Announcing the first Postgres extension to run WebAssembly

Ivan Enderlin
Aug 29, 2019 · 4 min read

WebAssembly is a portable binary format. That means the same program can run anywhere.

To uphold this bold statement, each language, platform and system must be able to run WebAssembly — as fast and safely as possible.

Let’s say it again. Wasmer is a WebAssembly runtime. We have successfully embedded the runtime in other languages:

The community has also embedded Wasmer in awesome projects:

It is now time to continue the story and to hang around… Postgres!

We are so happy to announce a new crazy idea: WebAssembly on Postgres. Yes, you read that correctly. On Postgres.

Calling a WebAssembly function from Postgres

As usual, we have to go through the installation process. There is no package manager for Postgres, so it’s a manual step. The Installation Section of the documentation explains the details; here is a summary:

Steps to install the Postgres WebAssembly extension.

Once the extension is installed, activated and initialized, we can start having fun!

The current API is rather small, however basic features are available. The goal is to gather a community and to design a pragmatic API together, discover the expectations, how developers would use this new technology inside a database engine.

Let’s see how it works. To instantiate a WebAssembly module, we use the wasm_new_instance function. It takes 2 arguments: The absolute path to the WebAssembly module, and a prefix for the module exported functions. Indeed, if a module exports a function named sum, then a Postgres function named prefix_sum calling the sum function will be created dynamically.

Let’s see it in action. Let’s start by editing a Rust program that compiles to WebAssembly:

A simple Rust program that compiles to WebAssembly, exposing a sum function.

Once this file compiled to simple.wasm, we can instantiate the module, and call the exported sum function:

Postgres and WebAssembly, hand in hand

Et voilà ! The ns_sum function calls the Rust sum function through WebAssembly! How fun is that 😄?

Inspect a WebAssembly instance

This section shows how to inspect a WebAssembly instance. At the same time, it quickly explains how the extension works under the hood.

The extension provides two foreign data wrappers, gathered together in the wasm foreign schema:

  • wasm.instances is a table with the id and wasm_file columns, respectively for the unique instance ID, and the path of the WebAssembly module,
  • wasm.exported_functions is a table with the instance_id,name, inputs, and outputs columns, respectively for the instance ID of the exported function, its name, its input types (already formatted for Postgres), and its output types (already formatted for Postgres).

Let’s see:

Based on these information, the wasm Postgres extension is able to generate the SQL function to call the WebAssembly exported functions.

It sounds simplistic, and… to be honest, it is! The trick is to use foreign data wrappers, which is an awesome feature of Postgres.

How fast is it, or: Is it an interesting alternative to PL/pgSQL?

As we said, the extension API is rather small for now. The idea is to explore, to experiment, to have fun with WebAssembly inside a database. It is particularly interesting in two cases:

  1. To write extensions or procedures with any languages that compile to WebAssembly in place of PL/pgSQL,
  2. To remove a potential performance bottleneck where speed is involved.

Thus we run a basic benchmark. Like most of the benchmarks out there, it must be taken with a grain of salt.

The goal is to compare the execution time between WebAssembly and PL/pgSQL, and see how both approaches scale.

The Postgres WebAssembly extension uses Wasmer as the runtime, compiled with the Cranelift backend (learn more about the different backends). We run the benchmark with Postgres 10, on a MacBook Pro 15" from 2016, 2.9Ghz Core i7 with 16Gb of memory.

The methodology is the following:

  • Load both the plpgsql_fibonacci and the wasm_fibonacci functions,
  • Run them with a query like SELECT *_fibonacci(n) FROM generate_series(1, 1000) where n has the following values: 50, 500, and 5000, so that we can observe how both approaches scale,
  • Write the timings down,
  • Run this methodology multiple times, and compute the median of the results.

Here come the results. The lower, the better.

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Comparing WebAssembly vs. PL/pgSQL when computing the Fibonacci sequence with n=50, 500 and 5000.

We notice that the Postgres WebAssembly extension is faster to run numeric computations. The WebAssembly approach scales pretty well compared to the PL/pgSQL approach, in this situation.

When to use the WebAssembly extension?

So far, the extension only supports integers (on 32- and 64-bits). The extension doesn’t support strings yet. It also doesn’t support records, views or other Postgres types. Keep in mind this is the very first step.

Hence, it is too soon to tell whether WebAssembly can be an alternative to PL/pgSQL. But regarding the benchmark results above, we are sure they can live side-by-side, WebAssembly has clearly a place in the ecosystem! And we want to continue to pursue this exploration.


We are already talking with people that are interested in using WebAssembly inside databases. If you have any particular use cases, please reach us at, or on Twitter at @wasmerio directly or me @mnt_io.

Everything is open source, as usual! Happy hacking.


Universal WebAssembly runtime

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