store.go

// Copyright 2014 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.

package kvserver

import (
	"bytes"
	"context"
	"fmt"
	"math"
	"os"
	"path/filepath"
	"runtime"
	"sort"
	"strings"
	"sync"
	"sync/atomic"
	"time"
	"unsafe"

	"github.com/cockroachdb/cockroach/pkg/base"
	"github.com/cockroachdb/cockroach/pkg/clusterversion"
	"github.com/cockroachdb/cockroach/pkg/config"
	"github.com/cockroachdb/cockroach/pkg/config/zonepb"
	"github.com/cockroachdb/cockroach/pkg/gossip"
	"github.com/cockroachdb/cockroach/pkg/keys"
	"github.com/cockroachdb/cockroach/pkg/kv"
	"github.com/cockroachdb/cockroach/pkg/kv/kvbase"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/batcheval"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/closedts/container"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/closedts/ctpb"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/compactor"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/idalloc"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/intentresolver"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/protectedts"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/raftentry"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/tscache"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/txnrecovery"
	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/txnwait"
	"github.com/cockroachdb/cockroach/pkg/roachpb"
	"github.com/cockroachdb/cockroach/pkg/rpc"
	"github.com/cockroachdb/cockroach/pkg/rpc/nodedialer"
	"github.com/cockroachdb/cockroach/pkg/settings"
	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
	"github.com/cockroachdb/cockroach/pkg/sql/sqlutil"
	"github.com/cockroachdb/cockroach/pkg/storage"
	"github.com/cockroachdb/cockroach/pkg/storage/cloud"
	"github.com/cockroachdb/cockroach/pkg/storage/enginepb"
	"github.com/cockroachdb/cockroach/pkg/util/contextutil"
	"github.com/cockroachdb/cockroach/pkg/util/envutil"
	"github.com/cockroachdb/cockroach/pkg/util/hlc"
	"github.com/cockroachdb/cockroach/pkg/util/limit"
	"github.com/cockroachdb/cockroach/pkg/util/log"
	"github.com/cockroachdb/cockroach/pkg/util/metric"
	"github.com/cockroachdb/cockroach/pkg/util/protoutil"
	"github.com/cockroachdb/cockroach/pkg/util/quotapool"
	"github.com/cockroachdb/cockroach/pkg/util/retry"
	"github.com/cockroachdb/cockroach/pkg/util/shuffle"
	"github.com/cockroachdb/cockroach/pkg/util/stop"
	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
	"github.com/cockroachdb/cockroach/pkg/util/tracing"
	"github.com/cockroachdb/cockroach/pkg/util/uuid"
	"github.com/cockroachdb/errors"
	"github.com/cockroachdb/logtags"
	"github.com/google/btree"
	"go.etcd.io/etcd/raft"
	"golang.org/x/time/rate"
)

const (
	// rangeIDAllocCount is the number of Range IDs to allocate per allocation.
	rangeIDAllocCount                 = 10
	defaultRaftHeartbeatIntervalTicks = 5

	// defaultRaftEntryCacheSize is the default size in bytes for a
	// store's Raft log entry cache.
	defaultRaftEntryCacheSize = 1 << 24 // 16M

	// replicaRequestQueueSize specifies the maximum number of requests to queue
	// for a replica.
	replicaRequestQueueSize = 100

	defaultGossipWhenCapacityDeltaExceedsFraction = 0.01

	// systemDataGossipInterval is the interval at which range lease
	// holders verify that the most recent system data is gossiped.
	// This ensures that system data is always eventually gossiped, even
	// if a range lease holder experiences a failure causing a missed
	// gossip update.
	systemDataGossipInterval = 1 * time.Minute
)

var storeSchedulerConcurrency = envutil.EnvOrDefaultInt(
	// For small machines, we scale the scheduler concurrency by the number of
	// CPUs. 8*runtime.NumCPU() was determined in 9a68241 (April 2017) as the
	// optimal concurrency level on 8 CPU machines. For larger machines, we've
	// seen (#56851) that this scaling curve can be too aggressive and lead to
	// too much contention in the Raft scheduler, so we cap the concurrency
	// level at 96.
	//
	// As of November 2020, this default value could be re-tuned.
	"COCKROACH_SCHEDULER_CONCURRENCY", min(8*runtime.NumCPU(), 96))

var logSSTInfoTicks = envutil.EnvOrDefaultInt(
	"COCKROACH_LOG_SST_INFO_TICKS_INTERVAL", 60)

