MySQL plugin

loadr-plugin-mysql adds MySQL as a load-test target. It is a native protocol plugin: MySQL support is not built into loadr core — the heavy sqlx driver ships only inside this plugin's dynamic library. The plugin enables only sqlx's mysql feature.

Advisory note. The mysql feature pulls in sqlx-mysql and its transitive rsa crate (a Marvin timing side-channel with no fixed release yet). rsa is only reachable for MySQL caching_sha2/sha256 password auth over a non-TLS connection, and load-test targets are operator-controlled, so this is accepted. If you only need PostgreSQL, install the advisory-clean PostgreSQL plugin instead — rsa lives only in this MySQL plugin.

Once installed, a request to a mysql:// URL routes straight to this plugin. The contract it uses is documented in Developing a plugin.

When to use

Reach for this when the thing under test is the database: validating a schema or index under write pressure, sizing a connection pool, finding the row count at which a query falls over, or proving latency holds at a steady query rate. For an application that merely uses a database behind an HTTP API, test the API with the http handler instead.

Build and install

cargo build -p loadr-plugin-mysql --release

# `loadr plugin install` copies a directory that holds plugin.toml next to the
# artifact named by its `entry`. Stage the built cdylib beside the manifest:
mkdir -p dist
cp plugins/loadr-plugin-mysql/plugin.toml dist/
cp target/release/libloadr_plugin_mysql.so dist/   # .dylib on macOS, .dll on Windows
loadr plugin install dist
loadr plugin info mysql

Installing copies plugin.toml and the artifact into ~/.loadr/plugins/mysql/. The manifest declares the URL scheme the plugin serves:

[plugin]
name = "mysql"
kind = "protocol"
type = "native"
entry = "libloadr_plugin_mysql.so"
schemes = ["mysql"]

The target URL

mysql://[user[:password]@]host[:port][/database][?params]

• scheme is mysql.
• port defaults to the MySQL standard port (3306).
• credentials, database, and query parameters are passed straight to the driver, so any URL sqlx accepts works here — including ?ssl-mode=REQUIRED for TLS.

Use it in a test

List the plugin under plugins: and target a mysql:// URL. The statement and its bind parameters go in the request's sql block:

plugins:
  - name: mysql         # or: { name: mysql, path: target/release/libloadr_plugin_mysql.so }

scenarios:
  main:
    executor: constant-vus
    vus: 10
    duration: 30s
    flow:
      - request:
          name: count in-stock products
          url: mysql://loadr:loadr@db.example.com:3306/loadr
          sql:
            query: SELECT COUNT(*) AS n FROM products WHERE stock > ?
            params: ["0"]
          checks:
            - { type: status, equals: 1 }                 # 1 = ok, 0 = DB error
            - { type: duration, name: query is fast, max: 250ms }

      - request:
          name: insert order
          url: mysql://loadr:loadr@db.example.com:3306/loadr
          sql:
            query: INSERT INTO orders (sku, qty) VALUES (?, ?)
            params: ["${row.sku}", "${row.qty}"]
          assert:
            - { type: status, equals: 1 }

A complete runnable plan is in examples/29-mysql.yaml.

Expressing the query

• query — the SQL to run. Use MySQL's ? placeholder syntax for parameters.
• params — positional bind values, bound safely by the driver (never string-spliced, so there is no SQL-injection surface). Each value is given as text; the plugin infers a type so comparisons against numeric columns work — a value that parses as an integer binds as an integer, a decimal as a float, everything else as text.

${...} interpolation works in both query and params, so per-VU values and data-feed columns flow straight into the statement. As a shorthand, a request with no sql block uses its body as the query text (no parameters); an empty query is rejected.

Status, rows, and errors

A request succeeds when the query executes without a database error:

extras carries:

• extras.backend — mysql.
• extras.rows — rows returned (row-producing statements) or affected (DML).

The response body is the row count rendered as text, so body-based checks and extraction still work.

Metrics

loadr turns the plugin's response into the mysql metric family:

thresholds:
  checks: [ "rate>0.99" ]
  mysql_req_duration: [ "p(95)<100ms" ]

A request is marked failed when the query errors (response status 0), so http_req_failed (the shared failure-rate metric) tracks DB errors too.

Connection pooling

The plugin keeps an internal sqlx::Pool keyed by the full connection URI, shared across every VU. A pool is itself a set of cheaply-cloned, reused connections, so one per distinct URI is the correct model under load — the first request for a URI establishes it, and all subsequent requests (any VU) reuse it. The plugin owns a single Tokio runtime and block_ons the async driver, because the protocol ABI is synchronous and carries no per-VU context across the FFI boundary.

Testing against a real server

The example harness brings up MySQL with a seeded products table:

docker compose -f examples/harness/docker-compose.yml up -d mysql

LOADR_TEST_MYSQL_URL=mysql://loadr:loadr@127.0.0.1:3306/loadr \
  cargo test -p loadr-plugin-mysql

The integration tests no-op when LOADR_TEST_MYSQL_URL is unset.