From 0c5736bf90cd4e5f6c7066610f64a9eb88a11631 Mon Sep 17 00:00:00 2001
From: Ti Chi Robot <ti-community-prow-bot@tidb.io>
Date: Tue, 27 Feb 2024 17:51:48 +0800
Subject: [PATCH] log_backup: added more info for slow regions in log backup
 advancer (#51137) (#51175)

close pingcap/tidb#51046
---
 br/pkg/streamhelper/advancer.go   | 36 ++++++++++++++++++++++++++++---
 br/pkg/streamhelper/regioniter.go | 13 +++++++++++
 metrics/log_backup.go             | 16 ++++++++++++++
 3 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/br/pkg/streamhelper/advancer.go b/br/pkg/streamhelper/advancer.go
index 74be82c1d0208..b3dba99b13292 100644
--- a/br/pkg/streamhelper/advancer.go
+++ b/br/pkg/streamhelper/advancer.go
@@ -5,6 +5,7 @@ package streamhelper
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"math"
 	"strings"
 	"sync"
@@ -272,20 +273,49 @@ func (c *CheckpointAdvancer) NewCheckpoints(cps *spans.ValueSortedFull) {
 	c.checkpoints = cps
 }
 
+func (c *CheckpointAdvancer) fetchRegionHint(ctx context.Context, startKey []byte) string {
+	region, err := locateKeyOfRegion(ctx, c.env, startKey)
+	if err != nil {
+		return errors.Annotate(err, "failed to fetch region").Error()
+	}
+	r := region.Region
+	l := region.Leader
+	prs := []int{}
+	for _, p := range r.GetPeers() {
+		prs = append(prs, int(p.StoreId))
+	}
+	metrics.LogBackupCurrentLastRegionID.Set(float64(r.Id))
+	metrics.LogBackupCurrentLastRegionLeaderStoreID.Set(float64(l.StoreId))
+	return fmt.Sprintf("ID=%d,Leader=%d,ConfVer=%d,Version=%d,Peers=%v,RealRange=%s",
+		r.GetId(), l.GetStoreId(), r.GetRegionEpoch().GetConfVer(), r.GetRegionEpoch().GetVersion(),
+		prs, logutil.StringifyRange{StartKey: r.GetStartKey(), EndKey: r.GetEndKey()})
+}
+
 func (c *CheckpointAdvancer) CalculateGlobalCheckpointLight(ctx context.Context,
 	threshold time.Duration) (spans.Valued, error) {
 	var targets []spans.Valued
 	var minValue spans.Valued
+	thresholdTso := tsoBefore(threshold)
 	c.WithCheckpoints(func(vsf *spans.ValueSortedFull) {
-		vsf.TraverseValuesLessThan(tsoBefore(threshold), func(v spans.Valued) bool {
+		vsf.TraverseValuesLessThan(thresholdTso, func(v spans.Valued) bool {
 			targets = append(targets, v)
 			return true
 		})
 		minValue = vsf.Min()
 	})
-	log.Info("[log backup advancer hint] current last region",
+	sctx, cancel := context.WithTimeout(ctx, time.Second)
+	// Always fetch the hint and update the metrics.
+	hint := c.fetchRegionHint(sctx, minValue.Key.StartKey)
+	logger := log.Debug
+	if minValue.Value < thresholdTso {
+		logger = log.Info
+	}
+	logger("current last region", zap.String("category", "log backup advancer hint"),
 		zap.Stringer("min", minValue), zap.Int("for-polling", len(targets)),
-		zap.String("min-ts", oracle.GetTimeFromTS(minValue.Value).Format(time.RFC3339)))
+		zap.String("min-ts", oracle.GetTimeFromTS(minValue.Value).Format(time.RFC3339)),
+		zap.String("region-hint", hint),
+	)
+	cancel()
 	if len(targets) == 0 {
 		return minValue, nil
 	}
diff --git a/br/pkg/streamhelper/regioniter.go b/br/pkg/streamhelper/regioniter.go
index a741824ea36c2..02d8ca9d94e94 100644
--- a/br/pkg/streamhelper/regioniter.go
+++ b/br/pkg/streamhelper/regioniter.go
@@ -82,6 +82,19 @@ func IterateRegion(cli TiKVClusterMeta, startKey, endKey []byte) *RegionIter {
 	}
 }
 
+// locateKeyOfRegion locates the place of the region in the key.
+func locateKeyOfRegion(ctx context.Context, cli TiKVClusterMeta, key []byte) (RegionWithLeader, error) {
+	regions, err := cli.RegionScan(ctx, key, kv.Key(key).Next(), 1)
+	if err != nil {
+		return RegionWithLeader{}, err
+	}
+	if len(regions) == 0 {
+		return RegionWithLeader{}, errors.Annotatef(berrors.ErrPDBatchScanRegion,
+			"scanning the key %s returns empty region", redact.Key(key))
+	}
+	return regions[0], nil
+}
+
 func CheckRegionConsistency(startKey, endKey []byte, regions []RegionWithLeader) error {
 	// current pd can't guarantee the consistency of returned regions
 	if len(regions) == 0 {
diff --git a/metrics/log_backup.go b/metrics/log_backup.go
index e11c82285b54e..f3c522024fc28 100644
--- a/metrics/log_backup.go
+++ b/metrics/log_backup.go
@@ -28,6 +28,9 @@ var (
 	RegionCheckpointRequest           *prometheus.CounterVec
 	RegionCheckpointFailure           *prometheus.CounterVec
 	RegionCheckpointSubscriptionEvent *prometheus.HistogramVec
+
+	LogBackupCurrentLastRegionID            prometheus.Gauge
+	LogBackupCurrentLastRegionLeaderStoreID prometheus.Gauge
 )
 
 // InitLogBackupMetrics initializes log backup metrics.
@@ -84,4 +87,17 @@ func InitLogBackupMetrics() {
 		Help:      "The region flush event size.",
 		Buckets:   prometheus.ExponentialBuckets(8, 2.0, 12),
 	}, []string{"store"})
+
+	LogBackupCurrentLastRegionID = NewGauge(prometheus.GaugeOpts{
+		Namespace: "tidb",
+		Subsystem: "log_backup",
+		Name:      "current_last_region_id",
+		Help:      "The id of the region have minimal checkpoint ts in the current running task.",
+	})
+	LogBackupCurrentLastRegionLeaderStoreID = NewGauge(prometheus.GaugeOpts{
+		Namespace: "tidb",
+		Subsystem: "log_backup",
+		Name:      "current_last_region_leader_store_id",
+		Help:      "The leader's store id of the region have minimal checkpoint ts in the current running task.",
+	})
 }