQL to Doris (JDBC Catalog, Flink CDC, Export/Import)
- MySQL to Doris (Flink CDC, JDBC Catalog, DataX)
- Elasticsearch to Doris (ES Catalog, inverted index migration)
- Other OLAP systems (ClickHouse, Greenplum, Hive/Iceberg/Hudi)

Each guide includes data type mappings, step-by-step instructions,
and troubleshooting for common issues. Chinese translations included.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dataroaring

docs/migration/elasticsearch-to-doris.md

@@ -0,0 +1,150 @@
+---
+{
+    "title": "Migration Overview",
+    "language": "en",
+    "description": "Guide to migrating data from various databases and data systems to Apache Doris"
+}
+---
+
+Apache Doris provides multiple methods to migrate data from various source systems. This guide helps you choose the best migration approach based on your source system and requirements.
+
+## Migration Paths
+
+| Source System | Recommended Method | Real-time Sync | Full Migration | Incremental |
+|---------------|-------------------|----------------|----------------|-------------|
+| [PostgreSQL](./postgresql-to-doris.md) | JDBC Catalog / Flink CDC | Yes | Yes | Yes |
+| [MySQL](./mysql-to-doris.md) | Flink CDC / JDBC Catalog | Yes | Yes | Yes |
+| [Elasticsearch](./elasticsearch-to-doris.md) | ES Catalog | No | Yes | Manual |
+| [ClickHouse](./other-olap-to-doris.md#clickhouse) | JDBC Catalog | No | Yes | Manual |
+| [Greenplum](./other-olap-to-doris.md#greenplum) | JDBC Catalog | No | Yes | Manual |
+| [Hive/Iceberg/Hudi](./other-olap-to-doris.md#data-lake) | Multi-Catalog | No | Yes | Yes |
+
+## Choosing a Migration Method
+
+### Catalog-Based Migration (Recommended)
+
+Doris's [Multi-Catalog](../lakehouse/lakehouse-overview.md) feature allows you to directly query external data sources without data movement. This is the recommended approach for:
+
+- **Initial exploration**: Query source data before deciding on migration strategy
+- **Hybrid queries**: Join data across Doris and external sources
+- **Incremental migration**: Gradually move data while keeping source accessible
+
+```sql
+-- Create a catalog to connect to your source
+CREATE CATALOG pg_catalog PROPERTIES (
+    'type' = 'jdbc',
+    'user' = 'username',
+    'password' = 'password',
+    'jdbc_url' = 'jdbc:postgresql://host:5432/database',
+    'driver_url' = 'postgresql-42.5.6.jar',
+    'driver_class' = 'org.postgresql.Driver'
+);
+
+-- Query source data directly
+SELECT * FROM pg_catalog.schema_name.table_name LIMIT 10;
+
+-- Migrate data with INSERT INTO SELECT
+INSERT INTO doris_db.doris_table
+SELECT * FROM pg_catalog.schema_name.source_table;
+```
+
+### Flink CDC (Real-time Synchronization)
+
+[Flink CDC](../ecosystem/flink-doris-connector.md) is ideal for:
+
+- **Real-time data sync**: Capture changes as they happen
+- **Full database migration**: Sync entire databases with automatic table creation
+- **Zero-downtime migration**: Keep source and Doris in sync during transition
+
+### Export-Import Method
+
+For scenarios where direct connectivity is limited:
+
+1. Export data from source system to files (CSV, Parquet, JSON)
+2. Stage files in object storage (S3, GCS, HDFS)
+3. Load into Doris using [S3 Load](../data-operate/import/data-source/amazon-s3.md) or [Broker Load](../data-operate/import/import-way/broker-load-manual.md)
+
+## Migration Planning Checklist
+
+Before migrating, consider the following:
+
+1. **Data Volume Assessment**
+   - Total data size and row count
+   - Daily/hourly data growth rate
+   - Historical data retention requirements
+
+2. **Schema Design**
+   - Choose appropriate [Data Model](../table-design/data-model/overview.md) (Duplicate, Unique, Aggregate)
+   - Plan [Partitioning](../table-design/data-partitioning/data-distribution.md) strategy
+   - Define [Bucketing](../table-design/data-partitioning/data-bucketing.md) keys
+
+3. **Data Type Mapping**
+   - Review type compatibility (see migration guides for specific mappings)
+   - Handle special types (arrays, JSON, timestamps with timezone)
+
+4. **Performance Requirements**
+   - Query latency expectations
+   - Concurrent query load
+   - Data freshness requirements
+
+5. **Migration Window**
+   - Acceptable downtime (if any)
+   - Sync vs. async migration needs
+
+## Best Practices
+
+### Start with a Pilot Table
+
+Before migrating your entire database, test with a representative table:
+
+```sql
+-- 1. Create the Doris table with appropriate schema
+CREATE TABLE pilot_table (
+    id INT,
+    created_at DATETIME,
+    data VARCHAR(255)
+)
+UNIQUE KEY(id)
+DISTRIBUTED BY HASH(id) BUCKETS 8;
+
+-- 2. Migrate data
+INSERT INTO pilot_table
+SELECT id, created_at, data
+FROM source_catalog.db.source_table;
+
+-- 3. Validate row counts
+SELECT COUNT(*) FROM pilot_table;
+SELECT COUNT(*) FROM source_catalog.db.source_table;
+```
+
+### Batch Large Migrations
+
+For tables with billions of rows, migrate in batches:
+
+```sql
+-- Migrate by date range
+INSERT INTO doris_table
+SELECT * FROM source_catalog.db.source_table
+WHERE created_at >= '2024-01-01' AND created_at < '2024-02-01';
+```
+
+### Monitor Migration Progress
+
+Track load jobs using:
+
+```sql
+-- Check active load jobs
+SHOW LOAD WHERE STATE = 'LOADING';
+
+-- Check recent load history
+SHOW LOAD ORDER BY CreateTime DESC LIMIT 10;
+```
+
+## Next Steps
+
+Choose your source system to see detailed migration instructions:
+
+- [PostgreSQL to Doris](./postgresql-to-doris.md)
+- [MySQL to Doris](./mysql-to-doris.md)
+- [Elasticsearch to Doris](./elasticsearch-to-doris.md)
+- [Other OLAP Systems to Doris](./other-olap-to-doris.md)