Add new metrics.

1. 'prometheus_tsdb_wal_truncate_fail' for failed WAL truncation.
2. 'prometheus_tsdb_checkpoint_delete_fail' for failed old checkpoint delete.

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

checkpoint.go

@@ -26,6 +26,7 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/pkg/errors"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/wal"
 )
@@ -102,7 +103,7 @@ const checkpointPrefix = "checkpoint."
 // it with the original WAL.
 //
 // Non-critical errors are logged and not returned.
-func Checkpoint(logger log.Logger, w *wal.WAL, m, n int, keep func(id uint64) bool, mint int64) (*CheckpointStats, error) {
+func Checkpoint(logger log.Logger, w *wal.WAL, m, n int, keep func(id uint64) bool, mint int64, checkpointDeleteFail prometheus.Counter) (*CheckpointStats, error) {
 	if logger == nil {
 		logger = log.NewNopLogger()
 	}
@@ -283,6 +284,7 @@ func Checkpoint(logger log.Logger, w *wal.WAL, m, n int, keep func(id uint64) bo
 		// occupying disk space.
 		// They will just be ignored since a higher checkpoint exists.
 		level.Error(logger).Log("msg", "delete old checkpoints", "err", err)
+		checkpointDeleteFail.Add(float64(1))
 	}
 	return stats, nil
 }

checkpoint_test.go

@@ -20,6 +20,7 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/labels"
 	"github.com/prometheus/tsdb/testutil"
@@ -139,7 +140,7 @@ func TestCheckpoint(t *testing.T) {
 
 	_, err = Checkpoint(nil, w, 100, 106, func(x uint64) bool {
 		return x%2 == 0
-	}, last/2)
+	}, last/2, prometheus.NewCounter(prometheus.CounterOpts{}))
 	testutil.Ok(t, err)
 
 	// Only the new checkpoint should be left.

head.go

@@ -89,6 +89,7 @@ type headMetrics struct {
 	maxTime              prometheus.GaugeFunc
 	samplesAppended      prometheus.Counter
 	walTruncateDuration  prometheus.Summary
+	checkpointDeleteFail prometheus.Counter
 }
 
 func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
@@ -150,6 +151,10 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 		Name: "prometheus_tsdb_head_samples_appended_total",
 		Help: "Total number of appended samples.",
 	})
+	m.checkpointDeleteFail = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "prometheus_tsdb_checkpoint_delete_fail",
+		Help: "Number of times deletion of old checkpoint failed.",
+	})
 
 	if r != nil {
 		r.MustRegister(
@@ -166,6 +171,7 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 			m.gcDuration,
 			m.walTruncateDuration,
 			m.samplesAppended,
+			m.checkpointDeleteFail,
 		)
 	}
 	return m
@@ -469,7 +475,7 @@ func (h *Head) Truncate(mint int64) error {
 	keep := func(id uint64) bool {
 		return h.series.getByID(id) != nil
 	}
-	if _, err = Checkpoint(h.logger, h.wal, m, n, keep, mint); err != nil {
+	if _, err = Checkpoint(h.logger, h.wal, m, n, keep, mint, h.metrics.checkpointDeleteFail); err != nil {
 		return errors.Wrap(err, "create checkpoint")
 	}
 	h.metrics.walTruncateDuration.Observe(time.Since(start).Seconds())

wal/wal.go

@@ -162,6 +162,7 @@ type WAL struct {
 	fsyncDuration   prometheus.Summary
 	pageFlushes     prometheus.Counter
 	pageCompletions prometheus.Counter
+	truncateFail    prometheus.Counter
 }
 
 // New returns a new WAL over the given directory.
@@ -201,8 +202,12 @@ func NewSize(logger log.Logger, reg prometheus.Registerer, dir string, segmentSi
 		Name: "prometheus_tsdb_wal_completed_pages_total",
 		Help: "Total number of completed pages.",
 	})
+	w.truncateFail = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "prometheus_tsdb_wal_truncate_fail",
+		Help: "Number of times WAL truncation failed.",
+	})
 	if reg != nil {
-		reg.MustRegister(w.fsyncDuration, w.pageFlushes, w.pageCompletions)
+		reg.MustRegister(w.fsyncDuration, w.pageFlushes, w.pageCompletions, w.truncateFail)
 	}
 
 	_, j, err := w.Segments()
@@ -530,6 +535,7 @@ func (w *WAL) Segments() (m, n int, err error) {
 func (w *WAL) Truncate(i int) error {
 	refs, err := listSegments(w.dir)
 	if err != nil {
+		w.truncateFail.Add(float64(1))
 		return err
 	}
 	for _, r := range refs {
@@ -537,6 +543,7 @@ func (w *WAL) Truncate(i int) error {
 			break
 		}
 		if err := os.Remove(filepath.Join(w.dir, r.s)); err != nil {
+			w.truncateFail.Add(float64(1))
 			return err
 		}
 	}