acceptance: enable tracing in acceptance/version-upgrade

If we introduced NPEs due to incompatibilities between versions, we
would want to find out. Enabling tracing globally while upgrading
clusters should help.

Release note: None

pkg/cmd/roachtest/versionupgrade.go

@@ -135,6 +135,11 @@ func runVersionUpgrade(ctx context.Context, t *test, c *cluster, buildVersion ve
 		//
 		// See the comment on createCheckpoints for details on fixtures.
 		uploadAndStartFromCheckpointFixture(c.All(), predecessorVersion),
+		// Turn tracing on globally to give it a fighting chance at exposing
+		// any crash-inducing incompatibilities or horrendous memory leaks.
+		// (It won't catch most memory leaks since this test doesn't run for
+		// too long or does too much work).
+		enableTracingGloballyStep,
 		uploadAndInitSchemaChangeWorkload(),
 		waitForUpgradeStep(c.All()),
 		testFeaturesStep,
@@ -354,6 +359,15 @@ func binaryUpgradeStep(nodes nodeListOption, newVersion string) versionStep {
 	}
 }
 
+func enableTracingGloballyStep(ctx context.Context, t *test, u *versionUpgradeTest) {
+	db := u.conn(ctx, t, 1)
+	// NB: this enables net/trace, and as a side effect creates verbose trace spans everywhere.
+	_, err := db.ExecContext(ctx, `SET CLUSTER SETTING trace.debug.enable = $1`, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func preventAutoUpgradeStep(node int) versionStep {
 	return func(ctx context.Context, t *test, u *versionUpgradeTest) {
 		db := u.conn(ctx, t, node)