// bulkIOWriteLimit is defined here because it is used by BulkIOWriteLimiter.
var bulkIOWriteLimit = settings.RegisterPublicByteSizeSetting(
	"kv.bulk_io_write.max_rate",
	"the rate limit (bytes/sec) to use for writes to disk on behalf of bulk io ops",
	1<<40,
)

// importRequestsLimit limits concurrent import requests.
var importRequestsLimit = settings.RegisterPositiveIntSetting(
	"kv.bulk_io_write.concurrent_import_requests",
	"number of import requests a store will handle concurrently before queuing",
	1,
)

// addSSTableRequestLimit limits concurrent AddSSTable requests.
var addSSTableRequestLimit = settings.RegisterPositiveIntSetting(
	"kv.bulk_io_write.concurrent_addsstable_requests",
	"number of AddSSTable requests a store will handle concurrently before queuing",
	1,
)

// concurrentRangefeedItersLimit limits concurrent rangefeed catchup iterators.
var concurrentRangefeedItersLimit = settings.RegisterPositiveIntSetting(
	"kv.rangefeed.concurrent_catchup_iterators",
	"number of rangefeeds catchup iterators a store will allow concurrently before queueing",
	64,
)

// raftLeadershipTransferTimeout limits the amount of time a drain command
// waits for lease transfers.
var raftLeadershipTransferWait = func() *settings.DurationSetting {
	s := settings.RegisterValidatedDurationSetting(
		raftLeadershipTransferWaitKey,
		"the amount of time a server waits to transfer range leases before proceeding with the rest of the shutdown process",
		5*time.Second,
		func(v time.Duration) error {
			if v < 0 {
				return errors.Errorf("cannot set %s to a negative duration: %s",
					raftLeadershipTransferWaitKey, v)
			}
			return nil
		},
	)
	s.SetVisibility(settings.Public)
	return s
}()

const raftLeadershipTransferWaitKey = "server.shutdown.lease_transfer_wait"

// ExportRequestsLimit is the number of Export requests that can run at once.
// Each extracts data from RocksDB to a temp file and then uploads it to cloud
// storage. In order to not exhaust the disk or memory, or saturate the network,
// limit the number of these that can be run in parallel. This number was chosen
// by a guessing - it could be improved by more measured heuristics. Exported
// here since we check it in in the caller to limit generated requests as well
// to prevent excessive queuing.
var ExportRequestsLimit = settings.RegisterPositiveIntSetting(
	"kv.bulk_io_write.concurrent_export_requests",
	"number of export requests a store will handle concurrently before queuing",
	3,
)

// TestStoreConfig has some fields initialized with values relevant in tests.
func TestStoreConfig(clock *hlc.Clock) StoreConfig {
	if clock == nil {
		clock = hlc.NewClock(hlc.UnixNano, time.Nanosecond)
	}
	st := cluster.MakeTestingClusterSettings()
	sc := StoreConfig{
		DefaultZoneConfig:           zonepb.DefaultZoneConfigRef(),
		DefaultSystemZoneConfig:     zonepb.DefaultSystemZoneConfigRef(),
		Settings:                    st,
		AmbientCtx:                  log.AmbientContext{Tracer: st.Tracer},
		Clock:                       clock,
		CoalescedHeartbeatsInterval: 50 * time.Millisecond,
		RaftHeartbeatIntervalTicks:  1,
		ScanInterval:                10 * time.Minute,
		TimestampCachePageSize:      tscache.TestSklPageSize,
		HistogramWindowInterval:     metric.TestSampleInterval,
		EnableEpochRangeLeases:      true,
		ClosedTimestamp:             container.NoopContainer(),
		ProtectedTimestampCache:     protectedts.EmptyCache(clock),
	}

