custom-scan-api

To add a custom scan node to the PostgreSQL query planner, you implement a CustomPathMethods struct and register it via planner hooks so the optimizer can consider your custom physical operator during query execution.

A CustomScan in PostgreSQL extension development is a framework interface that allows you to define specialized executor nodes and runtime states to handle custom physical operators like columnar scans or hardware-accelerated joins.

PostgreSQL executes custom executor nodes by invoking the registered CustomExec methods at runtime, processing the CustomScanState structures to run specialized logic integrated directly within the database executor subsystem.

You need to implement a CustomPath for a PostgreSQL extension when building distributed query engines or columnar storage systems that require deep integration with the planner to ensure custom operators are selected efficiently.

Yes, the PostgreSQL custom scan API supports parallel-aware execution logic, allowing extensions to define CustomPath, CustomScan, and CustomExec methods that participate in parallel query execution within the database engine.

Custom scan extensions in PostgreSQL require deep integration with the planner and executor subsystems, necessitating advanced knowledge of database internals to correctly register CustomPathMethods and manage parallel-aware execution logic without breaking query optimization.