// Copyright 2017 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package gcworker

import (
	"bytes"
	"context"
	"encoding/hex"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/pingcap/errors"
	"github.com/pingcap/failpoint"
	"github.com/pingcap/kvproto/pkg/errorpb"
	"github.com/pingcap/kvproto/pkg/keyspacepb"
	"github.com/pingcap/kvproto/pkg/kvrpcpb"
	"github.com/pingcap/kvproto/pkg/metapb"
	"github.com/pingcap/tidb/pkg/config"
	"github.com/pingcap/tidb/pkg/ddl"
	"github.com/pingcap/tidb/pkg/ddl/label"
	"github.com/pingcap/tidb/pkg/ddl/placement"
	"github.com/pingcap/tidb/pkg/ddl/util"
	"github.com/pingcap/tidb/pkg/domain/infosync"
	"github.com/pingcap/tidb/pkg/keyspace"
	"github.com/pingcap/tidb/pkg/kv"
	"github.com/pingcap/tidb/pkg/meta/model"
	"github.com/pingcap/tidb/pkg/metrics"
	"github.com/pingcap/tidb/pkg/parser/terror"
	"github.com/pingcap/tidb/pkg/privilege"
	"github.com/pingcap/tidb/pkg/session"
	sessiontypes "github.com/pingcap/tidb/pkg/session/types"
	"github.com/pingcap/tidb/pkg/sessionctx/variable"
	"github.com/pingcap/tidb/pkg/tablecodec"
	"github.com/pingcap/tidb/pkg/tidbworker"
	util2 "github.com/pingcap/tidb/pkg/util"
	"github.com/pingcap/tidb/pkg/util/codec"
	"github.com/pingcap/tidb/pkg/util/dbterror"
	"github.com/pingcap/tidb/pkg/util/intest"
	"github.com/pingcap/tidb/pkg/util/logutil"
	tikverr "github.com/tikv/client-go/v2/error"
	tikvstore "github.com/tikv/client-go/v2/kv"
	"github.com/tikv/client-go/v2/oracle"
	"github.com/tikv/client-go/v2/tikv"
	"github.com/tikv/client-go/v2/tikvrpc"
	"github.com/tikv/client-go/v2/txnkv/rangetask"
	tikvutil "github.com/tikv/client-go/v2/util"
	pd "github.com/tikv/pd/client"
	"go.uber.org/zap"
)

// GCWorker periodically triggers GC process on tikv server.
type GCWorker struct {
	uuid               string
	desc               string
	store              kv.Storage
	tikvStore          tikv.Storage
	pdClient           pd.Client
	gcIsRunning        bool
	lastFinish         time.Time
	cancel             context.CancelFunc
	done               chan error
	regionLockResolver tikv.RegionLockResolver

	isFirstTickFinished bool
}

func getTsFromPD(store kv.Storage, tikvStore tikv.Storage) (uint64, error) {
	if keyspace.IsKeyspaceUseKeyspaceLevelGC(store.GetCodec().GetKeyspaceMeta()) {
		return tikvStore.CurrentTimestamp(kv.GlobalTxnScope)
	}
	// For global GC.
	return store.CurrentAllTSOKeyspaceGroupMinTs()
}

// NewGCWorker creates a GCWorker instance.
func NewGCWorker(store kv.Storage, pdClient pd.Client) (*GCWorker, error) {
	tikvStore, ok := store.(tikv.Storage)
	if !ok {
		return nil, errors.New("GC should run against TiKV storage")
	}
	ts, err := getTsFromPD(store, tikvStore)
	if err != nil {
		return nil, errors.Trace(err)
	}
	hostName, err := os.Hostname()
	if err != nil {
		hostName = "unknown"
	}
	uuid := strconv.FormatUint(ts, 16)
	resolverIdentifier := fmt.Sprintf("gc-worker-%s", uuid)
	worker := &GCWorker{
		uuid:               uuid,
		desc:               fmt.Sprintf("host:%s, pid:%d, start at %s", hostName, os.Getpid(), time.Now()),
		store:              store,
		tikvStore:          tikvStore,
		pdClient:           pdClient,
		gcIsRunning:        false,
		lastFinish:         time.Now(),
		regionLockResolver: tikv.NewRegionLockResolver(resolverIdentifier, tikvStore),
		done:               make(chan error),
	}
	variable.RegisterStatistics(worker)
	return worker, nil
}

// Start starts the worker.
func (w *GCWorker) Start() {
	var ctx context.Context
	ctx, w.cancel = context.WithCancel(context.Background())
	ctx = kv.WithInternalSourceType(ctx, kv.InternalTxnGC)
	var wg sync.WaitGroup
	wg.Add(1)
	go w.start(ctx, &wg)
	wg.Wait() // Wait create session finish in worker, some test code depend on this to avoid race.
}

// Close stops background goroutines.
func (w *GCWorker) Close() {
	w.cancel()
}

const (
	booleanTrue  = "true"
	booleanFalse = "false"

	gcWorkerTickInterval = 8 * time.Minute
	gcWorkerLease        = 9 * time.Minute
	gcLeaderUUIDKey      = "tikv_gc_leader_uuid"
	gcLeaderDescKey      = "tikv_gc_leader_desc"
	gcLeaderLeaseKey     = "tikv_gc_leader_lease"

	gcLastRunTimeKey       = "tikv_gc_last_run_time"
	gcRunIntervalKey       = "tikv_gc_run_interval"
	gcDefaultRunInterval   = time.Minute * 10
	gcWaitTime             = time.Minute * 1
	gcRedoDeleteRangeDelay = 24 * time.Hour

	gcLifeTimeKey        = "tikv_gc_life_time"
	gcDefaultLifeTime    = time.Minute * 10
	gcMinLifeTime        = time.Minute * 10
	gcSafePointKey       = "tikv_gc_safe_point"
	gcConcurrencyKey     = "tikv_gc_concurrency"
	gcDefaultConcurrency = 2
	gcMinConcurrency     = 1
	gcMaxConcurrency     = 128

	gcEnableKey          = "tikv_gc_enable"
	gcDefaultEnableValue = true

	gcModeKey         = "tikv_gc_mode"
	gcModeCentral     = "central"
	gcModeDistributed = "distributed"
	gcModeDefault     = gcModeDistributed

	gcScanLockModeKey = "tikv_gc_scan_lock_mode"

	gcAutoConcurrencyKey     = "tikv_gc_auto_concurrency"
	gcDefaultAutoConcurrency = true

	gcWorkerServiceSafePointID = "gc_worker"

	// Status var names start with tidb_%
	tidbGCLastRunTime = "tidb_gc_last_run_time"
	tidbGCLeaderDesc  = "tidb_gc_leader_desc"
	tidbGCLeaderLease = "tidb_gc_leader_lease"
	tidbGCLeaderUUID  = "tidb_gc_leader_uuid"
	tidbGCSafePoint   = "tidb_gc_safe_point"

	// getAllKeyspacePageSize is the page size used to get all keyspaces.
	getAllKeyspacePageSize = 50

	// unboundedKey is the unbounded key used to resolve locks.
	unboundedKey = ""
)

var gcSafePointCacheInterval = tikv.GcSafePointCacheInterval

var gcVariableComments = map[string]string{
	gcLeaderUUIDKey:      "Current GC worker leader UUID. (DO NOT EDIT)",
	gcLeaderDescKey:      "Host name and pid of current GC leader. (DO NOT EDIT)",
	gcLeaderLeaseKey:     "Current GC worker leader lease. (DO NOT EDIT)",
	gcLastRunTimeKey:     "The time when last GC starts. (DO NOT EDIT)",
	gcRunIntervalKey:     "GC run interval, at least 10m, in Go format.",
	gcLifeTimeKey:        "All versions within life time will not be collected by GC, at least 10m, in Go format.",
	gcSafePointKey:       "All versions after safe point can be accessed. (DO NOT EDIT)",
	gcConcurrencyKey:     "How many goroutines used to do GC parallel, [1, 128], default 2",
	gcEnableKey:          "Current GC enable status",
	gcModeKey:            "Mode of GC, \"central\" or \"distributed\"",
	gcAutoConcurrencyKey: "Let TiDB pick the concurrency automatically. If set false, tikv_gc_concurrency will be used",
	gcScanLockModeKey:    "Mode of scanning locks, \"physical\" or \"legacy\".(Deprecated)",
}

const (
	unsafeDestroyRangeTimeout = 5 * time.Minute
	gcTimeout                 = 5 * time.Minute
)

func (w *GCWorker) start(ctx context.Context, wg *sync.WaitGroup) {
	logutil.Logger(ctx).Info("start", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid))

	w.tick(ctx) // Immediately tick once to initialize configs.
	wg.Done()

	tickInterval := gcWorkerTickInterval

	// For testing ONLY! Should not use in production environment.
	if hackInterval, err := time.ParseDuration(os.Getenv("HACK_GC_RUN_INTERVAL")); err == nil {
		tickInterval = hackInterval
		logutil.BgLogger().Warn("[gc worker] gc run interval hacked",
			zap.Duration("gc run interval", tickInterval))
	}

	ticker := time.NewTicker(tickInterval)
	defer ticker.Stop()
	defer func() {
		r := recover()
		if r != nil {
			logutil.Logger(ctx).Error("gcWorker",
				zap.Any("r", r),
				zap.Stack("stack"))
			metrics.PanicCounter.WithLabelValues(metrics.LabelGCWorker).Inc()
		}
	}()
	for {
		select {
		case <-ticker.C:
			w.tick(ctx)
		case err := <-w.done:
			w.gcIsRunning = false
			w.lastFinish = time.Now()
			w.isFirstTickFinished = true
			if err != nil {
				logutil.Logger(ctx).Error("runGCJob", zap.String("category", "gc worker"), zap.Error(err))
			}
		case <-ctx.Done():
			logutil.Logger(ctx).Info("quit", zap.String("category", "gc worker"), zap.String("uuid", w.uuid))
			return
		}
	}
}

func createSession(store kv.Storage) sessiontypes.Session {
	for {
		se, err := session.CreateSession(store)
		if err != nil {
			logutil.BgLogger().Warn("create session", zap.String("category", "gc worker"), zap.Error(err))
			continue
		}
		// Disable privilege check for gc worker session.
		privilege.BindPrivilegeManager(se, nil)
		se.GetSessionVars().CommonGlobalLoaded = true
		se.GetSessionVars().InRestrictedSQL = true
		se.GetSessionVars().SetDiskFullOpt(kvrpcpb.DiskFullOpt_AllowedOnAlmostFull)
		return se
	}
}

