pgx

Build Postgres Extensions with Rust!

pgx is a framework for developing PostgreSQL extensions in Rust and strives to be as idiomatic and safe as possible.

pgx supports Postgres v11-v15.

Feel free to join our Discord Server.

Key Features

• A fully managed development environment with cargo-pgx
  • cargo pgx new: Create new extensions quickly
  • cargo pgx init: Install new (or register existing) PostgreSQL installs
  • cargo pgx run: Run your extension and interactively test it in psql (or pgcli)
  • cargo pgx test: Unit-test your extension across multiple PostgreSQL versions
  • cargo pgx package: Create installation packages for your extension
  • More in the README.md!
• Target Multiple Postgres Versions
  • Support Postgres v11-v15 from the same codebase
  • Use Rust feature gating to use version-specific APIs
  • Seamlessly test against all versions
• Automatic Schema Generation
  • Implement extensions entirely in Rust
  • Automatic mapping for many Rust types into PostgreSQL
  • SQL schemas generated automatically (or manually via cargo pgx schema)
  • Include custom SQL with extension_sql! & extension_sql_file!
• Safety First
  • Translates Rust panic!s into Postgres ERRORs that abort the transaction, not the process
  • Memory Management follows Rust's drop semantics, even in the face of panic! and elog(ERROR)
  • #[pg_guard] procedural macro to ensure the above
  • Postgres Datums are Option<T> where T: FromDatum
    • NULL Datums are safely represented as Option::<T>::None
• First-class UDF support
  • Annotate functions with #[pg_extern] to expose them to Postgres
  • Return pgx::iter::SetOfIterator<'a, T> for RETURNS SETOF
  • Return pgx::iter::TableIterator<'a, T> for RETURNS TABLE (...)
  • Create trigger functions with #[pg_trigger]
• Easy Custom Types
  • #[derive(PostgresType)] to use a Rust struct as a Postgres type
    • By default, represented as a CBOR-encoded object in-memory/on-disk, and JSON as human-readable
    • Provide custom in-memory/on-disk/human-readable representations
  • #[derive(PostgresEnum)] to use a Rust enum as a Postgres enum
  • Composite types supported with the pgx::composite_type!("Sample") macro
• Server Programming Interface (SPI)
  • Safe access into SPI
  • Transparently return owned Datums from an SPI context
• Advanced Features
  • Safe access to Postgres' MemoryContext system via pgx::PgMemoryContexts
  • Executor/planner/transaction/subtransaction hooks
  • Safely use Postgres-provided pointers with pgx::PgBox<T> (akin to alloc::boxed::Box<T>)
  • #[pg_guard] proc-macro for guarding extern "C" Rust functions that need to be passed into Postgres
  • Access Postgres' logging system through eprintln!-like macros
  • Direct unsafe access to large parts of Postgres internals via the pgx::pg_sys module
  • New features added regularly!

System Requirements

• A Rust toolchain: rustc, cargo, and rustfmt. The recommended way to get these is from https://rustup.rs †
• git
• libclang 5.0 or greater (required by bindgen)
  • Ubuntu: apt install libclang-dev or apt install clang
  • RHEL: yum install clang
• tar
• bzip2
• GCC 7 or newer
• PostgreSQL's build dependencies ‡

† PGX has no MSRV policy, thus may require the latest stable version of Rust, available via Rustup

‡ A local PostgreSQL server installation is not required. cargo pgx can download and compile PostgreSQL versions on its own.

yum install centos-release-scl
yum install devtoolset-7
scl enable devtoolset-7 bash

Getting Started

First install the cargo-pgx sub-command and initialize the development environment:

cargo install --locked cargo-pgx
cargo pgx init

The init command downloads currently supported PostgreSQL versions, compiles them to ~/.pgx/, and runs initdb. It's also possible to use an existing (user-writable) PostgreSQL install, or install a subset of versions, see the README.md of cargo-pgx for details.

cargo pgx new my_extension
cd my_extension

This will create a new directory for the extension crate.

$ tree 
.
├── Cargo.toml
├── my_extension.control
├── sql
└── src
    └── lib.rs

2 directories, 3 files

The new extension includes an example, so you can go ahead and run it right away.

cargo pgx run

This compiles the extension to a shared library, copies it to the specified Postgres installation, starts that Postgres instance and connects you to a database named the same as the extension.

Once cargo-pgx drops us into psql we can load the extension and do a SELECT on the example function.

my_extension=# CREATE EXTENSION my_extension;
CREATE EXTENSION

my_extension=# SELECT hello_my_extension();
 hello_my_extension
---------------------
 Hello, my_extension
(1 row)

For more details on how to manage pgx extensions see Managing pgx extensions.

Upgrading

You can upgrade your current cargo-pgx installation by passing the --force flag to cargo install:

cargo install --force --locked cargo-pgx

As new Postgres versions are supported by pgx, you can re-run the pgx init process to download and compile them:

cargo pgx init

Mapping of Postgres types to Rust

There are also IntoDatum and FromDatum traits for implementing additional type conversions, along with #[derive(PostgresType)] and #[derive(PostgresEnum)] for automatic conversion of custom types.

