TOASTed Column Values Appear as null

Issue

When Fivetran syncs data from a read replica, large TOASTed (The Oversized-Attribute Storage Technique) column values appear as null in the destination. Smaller values in the same columns sync correctly.

Environment

Connector: Amazon RDS for PostgreSQL

Resolution

To resolve this issue, update the REPLICA IDENTITY of the affected table from DEFAULT to FULL. To learn how, see the PostgreSQL ALTER TABLE documentation.

Setting REPLICA IDENTITY FULL ensures that PostgreSQL includes the complete row image in replication events, allowing us to sync TOASTed values correctly.

Cause

When your table uses the default replica identity, PostgreSQL may omit unchanged TOASTed values from replication events, resulting in null column values in the destination.

Smaller values, such as those with a pg_column_size under 1000 bytes, sync correctly because they are stored inline and included in replication events.