#postgres #parser #query #postgressql

postgres-parser

An llvm-based safe wrapper for PostgresSQL’s query parser. Currently based on v12.3.

6 releases

0.0.8 Nov 8, 2020
0.0.7 Nov 7, 2020
0.0.4 Jun 7, 2020

#174 in Database interfaces

31 downloads per month

PostgreSQL

1MB
35K SLoC

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postgres-parser

This project is the beginnings of using Postgres v13.0's SQL Parser (effectively gram.y and the List *raw_parser(const char *str) function) from Rust.

The way this works is by downloading the Postgres source code, patching a few of its Makefiles (see patches/makefiles-13.0.patch), compiling it to LLVM IR, optimizing/assembling that to LLVM bitcode, performing link-time optimization (LTO) to generate a static library containing only the symbols/code necessary to properly use Postgres' raw_parser() function, and finally, linking against that library with Rust.

This is accomplished via a custom build.rs script, which shells out to build.sh to perform all the hard work.

At the end of the process we're left with a libpostgres_parser.a archive, which build.rs instructs cargo to link against.

Using this Crate

Using this create is just like any other. Add it as a dependency to your Cargo.toml:

[dependencies]
postgres-parser = "0.0.8"

Additionally, see the System Requirements section below.

Here's a simple example that outputs a SQL parse tree as JSON.

use postgres_parser::*;

fn main() {
    let args: Vec<String> = std::env::args().collect();
    let query_string = args.get(1).expect("no arguments");
    let parse_list = match parse_query(query_string) {
        Ok(query) => query,
        Err(e) => {
            eprintln!("{:?}", e);
            std::process::exit(1);
        }
    };

    let as_json = serde_json::to_string_pretty(&parse_list).expect("failed to convert to json");
    println!("{}", as_json);
}

System Requirements

For an Ubuntu-based Linux system you'll need:

$ sudo apt-get install clang llvm make curl
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

For MacOS you'll need:

$ brew install wget
$ brew install llvm
$ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

As Linux goes, so far this has been tested on Ubuntu 18.04 with LLVM 6.0.0, and Ubuntu 20.04 with LLVM 10.0.0.

You'll also want to make sure the LLVM and clang tools are on your $PATH. Especially the clang, opt, and llvm-ar tools.

Building

Build this just like any other Rust binary crate:

$ cargo build [--release]

This will take awhile as again, the build process:

  • Downloads Postgres source code
  • Configures Postgres
  • Compiles Postgres (in parallel up to # of your CPUS)
  • Optimizes the resulting LLVM ir into LLVM bitcode

On my relatively new MacBook Pro 16", this process takes about 2.5 minutes the first time.

On my incredibly old Mac Mini, running Ubuntu 16.04 (yikes!), this process takes about 25 minutes. So be patient if you have an older computer.

Subsequent builds (assuming no cargo clean) are able to elide all of the above steps as the final libpostgres_parser.a archive artifact is cached in the target/ directory.

Known Issues

  • While the postgres parser supports UTF8 input, enabling this somehow causes the resulting compiled binary to bloat to nearly 10 megabytes. Seemingly, including Postgres' SetDatabaseEncoding function causes LLVM's opt to fail to do proper global dead code elimination. This is being investigated. As such, input must match Postgres' SQL_ASCII encoding for now

  • Building on MacOS with XCode >=11.4.0 doesn't work. This appears to be a problem with these versions of XCode. This is the bug: https://openradar.appspot.com/FB7647406. This happens while building Postgres. Any suggestions for a work around would be greatly appreciated.

  • Single-threaded query parsing... Postgres isn't thread safe, so we're required to lock on a Mutex while parsing queries. Which means one-at-a-time. There may be some things we can do in the future to improve this situation. The underlying dilemma is around how Postgres allocates memory, and this approach to embedding Postgres' parser necessitates it use that system

Please Help!

We'd sincerely appreciate the time and effort you spend cloning this repo and at least trying to cargo test --all. If it doesn't work, or if these instructions are bad, we definitely want to know. We'd like this to be as easy as possible for everyone.

Furthermore, this is v0.0.1. Please feel free to submit bug reports, feature requests, and most especially Pull Requests.

Thanks

Thanks for checking this out. Here's the obligatory GitHub Sponsors link.

If you like what we're doing and where this is going, your sponsorship will keep us motivated.

Dependencies

~0.6–2.5MB
~56K SLoC