	// Use shorter Raft tick settings in order to minimize start up and failover
	// time in tests.
	sc.RaftElectionTimeoutTicks = 3
	sc.RaftTickInterval = 100 * time.Millisecond
	sc.SetDefaults()
	return sc
}

func newRaftConfig(
	strg raft.Storage, id uint64, appliedIndex uint64, storeCfg StoreConfig, logger raft.Logger,
) *raft.Config {
	return &raft.Config{
		ID:                        id,
		Applied:                   appliedIndex,
		ElectionTick:              storeCfg.RaftElectionTimeoutTicks,
		HeartbeatTick:             storeCfg.RaftHeartbeatIntervalTicks,
		MaxUncommittedEntriesSize: storeCfg.RaftMaxUncommittedEntriesSize,
		MaxCommittedSizePerReady:  storeCfg.RaftMaxCommittedSizePerReady,
		MaxSizePerMsg:             storeCfg.RaftMaxSizePerMsg,
		MaxInflightMsgs:           storeCfg.RaftMaxInflightMsgs,
		Storage:                   strg,
		Logger:                    logger,

		PreVote: true,
	}
}

// verifyKeys verifies keys. If checkEndKey is true, then the end key
// is verified to be non-nil and greater than start key. If
// checkEndKey is false, end key is verified to be nil. Additionally,
// verifies that start key is less than KeyMax and end key is less
// than or equal to KeyMax. It also verifies that a key range that
// contains range-local keys is completely range-local.
func verifyKeys(start, end roachpb.Key, checkEndKey bool) error {
	if bytes.Compare(start, roachpb.KeyMax) >= 0 {
		return errors.Errorf("start key %q must be less than KeyMax", start)
	}
	if !checkEndKey {
		if len(end) != 0 {
			return errors.Errorf("end key %q should not be specified for this operation", end)
		}
		return nil
	}
	if end == nil {
		return errors.Errorf("end key must be specified")
	}
	if bytes.Compare(roachpb.KeyMax, end) < 0 {
		return errors.Errorf("end key %q must be less than or equal to KeyMax", end)
	}
	{
		sAddr, err := keys.Addr(start)
		if err != nil {
			return err
		}
		eAddr, err := keys.Addr(end)
		if err != nil {
			return err
		}
		if !sAddr.Less(eAddr) {
			return errors.Errorf("end key %q must be greater than start %q", end, start)
		}
		if !bytes.Equal(sAddr, start) {
			if bytes.Equal(eAddr, end) {
				return errors.Errorf("start key is range-local, but end key is not")
			}
		} else if bytes.Compare(start, keys.LocalMax) < 0 {
			// It's a range op, not local but somehow plows through local data -
			// not cool.
			return errors.Errorf("start key in [%q,%q) must be greater than LocalMax", start, end)
		}
	}

	return nil
}

// rangeKeyItem is a common interface for roachpb.Key and Range.
type rangeKeyItem interface {
	startKey() roachpb.RKey
}

// rangeBTreeKey is a type alias of roachpb.RKey that implements the
// rangeKeyItem interface and the btree.Item interface.
type rangeBTreeKey roachpb.RKey

var _ rangeKeyItem = rangeBTreeKey{}

func (k rangeBTreeKey) startKey() roachpb.RKey {
	return (roachpb.RKey)(k)
}

var _ btree.Item = rangeBTreeKey{}

func (k rangeBTreeKey) Less(i btree.Item) bool {
	return k.startKey().Less(i.(rangeKeyItem).startKey())
}