// GetScope gets the status variables scope.
func (w *GCWorker) GetScope(status string) variable.ScopeFlag {
	return variable.DefaultStatusVarScopeFlag
}

// Stats returns the server statistics.
func (w *GCWorker) Stats(vars *variable.SessionVars) (map[string]any, error) {
	m := make(map[string]any)
	if v, err := w.loadValueFromSysTable(gcLeaderUUIDKey); err == nil {
		m[tidbGCLeaderUUID] = v
	}
	if v, err := w.loadValueFromSysTable(gcLeaderDescKey); err == nil {
		m[tidbGCLeaderDesc] = v
	}
	if v, err := w.loadValueFromSysTable(gcLeaderLeaseKey); err == nil {
		m[tidbGCLeaderLease] = v
	}
	if v, err := w.loadValueFromSysTable(gcLastRunTimeKey); err == nil {
		m[tidbGCLastRunTime] = v
	}
	if v, err := w.loadValueFromSysTable(gcSafePointKey); err == nil {
		m[tidbGCSafePoint] = v
	}
	return m, nil
}

func (w *GCWorker) tick(ctx context.Context) {
	isLeader, err := w.checkLeader(ctx)
	if err != nil {
		logutil.Logger(ctx).Warn("check leader", zap.String("category", "gc worker"), zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("check_leader").Inc()
		return
	}
	if isLeader {
		err = w.leaderTick(ctx)
		if err != nil {
			logutil.Logger(ctx).Warn("leader tick", zap.String("category", "gc worker"), zap.Error(err))
		}
	} else {
		// Config metrics should always be updated by leader, set them to 0 when current instance is not leader.
		metrics.GCConfigGauge.WithLabelValues(gcRunIntervalKey).Set(0)
		metrics.GCConfigGauge.WithLabelValues(gcLifeTimeKey).Set(0)
	}
}

func (w *GCWorker) isCurrentKeyspaceUseKeyspaceLevelGC() bool {
	if w.store == nil || w.store.GetCodec() == nil {
		return false
	}

	return keyspace.IsKeyspaceUseKeyspaceLevelGC(w.store.GetCodec().GetKeyspaceMeta())
}

// getGCSafePoint returns the current gc safe point.
func (w *GCWorker) getGCSafePoint(ctx context.Context, pdClient pd.Client) (uint64, error) {
	// If there is try to set gc safepoint is 0, the interface will not set gc safepoint to 0,
	// it will return current gc safepoint.
	var gcSafePoint uint64
	var err error
	if w.isCurrentKeyspaceUseKeyspaceLevelGC() {
		keyspaceID := uint32(w.store.GetCodec().GetKeyspaceID())
		gcSafePoint, err = pdClient.UpdateGCSafePointV2(ctx, keyspaceID, 0)
		if err != nil {
			return 0, errors.Trace(err)
		}
	} else {
		gcSafePoint, err = pdClient.UpdateGCSafePoint(ctx, 0)
	}
	if err != nil {
		return 0, errors.Trace(err)
	}
	return gcSafePoint, nil
}

func (w *GCWorker) logIsGCSafePointTooEarly(ctx context.Context, safePoint uint64) error {
	now, err := w.getOracleTime()
	if err != nil {
		return errors.Trace(err)
	}

	checkTs := oracle.GoTimeToTS(now.Add(-gcDefaultLifeTime * 2))
	if checkTs > safePoint {
		logutil.Logger(ctx).Info("gc safepoint is too early. "+
			"Maybe there is a bit BR/Lightning/CDC task, "+
			"or a long transaction is running "+
			"or need a tidb without setting keyspace-name to calculate and update gc safe point.",
			zap.String("category", "gc worker"))
	}
	return nil
}

func (w *GCWorker) isNeedToWait() bool {
	if config.GetGlobalConfig().EnableGCFastStart && !intest.InTest {
		return time.Since(w.lastFinish) < gcWaitTime && w.isFirstTickFinished
	}
	return time.Since(w.lastFinish) < gcWaitTime
}

func (w *GCWorker) runKeyspaceDeleteRangeByGlobalGCSafePoint(ctx context.Context, concurrency gcConcurrency) error {
	// Check the current keyspace is valid.
	if !keyspace.IsKeyspaceMetaNotNilAndUseGlobalGC(w.store.GetCodec().GetKeyspaceMeta()) {
		// Serverless logic.
		return errors.New("run keyspace delete ranges with global GC safe point, but the keyspace is not valid")
	}
	// Get global GC safe point from PD.
	// The global GC safe point is updated only after the global GC have done resolveLocks phase globally.
	// So, in the following code, resolveLocks must have been done by the global GC on the ranges to be deleted,
	// so it's safe to delete the ranges.
	safePoint, err := w.getGCSafePoint(ctx, w.pdClient)
	if err != nil {
		logutil.Logger(ctx).Info("get gc safe point error", zap.String("category", "gc worker"), zap.Error(errors.Trace(err)))
		return nil
	}

	if safePoint == 0 {
		logutil.Logger(ctx).Info("skip keyspace delete range, because gc safe point is 0", zap.String("category", "gc worker"))
		return nil
	}

	err = w.logIsGCSafePointTooEarly(ctx, safePoint)
	if err != nil {
		logutil.Logger(ctx).Info("log is gc safe point is too early error", zap.String("category", "gc worker"), zap.Error(errors.Trace(err)))
		return nil
	}

	keyspaceID := w.store.GetCodec().GetKeyspaceID()
	logutil.Logger(ctx).Info("start keyspace delete range", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("concurrency", concurrency.v),
		zap.Uint32("keyspace-id", uint32(keyspaceID)),
		zap.Uint64("gc-safe-point", safePoint))

	// Do deleteRanges.
	err = w.deleteRanges(ctx, safePoint, concurrency)
	if err != nil {
		logutil.Logger(ctx).Error("delete range returns an error", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("delete_range").Inc()
		return errors.Trace(err)
	}

	return nil
}

// leaderTick of GC worker checks if it should start a GC job every tick.
func (w *GCWorker) leaderTick(ctx context.Context) error {
	if w.gcIsRunning {
		logutil.Logger(ctx).Info("there's already a gc job running, skipped", zap.String("category", "gc worker"),
			zap.String("leaderTick on", w.uuid))
		return nil
	}

	concurrency, err := w.getGCConcurrency(ctx)
	if err != nil {
		logutil.Logger(ctx).Info("failed to get gc concurrency.", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		return errors.Trace(err)
	}

	/* If TIDB is configured with 'keyspace-name',
	   and there's no configuration for 'gc_management_type'
	   or 'gc_management_type' = 'global_gc' in the current keyspace meta config,
	   There will be several special points:
	    1. The GC management type of this keyspace is global GC.
	       The keyspace which already uses the global GC cannot be changed to use keyspace level GC now.
	    2. The keyspace which uses the global GC will have its own GC worker leader.
	       However, the GC worker leader of the current keyspace will not calculate the GC safe point
	       and resolve locks, it will only do 'deleteRanges' within the current keyspace range.
	    3. The keyspace which uses the global GC needs at least one TiDB without `keyspace-name`
	       in the whole cluster as a global GC worker. The global GC worker will calculate
	       and update the global GC safe point and resolve locks in the Null Keyspace range and in keyspaces
	       which is using the global GC range.
	*/
	if keyspace.IsKeyspaceMetaNotNilAndUseGlobalGC(w.store.GetCodec().GetKeyspaceMeta()) {
		failpoint.Inject("testKsInGlobalGC", func(v failpoint.Value) {
			ms := v.(int)
			time.Sleep(time.Duration(ms) * time.Millisecond)
			failpoint.Return(errors.New("testKsInGlobalGCInjectedError"))
		})
		// If the keyspace use global GC safe point, the gc worker leader of this keyspace should only do delete ranges logic.
		err = w.runKeyspaceGCJobInGlobalGC(ctx, concurrency)
		if err != nil {
			return errors.Trace(err)
		}
		return nil
	}

	ok, safePoint, err := w.prepare(ctx)
	if err != nil {
		metrics.GCJobFailureCounter.WithLabelValues("prepare").Inc()
		return errors.Trace(err)
	} else if !ok {
		return nil
	}
	// When the worker is just started, or an old GC job has just finished,
	// wait a while before starting a new job.
	if w.isNeedToWait() {
		logutil.Logger(ctx).Info("another gc job has just finished, skipped.", zap.String("category", "gc worker"),
			zap.String("leaderTick on ", w.uuid))
		return nil
	}

	w.gcIsRunning = true
	logutil.Logger(ctx).Info("starts the whole job", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Uint64("safePoint", safePoint),
		zap.Int("concurrency", concurrency.v))
	go func() {
		w.done <- w.runGCJob(ctx, safePoint, concurrency)
	}()
	return nil
}

func (w *GCWorker) runKeyspaceGCJobInGlobalGC(ctx context.Context, concurrency gcConcurrency) error {
	// When the worker is just started, or an old GC job has just finished,
	// wait a while before starting a new job.
	if time.Since(w.lastFinish) < gcWaitTime {
		logutil.Logger(ctx).Info("another keyspace gc job has just finished, skipped.", zap.String("category", "gc worker"),
			zap.String("leaderTick on ", w.uuid))
		return nil
	}

	now, err := w.getOracleTime()
	if err != nil {
		return errors.Trace(err)
	}
	ok, err := w.checkGCInterval(now)
	if err != nil || !ok {
		return errors.Trace(err)
	}

	go func() {
		w.done <- w.runKeyspaceDeleteRangeByGlobalGCSafePoint(ctx, concurrency)
	}()

	err = w.saveTime(gcLastRunTimeKey, now)
	if err != nil {
		return errors.Trace(err)
	}