Digging Deeper

• cargo-pgx sub-command
• Custom Types
• Postgres Operator Functions and Operator Classes/Families
• Shared Memory Support
• various examples

Caveats & Known Issues

There's probably more than are listed here, but a primary things of note are:

• Threading is not really supported. Postgres is strictly single-threaded. As such, if you do venture into using threads, those threads MUST NOT call any internal Postgres function, or otherwise use any Postgres-provided pointer. There's also a potential problem with Postgres' use of sigprocmask. This was being discussed on the -hackers list, even with a patch provided, but the conversation seems to have stalled (https://www.postgresql.org/message-id/flat/5EF20168.2040508%40anastigmatix.net#4533edb74194d30adfa04a6a2ce635ba).
• How to correctly interact with Postgres in an async context remains unexplored.
• pgx wraps a lot of unsafe code, some of which has poorly-defined safety conditions. It may be easy to induce illogical and undesirable behaviors even from safe code with pgx, and some of these wrappers may be fundamentally unsound. Please report any issues that may arise.
• Not all of Postgres' internals are included or even wrapped. This isn't due to it not being possible, it's simply due to it being an incredibly large task. If you identify internal Postgres APIs you need, open an issue and we'll get them exposed, at least through the pgx::pg_sys module.
• Windows is not supported. It could be, but will require a bit of work with cargo-pgx and figuring out how to compile pgx's "cshim" static library.
• Sessions started before ALTER EXTENSION my_extension UPDATE; will continue to see the old version of my_extension. New sessions will see the updated version of the extension.
• pgx is used by many "in production", but it is not "1.0.0" or above, despite that being recommended by SemVer for production-quality software. This is because there are many unresolved soundness and ergonomics questions that will likely require breaking changes to resolve, in some cases requiring cutting-edge Rust features to be able to expose sound interfaces. While a 1.0.0 release is intended at some point, it seems prudent to wait until it seems like a 2.0.0 release would not be needed the next week and the remaining questions can be deferred.

TODO

There's a few things on our immediate TODO list

• Automatic extension schema upgrade scripts, based on diffs from a previous git tag and HEAD. Likely, this will be built into the cargo-pgx subcommand and make use of https://github.com/zombodb/postgres-parser.
• More examples -- especially around memory management and the various derive macros #[derive(PostgresType/Enum)]

Feature Flags

PGX has optional feature flags for Rust code that do not involve configuring the version of Postgres used, but rather extend additional support for other kinds of Rust code. These are not included by default.

"time-crate": interop with the time crate

pgx once used direct interop with the excellent time crate. However, due to complications involving performance and accurate interop with Postgres, this feature is now considered deprecated in favor of a lower-overhead interop. You may still request implementations of TryFrom<time::Type> for pgx::MatchingType and From<time::Type> for pgx::MatchingType by enabling the "time-crate" feature.

"unsafe-postgres": Allow compilation for Postgres forks that have a different ABI

As of Postgres v15, forks are allowed to specify they use a different ABI than canonical Postgres. Since pgx makes countless assumptions about Postgres' internal ABI it is not possible for it to guarantee that a compiled pgx extension will probably execute within such a Postgres fork. You, dear compiler runner, can make this guarantee for yourself by specifying the unsafe-postgres feature flag. Otherwise, a pgx extension will fail to compile with an error similar to:

error[E0080]: evaluation of constant value failed
   --> pgx/src/lib.rs:151:5
    |
151 | /     assert!(
152 | |         same_slice(pg_sys::FMGR_ABI_EXTRA, b"xPostgreSQL\0"),
153 | |         "Unsupported Postgres ABI. Perhaps you need `--features unsafe-postgres`?",
154 | |     );
    | |_____^ the evaluated program panicked at 'Unsupported Postgres ABI. Perhaps you need `--features unsafe-postgres`?', pgx/src/lib.rs:151:5
    |

Contributing

We are most definitely open to contributions of any kind. Bug Reports, Feature Requests, Documentation, and even sponsorships.

If you'd like to contribute code via a Pull Request, please make it against our develop branch. The master branch is meant to represent what is currently available on crates.io.

Providing wrappers for Postgres' internals is not a straightforward task, and completely wrapping it is going to take quite a bit of time. pgx is generally ready for use now, and it will continue to be developed as time goes on. Your feedback about what you'd like to be able to do with pgx is greatly appreciated.

Hacking

If you're hacking on pgx and want to ensure your test will run correctly, you need to have the current implementation of cargo-pgx (from the revision you're working on) in your PATH.

An easy way would be to install cargo-local-install:

cargo install cargo-local-install

and then run cargo local-install to install cargo-pgx as specified in top-level's Cargo.toml.

Don't forget to prepend /path/to/pgx/bin to your PATH!

This approach can also be used in extensions to ensure a matching version of cargo-pgx is used.

License

Portions Copyright 2019-2021 ZomboDB, LLC.  
Portions Copyright 2021-2022 Technology Concepts & Design, Inc. <support@tcdi.com>. 
All rights reserved.
Use of this source code is governed by the MIT license that can be found in the LICENSE file.