Preserve most recent branch builds

Co-authored-by: Alexandre Fayolle
Co-authored-by: Laurent Mignon

README.md

@@ -64,6 +64,7 @@ For running the builds:
 For running the controller (runboat itself):
 
 - Python 3.10
+- sqlite3 >= 3.25
 - `kubectl`
 - A `KUBECONFIG` or an in-cluster service account that provides access to the namespace
   where the builds are deployed, with permissions to create and delete Service, Job,

src/runboat/db.py

@@ -187,10 +187,26 @@ class BuildsDb:
         return [self._build_from_row(row) for row in rows]
 
     def oldest_stopped(self, limit: int) -> list[Build]:
-        """Return a list of oldest stopped builds."""
+        """Return a list of oldest stopped builds.
+
+        Exclude the most recent build of each branch that we want to
+        preserve from eviction.
+        """
         rows = self._con.execute(
-            "SELECT * FROM builds WHERE status IN (?, ?, ?) "
-            "ORDER BY last_scaled LIMIT ?",
+            """\
+                SELECT * FROM (
+                    SELECT
+                        ROW_NUMBER () OVER (
+                            PARTITION BY repo, target_branch, pr
+                            ORDER BY created DESC
+                        ) AS rownum,
+                        *
+                    FROM builds
+                )
+                WHERE status IN (?, ?, ?) AND (rownum != 1 OR pr IS NOT NULL)
+                ORDER BY last_scaled
+                LIMIT ?
+            """,
             (BuildStatus.stopping, BuildStatus.stopped, BuildStatus.failed, limit),
         ).fetchall()
         return [self._build_from_row(row) for row in rows]

tests/test_db.py

@@ -14,6 +14,8 @@ def _make_build(
     repo: str | None = None,
     target_branch: str | None = None,
     pr: int | None = None,
+    last_scaled: datetime.datetime | None = None,
+    created: datetime.datetime | None = None,
 ) -> Build:
     name = name or "build-a"
     return Build(
@@ -29,8 +31,8 @@ def _make_build(
         status=status or BuildStatus.starting,
         init_status=init_status or BuildInitStatus.todo,
         desired_replicas=0,
-        last_scaled=datetime.datetime(2021, 10, 1, 12, 0, 0),
-        created=datetime.datetime(2021, 10, 1, 11, 0, 0),
+        last_scaled=last_scaled or datetime.datetime(2021, 10, 1, 12, 0, 0),
+        created=created or datetime.datetime(2021, 10, 1, 11, 0, 0),
     )
 
 
@@ -158,3 +160,40 @@ def test_repos() -> None:
     db.add(_make_build(name="b1", repo="oca/repo1"))
     db.add(_make_build(name="b2", repo="oca/repo2"))
     assert db.repos() == [Repo(name="oca/repo1"), Repo(name="oca/repo2")]
+
+
+def test_oldest_stopped() -> None:
+    db = BuildsDb()
+    db.add(
+        _make_build(
+            name="b1",
+            repo="oca/repo1",
+            target_branch="15.0",
+            status=BuildStatus.stopped,
+            last_scaled=datetime.datetime(2021, 10, 11, 12, 0, 0),
+            created=datetime.datetime(2021, 10, 11, 12, 0, 0),
+        )
+    )
+    db.add(
+        _make_build(
+            name="b2",
+            repo="oca/repo1",
+            target_branch="15.0",
+            status=BuildStatus.stopped,
+            last_scaled=datetime.datetime(2021, 10, 11, 12, 0, 2),
+            created=datetime.datetime(2021, 10, 11, 12, 0, 2),
+        )
+    )
+    # a PR that is most recent than the latest branch build
+    db.add(
+        _make_build(
+            name="pr1",
+            repo="oca/repo1",
+            target_branch="15.0",
+            pr=1,
+            status=BuildStatus.stopped,
+            last_scaled=datetime.datetime(2021, 10, 11, 12, 0, 4),
+            created=datetime.datetime(2021, 10, 11, 12, 0, 4),
+        )
+    )
+    assert [b.name for b in db.oldest_stopped(limit=3)] == ["b1", "pr1"]