	return nil
}

// prepare checks preconditions for starting a GC job. It returns a bool
// that indicates whether the GC job should start and the new safePoint.
func (w *GCWorker) prepare(ctx context.Context) (bool, uint64, error) {
	// Add a transaction here is to prevent following situations:
	// 1. GC check gcEnable is true, continue to do GC
	// 2. The user sets gcEnable to false
	// 3. The user gets `tikv_gc_safe_point` value is t1, then the user thinks the data after time t1 won't be clean by GC.
	// 4. GC update `tikv_gc_safe_point` value to t2, continue do GC in this round.
	// Then the data record that has been dropped between time t1 and t2, will be cleaned by GC, but the user thinks the data after t1 won't be clean by GC.
	se := createSession(w.store)
	defer se.Close()
	_, err := se.ExecuteInternal(ctx, "BEGIN")
	if err != nil {
		return false, 0, errors.Trace(err)
	}
	doGC, safePoint, err := w.checkPrepare(ctx)
	if doGC {
		err = se.CommitTxn(ctx)
		if err != nil {
			return false, 0, errors.Trace(err)
		}
	} else {
		se.RollbackTxn(ctx)
	}
	return doGC, safePoint, errors.Trace(err)
}

func (w *GCWorker) checkPrepare(ctx context.Context) (bool, uint64, error) {
	enable, err := w.checkGCEnable()
	if err != nil {
		return false, 0, errors.Trace(err)
	}

	if !enable {
		logutil.Logger(ctx).Warn("gc status is disabled.", zap.String("category", "gc worker"))
		return false, 0, nil
	}
	now, err := w.getOracleTime()
	if err != nil {
		return false, 0, errors.Trace(err)
	}
	ok, err := w.checkGCInterval(now)
	if err != nil || !ok {
		return false, 0, errors.Trace(err)
	}
	newSafePoint, newSafePointValue, err := w.calcNewSafePoint(ctx, now)
	if err != nil || newSafePoint == nil {
		return false, 0, errors.Trace(err)
	}
	err = w.saveTime(gcLastRunTimeKey, now)
	if err != nil {
		return false, 0, errors.Trace(err)
	}
	err = w.saveTime(gcSafePointKey, *newSafePoint)
	if err != nil {
		return false, 0, errors.Trace(err)
	}
	return true, newSafePointValue, nil
}

func (w *GCWorker) calcGlobalMinStartTS(ctx context.Context) (uint64, error) {
	kvs, err := w.tikvStore.GetSafePointKV().GetWithPrefix(infosync.ServerMinStartTSPath)
	if err != nil {
		return 0, err
	}

	var globalMinStartTS uint64 = math.MaxUint64
	for _, v := range kvs {
		minStartTS, err := strconv.ParseUint(string(v.Value), 10, 64)
		if err != nil {
			logutil.Logger(ctx).Warn("parse minStartTS failed", zap.Error(err))
			continue
		}
		if minStartTS < globalMinStartTS {
			globalMinStartTS = minStartTS
		}
	}
	return globalMinStartTS, nil
}

// calcNewSafePoint uses the current global transaction min start timestamp to calculate the new safe point.
func (w *GCWorker) calcSafePointByMinStartTS(ctx context.Context, safePoint uint64) uint64 {
	globalMinStartTS, err := w.calcGlobalMinStartTS(ctx)
	if err != nil {
		logutil.Logger(ctx).Warn("get all minStartTS failed", zap.Error(err))
		return safePoint
	}

	// If the lock.ts <= max_ts(safePoint), it will be collected and resolved by the gc worker,
	// the locks of ongoing pessimistic transactions could be resolved by the gc worker and then
	// the transaction is aborted, decrement the value by 1 to avoid this.
	globalMinStartAllowedTS := globalMinStartTS
	if globalMinStartTS > 0 {
		globalMinStartAllowedTS = globalMinStartTS - 1
	}

	if globalMinStartAllowedTS < safePoint {
		logutil.Logger(ctx).Info("gc safepoint blocked by a running session", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("globalMinStartTS", globalMinStartTS),
			zap.Uint64("globalMinStartAllowedTS", globalMinStartAllowedTS),
			zap.Uint64("safePoint", safePoint))
		safePoint = globalMinStartAllowedTS
	}
	return safePoint
}

func (w *GCWorker) getOracleTime() (time.Time, error) {
	ts, err := getTsFromPD(w.store, w.tikvStore)
	if err != nil {
		return time.Time{}, errors.Trace(err)
	}
	return oracle.GetTimeFromTS(ts), nil
}

func (w *GCWorker) checkGCEnable() (bool, error) {
	return w.loadBooleanWithDefault(gcEnableKey, gcDefaultEnableValue)
}

func (w *GCWorker) checkUseAutoConcurrency() (bool, error) {
	return w.loadBooleanWithDefault(gcAutoConcurrencyKey, gcDefaultAutoConcurrency)
}

func (w *GCWorker) loadBooleanWithDefault(key string, defaultValue bool) (bool, error) {
	str, err := w.loadValueFromSysTable(key)
	if err != nil {
		return false, errors.Trace(err)
	}
	if str == "" {
		// Save default value for gc enable key. The default value is always true.
		defaultValueStr := booleanFalse
		if defaultValue {
			defaultValueStr = booleanTrue
		}
		err = w.saveValueToSysTable(key, defaultValueStr)
		if err != nil {
			return defaultValue, errors.Trace(err)
		}
		return defaultValue, nil
	}
	return strings.EqualFold(str, booleanTrue), nil
}

type gcConcurrency struct {
	v      int
	isAuto bool
}

func (w *GCWorker) getGCConcurrency(ctx context.Context) (gcConcurrency, error) {
	useAutoConcurrency, err := w.checkUseAutoConcurrency()
	if err != nil {
		logutil.Logger(ctx).Error("failed to load config gc_auto_concurrency. use default value.", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		useAutoConcurrency = gcDefaultAutoConcurrency
	}
	if !useAutoConcurrency {
		v, err := w.loadGCConcurrencyWithDefault()
		return gcConcurrency{v, useAutoConcurrency}, err
	}

	stores, err := w.getStoresForGC(ctx)
	concurrency := len(stores)
	if err != nil {
		logutil.Logger(ctx).Error("failed to get up stores to calculate concurrency. use config.", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))

		concurrency, err = w.loadGCConcurrencyWithDefault()
		if err != nil {
			logutil.Logger(ctx).Error("failed to load gc concurrency from config. use default value.", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Error(err))
			concurrency = gcDefaultConcurrency
		}
	}

	if concurrency == 0 {
		logutil.Logger(ctx).Error("no store is up", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid))
		return gcConcurrency{0, useAutoConcurrency}, errors.New("[gc worker] no store is up")
	}

	return gcConcurrency{concurrency, useAutoConcurrency}, nil
}

func (w *GCWorker) checkGCInterval(now time.Time) (bool, error) {
	runInterval, err := w.loadDurationWithDefault(gcRunIntervalKey, gcDefaultRunInterval)
	if err != nil {
		return false, errors.Trace(err)
	}

	// For testing ONLY! Should not use in production environment.
	if hackInterval, err := time.ParseDuration(os.Getenv("HACK_GC_RUN_INTERVAL")); err == nil {
		*runInterval = hackInterval
	}

	metrics.GCConfigGauge.WithLabelValues(gcRunIntervalKey).Set(runInterval.Seconds())
	lastRun, err := w.loadTime(gcLastRunTimeKey)
	if err != nil {
		return false, errors.Trace(err)
	}

	if lastRun != nil && lastRun.Add(*runInterval).After(now) {
		logutil.BgLogger().Debug("skipping garbage collection because gc interval hasn't elapsed since last run", zap.String("category", "gc worker"),
			zap.String("leaderTick on", w.uuid),
			zap.Duration("interval", *runInterval),
			zap.Time("last run", *lastRun))
		return false, nil
	}

	return true, nil
}

// validateGCLifeTime checks whether life time is small than min gc life time.
func (w *GCWorker) validateGCLifeTime(lifeTime time.Duration) (time.Duration, error) {
	if lifeTime >= gcMinLifeTime {
		return lifeTime, nil
	}

	logutil.BgLogger().Info("invalid gc life time", zap.String("category", "gc worker"),
		zap.Duration("get gc life time", lifeTime),
		zap.Duration("min gc life time", gcMinLifeTime))

	err := w.saveDuration(gcLifeTimeKey, gcMinLifeTime)
	return gcMinLifeTime, err
}

func (w *GCWorker) calcNewSafePoint(ctx context.Context, now time.Time) (*time.Time, uint64, error) {
	lifeTime, err := w.loadDurationWithDefault(gcLifeTimeKey, gcDefaultLifeTime)
	if err != nil {
		return nil, 0, errors.Trace(err)
	}
	*lifeTime, err = w.validateGCLifeTime(*lifeTime)
	if err != nil {
		return nil, 0, err
	}

	// For testing ONLY! Should not use in production environment.
	if hackLifeTime, err := time.ParseDuration(os.Getenv("HACK_GC_LIFE_TIME")); err == nil {
		*lifeTime = hackLifeTime
		logutil.BgLogger().Warn("[gc worker] gc life time hacked",
			zap.Duration("gc life time", *lifeTime))
	}

	metrics.GCConfigGauge.WithLabelValues(gcLifeTimeKey).Set(lifeTime.Seconds())

	lastSafePoint, err := w.loadTime(gcSafePointKey)
	if err != nil {
		return nil, 0, errors.Trace(err)
	}

	safePointValue := w.calcSafePointByMinStartTS(ctx, oracle.GoTimeToTS(now.Add(-*lifeTime)))
	safePointValue, err = w.setGCWorkerServiceSafePoint(ctx, safePointValue)
	if err != nil {
		return nil, 0, errors.Trace(err)
	}

	// safepoint is recorded in time.Time format which strips the logical part of the timestamp.
	// To prevent the GC worker from keeping working due to the loss of logical part when the
	// safe point isn't changed, we should compare them in time.Time format.
	safePoint := oracle.GetTimeFromTS(safePointValue)
	// We should never decrease safePoint.
	if lastSafePoint != nil && !safePoint.After(*lastSafePoint) {
		logutil.BgLogger().Info("last safe point is later than current one."+
			"No need to gc."+
			"This might be caused by manually enlarging gc lifetime",
			zap.String("category", "gc worker"),
			zap.String("leaderTick on", w.uuid),
			zap.Time("last safe point", *lastSafePoint),
			zap.Time("current safe point", safePoint))
		return nil, 0, nil
	}
	return &safePoint, safePointValue, nil
}