// A NotBootstrappedError indicates that an engine has not yet been
// bootstrapped due to a store identifier not being present.
type NotBootstrappedError struct{}

// Error formats error.
func (e *NotBootstrappedError) Error() string {
	return "store has not been bootstrapped"
}

// A storeReplicaVisitor calls a visitor function for each of a store's
// initialized Replicas (in unspecified order). It provides an option
// to visit replicas in increasing RangeID order.
type storeReplicaVisitor struct {
	store   *Store
	repls   []*Replica // Replicas to be visited
	ordered bool       // Option to visit replicas in sorted order
	visited int        // Number of visited ranges, -1 before first call to Visit()
}

// Len implements sort.Interface.
func (rs storeReplicaVisitor) Len() int { return len(rs.repls) }

// Less implements sort.Interface.
func (rs storeReplicaVisitor) Less(i, j int) bool { return rs.repls[i].RangeID < rs.repls[j].RangeID }

// Swap implements sort.Interface.
func (rs storeReplicaVisitor) Swap(i, j int) { rs.repls[i], rs.repls[j] = rs.repls[j], rs.repls[i] }

// newStoreReplicaVisitor constructs a storeReplicaVisitor.
func newStoreReplicaVisitor(store *Store) *storeReplicaVisitor {
	return &storeReplicaVisitor{
		store:   store,
		visited: -1,
	}
}

// InOrder tells the visitor to visit replicas in increasing RangeID order.
func (rs *storeReplicaVisitor) InOrder() *storeReplicaVisitor {
	rs.ordered = true
	return rs
}

// Visit calls the visitor with each Replica until false is returned.
func (rs *storeReplicaVisitor) Visit(visitor func(*Replica) bool) {
	// Copy the range IDs to a slice so that we iterate over some (possibly
	// stale) view of all Replicas without holding the Store lock. In particular,
	// no locks are acquired during the copy process.
	rs.repls = nil
	rs.store.mu.replicas.Range(func(k int64, v unsafe.Pointer) bool {
		rs.repls = append(rs.repls, (*Replica)(v))
		return true
	})

	if rs.ordered {
		// If the replicas were requested in sorted order, perform the sort.
		sort.Sort(rs)
	} else {
		// The Replicas are already in "unspecified order" due to map iteration,
		// but we want to make sure it's completely random to prevent issues in
		// tests where stores are scanning replicas in lock-step and one store is
		// winning the race and getting a first crack at processing the replicas on
		// its queues.
		//
		// TODO(peter): Re-evaluate whether this is necessary after we allow
		// rebalancing away from the leaseholder. See TestRebalance_3To5Small.
		shuffle.Shuffle(rs)
	}

	rs.visited = 0
	for _, repl := range rs.repls {
		// TODO(tschottdorf): let the visitor figure out if something's been
		// destroyed once we return errors from mutexes (#9190). After all, it
		// can still happen with this code.
		rs.visited++
		repl.mu.RLock()
		destroyed := repl.mu.destroyStatus
		initialized := repl.isInitializedRLocked()
		repl.mu.RUnlock()
		if initialized && destroyed.IsAlive() && !visitor(repl) {
			break
		}
	}
	rs.visited = 0
}

// EstimatedCount returns an estimated count of the underlying store's
// replicas.
//
// TODO(tschottdorf): this method has highly doubtful semantics.
func (rs *storeReplicaVisitor) EstimatedCount() int {
	if rs.visited <= 0 {
		return rs.store.ReplicaCount()
	}
	return len(rs.repls) - rs.visited
}

