jobs: Remove unnecessary and expensive scheduled jobs metrics.

Remove `schedules.round.schedules-ready-to-run` and `schedules.round.num-jobs-running`
metrics from job scheduler.  These metrics are very expensive to compute as they
involve running wider table scans against both `system.jobs` and `system.scheduled_job`.

In addition to being expensive to compute, these metrics are not needed since
the query can be executed directly if needed, and, in addition these metrics are confusing
since these metrics are per node, while the number of running jobs/schedules is cluster wide.
More importantly, they can lead to job scheduler query being more expensive since they increase
the read set of the scheduler transaction, thus causing txn restarts to be more expensive.

Fixes #78447

Release Notes (enterprise): Remove expensive, unnecessary, and never used
`schedules.round.schedules-ready-to-run` and `schedules.round.num-jobs-running` metrics from
job schedulers.

Release Justification: Stability fix for scheduled job system.

pkg/jobs/job_scheduler.go

@@ -26,7 +26,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/colinfo"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/sessiondata"
-	"github.com/cockroachdb/cockroach/pkg/sql/sqlutil"
 	"github.com/cockroachdb/cockroach/pkg/util/contextutil"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/metric"
@@ -118,14 +117,11 @@ const recheckRunningAfter = 1 * time.Minute
 
 type loopStats struct {
 	rescheduleWait, rescheduleSkip, started int64
-	readyToRun, jobsRunning                 int64
 	malformed                               int64
 }
 
 func (s *loopStats) updateMetrics(m *SchedulerMetrics) {
 	m.NumStarted.Update(s.started)
-	m.ReadyToRun.Update(s.readyToRun)
-	m.NumRunning.Update(s.jobsRunning)
 	m.RescheduleSkip.Update(s.rescheduleSkip)
 	m.RescheduleWait.Update(s.rescheduleWait)
 	m.NumMalformedSchedules.Update(s.malformed)
@@ -194,36 +190,6 @@ func (s *jobScheduler) processSchedule(
 	return schedule.Update(ctx, s.InternalExecutor, txn)
 }
 
-// TODO(yevgeniy): Re-evaluate if we need to have per-loop execution statistics.
-func newLoopStats(
-	ctx context.Context, env scheduledjobs.JobSchedulerEnv, ex sqlutil.InternalExecutor, txn *kv.Txn,
-) (*loopStats, error) {
-	numRunningJobsStmt := fmt.Sprintf(
-		"SELECT count(*) FROM %s WHERE created_by_type = '%s' AND status NOT IN ('%s', '%s', '%s', '%s')",
-		env.SystemJobsTableName(), CreatedByScheduledJobs,
-		StatusSucceeded, StatusCanceled, StatusFailed, StatusRevertFailed)
-	readyToRunStmt := fmt.Sprintf(
-		"SELECT count(*) FROM %s WHERE next_run < %s",
-		env.ScheduledJobsTableName(), env.NowExpr())
-	statsStmt := fmt.Sprintf(
-		"SELECT (%s) numReadySchedules, (%s) numRunningJobs",
-		readyToRunStmt, numRunningJobsStmt)
-
-	datums, err := ex.QueryRowEx(ctx, "scheduler-stats", txn,
-		sessiondata.InternalExecutorOverride{User: security.NodeUserName()},
-		statsStmt)
-	if err != nil {
-		return nil, err
-	}
-	if datums == nil {
-		return nil, errors.New("failed to read scheduler stats")
-	}
-	stats := &loopStats{}
-	stats.readyToRun = int64(tree.MustBeDInt(datums[0]))
-	stats.jobsRunning = int64(tree.MustBeDInt(datums[1]))
-	return stats, nil
-}
-
 type savePointError struct {
 	err error
 }
@@ -268,11 +234,7 @@ func withSavePoint(ctx context.Context, txn *kv.Txn, fn func() error) error {
 func (s *jobScheduler) executeSchedules(
 	ctx context.Context, maxSchedules int64, txn *kv.Txn,
 ) (retErr error) {
-	stats, err := newLoopStats(ctx, s.env, s.InternalExecutor, txn)
-	if err != nil {
-		return err
-	}
-
+	var stats loopStats
 	defer stats.updateMetrics(&s.metrics)
 