// setGCWorkerServiceSafePoint sets the given safePoint as TiDB's service safePoint to PD, and returns the current minimal
// service safePoint among all services.
func (w *GCWorker) setGCWorkerServiceSafePoint(ctx context.Context, safePoint uint64) (uint64, error) {
	// Sets TTL to MAX to make it permanently valid.
	var minSafePoint uint64
	var err error
	// Sets TTL to MAX to make it permanently valid.
	ttl := int64(math.MaxInt64)

	if w.isCurrentKeyspaceUseKeyspaceLevelGC() {
		keyspaceID := uint32(w.store.GetCodec().GetKeyspaceID())
		minSafePoint, err = w.pdClient.UpdateServiceSafePointV2(ctx, keyspaceID, gcWorkerServiceSafePointID, ttl, safePoint)
		logutil.Logger(ctx).Info("[gc worker] update keyspace gc worker service safe point ",
			zap.String("uuid", w.uuid),
			zap.Uint32("keyspace-id", keyspaceID),
			zap.Uint64("req-service-safe-point", safePoint),
			zap.Uint64("resp-min-service-safe-point", minSafePoint))
	} else {
		// It is the situation when the keyspace is not set.
		minSafePoint, err = w.pdClient.UpdateServiceGCSafePoint(ctx, gcWorkerServiceSafePointID, ttl, safePoint)
		logutil.Logger(ctx).Info("[gc worker] update gc worker service safe point",
			zap.String("uuid", w.uuid),
			zap.Uint64("req-service-safe-point", safePoint),
			zap.Uint64("resp-min-service-safe-point", minSafePoint))
	}
	if err != nil {
		logutil.Logger(ctx).Error("failed to update service safe point", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("update_service_safe_point").Inc()
		return 0, errors.Trace(err)
	}
	if minSafePoint < safePoint {
		logutil.Logger(ctx).Info("there's another service in the cluster requires an earlier safe point. "+
			"gc will continue with the earlier one",
			zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("ourSafePoint", safePoint),
			zap.Uint64("minSafePoint", minSafePoint),
		)
		safePoint = minSafePoint
	}
	return safePoint, nil
}

func (w *GCWorker) runGCJob(ctx context.Context, safePoint uint64, concurrency gcConcurrency) error {
	failpoint.Inject("mockRunGCJobFail", func() {
		failpoint.Return(errors.New("mock failure of runGCJoB"))
	})
	metrics.GCWorkerCounter.WithLabelValues("run_job").Inc()

	err := w.resolveLocks(ctx, safePoint, concurrency.v)
	if err != nil {
		logutil.Logger(ctx).Error("resolve locks returns an error", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("resolve_lock").Inc()
		return errors.Trace(err)
	}

	// Save safe point to pd.
	err = w.saveSafePoint(w.tikvStore.GetSafePointKV(), safePoint)
	if err != nil {
		logutil.Logger(ctx).Error("failed to save safe point to PD", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("save_safe_point").Inc()
		return errors.Trace(err)
	}
	// Sleep to wait for all other tidb instances update their safepoint cache.
	time.Sleep(gcSafePointCacheInterval)

	err = w.deleteRanges(ctx, safePoint, concurrency)
	if err != nil {
		logutil.Logger(ctx).Error("delete range returns an error", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("delete_range").Inc()
		return errors.Trace(err)
	}
	err = w.redoDeleteRanges(ctx, safePoint, concurrency)
	if err != nil {
		logutil.Logger(ctx).Error("redo-delete range returns an error", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("redo_delete_range").Inc()
		return errors.Trace(err)
	}

	if w.checkUseDistributedGC() {
		err = w.uploadSafePointToPD(ctx, safePoint)
		if err != nil {
			logutil.Logger(ctx).Error("failed to upload safe point to PD", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Error(err))
			metrics.GCJobFailureCounter.WithLabelValues("upload_safe_point").Inc()
			return errors.Trace(err)
		}
	} else {
		err = w.doGC(ctx, safePoint, concurrency.v)
		if err != nil {
			logutil.Logger(ctx).Error("do GC returns an error", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Error(err))
			metrics.GCJobFailureCounter.WithLabelValues("gc").Inc()
			return errors.Trace(err)
		}
	}

	// Handle GCV2 tidb worker after a round of GC.
	if w.isCurrentKeyspaceUseKeyspaceLevelGC() {
		// If current TiDB is the master, it should send a heartbeat to tidb worker service
		// in order to prevent unnecessary activation of the GCV2 tidb worker.
		if tidbworker.IsMaster() || tidbworker.IsTTLTaskWorker() {
			gcLifeTime, err := w.loadDurationWithDefault(gcLifeTimeKey, gcDefaultLifeTime)
			if err != nil {
				logutil.Logger(ctx).Error("[tidb worker] failed to load gc life time",
					zap.Error(err))
				return errors.Trace(err)
			}
			err = tidbworker.GlobalTiDBWorkerManager.RegisterGCV2(ctx, safePoint, int64(*gcLifeTime/time.Second))
			if err != nil {
				logutil.Logger(ctx).Error("[tidb worker] failed to register gc v2 job",
					zap.Uint64("safe-point", safePoint),
					zap.Error(err))
				return errors.Trace(err)
			}
		}
		// If current TiDB is master or worker, it should notify tidb worker service that it
		// has finished a round of GC.
		if tidbworker.IsMaster() || tidbworker.IsGCV2Worker() || tidbworker.IsTTLTaskWorker() {
			err = tidbworker.GlobalTiDBWorkerManager.RecycleGCV2(ctx, safePoint)
			if err != nil {
				logutil.Logger(ctx).Error("[tidb worker] failed to recycle gc v2 job",
					zap.Uint64("safe-point", safePoint),
					zap.Error(err))
				return errors.Trace(err)
			}
		}
	}

	return nil
}

// deleteRanges processes all delete range records whose ts < safePoint in table `gc_delete_range`
// `concurrency` specifies the concurrency to send NotifyDeleteRange.
func (w *GCWorker) deleteRanges(
	ctx context.Context,
	safePoint uint64,
	concurrency gcConcurrency,
) error {
	metrics.GCWorkerCounter.WithLabelValues("delete_range").Inc()

	s := createSession(w.store)
	defer s.Close()
	ranges, err := util.LoadDeleteRanges(ctx, s, safePoint)
	if err != nil {
		return errors.Trace(err)
	}

	v2, err := util.IsRaftKv2(ctx, s)
	if err != nil {
		return errors.Trace(err)
	}
	// Cache table ids on which placement rules have been GC-ed, to avoid redundantly GC the same table id multiple times.
	var gcPlacementRuleCache sync.Map

	logutil.Logger(ctx).Info("start delete ranges", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("ranges", len(ranges)))
	startTime := time.Now()

	deleteRangeConcurrency := w.calcDeleteRangeConcurrency(concurrency, len(ranges))
	concurrencyLimiter := make(chan struct{}, deleteRangeConcurrency)

	f := func(r util.DelRangeTask) {
		var err error
		defer func() {
			<-concurrencyLimiter
		}()
		se := createSession(w.store)
		defer se.Close()

		startKey, endKey := r.Range()
		if v2 {
			// In raftstore-v2, we use delete range instead to avoid deletion omission
			task := rangetask.NewDeleteRangeTask(w.tikvStore, startKey, endKey, deleteRangeConcurrency)
			err = task.Execute(ctx)
		} else {
			err = w.doUnsafeDestroyRangeRequest(ctx, startKey, endKey)
		}
		failpoint.Inject("ignoreDeleteRangeFailed", func() {
			err = nil
		})

		if err != nil {
			logutil.Logger(ctx).Error("delete range failed on range", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Stringer("startKey", startKey),
				zap.Stringer("endKey", endKey),
				zap.Error(err))
			return
		}

		err = doGCPlacementRules(se, safePoint, r, &gcPlacementRuleCache)
		if err != nil {
			logutil.Logger(ctx).Error("gc placement rules failed on range", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Int64("jobID", r.JobID),
				zap.Int64("elementID", r.ElementID),
				zap.Error(err))
			return
		}
		// We only delete rules, so concurrently updating rules should not return errors.
		if err := w.doGCLabelRules(r); err != nil {
			logutil.Logger(ctx).Error("gc label rules failed on range", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Int64("jobID", r.JobID),
				zap.Int64("elementID", r.ElementID),
				zap.Error(err))
			return
		}

		err = util.CompleteDeleteRange(se, r, !v2)
		if err != nil {
			logutil.Logger(ctx).Error("failed to mark delete range task done", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Stringer("startKey", startKey),
				zap.Stringer("endKey", endKey),
				zap.Error(err))
			metrics.GCUnsafeDestroyRangeFailuresCounterVec.WithLabelValues("save").Inc()
		}
	}
	var wg util2.WaitGroupWrapper
	for i := range ranges {
		r := ranges[i]
		concurrencyLimiter <- struct{}{}
		wg.Run(func() { f(r) })
	}
	wg.Wait()

	logutil.Logger(ctx).Info("finish delete ranges", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("num of ranges", len(ranges)),
		zap.Duration("cost time", time.Since(startTime)))
	metrics.GCHistogram.WithLabelValues("delete_ranges").Observe(time.Since(startTime).Seconds())
	return nil
}

const (
	// ConcurrencyDivisor reduces the input concurrency to avoid overwhelming the system
	ConcurrencyDivisor = 4
	// RequestsPerThread is the number of requests handled by a single thread
	RequestsPerThread = 100000
)

// calcDeleteRangeConcurrency calculates the concurrency of deleteRanges.
//
// There was only one concurrency for resolveLocks. When parallelizing deleteRanges, its concurrency is controlled by
// the same variable TiDBGCConcurrency. As requested by PM, the first priority is to ensure the stability of the system,
// so the concurrency of deleteRanges is reduced to avoid overwhelming the system.
//
// Assuming an average request takes 50ms:
// With ideal parallelism and sufficient concurrency,
// the maximum duration for a round of deleteRanges is 100,000 * 50ms = 5,000s.
// These values are conservatively chosen to minimize GC impact on foreground requests
func (w *GCWorker) calcDeleteRangeConcurrency(concurrency gcConcurrency, rangeNum int) int {
	maxConcurrency := max(1, concurrency.v/ConcurrencyDivisor)
	threadsBasedOnRequests := max(1, rangeNum/RequestsPerThread)
	if concurrency.isAuto {
		return min(maxConcurrency, threadsBasedOnRequests)
	}
	return maxConcurrency
}

