1.. taskcluster_caches:
2
3Caches
4======
5
6There are various caches used by the in-tree tasks. This page attempts to
7document them and their appropriate use.
8
9Caches are essentially isolated filesystems that are persisted between
10tasks. For example, if 2 tasks run on a worker - one after the other -
11and both tasks request the same cache, the subsequent task will be
12able to see files in the cache that were created by the first task.
13It's also worth noting that TaskCluster workers ensure a cache can only
14be used by 1 task at a time. If a worker is simultaneously running
15multiple tasks requesting the same named cache, the worker will
16have multiple caches of the same name on the worker.
17
18Caches and ``run-task``
19-----------------------
20
21``run-task`` is our generic task wrapper script. It does common activities
22like ensure a version control checkout is present.
23
24One of the roles of ``run-task`` is to verify and sanitize caches.
25It does this by storing state in a cache on its first use. If the recorded
26*capabilities* of an existing cache don't match expectations for the
27current task, ``run-task`` bails. This ensures that caches are only
28reused by tasks with similar execution *profiles*. This prevents
29accidental cache use across incompatible tasks. It also allows run-task
30to make assumptions about the state of caches, which can help avoid
31costly operations.
32
33In addition, the hash of ``run-task`` is used to derive the cache name.
34So any time ``run-task`` changes, a new set of caches are used. This
35ensures that any backwards incompatible changes or bug fixes to
36``run-task`` result in fresh caches.
37
38Some caches are reserved for use with run-task. That property will be denoted
39below.
40
41Common Caches
42-------------
43
44Version Control Caches
45::::::::::::::::::::::
46
47``level-{{level}}-checkouts-{{hash}}``
48   This cache holds version control checkouts, each in a subdirectory named
49   after the repo (e.g., ``gecko``).
50
51   Checkouts should be read-only. If a task needs to create new files from
52   content of a checkout, this content should be written in a separate
53   directory/cache (like a workspace).
54
55   This cache name pattern is managed by ``run-task`` and must only be
56   used with ``run-task``.
57
58``level-{{level}}-checkouts-sparse-{{hash}}``
59   This is like the above but is used when the checkout is sparse (contains
60   a subset of files).
61
62``level-{{level}}-checkouts-{{version}}`` (deprecated)
63   This cache holds version control checkouts, each in a subdirectory named
64   after the repo (e.g., ``gecko``).
65
66   Checkouts should be read-only. If a task needs to create new files from
67   content of a checkout, this content should be written in a separate
68   directory/cache (like a workspace).
69
70   A ``version`` parameter appears in the cache name to allow
71   backwards-incompatible changes to the cache's behavior.
72
73   The ``hg-store`` contains a `shared store <https://www.mercurial-scm.org/wiki/ShareExtension>`
74   that is is used by ``hg robustcheckout``. If you are using ``run-task`` you
75   should set the ``HG_STORE_PATH`` environment variable to point to this
76   directory. If you are using ``hg robustcheckout``, pass this directory to the
77   ``--sharebase`` option.
78
79Workspace Caches
80::::::::::::::::
81
82``level-{{level}}-*-workspace``
83   These caches (of various names typically ending with ``workspace``)
84   contain state to be shared between task invocations. Use cases are
85   dependent on the task.
86
87Other
88:::::
89
90``level-{{level}}-tooltool-cache-{{hash}}``
91   Tooltool invocations should use this cache. Tooltool will store files here
92   indexed by their hash.
93
94   This cache name pattern is reserved for use with ``run-task`` and must only
95   be used by ``run-task``
96
97``tooltool-cache`` (deprecated)
98   Legacy location for tooltool files. Use the per-level one instead.
99