// A Store maintains a map of ranges by start key. A Store corresponds
// to one physical device.
type Store struct {
	Ident              *roachpb.StoreIdent // pointer to catch access before Start() is called
	cfg                StoreConfig
	db                 *kv.DB
	engine             storage.Engine       // The underlying key-value store
	compactor          *compactor.Compactor // Schedules compaction of the engine
	tsCache            tscache.Cache        // Most recent timestamps for keys / key ranges
	allocator          Allocator            // Makes allocation decisions
	replRankings       *replicaRankings
	storeRebalancer    *StoreRebalancer
	rangeIDAlloc       *idalloc.Allocator          // Range ID allocator
	gcQueue            *gcQueue                    // Garbage collection queue
	mergeQueue         *mergeQueue                 // Range merging queue
	splitQueue         *splitQueue                 // Range splitting queue
	replicateQueue     *replicateQueue             // Replication queue
	replicaGCQueue     *replicaGCQueue             // Replica GC queue
	raftLogQueue       *raftLogQueue               // Raft log truncation queue
	raftSnapshotQueue  *raftSnapshotQueue          // Raft repair queue
	tsMaintenanceQueue *timeSeriesMaintenanceQueue // Time series maintenance queue
	scanner            *replicaScanner             // Replica scanner
	consistencyQueue   *consistencyQueue           // Replica consistency check queue
	metrics            *StoreMetrics
	intentResolver     *intentresolver.IntentResolver
	recoveryMgr        txnrecovery.Manager
	raftEntryCache     *raftentry.Cache
	limiters           batcheval.Limiters
	txnWaitMetrics     *txnwait.Metrics
	sstSnapshotStorage SSTSnapshotStorage
	protectedtsCache   protectedts.Cache

	// gossipRangeCountdown and leaseRangeCountdown are countdowns of
	// changes to range and leaseholder counts, after which the store
	// descriptor will be re-gossiped earlier than the normal periodic
	// gossip interval. Updated atomically.
	gossipRangeCountdown int32
	gossipLeaseCountdown int32
	// gossipQueriesPerSecondVal and gossipWritesPerSecond serve similar
	// purposes, but simply record the most recently gossiped value so that we
	// can tell if a newly measured value differs by enough to justify
	// re-gossiping the store.
	gossipQueriesPerSecondVal syncutil.AtomicFloat64
	gossipWritesPerSecondVal  syncutil.AtomicFloat64

	coalescedMu struct {
		syncutil.Mutex
		heartbeats         map[roachpb.StoreIdent][]RaftHeartbeat
		heartbeatResponses map[roachpb.StoreIdent][]RaftHeartbeat
	}
	// 1 if the store was started, 0 if it wasn't. To be accessed using atomic
	// ops.
	started int32
	stopper *stop.Stopper
	// The time when the store was Start()ed, in nanos.
	startedAt    int64
	nodeDesc     *roachpb.NodeDescriptor
	initComplete sync.WaitGroup // Signaled by async init tasks

	// Semaphore to limit concurrent non-empty snapshot application.
	snapshotApplySem chan struct{}

	// Track newly-acquired expiration-based leases that we want to proactively
	// renew. An object is sent on the signal whenever a new entry is added to
	// the map.
	renewableLeases       syncutil.IntMap // map[roachpb.RangeID]*Replica
	renewableLeasesSignal chan struct{}

	// draining holds a bool which indicates whether this store is draining. See
	// SetDraining() for a more detailed explanation of behavior changes.
	//
	// TODO(bdarnell,tschottdorf): Would look better inside of `mu`, which at
	// the time of its creation was riddled with deadlock (but that situation
	// has likely improved).
	draining atomic.Value