// redoDeleteRanges checks all deleted ranges whose ts is at least `lifetime + 24h` ago. See TiKV RFC #2.
// `concurrency` specifies the concurrency to send NotifyDeleteRange.
func (w *GCWorker) redoDeleteRanges(ctx context.Context, safePoint uint64,
	concurrency gcConcurrency) error {
	metrics.GCWorkerCounter.WithLabelValues("redo_delete_range").Inc()

	// We check delete range records that are deleted about 24 hours ago.
	redoDeleteRangesTs := safePoint - oracle.ComposeTS(int64(gcRedoDeleteRangeDelay.Seconds())*1000, 0)

	se := createSession(w.store)
	ranges, err := util.LoadDoneDeleteRanges(ctx, se, redoDeleteRangesTs)
	se.Close()
	if err != nil {
		return errors.Trace(err)
	}

	logutil.Logger(ctx).Info("start redo-delete ranges", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("num of ranges", len(ranges)))
	startTime := time.Now()

	deleteRangeConcurrency := w.calcDeleteRangeConcurrency(concurrency, len(ranges))
	concurrencyLimiter := make(chan struct{}, deleteRangeConcurrency)

	f := func(r util.DelRangeTask) {
		defer func() {
			<-concurrencyLimiter
		}()
		var err error
		startKey, endKey := r.Range()

		err = w.doUnsafeDestroyRangeRequest(ctx, startKey, endKey)
		if err != nil {
			logutil.Logger(ctx).Error("redo-delete range failed on range", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Stringer("startKey", startKey),
				zap.Stringer("endKey", endKey),
				zap.Error(err))
			return
		}
		se := createSession(w.store)
		err = util.DeleteDoneRecord(se, r)
		se.Close()
		if err != nil {
			logutil.Logger(ctx).Error("failed to remove delete_range_done record", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Stringer("startKey", startKey),
				zap.Stringer("endKey", endKey),
				zap.Error(err))
			metrics.GCUnsafeDestroyRangeFailuresCounterVec.WithLabelValues("save_redo").Inc()
		}
	}
	var wg util2.WaitGroupWrapper
	for i := range ranges {
		r := ranges[i]
		concurrencyLimiter <- struct{}{}
		wg.Run(func() { f(r) })
	}
	wg.Wait()
	logutil.Logger(ctx).Info("finish redo-delete ranges", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("num of ranges", len(ranges)),
		zap.Duration("cost time", time.Since(startTime)))
	metrics.GCHistogram.WithLabelValues("redo_delete_ranges").Observe(time.Since(startTime).Seconds())
	return nil
}

func (w *GCWorker) doUnsafeDestroyRangeRequest(
	ctx context.Context, startKey []byte, endKey []byte,
) error {
	// Get all stores every time deleting a region. So the store list is less probably to be stale.
	stores, err := w.getStoresForGC(ctx)
	if err != nil {
		logutil.Logger(ctx).Error("delete ranges: got an error while trying to get store list from PD", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCUnsafeDestroyRangeFailuresCounterVec.WithLabelValues("get_stores").Inc()
		return errors.Trace(err)
	}

	req := tikvrpc.NewRequest(tikvrpc.CmdUnsafeDestroyRange, &kvrpcpb.UnsafeDestroyRangeRequest{
		StartKey: startKey,
		EndKey:   endKey,
	}, kvrpcpb.Context{DiskFullOpt: kvrpcpb.DiskFullOpt_AllowedOnAlmostFull})

	var wg sync.WaitGroup
	errChan := make(chan error, len(stores))

	for _, store := range stores {
		address := store.Address
		storeID := store.Id
		wg.Add(1)
		go func() {
			defer wg.Done()

			resp, err1 := w.tikvStore.GetTiKVClient().SendRequest(ctx, address, req, unsafeDestroyRangeTimeout)
			if err1 == nil {
				if resp == nil || resp.Resp == nil {
					err1 = errors.Errorf("unsafe destroy range returns nil response from store %v", storeID)
				} else {
					errStr := (resp.Resp.(*kvrpcpb.UnsafeDestroyRangeResponse)).Error
					if len(errStr) > 0 {
						err1 = errors.Errorf("unsafe destroy range failed on store %v: %s", storeID, errStr)
					}
				}
			}

			if err1 != nil {
				metrics.GCUnsafeDestroyRangeFailuresCounterVec.WithLabelValues("send").Inc()
			}
			errChan <- err1
		}()
	}

	var errs []string
	for range stores {
		err1 := <-errChan
		if err1 != nil {
			errs = append(errs, err1.Error())
		}
	}

	wg.Wait()

	if len(errs) > 0 {
		return errors.Errorf("[gc worker] destroy range finished with errors: %v", errs)
	}

	return nil
}

// needsGCOperationForStore checks if the store-level requests related to GC needs to be sent to the store. The store-level
// requests includes UnsafeDestroyRange, PhysicalScanLock, etc.
func needsGCOperationForStore(store *metapb.Store) (bool, error) {
	// TombStone means the store has been removed from the cluster and there isn't any peer on the store, so needn't do GC for it.
	// Offline means the store is being removed from the cluster and it becomes tombstone after all peers are removed from it,
	// so we need to do GC for it.
	if store.State == metapb.StoreState_Tombstone {
		return false, nil
	}

	engineLabel := ""
	for _, label := range store.GetLabels() {
		if label.GetKey() == placement.EngineLabelKey {
			engineLabel = label.GetValue()
			break
		}
	}

	switch engineLabel {
	case placement.EngineLabelTiFlash:
		// For a TiFlash node, it uses other approach to delete dropped tables, so it's safe to skip sending
		// UnsafeDestroyRange requests; it has only learner peers and their data must exist in TiKV, so it's safe to
		// skip physical resolve locks for it.
		return false, nil

	case placement.EngineLabelTiFlashCompute:
		logutil.BgLogger().Debug("will ignore gc tiflash_compute node", zap.String("category", "gc worker"))
		return false, nil

	case placement.EngineLabelTiKV, "":
		// If no engine label is set, it should be a TiKV node.
		return true, nil

	default:
		return true, errors.Errorf("unsupported store engine \"%v\" with storeID %v, addr %v",
			engineLabel,
			store.GetId(),
			store.GetAddress())
	}
}

// getStoresForGC gets the list of stores that needs to be processed during GC.
func (w *GCWorker) getStoresForGC(ctx context.Context) ([]*metapb.Store, error) {
	stores, err := w.pdClient.GetAllStores(ctx)
	if err != nil {
		return nil, errors.Trace(err)
	}

	upStores := make([]*metapb.Store, 0, len(stores))
	for _, store := range stores {
		needsGCOp, err := needsGCOperationForStore(store)
		if err != nil {
			return nil, errors.Trace(err)
		}
		if needsGCOp {
			upStores = append(upStores, store)
		}
	}
	return upStores, nil
}

func (w *GCWorker) getStoresMapForGC(ctx context.Context) (map[uint64]*metapb.Store, error) {
	stores, err := w.getStoresForGC(ctx)
	if err != nil {
		return nil, err
	}

	storesMap := make(map[uint64]*metapb.Store, len(stores))
	for _, store := range stores {
		storesMap[store.Id] = store
	}

	return storesMap, nil
}

func (w *GCWorker) loadGCConcurrencyWithDefault() (int, error) {
	str, err := w.loadValueFromSysTable(gcConcurrencyKey)
	if err != nil {
		return gcDefaultConcurrency, errors.Trace(err)
	}
	if str == "" {
		err = w.saveValueToSysTable(gcConcurrencyKey, strconv.Itoa(gcDefaultConcurrency))
		if err != nil {
			return gcDefaultConcurrency, errors.Trace(err)
		}
		return gcDefaultConcurrency, nil
	}

	jobConcurrency, err := strconv.Atoi(str)
	if err != nil {
		return gcDefaultConcurrency, err
	}

	if jobConcurrency < gcMinConcurrency {
		jobConcurrency = gcMinConcurrency
	}

	if jobConcurrency > gcMaxConcurrency {
		jobConcurrency = gcMaxConcurrency
	}

	return jobConcurrency, nil
}

// Central mode is deprecated in v5.0. This function will always return true.
func (w *GCWorker) checkUseDistributedGC() bool {
	mode, err := w.loadValueFromSysTable(gcModeKey)
	if err == nil && mode == "" {
		err = w.saveValueToSysTable(gcModeKey, gcModeDefault)
	}
	if err != nil {
		logutil.BgLogger().Error("failed to load gc mode, fall back to distributed mode", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Error(err))
		metrics.GCJobFailureCounter.WithLabelValues("check_gc_mode").Inc()
	} else if strings.EqualFold(mode, gcModeCentral) {
		logutil.BgLogger().Warn("distributed mode will be used as central mode is deprecated", zap.String("category", "gc worker"))
	} else if !strings.EqualFold(mode, gcModeDistributed) {
		logutil.BgLogger().Warn("distributed mode will be used", zap.String("category", "gc worker"),
			zap.String("invalid gc mode", mode))
	}
	return true
}

func (w *GCWorker) resolveLocks(
	ctx context.Context,
	safePoint uint64,
	concurrency int,
) error {
	metrics.GCWorkerCounter.WithLabelValues("resolve_locks").Inc()
	logutil.Logger(ctx).Info("start resolve locks", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Uint64("safePoint", safePoint),
		zap.Int("concurrency", concurrency))
	startTime := time.Now()

	handler := func(ctx context.Context, r tikvstore.KeyRange) (rangetask.TaskStat, error) {
		scanLimit := uint32(tikv.GCScanLockLimit)
		failpoint.Inject("lowScanLockLimit", func() {
			scanLimit = 3
		})
		return tikv.ResolveLocksForRange(ctx, w.regionLockResolver, safePoint, r.StartKey, r.EndKey, tikv.NewGcResolveLockMaxBackoffer, scanLimit)
	}

	runner := rangetask.NewRangeTaskRunner("resolve-locks-runner", w.tikvStore, concurrency, handler)
	// Run resolve lock on the whole TiKV cluster. Empty keys means the range is unbounded.
	err := w.resolveLocksWithBounded(ctx, runner, safePoint)
	if err != nil {
		logutil.Logger(ctx).Error("resolve locks failed", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("safePoint", safePoint),
			zap.Error(err))
		return errors.Trace(err)
	}

