MongoDB plugin

loadr-plugin-mongo adds MongoDB as a load-test target. It is a native protocol plugin: MongoDB support is not built into loadr core — the heavy mongodb Rust driver ships only inside this plugin's dynamic library. Once the plugin is installed, a request to a mongodb:// (or mongo://) URL routes straight to it.

It is the first plugin built on loadr's runtime protocol-plugin path; the contract it uses is documented in Developing a plugin.

Build and install

cargo build -p loadr-plugin-mongo --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-mongo/plugin.toml dist/
cp target/release/libloadr_plugin_mongo.so dist/   # .dylib on macOS, .dll on Windows
loadr plugin install dist
loadr plugin info mongo

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

[plugin]
name = "mongo"
kind = "protocol"
type = "native"
entry = "libloadr_plugin_mongo.so"
schemes = ["mongodb", "mongo"]

Use it in a test

List the plugin under plugins: and target a mongodb:// URL. The operation is described by the request's plugin: block:

plugins:
  - name: mongo            # or: { name: mongo, path: target/release/libloadr_plugin_mongo.so }

scenarios:
  main:
    executor: constant-vus
    vus: 5
    duration: 15s
    flow:
      - request:
          name: insert product
          url: mongodb://user:pass@host:27017/loadr
          plugin:
            operation: insert
            collection: products
            document: { name: "vu-${vu}-item", price: 12.5, stock: 3 }
          assert:
            - { type: status, equals: 1 }      # 1 = ok, 0 = driver error

      - request:
          name: find cheap products
          url: mongodb://user:pass@host:27017/loadr
          plugin:
            operation: find
            collection: products
            filter: { price: { $lt: 50 } }
            limit: 100

      - request:
          name: stock by tag
          url: mongodb://user:pass@host:27017/loadr
          plugin:
            operation: aggregate
            collection: products
            pipeline:
              - { $unwind: "$tags" }
              - { $group: { _id: "$tags", total: { $sum: "$stock" } } }

A complete runnable plan is in examples/28-mongo.yaml.

Request options (`plugin:` block)

Key	Type	Used by	Notes
`operation`	string	all	`insert`, `find`, `update`, `delete`, `aggregate`, `command`
`database`	string	all (optional)	Defaults to the database in the URI path
`collection`	string	all except `command`	Required
`document`	object	`insert`	Insert one document
`documents`	array	`insert`	Insert many documents
`filter`	object	`find`, `update`, `delete`	Defaults to `{}` (match all)
`update`	object	`update`	e.g. `{ "$set": { ... } }`
`pipeline`	array	`aggregate`	Aggregation stages
`command`	object	`command`	Raw database command
`limit`	integer	`find`	Optional
`multi`	bool	`update`, `delete`	Operate on many docs (default `false`)

${...} placeholders inside any string leaf are interpolated by loadr before the plugin runs, so values can reference VU state, variables, and data feeds.

Metrics

loadr turns the plugin's response into a dedicated metric family named after the protocol (mongo):

Metric	Kind	Meaning
`mongo_reqs`	counter	One per operation
`mongo_req_duration`	trend	Operation latency (ms)
`mongo_docs`	counter	Documents inserted / matched+modified / deleted / returned

A request is marked failed when the operation errors (response status 0). http_req_failed therefore tracks the Mongo failure rate too, and checks / assert entries can gate on status (1 = ok).

Connection pooling

The plugin keeps an internal pool of mongodb::Client handles keyed by the full connection URI, shared across every VU. A Client is itself an internally pooled, cheaply-cloned handle, 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 mongo:7 with seed data:

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

LOADR_TEST_MONGO_URL=mongodb://loadr:loadr@127.0.0.1:27017/loadr \
  cargo test -p loadr-plugin-mongo

The integration tests no-op when LOADR_TEST_MONGO_URL is unset.

loadr — the load testing platform