	// Locking notes: To avoid deadlocks, the following lock order must be
	// obeyed: baseQueue.mu < Replica.raftMu < Replica.readOnlyCmdMu < Store.mu
	// < Replica.mu < Replica.unreachablesMu < Store.coalescedMu < Store.scheduler.mu.
	// (It is not required to acquire every lock in sequence, but when multiple
	// locks are held at the same time, it is incorrect to acquire a lock with
	// "lesser" value in this sequence after one with "greater" value).
	//
	// Methods of Store with a "Locked" suffix require that
	// Store.mu.Mutex be held. Other locking requirements are indicated
	// in comments.
	//
	// The locking structure here is complex because A) Store is a
	// container of Replicas, so it must generally be consulted before
	// doing anything with any Replica, B) some Replica operations
	// (including splits) modify the Store. Therefore we generally lock
	// Store.mu to find a Replica, release it, then call a method on the
	// Replica. These short-lived locks of Store.mu and Replica.mu are
	// often surrounded by a long-lived lock of Replica.raftMu as
	// described below.
	//
	// There are two major entry points to this stack of locks:
	// Store.Send (which handles incoming RPCs) and raft-related message
	// processing (including handleRaftReady on the processRaft
	// goroutine and HandleRaftRequest on GRPC goroutines). Reads are
	// processed solely through Store.Send; writes start out on
	// Store.Send until they propose their raft command and then they
	// finish on the raft goroutines.
	//
	// TODO(bdarnell): a Replica could be destroyed immediately after
	// Store.Send finds the Replica and releases the lock. We need
	// another RWMutex to be held by anything using a Replica to ensure
	// that everything is finished before releasing it. #7169
	//
	// Detailed description of the locks:
	//
	// * Replica.raftMu: Held while any raft messages are being processed
	//   (including handleRaftReady and HandleRaftRequest) or while the set of
	//   Replicas in the Store is being changed (which may happen outside of raft
	//   via the replica GC queue).
	//
	//   If holding raftMus for multiple different replicas simultaneously,
	//   acquire the locks in the order that the replicas appear in replicasByKey.
	//
	// * Replica.readOnlyCmdMu (RWMutex): Held in read mode while any
	//   read-only command is in progress on the replica; held in write
	//   mode while executing a commit trigger. This is necessary
	//   because read-only commands mutate the Replica's timestamp cache
	//   (while holding Replica.mu in addition to readOnlyCmdMu). The
	//   RWMutex ensures that no reads are being executed during a split
	//   (which copies the timestamp cache) while still allowing
	//   multiple reads in parallel (#3148). TODO(bdarnell): this lock
	//   only needs to be held during splitTrigger, not all triggers.
	//
	// * baseQueue.mu: The mutex contained in each of the store's queues (such
	//   as the replicate queue, replica GC queue, GC queue, ...). The mutex is
	//   typically acquired when deciding whether to add a replica to the respective
	//   queue.
	//
	// * Store.mu: Protects the Store's map of its Replicas. Acquired and
	//   released briefly at the start of each request; metadata operations like
	//   splits acquire it again to update the map. Even though these lock
	//   acquisitions do not make up a single critical section, it is safe thanks
	//   to Replica.raftMu which prevents any concurrent modifications.
	//
	// * Replica.mu: Protects the Replica's in-memory state. Acquired
	//   and released briefly as needed (note that while the lock is
	//   held "briefly" in that it is not held for an entire request, we
	//   do sometimes do I/O while holding the lock, as in
	//   Replica.Entries). This lock should be held when calling any
	//   methods on the raft group. Raft may call back into the Replica
	//   via the methods of the raft.Storage interface, which assume the
	//   lock is held even though they do not follow our convention of
	//   the "Locked" suffix.
	//
	// * Store.scheduler.mu: Protects the Raft scheduler internal
	//   state. Callbacks from the scheduler are performed while not holding this
	//   mutex in order to observe the above ordering constraints.
	//
	// Splits and merges deserve special consideration: they operate on two
	// ranges. For splits, this might seem fine because the right-hand range is
	// brand new, but an uninitialized version may have been created by a raft
	// message before we process the split (see commentary on
	// Replica.splitTrigger). We make this safe, for both splits and merges, by
	// locking the right-hand range for the duration of the Raft command
	// containing the split/merge trigger.
	//
	// Note that because we acquire and release Store.mu and Replica.mu
	// repeatedly rather than holding a lock for an entire request, we are
	// actually relying on higher-level locks to ensure that things don't change
	// out from under us. In particular, handleRaftReady accesses the replicaID
	// more than once, and we rely on Replica.raftMu to ensure that this is not
	// modified by a concurrent HandleRaftRequest. (#4476)

