Here’s a well-structured draft for your technical blog post based on the provided Rust + pgrx Foreign Data Wrapper (FDW) code.
🚀 Building a Simple PostgreSQL FDW with Rust and pgrx
PostgreSQL Foreign Data Wrappers (FDW) enable PostgreSQL to query external data sources as if they were regular tables. Traditionally, FDWs are written in C, but with pgrx
, we can now build PostgreSQL extensions — including FDWs — in Rust, unlocking safety and modern tooling.
In this post, we’ll walk through creating a simple FDW using Rust and pgrx
that simulates reading rows from an external source (e.g., Redis or API). While it’s a stub, it demonstrates how to implement the core FDW lifecycle.
🛠️ What Can You Build with pgrx
?
- ✅ SQL Functions: Scalar, aggregate, and set-returning functions.
- ✅ Custom Types: Define composite types or enums in Rust.
- ✅ Foreign Data Wrappers (FDWs): Like the one in your example — connect PostgreSQL to external systems (Redis, APIs, file systems, etc.).
- ✅ Index Access Methods: Implement new index types.
- ✅ Background Workers: Run tasks in the background inside PostgreSQL.
- ✅ Hooks: Intercept or modify PostgreSQL internal behavior (like planner or executor hooks).
🌐 Under the hood:
- PostgreSQL communicates via C APIs.
pgrx
provides Rust-safe bindings to these APIs.- Memory management is handled carefully via
PgMemoryContexts
, matching PostgreSQL’s memory context model. - Rust functions are exposed to PostgreSQL as SQL-callable functions with the
#[pg_extern]
macro.
🏗️ Key Components of an default_fdw
PostgreSQL FDWs consist of several callback functions that handle different phases of query planning and execution: