perf(scheduler): harden jobs for scalable execution

server/internal/scheduler/monitoring_retention_worker_test.go

@@ -0,0 +1,36 @@
+package scheduler
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestBatchDeleteSQLUsesBoundedSkipLockedDelete(t *testing.T) {
+	sql := batchDeleteSQL("monitoring_collect_tasks", "id", "business_date < $1::date", "business_date ASC, id ASC")
+
+	for _, want := range []string{
+		"LIMIT $2",
+		"FOR UPDATE SKIP LOCKED",
+		"DELETE FROM monitoring_collect_tasks t",
+		"USING doomed",
+		"WHERE t.id = doomed.id",
+	} {
+		if !strings.Contains(sql, want) {
+			t.Fatalf("batchDeleteSQL missing %q in SQL:\n%s", want, sql)
+		}
+	}
+	if strings.Contains(sql, "COUNT(*) FROM monitoring_collect_tasks") {
+		t.Fatalf("batchDeleteSQL must not count full candidate set:\n%s", sql)
+	}
+}
+
+func TestBatchProbeSQLCapsDryRunProbe(t *testing.T) {
+	sql := batchProbeSQL("monitoring_collect_tasks", "id", "business_date < $1::date", "business_date ASC, id ASC")
+
+	if !strings.Contains(sql, "LIMIT $2") {
+		t.Fatalf("batchProbeSQL should cap dry-run probe:\n%s", sql)
+	}
+	if !strings.Contains(sql, "SELECT COUNT(*)::bigint") {
+		t.Fatalf("batchProbeSQL should count only the limited candidate subquery:\n%s", sql)
+	}
+}