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Code Engine - Powered by Wasm

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The Code Engine feature in SingleStore supports creating functions (UDFs and TVFs) using code compiled to WebAssembly (Wasm). The Code Engine uses the wasmtime runtime to compile and run WebAssembly code. Refer to Wasmtime for more information.

This feature supports any language that can compile to the Wasm core specification, which allows you to create UDFs/TVFs in a language of your choice using existing code libraries and run them in a sandboxed environment for enhanced security. Each Wasm function instance runs in its own in-process sandbox. It uses a linear memory model and provides hard memory protection boundaries. By default, each Wasm function sandbox is allocated 16MB of memory. You can use the GROW TO clause to modify the memory allocated to a Wasm function sandbox.

The Wasm UDF/TVF must not require runtime capabilities that the database does not provide out of the box. For example, a Wasm UDF/TVF can not make system calls, open files, open sockets, send network messages, create processes, or create threads. SingleStore does not support these operations out of the box to protect the security and integrity of its service process.

Wasm modules are serialized to the plancache. Because Wasm modules can be significantly large in size, if the value of Alloc_compiled_unit_sections exceeds Effective_compiled_images_eviction_memory_limit_mb, compiled images are evicted from memory. The Effective_compiled_images_eviction_memory_limit_mb is derived from compiled_images_eviction_memory_limit_mb and compiled_images_eviction_memory_limit_percent variables. They can be set both at startup and runtime. Refer to Managing Plancache Memory and Disk Usage for more information. The eviction task runs in the background once per second.

Once a Wasm function is added to SingleStore, it becomes a part of the database. Hence, it is also included in the database backup and restore operations.

If your logic and data structures can be implemented in PSQL with reasonable effort in a way that performs well, use PSQL. For information on creating PSQL functions or procedures, refer to Procedural Extensions. For integrating more complex logic and data structures, or using existing C/C++ or Rust code, SingleStore recommends using Wasm-based functions.

For more information, refer to the relevant topics:

Wasm Application Binary Interfaces (ABIs)

Information on supported Wasm ABIs. SingleStore supports both the Basic and Canonical ABIs.

Configure Wasm

Configure Wasm extensibility using engine variables.

Create Wasm UDFs

Create Wasm-based user-defined functions (UDFs).

Create Wasm TVFs

Create Wasm-based user-defined table-valued functions (TVFs).

Choose Between PSQL, Wasm-based, and External Functions

Understand when to use PSQL, Wasm-based, or external functions.

Procedural Extensions

Information on creating Procedural SQL (PSQL) functions or procedures.

Prerequisites

You can build Wasm extensions for SingleStore on Mac, Windows, or Linux. To build Wasm extensions, you'll need:

FAQs

  • Can I use a Wasm binary outside of the SingleStore database once it is imported into the database?

    No. Once a Wasm binary is imported into a SingleStore database, you cannot use it for applications outside the database. However, you can make a copy of the binary and use it instead.

  • What happens if there is a mismatch between the WIT file and the generated code?

    A mismatch may cause a Wasm trap or unexpected results. The exact behavior depends on how the Wasm program interprets the arguments.

  • Can I reverse engineer a Wasm binary once it is imported into the database?

    No. Once a Wasm binary is imported into the database, it's not possible to see the binary data, it can only be executed. Hence, you can only reverse engineer the Wasm binary behaviorally and not by disassembling the binary.

  • What happens when a Wasm function crashes or runs out of memory?

    If a Wasm function crashes or runs out of memory, it causes the query to fail and returns an error. If possible, the error message may include a stack into the Wasm function.

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Last modified: March 25, 2025

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Verification instructions

Note: You must install cosign to verify the authenticity of the SingleStore file.

Use the following steps to verify the authenticity of singlestoredb-server, singlestoredb-toolbox, singlestoredb-studio, and singlestore-client SingleStore files that have been downloaded.

You may perform the following steps on any computer that can run cosign, such as the main deployment host of the cluster.

  1. (Optional) Run the following command to view the associated signature files.

    curl undefined

  2. Download the signature file from the SingleStore release server.

    • Option 1: Click the Download Signature button next to the SingleStore file.

    • Option 2: Copy and paste the following URL into the address bar of your browser and save the signature file.

    • Option 3: Run the following command to download the signature file.

      curl -O undefined

  3. After the signature file has been downloaded, run the following command to verify the authenticity of the SingleStore file.

    echo -n undefined |
        cosign verify-blob --certificate-oidc-issuer https://oidc.eks.us-east-1.amazonaws.com/id/CCDCDBA1379A5596AB5B2E46DCA385BC \
          --certificate-identity https://kubernetes.io/namespaces/freya-production/serviceaccounts/job-worker \
          --bundle undefined \
          --new-bundle-format -
    Verified OK