Merge branch '33772-readonly-gitlab-ci-cache' into 'master'

Introduce cache policies for CI jobs

Closes #33772

See merge request !12483

1 files changed, 47 insertions, 0 deletions

diff --git a/doc/ci/yaml/README.md b/doc/ci/yaml/README.md
index 8a0662db6fd..724843a4d56 100644
--- a/doc/ci/yaml/README.md
+++ b/doc/ci/yaml/README.md
@@ -306,6 +306,53 @@ cache:
   untracked: true
 ```
 
+### cache:policy
+
+> Introduced in GitLab 9.4.
+
+The default behaviour of a caching job is to download the files at the start of
+execution, and to re-upload them at the end. This allows any changes made by the
+job to be persisted for future runs, and is known as the `pull-push` cache
+policy.
+
+If you know the job doesn't alter the cached files, you can skip the upload step
+by setting `policy: pull` in the job specification. Typically, this would be
+twinned with an ordinary cache job at an earlier stage to ensure the cache
+is updated from time to time:
+
+```yaml
+stages:
+  - setup
+  - test
+
+prepare:
+  stage: setup
+  cache:
+    key: gems
+    paths:
+      - vendor/bundle
+  script:
+    - bundle install --deployment
+
+rspec:
+  stage: test
+  cache:
+    key: gems
+    paths:
+      - vendor/bundle
+    policy: pull
+  script:
+    - bundle exec rspec ...
+```
+
+This helps to speed up job execution and reduce load on the cache server,
+especially when you have a large number of cache-using jobs executing in
+parallel.
+
+Additionally, if you have a job that unconditionally recreates the cache without
+reference to its previous contents, you can use `policy: push` in that job to
+skip the download step.
+
 ## Jobs
 
 `.gitlab-ci.yml` allows you to specify an unlimited number of jobs. Each job