Caching

Unlike other tools you may have used, turbo can cache emitted files and logs of previously run commands. It does this so it can skip work that's already been done, yielding incredible time savings.

By default, turbo run considers any files emitted in the dist/** or build/** folders of a package task (defined in that package's package.json scripts object) to be cacheable. In addition, turbo run treats logs (stderr andstdout), which are automatically written to .turbo/run-<command>.log, as a cacheable artifact. By treating logs as artifacts, you can cache just about any command in your Turborepo.

Configuring Cache Outputs#

Using pipeline, you can configure cache conventions across your Turborepo.

To override the default cache output behavior, pass an array of globs to a pipeline.<task>.outputs array. Any file that satisfies the glob patterns for a task will be treated as artifact.

{
  "$schema": "https://turborepo.org/schema.json",
  "pipeline": {
    "build": {
      "outputs": ["dist/**", ".next/**"],
      "dependsOn": ["^build"]
    },
    "test": {
      "outputs": [], // leave empty to only cache logs
      "dependsOn": ["build"]
    }
  }
}

If your task does not emit any files (e.g. unit tests with Jest), set outputs to an empty array (i.e. []). Turborepo will automagically cache the logs for you.

With the above pipeline configuration and proper output folders, if you were to run:

# Run `build` npm script in all packages and apps and cache the output.
turbo run build test

And open up your node_modules/.cache/turbo, you should see the cached artifacts.

Turn off caching#

Sometimes you really don't need or want this cache behavior (such as when you're doing something with live reloading such as next dev or react-scripts start). To entirely disable caching, append --no-cache to any command:

# Run `dev` npm script in all packages and apps in parallel,
# but don't cache the output
turbo run dev --parallel --no-cache

You can also always disable caching on a specific task by setting cache to false in your Turborepo pipeline:

{
  "$schema": "https://turborepo.org/schema.json",
  "pipeline": {
    "dev": {
      "cache": false
    }
  }
}

Alter Caching Based on Environment Variables and Files#

For some tasks, you may not want a cache miss if an irrelevant file has changed. For instance, updating README.md might not need to trigger a cache miss for the test task. You can use inputs to restrict the set of files turbo considers for a particular task. In this case, only consider .ts and .tsx files relevant for determining a cache hit on the test task:

{
  "$schema": "https://turborepo.org/schema.json",
  "pipeline": {
    // ...other tasks
    "test": {
      "outputs": [], // leave empty to only cache logs
      "dependsOn": ["build"],
      "inputs": ["src/**/*.tsx", "src/**/*.ts", "test/**/*.ts"]
    }
  }
}

When you use turbo with tools which inline environment variables at build time (e.g. Next.js or Create React App), it is important you tell turbo about it. Otherwise, you could ship a cached artifact with the wrong environment variables!

Luckily, you can control turbo's cache fingerprinting (a.k.a. hashing) behavior based on the values of both environment variables and the contents of files:

• Including environment variables in a dependsOn in your pipeline definition prefixed by a $ will impact the cache fingerprint on a per-task or per-package-task basis.
• Including environment variables in globalDependencies list prefixed by a $ will impact the cache fingerprint of all tasks.
• Including files or globs of files in globalDependencies will impact the cache fingerprint of all tasks.
• The value of any environment variable that includes THASH in its name will impact the cache fingerprint of all tasks.

{
  "$schema": "https://turborepo.org/schema.json",
  "pipeline": {
    "build": {
      "dependsOn": [
        "^build",
        // env vars will impact hashes of all "build" tasks
        "$SOME_ENV_VAR",
      ],
      "outputs": ["dist/**"]
    },
    "web#build": { // override settings for the "build" task for the "web" app
      "dependsOn": [
        "^build",
        // env vars that will impact the hash of "build" task for only "web" app
        "$STRIPE_SECRET_KEY",
        "$NEXT_PUBLIC_STRIPE_PUBLIC_KEY",
        "$NEXT_PUBLIC_ANALYTICS_ID",
      ],
      "outputs": [".next/**"],
    },
    "docs#build": { // override settings for the "build" task for the "docs" app
      "dependsOn": [
        "^build",
        // env vars that will impact the hash of "build" task for only "docs" app
        "$STRIPE_SECRET_KEY",
        "$NEXT_PUBLIC_STRIPE_PUBLIC_KEY",
        "$NEXT_PUBLIC_ANALYTICS_ID",
      ],
      "outputs": [".next/**"],
    }
  },
  "baseBranch": "origin/main",
  "globalDependencies": [
    "$GITHUB_TOKEN",// env var that will impact the hashes of all tasks,
    "tsconfig.json", // file contents will impact the hashes of all tasks,
    ".env.*", // glob file contents will impact the hashes of all tasks,
  ]
}

Force overwrite cache#

Conversely, if you want to force turbo to re-execute a previously cached task, add the --force flag:

# Run `build` npm script in all packages and apps,
# ignoring cache hits.
turbo run build --force

Logs#

Not only does turbo cache the output of your tasks, it also records the terminal output (i.e. combined stdout and stderr) to (<package>/.turbo/run-<command>.log). When turbo encounters a cached task, it will replay the output as if it happened again, but instantly, with the package name slightly dimmed.

Hashing#

By now, you're probably wondering how turbo decides what constitutes a cache hit vs. miss for a given task. Good question!

First turbo constructs a hash of the current global state of the monorepo:

• The contents of any files that satisfy the glob patterns and any the values of environment variables listed in globalDependencies
• The sorted list environment variable key-value pairs that includes THASH anywhere in their names (e.g. STRIPE_PUBLIC_THASH_SECRET_KEY but not STRIPE_PUBLIC_KEY)

Then it adds on more factors relative to a given package's task:

• Hash the contents of all not-gitignored files in the package folder or the files matching the inputs globs, if present
• The hashes of all internal dependencies
• The outputs option specified in the pipeline
• The set of resolved versions of all installed dependencies, devDependencies, and optionalDependencies specified in a package's package.json from the root lockfile
• The package task's name
• The sorted list of environment variable key-value pairs that correspond to the environment variable names listed in applicable pipeline.<task-or-package-task>.dependsOn list.

Once turbo encounters a given package's task in its execution, it checks the cache (both locally and remotely) for a matching hash. If it's a match, it skips executing that task, moves or downloads the cached output into place and replays the previously recorded logs instantly. If there isn't anything in the cache (either locally or remotely) that matches the calculated hash, turbo will execute the task locally and then cache the specified outputs using the hash as an index.

The hash of a given task is injected at execution time as an environment variable TURBO_HASH. This value can be useful in stamping outputs or tagging Dockerfile etc.