	logutil.Logger(ctx).Info("finish resolve locks", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Uint64("safePoint", safePoint),
		zap.Int("regions", runner.CompletedRegions()))
	metrics.GCHistogram.WithLabelValues("resolve_locks").Observe(time.Since(startTime).Seconds())
	return nil
}

func (w *GCWorker) resolveLocksWithBounded(ctx context.Context, runner *rangetask.Runner, safePoint uint64) error {
	var err error
	var txnLeftBound []byte
	var txnRightBound []byte

	if w.isCurrentKeyspaceUseKeyspaceLevelGC() {
		failpoint.Inject("testLegacyResolveKeyspaceLocks", func(v failpoint.Value) {
			ms := v.(int)
			time.Sleep(time.Duration(ms) * time.Millisecond)
			failpoint.Return(errors.New("ResolveKeyspaceLocksInjectedError"))
		})
		// When the current keyspace uses keyspace level GC, ResolveLocksForRange only resolves specified keyspace locks.
		keyspaceID := uint32(w.store.GetCodec().GetKeyspaceID())
		// Resolve locks in the `keyspaceID` range.
		// If TiDB sets keyspace-name, the keyspace prefix of the 'startKey' and 'endKey' of the resolve locks
		// is added in the encodeRange function in client-go before the request is sent.
		// So if we want to resolve locks on the full range of the current keyspace, then startKey and endKey should be []byte(unboundedKey).
		err = runner.RunOnRange(ctx, []byte(unboundedKey), []byte(unboundedKey))
		if err != nil {
			logutil.Logger(ctx).Error("[gc worker] resolve locks by keyspace range failed",
				zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Uint32("keyspace-id", keyspaceID),
				zap.Uint64("gc-safe-point", safePoint),
				zap.String("txn-left-bound", hex.EncodeToString(txnLeftBound)),
				zap.String("txn-right-bound", hex.EncodeToString(txnRightBound)),
				zap.Error(err))
			return errors.Trace(err)
		}
	} else {
		logutil.Logger(ctx).Info("[gc worker] start resolve locks in null keyspace range and range of keyspace which is use global gc.")
		err = w.resolveLocksInGlobalGC(ctx, runner, safePoint)
		if err != nil {
			logutil.Logger(ctx).Error("[gc worker] resolve locks all keyspace failed", zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Uint64("safe-point", safePoint),
				zap.Error(err))
			return errors.Trace(err)
		}
	}

	return nil
}

func (w *GCWorker) getAllKeyspace(ctx context.Context) ([]*keyspacepb.KeyspaceMeta, error) {
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	var allkeyspaces []*keyspacepb.KeyspaceMeta
	startID := uint32(0)
	for {
		keyspacesList, err := w.pdClient.GetAllKeyspaces(ctx, startID, getAllKeyspacePageSize)
		if err != nil {
			logutil.Logger(ctx).Error("get all keyspaces error", zap.Error(err))
			return nil, err
		}

		if len(keyspacesList) == 0 {
			break
		}

		allkeyspaces = append(allkeyspaces, keyspacesList...)
		latestKeyspace := keyspacesList[len(keyspacesList)-1]
		startID = latestKeyspace.Id + 1
	}
	return allkeyspaces, nil
}

// resolveLocksInGlobalGC performs resolve locks in global GC mode.
func (w *GCWorker) resolveLocksInGlobalGC(ctx context.Context, runner *rangetask.Runner, safePoint uint64) error {
	// keyspaces, err := w.getAllKeyspace(ctx)
	// if err != nil {
	// 	logutil.Logger(ctx).Warn("[gc worker] get all keyspace err.", zap.Error(errors.Trace(err)))
	// 	return err
	// }

	// skip get all keyspace,in starter & essential env.
	keyspaces := make([]*keyspacepb.KeyspaceMeta, 0)
	var err error

	logutil.Logger(ctx).Info("[gc worker] start resolving locks in global GC mode")

	// There are 3 steps to resolving locks in global GC.
	// step 1. Resolve locks in [ unbounded, Raw KV left bound ),
	//         and skip RawKV ranges.
	// step 2. Resolve locks in [ Raw KV right bound, keyspace 0 txn left bound ).
	// step 3. Resolve locks in [ keyspace txn left bound, keyspace txn right bound ).
	//         for all keyspaces with keyspace level GC disabled.
	// step 4. Resolve locks in [ max keyspace txn right bound, unbounded ).

	// step 1. Resolve locks in [ unbounded, Raw KV left bound ),
	//         and skip RawKV ranges.
	txnLeftBound := []byte(unboundedKey)
	txnRightBound := []byte{keyspace.RawKVLeftBoundaryPrefix}
	err = runner.RunOnRange(ctx, txnLeftBound, txnRightBound)
	if err != nil {
		logutil.Logger(ctx).Error("[gc worker] resolve locks by range failed",
			zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("gc-safe-point", safePoint),
			zap.String("txn-left-bound", hex.EncodeToString(txnLeftBound)),
			zap.String("txn-right-bound", hex.EncodeToString(txnRightBound)),
			zap.Error(err))
		return errors.Trace(err)
	}

	// step 2. Resolve locks in [ Raw KV right bound, keyspace 0 txn left bound ).
	txnLeftBound = []byte{keyspace.RawKVRightBoundaryPrefix}
	txnRightBound = keyspace.GetKeyspaceTxnLeftBound(0)
	err = runner.RunOnRange(ctx, txnLeftBound, txnRightBound)
	if err != nil {
		logutil.Logger(ctx).Error("[gc worker] resolve locks by range failed",
			zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("gc-safe-point", safePoint),
			zap.String("txn-left-bound", hex.EncodeToString(txnLeftBound)),
			zap.String("txn-right-bound", hex.EncodeToString(txnRightBound)),
			zap.Error(err))
		return errors.Trace(err)
	}

	// step 3. Resolve locks in [ keyspace txn left bound, keyspace txn right bound ).
	//         for all keyspaces with keyspace level GC disabled.
	for i := range keyspaces {
		keyspaceMeta := keyspaces[i]
		// Skip the keyspace which state is not enabled or not use global GC.
		if keyspaceMeta.State != keyspacepb.KeyspaceState_ENABLED || !keyspace.IsKeyspaceMetaNotNilAndUseGlobalGC(keyspaceMeta) {
			logutil.BgLogger().Debug("[gc worker] skip resolve locks in this keyspace range", zap.Any("keyspace-meta", keyspaceMeta))
			continue
		}

		logutil.Logger(ctx).Info("[gc worker] start resolve locks in the keyspace range", zap.Uint32("KeyspaceID", keyspaceMeta.Id))
		txnLeftBound, txnRightBound = keyspace.GetKeyspaceTxnRange(keyspaceMeta.Id)

		err = runner.RunOnRange(ctx, txnLeftBound, txnRightBound)
		if err != nil {
			logutil.Logger(ctx).Error("[gc worker] resolve locks by range failed",
				zap.String("category", "gc worker"),
				zap.String("uuid", w.uuid),
				zap.Uint64("gc-safe-point", safePoint),
				zap.String("txn-left-bound", hex.EncodeToString(txnLeftBound)),
				zap.String("txn-right-bound", hex.EncodeToString(txnRightBound)),
				zap.Error(err))
			return errors.Trace(err)
		}
	}

	// step 4. Resolve locks in [ max keyspace txn right bound, unbounded ).
	txnLeftBound = []byte{keyspace.MaxKeyspaceRightBoundaryPrefix}
	txnRightBound = []byte(unboundedKey)
	err = runner.RunOnRange(ctx, txnLeftBound, txnRightBound)
	if err != nil {
		logutil.Logger(ctx).Error("[gc worker] resolve locks by range failed",
			zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("gc-safe-point", safePoint),
			zap.String("txn-left-bound", hex.EncodeToString(txnLeftBound)),
			zap.String("txn-right-bound", hex.EncodeToString(txnRightBound)),
			zap.Error(err))
		return errors.Trace(err)
	}

	return nil
}

const gcOneRegionMaxBackoff = 20000

func (w *GCWorker) uploadSafePointToPD(ctx context.Context, safePoint uint64) error {
	var newSafePoint uint64
	var err error

	bo := tikv.NewBackofferWithVars(ctx, gcOneRegionMaxBackoff, nil)
	for {
		if w.isCurrentKeyspaceUseKeyspaceLevelGC() {
			keyspaceID := uint32(w.store.GetCodec().GetKeyspaceID())
			newSafePoint, err = w.pdClient.UpdateGCSafePointV2(ctx, keyspaceID, safePoint)
			logutil.Logger(ctx).Info("[gc worker] update keyspace gc safe point",
				zap.String("uuid", w.uuid),
				zap.Uint32("keyspace-id", keyspaceID),
				zap.Uint64("req-gc-safe-point", safePoint),
				zap.Uint64("resp-gc-safe-point", newSafePoint))
		} else {
			newSafePoint, err = w.pdClient.UpdateGCSafePoint(ctx, safePoint)
			logutil.Logger(ctx).Info("[gc worker] update global gc safe point",
				zap.String("uuid", w.uuid),
				zap.Uint64("req-gc-safe-point", safePoint),
				zap.Uint64("resp-gc-safe-point", newSafePoint))
		}
		if err != nil {
			if errors.Cause(err) == context.Canceled {
				return errors.Trace(err)
			}
			err = bo.Backoff(tikv.BoPDRPC(), errors.Errorf("failed to upload safe point to PD, err: %v", err))
			if err != nil {
				return errors.Trace(err)
			}
			continue
		}
		break
	}

	if newSafePoint != safePoint {
		logutil.Logger(ctx).Warn("PD rejected safe point", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Uint64("our safe point", safePoint),
			zap.Uint64("using another safe point", newSafePoint))
		return errors.Errorf("PD rejected our safe point %v but is using another safe point %v", safePoint, newSafePoint)
	}
	logutil.Logger(ctx).Info("sent safe point to PD", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Uint64("safe point", safePoint))
	return nil
}

func (w *GCWorker) doGCForRange(ctx context.Context, startKey []byte, endKey []byte, safePoint uint64) (rangetask.TaskStat, error) {
	var stat rangetask.TaskStat
	defer func() {
		metrics.GCActionRegionResultCounter.WithLabelValues("success").Add(float64(stat.CompletedRegions))
		metrics.GCActionRegionResultCounter.WithLabelValues("fail").Add(float64(stat.FailedRegions))
	}()
	key := startKey
	for {
		bo := tikv.NewBackofferWithVars(ctx, gcOneRegionMaxBackoff, nil)
		loc, err := w.tikvStore.GetRegionCache().LocateKey(bo, key)
		if err != nil {
			return stat, errors.Trace(err)
		}

		var regionErr *errorpb.Error
		regionErr, err = w.doGCForRegion(bo, safePoint, loc.Region)

