Raise a check's store without durability and remove what earlier holders left (hq issue 306)

On the control node the store-bound packages of the controller's suite ran
five to seven times slower than on any other holder, and every controller
check that landed there ran past the suite's thirty minutes: a throwaway
store flushing to a disk the mesh's own store, bus and forge keep busy.
A store that lives for one check needs no crash safety.

A holder recreated mid-check left the check's store and bus running, and
the redelivery went to another machine, so nothing removed them: eleven
pairs across four machines. A starting holder has taken nothing, so every
container labelled with an ask of the seat is an earlier holder's.

internal/builder/check_test.go

@@ -33,6 +33,43 @@ func TestTheStoreAndBusAChecksStandsOnAreTheOnesTheMeshRuns(t *testing.T) {
 	}
 }
 
+// **Issue 306**: the throwaway store is raised without durability — it lives for one check — so a suite
+// that makes a database per test does not wait on the disk of a busy machine for every flush.
+func TestTheThrowawayStoreFlushesNothing(t *testing.T) {
+	said := strings.Join(StoreSettings, " ")
+	for _, want := range []string{"-c fsync=off", "-c synchronous_commit=off", "-c full_page_writes=off"} {
+		if !strings.Contains(said, want) {
+			t.Errorf("the store is raised with %q, not %q", said, want)
+		}
+	}
+	if os.Getenv("MESH_TEST_DOCKER") != "1" {
+		t.Skip("MESH_TEST_DOCKER=1: the settings are proven on a raised store")
+	}
+	id := fmt.Sprintf("check-store-%d", time.Now().UnixNano())
+	labelledRun := Labelled(Command, id)
+	t.Cleanup(func() { _, _ = RemoveContainersOf(context.Background(), Command, id) })
+	if _, err := throwaway(t.Context(), labelledRun, Command, id+"-store", StoreImage("17.11"), 5432,
+		[]string{"-e", "POSTGRES_PASSWORD=check"}, StoreSettings); err != nil {
+		t.Fatal(err)
+	}
+	if err := waitFor(t.Context(), Command, id+"-store", []string{"pg_isready", "-U", "postgres"}); err != nil {
+		t.Fatal(err)
+	}
+	for setting, want := range map[string]string{"fsync": "off", "synchronous_commit": "off", "full_page_writes": "off"} {
+		var got string
+		for try := 0; try < 10; try++ {
+			out, err := exec.Command("docker", "exec", id+"-store", "psql", "-U", "postgres", "-tAc", "SHOW "+setting).CombinedOutput()
+			if got = strings.TrimSpace(string(out)); err == nil {
+				break
+			}
+			time.Sleep(500 * time.Millisecond)
+		}
+		if got != want {
+			t.Errorf("%s is %q on the raised store", setting, got)
+		}
+	}
+}
+
 // aRepository is a git repository holding these files, committed, and its head.
 func aCheckedRepository(t *testing.T, files map[string]string) (string, string) {
 	t.Helper()