sunchao commented on code in PR #7311:
URL: https://github.com/apache/datafusion-comet/pull/7311#discussion_r4419236992
##########
.github/workflows/README.md:
##########
@@ -198,6 +200,91 @@ still needs its label, so a `labeled` run there adds
`spark_3_4` or nothing.
`check-ci-config.py` pins that wiring, because a dropped variable reads as an
empty string and would route the pull request as if it targeted `main`.
+## Fork runs
+
+Nearly every pull request comes from a fork, and the PR tier is the
+largest share of the runner-hours CI spends (about 60% in the week to
+2026-10-28, label runs included). A fork pull request therefore does not run
+the PR tier on ASF's runners. The contributor's fork runs it, and the merge
+queue, which stays on ASF, runs the queue tier on the merge result before
+anything lands. That is the PR tier plus Spark SQL on 4.1, Iceberg 1.11, macOS
and
+the other queue-tier jobs, with path filters still applied; the nightly-only
and
+label-only suites are not part of it. The design follows `apache/datafusion`
(#25591) and `apache/arrow-rs`
+(#11788). Three files carry it:
+
+| File | Role
|
+| -------------------- |
----------------------------------------------------------------------------------------------------------------------------------------------------------
|
+| `ci_fork.yml` | Fires on a push to any branch of a fork except
`asf-site` and calls `ci.yml`, after cancelling the branch's older runs. Its
jobs are skipped upstream. |
+| `compute-changes.py` | `is_fork_push` gives a fork the `pr` tier.
`is_fork_pull_request` takes the `pr` tier away upstream, and leaves every
`run-*` label and the `labeled` run. |
+| `fork_ci_status.yml` | Mirrors the fork's run onto the pull request as the
`CI (fork)` check, on `workflow_run` and every 15 minutes.
|
+
+Things that follow from that, and are easy to break:
+
+- **The fork result is advisory.** `Required Checks` does not depend on
+ `CI (fork)`, because a contributor controls the workflow that produced it. A
+ green fork run that never ran the tests costs one queue slot, not a bad
merge.
+- **Every branch of a fork runs through `ci_fork.yml`, `main` included.**
+ `ci.yml` also triggers on push to `main`, in a fork as upstream, so its
+ `Preflight` skips any fork push that did not come through `ci_fork.yml`,
which
+ it tells apart by the caller's `github.workflow`, and `required_checks` skips
+ itself when `Preflight` does. That starts no runner for a fork's schedule or
+ for a second copy of a push, and leaves the bridge one workflow to look up. A
+ push that adds nothing to upstream `main`, such as a sync of the fork,
selects
+ no suite, so it starts only `Preflight` and `Detect changes` and warms no
Review Comment:
A successful empty fork sync also starts `Cancel superseded runs` and
`Required Checks`. The cancellation job runs before `Preflight`, and the
aggregator runs whenever `Preflight` wasn’t skipped. Could this simply say “a
sync that adds nothing to upstream `main` selects no build or test suite and
doesn’t write to the build caches”? That describes the saving without
undercounting runner jobs.
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