195 lines
6.3 KiB
Markdown
195 lines
6.3 KiB
Markdown
# How Caching Works
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Before running any task, Nx computes its computation hash. As long as the computation hash is the same, the output of
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running the task is the same.
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By default, the computation hash for - say - `nx test remixapp` includes:
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- All the source files of `remixapp` and its dependencies
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- Relevant global configuration
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- Versions of external dependencies
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- Runtime values provisioned by the user such as the version of Node
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- CLI Command flags
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> This behavior is customizable. For instance, lint checks may only depend on the source code of the project and global
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> configs. Builds can depend on the dts files of the compiled libs instead of their source.
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After Nx computes the hash for a task, it then checks if it ran this exact computation before. First, it checks
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locally, and then if it is missing, and if a remote cache is configured, it checks remotely.
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If Nx finds the computation, Nx retrieves it and replays it. Nx places the right files in the right folders and
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prints the terminal output. From the user’s point of view, the command ran the same, just a lot faster.
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If Nx doesn’t find a corresponding computation hash, Nx runs the task, and after it completes, it takes the
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outputs and the terminal logs and stores them locally (and if configured remotely as well). All of this happens
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transparently, so you don’t have to worry about it.
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Although conceptually this is fairly straightforward, Nx optimizes this to make this experience good for you. For
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instance, Nx:
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- Captures stdout and stderr to make sure the replayed output looks the same, including on Windows.
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- Minimizes the IO by remembering what files are replayed where.
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- Only shows relevant output when processing a large task graph.
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- Provides affordances for troubleshooting cache misses. And many other optimizations.
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As your workspace grows, the task graph looks more like this:
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All of these optimizations are crucial for making Nx usable for any non-trivial workspace. Only the minimum amount of
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work happens. The rest is either left as is or restored from the cache.
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## Source Code Hash Inputs
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The result of building/testing an application or a library depends on the source code of that project and all the source
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codes of all the libraries it depends on (directly or indirectly).
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By default, Nx is conservative. When running,
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say, `nx run test --script=remixapp` Nx will consider all the files in the `remixapp` directory and all the files
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in the `header` and `footer` directories (`remixapp` dependencies). This would result in unnecessary cache misses. For
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instance, we know that changing a `footer`'s spec file will not change the result of the test command above.
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We can define a more precise configuration as follows:
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```json title="nx.json"
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{
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"namedInputs": {
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"default": ["{projectRoot}/**/*"],
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"production": ["!{projectRoot}/**/*.spec.tsx"]
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},
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"targetDefaults": {
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"build": {
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"inputs": ["production", "^production"]
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},
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"test": {
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"inputs": ["default", "^production", "{workspaceRoot}/jest.config.ts"]
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}
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}
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}
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```
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With this configuration, the build script will only consider the non-test files of `remixapp`, `header` and `footer`.
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The test script will consider all the source files for the project under test and only non-test files of its
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dependencies. The test script will also consider the jest config file at the root of the workspace.
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## Runtime Hash Inputs
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Your targets can also depend on runtime values.
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```json title="nx.json"
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{
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"targetDefaults": {
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"build": {
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"inputs": [{ "env": "MY_ENV_NAME" }, { "runtime": "node -v" }]
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}
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}
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}
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```
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## Args Hash Inputs
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Finally, in addition to Source Code Hash Inputs and Runtime Hash Inputs, Nx needs to consider the arguments: For
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example, `nx build remixapp` and `nx build remixapp -- --flag=true` produce different
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results.
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Note, only the flags passed to the npm scripts itself affect results of the computation. For instance, the following
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commands are identical from the caching perspective.
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```bash
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npx nx build remixapp
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npx nx run-many --target=build --projects=remixapp
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```
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In other words, Nx does not cache what the developer types into the terminal.
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If you build/test/lint… multiple projects, each individual build has its own hash value and will either be retrieved
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from
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cache or run. This means that from the caching point of view, the following command:
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```bash
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npx nx run-many --target=build --projects=header,footer
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```
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is identical to the following two commands:
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```bash
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npx nx build header
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npx nx build footer
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```
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## What is Cached
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Nx works on the process level. Regardless of the tools used to build/test/lint/etc.. your project, the results are
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cached.
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Nx sets up hooks to collect stdout/stderr before running the command. All the output is cached and then replayed
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during a cache hit.
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Nx also caches the files generated by a command. The list of files/folders is listed in the `outputs` property of the project's `package.json`:
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```json title="package.json"
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{
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"nx": {
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"targets": {
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"build": {
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"outputs": ["{projectRoot}/build", "{projectRoot}/public/build"]
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}
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}
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}
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}
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```
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If the `outputs` property for a given target isn't defined in the project'
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s `package.json` file, Nx will look at the `targetDefaults` section of `nx.json`:
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```json title="nx.json"
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{
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...
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"targetDefaults": {
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"build": {
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"dependsOn": [
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"^build"
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],
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"outputs": [
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"{projectRoot}/dist",
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"{projectRoot}/build",
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"{projectRoot}/public/build"
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]
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}
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}
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}
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```
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If neither is defined, Nx defaults to caching `dist` and `build` at the root of the repository.
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## Skipping Cache
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Sometimes you want to skip the cache. If, for example, you are measuring the performance of a command, you can use
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the `--skip-nx-cache` flag to skip checking the computation cache.
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```bash
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npx nx run build --skip-nx-cache
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npx nx run test --skip-nx-cache
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```
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## Customizing the Cache Location
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The cache is stored in `node_modules/.cache/nx` by default. To change the cache location, update the `cacheDirectory` option for the task runner in `nx.json`:
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```json
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{
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"tasksRunnerOptions": {
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"default": {
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"options": {
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"cacheableOperations": ["build", "test"],
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"cacheDirectory": "/tmp/mycache"
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}
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}
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}
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}
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```
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