.. taskcluster_caches: Caches ====== There are various caches used by the in-tree tasks. This page attempts to document them and their appropriate use. Caches are essentially isolated filesystems that are persisted between tasks. For example, if 2 tasks run on a worker - one after the other - and both tasks request the same cache, the subsequent task will be able to see files in the cache that were created by the first task. It's also worth noting that TaskCluster workers ensure a cache can only be used by 1 task at a time. If a worker is simultaneously running multiple tasks requesting the same named cache, the worker will have multiple caches of the same name on the worker. Caches and ``run-task`` ----------------------- ``run-task`` is our generic task wrapper script. It does common activities like ensure a version control checkout is present. One of the roles of ``run-task`` is to verify and sanitize caches. It does this by storing state in a cache on its first use. If the recorded *capabilities* of an existing cache don't match expectations for the current task, ``run-task`` bails. This ensures that caches are only reused by tasks with similar execution *profiles*. This prevents accidental cache use across incompatible tasks. It also allows run-task to make assumptions about the state of caches, which can help avoid costly operations. In addition, the hash of ``run-task`` is used to derive the cache name. So any time ``run-task`` changes, a new set of caches are used. This ensures that any backwards incompatible changes or bug fixes to ``run-task`` result in fresh caches. Some caches are reserved for use with run-task. That property will be denoted below. Common Caches ------------- Version Control Caches :::::::::::::::::::::: ``level-{{level}}-checkouts-{{hash}}`` This cache holds version control checkouts, each in a subdirectory named after the repo (e.g., ``gecko``). Checkouts should be read-only. If a task needs to create new files from content of a checkout, this content should be written in a separate directory/cache (like a workspace). This cache name pattern is managed by ``run-task`` and must only be used with ``run-task``. ``level-{{level}}-checkouts-sparse-{{hash}}`` This is like the above but is used when the checkout is sparse (contains a subset of files). ``level-{{level}}-checkouts-{{version}}`` (deprecated) This cache holds version control checkouts, each in a subdirectory named after the repo (e.g., ``gecko``). Checkouts should be read-only. If a task needs to create new files from content of a checkout, this content should be written in a separate directory/cache (like a workspace). A ``version`` parameter appears in the cache name to allow backwards-incompatible changes to the cache's behavior. The ``hg-store`` contains a `shared store ` that is is used by ``hg robustcheckout``. If you are using ``run-task`` you should set the ``HG_STORE_PATH`` environment variable to point to this directory. If you are using ``hg robustcheckout``, pass this directory to the ``--sharebase`` option. Workspace Caches :::::::::::::::: ``level-{{level}}-*-workspace`` These caches (of various names typically ending with ``workspace``) contain state to be shared between task invocations. Use cases are dependent on the task. Other ::::: ``level-{{level}}-tooltool-cache-{{hash}}`` Tooltool invocations should use this cache. Tooltool will store files here indexed by their hash. This cache name pattern is reserved for use with ``run-task`` and must only be used by ``run-task`` ``tooltool-cache`` (deprecated) Legacy location for tooltool files. Use the per-level one instead.