		// we check regionErr here first, because we know 'regionErr' and 'err' should not return together, to keep it to
		// make the process correct.
		if regionErr != nil {
			err = bo.Backoff(tikv.BoRegionMiss(), errors.New(regionErr.String()))
			if err == nil {
				continue
			}
		}

		if err != nil {
			logutil.BgLogger().Warn("[gc worker]",
				zap.String("uuid", w.uuid),
				zap.String("gc for range", fmt.Sprintf("[%d, %d)", startKey, endKey)),
				zap.Uint64("safePoint", safePoint),
				zap.Error(err))
			stat.FailedRegions++
		} else {
			stat.CompletedRegions++
		}

		key = loc.EndKey
		if len(key) == 0 || bytes.Compare(key, endKey) >= 0 {
			break
		}
	}

	return stat, nil
}

// doGCForRegion used for gc for region.
// these two errors should not return together, for more, see the func 'doGC'
func (w *GCWorker) doGCForRegion(bo *tikv.Backoffer, safePoint uint64, region tikv.RegionVerID) (*errorpb.Error, error) {
	req := tikvrpc.NewRequest(tikvrpc.CmdGC, &kvrpcpb.GCRequest{
		SafePoint: safePoint,
	})

	resp, err := w.tikvStore.SendReq(bo, req, region, gcTimeout)
	if err != nil {
		return nil, errors.Trace(err)
	}
	regionErr, err := resp.GetRegionError()
	if err != nil {
		return nil, errors.Trace(err)
	}
	if regionErr != nil {
		return regionErr, nil
	}

	if resp.Resp == nil {
		return nil, errors.Trace(tikverr.ErrBodyMissing)
	}
	gcResp := resp.Resp.(*kvrpcpb.GCResponse)
	if gcResp.GetError() != nil {
		return nil, errors.Errorf("unexpected gc error: %s", gcResp.GetError())
	}

	return nil, nil
}

func (w *GCWorker) doGC(ctx context.Context, safePoint uint64, concurrency int) error {
	metrics.GCWorkerCounter.WithLabelValues("do_gc").Inc()
	logutil.Logger(ctx).Info("start doing gc for all keys", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Int("concurrency", concurrency),
		zap.Uint64("safePoint", safePoint))
	startTime := time.Now()

	runner := rangetask.NewRangeTaskRunner(
		"gc-runner",
		w.tikvStore,
		concurrency,
		func(ctx context.Context, r tikvstore.KeyRange) (rangetask.TaskStat, error) {
			return w.doGCForRange(ctx, r.StartKey, r.EndKey, safePoint)
		})

	err := runner.RunOnRange(ctx, []byte(unboundedKey), []byte(unboundedKey))
	if err != nil {
		logutil.Logger(ctx).Warn("failed to do gc for all keys", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid),
			zap.Int("concurrency", concurrency),
			zap.Error(err))
		return errors.Trace(err)
	}

	successRegions := runner.CompletedRegions()
	failedRegions := runner.FailedRegions()

	logutil.Logger(ctx).Info("finished doing gc for all keys", zap.String("category", "gc worker"),
		zap.String("uuid", w.uuid),
		zap.Uint64("safePoint", safePoint),
		zap.Int("successful regions", successRegions),
		zap.Int("failed regions", failedRegions),
		zap.Duration("total cost time", time.Since(startTime)))
	metrics.GCHistogram.WithLabelValues("do_gc").Observe(time.Since(startTime).Seconds())

	return nil
}

func (w *GCWorker) checkLeader(ctx context.Context) (bool, error) {
	metrics.GCWorkerCounter.WithLabelValues("check_leader").Inc()
	se := createSession(w.store)
	defer se.Close()

	_, err := se.ExecuteInternal(ctx, "BEGIN")
	if err != nil {
		return false, errors.Trace(err)
	}
	leader, err := w.loadValueFromSysTable(gcLeaderUUIDKey)
	if err != nil {
		se.RollbackTxn(ctx)
		return false, errors.Trace(err)
	}
	logutil.BgLogger().Info("got leader", zap.String("category", "gc worker"), zap.String("uuid", leader))
	if leader == w.uuid {
		err = w.saveTime(gcLeaderLeaseKey, time.Now().Add(gcWorkerLease))
		if err != nil {
			se.RollbackTxn(ctx)
			return false, errors.Trace(err)
		}
		err = se.CommitTxn(ctx)
		if err != nil {
			return false, errors.Trace(err)
		}
		return true, nil
	}

	se.RollbackTxn(ctx)

	_, err = se.ExecuteInternal(ctx, "BEGIN")
	if err != nil {
		return false, errors.Trace(err)
	}
	lease, err := w.loadTime(gcLeaderLeaseKey)
	if err != nil {
		se.RollbackTxn(ctx)
		return false, errors.Trace(err)
	}
	if lease == nil || lease.Before(time.Now()) {
		logutil.BgLogger().Debug("register as leader", zap.String("category", "gc worker"),
			zap.String("uuid", w.uuid))
		metrics.GCWorkerCounter.WithLabelValues("register_leader").Inc()

		err = w.saveValueToSysTable(gcLeaderUUIDKey, w.uuid)
		if err != nil {
			se.RollbackTxn(ctx)
			return false, errors.Trace(err)
		}
		err = w.saveValueToSysTable(gcLeaderDescKey, w.desc)
		if err != nil {
			se.RollbackTxn(ctx)
			return false, errors.Trace(err)
		}
		err = w.saveTime(gcLeaderLeaseKey, time.Now().Add(gcWorkerLease))
		if err != nil {
			se.RollbackTxn(ctx)
			return false, errors.Trace(err)
		}
		err = se.CommitTxn(ctx)
		if err != nil {
			return false, errors.Trace(err)
		}
		return true, nil
	}
	se.RollbackTxn(ctx)
	return false, nil
}

func (w *GCWorker) saveSafePoint(kv tikv.SafePointKV, t uint64) error {
	s := strconv.FormatUint(t, 10)
	err := kv.Put(tikv.GcSavedSafePoint, s)
	if err != nil {
		logutil.BgLogger().Error("save safepoint failed", zap.Error(err))
		return errors.Trace(err)
	}
	return nil
}

func (w *GCWorker) saveTime(key string, t time.Time) error {
	err := w.saveValueToSysTable(key, t.Format(tikvutil.GCTimeFormat))
	return errors.Trace(err)
}

func (w *GCWorker) loadTime(key string) (*time.Time, error) {
	str, err := w.loadValueFromSysTable(key)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if str == "" {
		return nil, nil
	}
	t, err := tikvutil.CompatibleParseGCTime(str)
	if err != nil {
		return nil, errors.Trace(err)
	}
	return &t, nil
}

func (w *GCWorker) saveDuration(key string, d time.Duration) error {
	err := w.saveValueToSysTable(key, d.String())
	return errors.Trace(err)
}

func (w *GCWorker) loadDuration(key string) (*time.Duration, error) {
	str, err := w.loadValueFromSysTable(key)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if str == "" {
		return nil, nil
	}
	d, err := time.ParseDuration(str)
	if err != nil {
		return nil, errors.Trace(err)
	}
	return &d, nil
}

func (w *GCWorker) loadDurationWithDefault(key string, def time.Duration) (*time.Duration, error) {
	d, err := w.loadDuration(key)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if d == nil {
		err = w.saveDuration(key, def)
		if err != nil {
			return nil, errors.Trace(err)
		}
		return &def, nil
	}
	return d, nil
}

func (w *GCWorker) loadValueFromSysTable(key string) (string, error) {
	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnGC)
	se := createSession(w.store)
	defer se.Close()
	rs, err := se.ExecuteInternal(ctx, `SELECT HIGH_PRIORITY (variable_value) FROM mysql.tidb WHERE variable_name=%? FOR UPDATE`, key)
	if rs != nil {
		defer terror.Call(rs.Close)
	}
	if err != nil {
		return "", errors.Trace(err)
	}
	req := rs.NewChunk(nil)
	err = rs.Next(ctx, req)
	if err != nil {
		return "", errors.Trace(err)
	}
	if req.NumRows() == 0 {
		logutil.BgLogger().Debug("load kv", zap.String("category", "gc worker"),
			zap.String("key", key))
		return "", nil
	}
	value := req.GetRow(0).GetString(0)
	logutil.BgLogger().Debug("load kv", zap.String("category", "gc worker"),
		zap.String("key", key),
		zap.String("value", value))
	return value, nil
}

func (w *GCWorker) saveValueToSysTable(key, value string) error {
	const stmt = `INSERT HIGH_PRIORITY INTO mysql.tidb VALUES (%?, %?, %?)
			       ON DUPLICATE KEY
			       UPDATE variable_value = %?, comment = %?`
	se := createSession(w.store)
	defer se.Close()
	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnGC)
	_, err := se.ExecuteInternal(ctx, stmt,
		key, value, gcVariableComments[key],
		value, gcVariableComments[key])
	logutil.BgLogger().Debug("save kv", zap.String("category", "gc worker"),
		zap.String("key", key),
		zap.String("value", value),
		zap.Error(err))
	return errors.Trace(err)
}

// GC placement rules when the partitions are removed by the GC worker.
// Placement rules cannot be removed immediately after drop table / truncate table,
// because the tables can be flashed back or recovered.
func doGCPlacementRules(se sessiontypes.Session, _ uint64,
	dr util.DelRangeTask, gcPlacementRuleCache *sync.Map) (err error) {
	// Get the job from the job history
	var historyJob *model.Job
	failpoint.Inject("mockHistoryJobForGC", func(v failpoint.Value) {
		mockJ := &model.Job{
			Version: model.GetJobVerInUse(),
			ID:      dr.JobID,
			Type:    model.ActionDropTable,
			TableID: int64(v.(int)),
		}
		mockJ.FillFinishedArgs(&model.DropTableArgs{
			OldPartitionIDs: []int64{int64(v.(int))},
		})
		bytes, err1 := mockJ.Encode(true)
		if err1 != nil {
			return
		}
		historyJob = &model.Job{}
		err1 = historyJob.Decode(bytes)
		if err1 != nil {
			return
		}
	})
	if historyJob == nil {
		historyJob, err = ddl.GetHistoryJobByID(se, dr.JobID)
		if err != nil {
			return
		}
		if historyJob == nil {
			return dbterror.ErrDDLJobNotFound.GenWithStackByArgs(dr.JobID)
		}
	}