 	findSchedulesStmt := getFindSchedulesStatement(s.env, maxSchedules)
@@ -308,10 +270,10 @@ func (s *jobScheduler) executeSchedules(
 				return contextutil.RunWithTimeout(
 					ctx, fmt.Sprintf("process-schedule-%d", schedule.ScheduleID()), timeout,
 					func(ctx context.Context) error {
-						return s.processSchedule(ctx, schedule, numRunning, stats, txn)
+						return s.processSchedule(ctx, schedule, numRunning, &stats, txn)
 					})
 			}
-			return s.processSchedule(ctx, schedule, numRunning, stats, txn)
+			return s.processSchedule(ctx, schedule, numRunning, &stats, txn)
 		}); processErr != nil {
 			if errors.HasType(processErr, (*savePointError)(nil)) {
 				return errors.Wrapf(processErr, "savepoint error for schedule %d", schedule.ScheduleID())

pkg/jobs/job_scheduler_test.go

@@ -454,8 +454,13 @@ func TestJobSchedulerDaemonHonorsMaxJobsLimit(t *testing.T) {
 	daemon := newJobScheduler(h.cfg, h.env, metric.NewRegistry())
 	daemon.runDaemon(ctx, stopper)
 
+	readyToRunStmt := fmt.Sprintf(
+		"SELECT count(*) FROM %s WHERE next_run < %s",
+		h.env.ScheduledJobsTableName(), h.env.NowExpr())
 	testutils.SucceedsSoon(t, func() error {
-		if ready := daemon.metrics.ReadyToRun.Value(); numJobs != ready {
+		var ready int
+		h.sqlDB.QueryRow(t, readyToRunStmt).Scan(&ready)
+		if ready != numJobs-jobsPerIteration {
 			return errors.Errorf("waiting for metric %d = %d", ready, numJobs)
 		}
 		return nil

pkg/jobs/schedule_metrics.go

@@ -31,12 +31,8 @@ func (m *ExecutorMetrics) MetricStruct() {}
 
 // SchedulerMetrics are metrics specific to job scheduler daemon.
 type SchedulerMetrics struct {
-	// Number of schedules that were ready to execute.
-	ReadyToRun *metric.Gauge
 	// Number of scheduled jobs started.
 	NumStarted *metric.Gauge
-	// Number of jobs started by schedules that are currently running.
-	NumRunning *metric.Gauge
 	// Number of schedules rescheduled due to SKIP policy.
 	RescheduleSkip *metric.Gauge
 	// Number of schedules rescheduled due to WAIT policy.
@@ -51,20 +47,6 @@ type SchedulerMetrics struct {
 // MakeSchedulerMetrics returns metrics for scheduled job daemon.
 func MakeSchedulerMetrics() SchedulerMetrics {
 	return SchedulerMetrics{
-		ReadyToRun: metric.NewGauge(metric.Metadata{
-			Name:        "schedules.round.schedules-ready-to-run",
-			Help:        "The number of jobs ready to execute",
-			Measurement: "Schedules",
-			Unit:        metric.Unit_COUNT,
-		}),
-
-		NumRunning: metric.NewGauge(metric.Metadata{
-			Name:        "schedules.round.num-jobs-running",
-			Help:        "The number of jobs started by schedules that are currently running",
-			Measurement: "Jobs",
-			Unit:        metric.Unit_COUNT,
-		}),
-
 		NumStarted: metric.NewGauge(metric.Metadata{
 			Name:        "schedules.round.jobs-started",
 			Help:        "The number of jobs started",