Different Ways to Transfer Large Data from One PostgreSQL Database to Another

Large data migration between Postgre-SQL databases needs to be done with precaution to avoid inefficiency, loss of data, or downtime. Below are different methods used under different circumstances depending on database size, network status, and real-time needs.

This method entails copying the schema and data of the database into a file and restoring it to the destination database.

• Method: Employing logical dump tools such as pg_dump and pg_restore to import and export data.
• Best For: Small and medium databases for which downtime can be tolerated.
• Pros: Easy, dependable, and does not need direct connectivity with the database.
• Cons: Too slow with big datasets and introduces downtime in the restore phase.

Instead of exporting structured data, this method copies entire database files between servers.

• Method: Uses pg_basebackup or direct file copy from PostgreSQL’s data directory.
• Best For: Transferring entire databases between servers running the same PostgreSQL version.
• Advantages: Faster than logical backup; preserves indexes and configurations.
• Disadvantages: Requires database downtime and direct access to filesystem.

For continuous, real-time data transfer, PostgreSQL's built-in streaming replication can be used.

• Method: Configures a secondary (replica) database that continuously syncs with the primary.
• Best For: Large datasets that need minimal downtime and consistency.
• Advantages: Keeps the replica in sync with the primary; efficient for real-time data transfer.
• Disadvantages: Requires continuous network connection and does not work for selective table transfers.

Unlike physical replication, logical replication allows transferring specific tables or schemas between databases.

• Method: Uses pglogical or PostgreSQL's built-in logical replication feature.
• Best For: When only a subset of data needs to be transferred incrementally.
• Advantages: Flexible, supports selective table replication without needing full database access.
• Disadvantages: Requires PostgreSQL 10+ and additional setup for conflict resolution.

FDW allows a PostgreSQL instance to query and fetch data from another PostgreSQL instance directly.

• Method: Uses postgres_fdw extension to access and copy data between databases.
• Best For: When live data needs to be accessed before full migration.
• Advantages: Allows cross-database querying and selective data transfer.
• Disadvantages: Performance issues for very large datasets; not optimized for bulk transfer.

Third-party ETL tools may assist in big-scale migration with the support of data transformation.

• Method: Applications such as Apache Nifi, Talend, or AWS DMS can perform extraction, transformation, and load operations among databases.
• Best For: Sophisticated migrations with data cleansing and transformation.

This method transfers data using SQL-based insertion from one database to another.

• Method: Use INSERT INTO ... SELECT * FROM ... via database links or FDW.
• Best For: Small to medium datasets where speed is not a major concern.
• Advantages: Simple and works without additional tools.
• Disadvantages: Can be slow for very large tables and may require locking 

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