	// Notify PD to drop the placement rules of partition-ids and table-id, even if there may be no placement rules.
	var physicalTableIDs []int64
	switch historyJob.Type {
	case model.ActionDropTable:
		var args *model.DropTableArgs
		args, err = model.GetFinishedDropTableArgs(historyJob)
		if err != nil {
			return
		}
		physicalTableIDs = append(args.OldPartitionIDs, historyJob.TableID)
	case model.ActionTruncateTable, model.ActionTruncateTablePartition:
		var args *model.TruncateTableArgs
		args, err = model.GetFinishedTruncateTableArgs(historyJob)
		if err != nil {
			return
		}
		physicalTableIDs = args.OldPartitionIDs
		if historyJob.Type == model.ActionTruncateTable {
			physicalTableIDs = append(physicalTableIDs, historyJob.TableID)
		}
	case model.ActionDropTablePartition, model.ActionReorganizePartition,
		model.ActionRemovePartitioning, model.ActionAlterTablePartitioning:
		args, err2 := model.GetFinishedTablePartitionArgs(historyJob)
		if err2 != nil {
			return err2
		}
		physicalTableIDs = args.OldPhysicalTblIDs
	case model.ActionDropSchema:
		args, err2 := model.GetFinishedDropSchemaArgs(historyJob)
		if err2 != nil {
			return err2
		}
		physicalTableIDs = args.AllDroppedTableIDs
	}

	// Skip table ids that's already successfully handled.
	tmp := physicalTableIDs[:0]
	for _, id := range physicalTableIDs {
		if _, ok := gcPlacementRuleCache.Load(id); !ok {
			tmp = append(tmp, id)
		}
	}
	physicalTableIDs = tmp

	if len(physicalTableIDs) == 0 {
		return
	}

	if err := infosync.DeleteTiFlashPlacementRules(context.Background(), physicalTableIDs); err != nil {
		logutil.BgLogger().Error("delete placement rules failed", zap.Error(err), zap.Int64s("tableIDs", physicalTableIDs))
	}
	bundles := make([]*placement.Bundle, 0, len(physicalTableIDs))
	for _, id := range physicalTableIDs {
		bundles = append(bundles, placement.NewBundle(id))
	}
	err = infosync.PutRuleBundlesWithDefaultRetry(context.TODO(), bundles)
	if err != nil {
		return
	}

	// Cache the table id if its related rule are deleted successfully.
	for _, id := range physicalTableIDs {
		gcPlacementRuleCache.Store(id, struct{}{})
	}
	return nil
}

func (w *GCWorker) doGCLabelRules(dr util.DelRangeTask) (err error) {
	// Get the job from the job history
	var historyJob *model.Job
	failpoint.Inject("mockHistoryJob", func(v failpoint.Value) {
		mockJ := &model.Job{
			Version: model.GetJobVerInUse(),
			ID:      dr.JobID,
			Type:    model.ActionDropTable,
		}
		mockJ.FillFinishedArgs(&model.DropTableArgs{
			OldRuleIDs: []string{v.(string)},
		})
		bytes, err1 := mockJ.Encode(true)
		if err1 != nil {
			return
		}
		historyJob = &model.Job{}
		if err1 = historyJob.Decode(bytes); err1 != nil {
			return
		}
	})
	if historyJob == nil {
		se := createSession(w.store)
		historyJob, err = ddl.GetHistoryJobByID(se, dr.JobID)
		se.Close()
		if err != nil {
			return
		}
		if historyJob == nil {
			return dbterror.ErrDDLJobNotFound.GenWithStackByArgs(dr.JobID)
		}
	}

	if historyJob.Type == model.ActionDropTable {
		var (
			args  *model.DropTableArgs
			rules map[string]*label.Rule
		)
		args, err = model.GetFinishedDropTableArgs(historyJob)
		if err != nil {
			return
		}
		physicalTableIDs, ruleIDs := args.OldPartitionIDs, args.OldRuleIDs
		// TODO: Here we need to get rules from PD and filter the rules which is not elegant. We should find a better way.
		rules, err = infosync.GetLabelRules(context.TODO(), ruleIDs)
		if err != nil {
			return
		}

		ruleIDs = getGCRules(append(physicalTableIDs, historyJob.TableID), rules)
		patch := label.NewRulePatch([]*label.Rule{}, ruleIDs)
		err = infosync.UpdateLabelRules(context.TODO(), patch)
	}
	return
}

func getGCRules(ids []int64, rules map[string]*label.Rule) []string {
	oldRange := make(map[string]struct{})
	for _, id := range ids {
		startKey := hex.EncodeToString(codec.EncodeBytes(nil, tablecodec.GenTablePrefix(id)))
		endKey := hex.EncodeToString(codec.EncodeBytes(nil, tablecodec.GenTablePrefix(id+1)))
		oldRange[startKey+endKey] = struct{}{}
	}

	var gcRules []string
	for _, rule := range rules {
		find := false
		for _, d := range rule.Data.([]any) {
			if r, ok := d.(map[string]any); ok {
				nowRange := fmt.Sprintf("%s%s", r["start_key"], r["end_key"])
				if _, ok := oldRange[nowRange]; ok {
					find = true
				}
			}
		}
		if find {
			gcRules = append(gcRules, rule.ID)
		}
	}
	return gcRules
}

// RunGCJob sends GC command to KV. It is exported for kv api, do not use it with GCWorker at the same time.
// only use for test
func RunGCJob(ctx context.Context, regionLockResolver tikv.RegionLockResolver, s tikv.Storage, pd pd.Client, safePoint uint64, identifier string, concurrency int) error {
	gcWorker := &GCWorker{
		tikvStore:          s,
		uuid:               identifier,
		pdClient:           pd,
		regionLockResolver: regionLockResolver,
	}

	if concurrency <= 0 {
		return errors.Errorf("[gc worker] gc concurrency should greater than 0, current concurrency: %v", concurrency)
	}

	safePoint, err := gcWorker.setGCWorkerServiceSafePoint(ctx, safePoint)
	if err != nil {
		return errors.Trace(err)
	}

	err = gcWorker.resolveLocks(ctx, safePoint, concurrency)
	if err != nil {
		return errors.Trace(err)
	}

	err = gcWorker.saveSafePoint(gcWorker.tikvStore.GetSafePointKV(), safePoint)
	if err != nil {
		return errors.Trace(err)
	}
	// Sleep to wait for all other tidb instances update their safepoint cache.
	time.Sleep(gcSafePointCacheInterval)
	err = gcWorker.doGC(ctx, safePoint, concurrency)
	if err != nil {
		return errors.Trace(err)
	}
	return nil
}

// RunDistributedGCJob notifies TiKVs to do GC. It is exported for kv api, do not use it with GCWorker at the same time.
// This function may not finish immediately because it may take some time to do resolveLocks.
// Param concurrency specifies the concurrency of resolveLocks phase.
func RunDistributedGCJob(ctx context.Context, regionLockResolver tikv.RegionLockResolver, s tikv.Storage, pd pd.Client, safePoint uint64, identifier string, concurrency int) error {
	gcWorker := &GCWorker{
		tikvStore:          s,
		uuid:               identifier,
		pdClient:           pd,
		regionLockResolver: regionLockResolver,
	}

	safePoint, err := gcWorker.setGCWorkerServiceSafePoint(ctx, safePoint)
	if err != nil {
		return errors.Trace(err)
	}
	err = gcWorker.resolveLocks(ctx, safePoint, concurrency)
	if err != nil {
		return errors.Trace(err)
	}

	// Save safe point to pd.
	err = gcWorker.saveSafePoint(gcWorker.tikvStore.GetSafePointKV(), safePoint)
	if err != nil {
		return errors.Trace(err)
	}
	// Sleep to wait for all other tidb instances update their safepoint cache.
	time.Sleep(gcSafePointCacheInterval)

	err = gcWorker.uploadSafePointToPD(ctx, safePoint)
	if err != nil {
		return errors.Trace(err)
	}
	return nil
}

// RunResolveLocks resolves all locks before the safePoint.
// It is exported only for test, do not use it in the production environment.
func RunResolveLocks(ctx context.Context, s tikv.Storage, pd pd.Client, safePoint uint64, identifier string, concurrency int) error {
	gcWorker := &GCWorker{
		tikvStore:          s,
		uuid:               identifier,
		pdClient:           pd,
		regionLockResolver: tikv.NewRegionLockResolver("test-resolver", s),
	}
	return gcWorker.resolveLocks(ctx, safePoint, concurrency)
}

// MockGCWorker is for test.
type MockGCWorker struct {
	worker *GCWorker
}

// NewMockGCWorker creates a MockGCWorker instance ONLY for test.
func NewMockGCWorker(store kv.Storage) (*MockGCWorker, error) {
	tikvStore := store.(tikv.Storage)
	ts, err := getTsFromPD(store, tikvStore)
	if err != nil {
		return nil, errors.Trace(err)
	}
	hostName, err := os.Hostname()
	if err != nil {
		hostName = "unknown"
	}
	worker := &GCWorker{
		uuid:        strconv.FormatUint(ts, 16),
		desc:        fmt.Sprintf("host:%s, pid:%d, start at %s", hostName, os.Getpid(), time.Now()),
		store:       store,
		tikvStore:   store.(tikv.Storage),
		gcIsRunning: false,
		lastFinish:  time.Now(),
		done:        make(chan error),
		pdClient:    store.(tikv.Storage).GetRegionCache().PDClient(),
	}
	return &MockGCWorker{worker: worker}, nil
}

// DeleteRanges calls deleteRanges internally, just for test.
func (w *MockGCWorker) DeleteRanges(ctx context.Context, safePoint uint64) error {
	logutil.Logger(ctx).Error("deleteRanges is called")
	ctx = kv.WithInternalSourceType(ctx, kv.InternalTxnGC)
	return w.worker.deleteRanges(ctx, safePoint, gcConcurrency{1, false})
}