	mu struct {
		syncutil.RWMutex
		// Map of replicas by Range ID (map[roachpb.RangeID]*Replica). This
		// includes `uninitReplicas`. May be read without holding Store.mu.
		replicas syncutil.IntMap
		// A btree key containing objects of type *Replica or *ReplicaPlaceholder.
		// Both types have an associated key range; the btree is keyed on their
		// start keys.
		replicasByKey  *btree.BTree
		uninitReplicas map[roachpb.RangeID]*Replica // Map of uninitialized replicas by Range ID
		// replicaPlaceholders is a map to access all placeholders, so they can
		// be directly accessed and cleared after stepping all raft groups. This
		// is always in sync with the placeholders in replicasByKey.
		replicaPlaceholders map[roachpb.RangeID]*ReplicaPlaceholder
	}

	// The unquiesced subset of replicas.
	unquiescedReplicas struct {
		syncutil.Mutex
		m map[roachpb.RangeID]struct{}
	}

	// The subset of replicas with active rangefeeds.
	rangefeedReplicas struct {
		syncutil.Mutex
		m map[roachpb.RangeID]struct{}
	}

	// replicaQueues is a map of per-Replica incoming request queues. These
	// queues might more naturally belong in Replica, but are kept separate to
	// avoid reworking the locking in getOrCreateReplica which requires
	// Replica.raftMu to be held while a replica is being inserted into
	// Store.mu.replicas.
	replicaQueues syncutil.IntMap // map[roachpb.RangeID]*raftRequestQueue

	scheduler *raftScheduler

	// livenessMap is a map from nodeID to a bool indicating
	// liveness. It is updated periodically in raftTickLoop().
	livenessMap atomic.Value

	// cachedCapacity caches information on store capacity to prevent
	// expensive recomputations in case leases or replicas are rapidly
	// rebalancing.
	cachedCapacity struct {
		syncutil.Mutex
		roachpb.StoreCapacity
	}

	counts struct {
		// Number of placeholders removed due to error.
		removedPlaceholders int32
		// Number of placeholders successfully filled by a snapshot.
		filledPlaceholders int32
		// Number of placeholders removed due to a snapshot that was dropped by
		// raft.
		droppedPlaceholders int32
	}

	computeInitialMetrics sync.Once
}

var _ kv.Sender = &Store{}

// A StoreConfig encompasses the auxiliary objects and configuration
// required to create a store.
// All fields holding a pointer or an interface are required to create
// a store; the rest will have sane defaults set if omitted.
type StoreConfig struct {
	AmbientCtx log.AmbientContext
	base.RaftConfig

	DefaultZoneConfig       *zonepb.ZoneConfig
	DefaultSystemZoneConfig *zonepb.ZoneConfig
	Settings                *cluster.Settings
	Clock                   *hlc.Clock
	DB                      *kv.DB
	Gossip                  *gossip.Gossip
	NodeLiveness            *NodeLiveness
	StorePool               *StorePool
	Transport               *RaftTransport
	NodeDialer              *nodedialer.Dialer
	RPCContext              *rpc.Context
	RangeDescriptorCache    kvbase.RangeDescriptorCache

	ClosedTimestamp *container.Container

	// SQLExecutor is used by the store to execute SQL statements.
	SQLExecutor sqlutil.InternalExecutor

	// TimeSeriesDataStore is an interface used by the store's time series
	// maintenance queue to dispatch individual maintenance tasks.
	TimeSeriesDataStore TimeSeriesDataStore

	// CoalescedHeartbeatsInterval is the interval for which heartbeat messages
	// are queued and then sent as a single coalesced heartbeat; it is a
	// fraction of the RaftTickInterval so that heartbeats don't get delayed by
	// an entire tick. Delaying coalescing heartbeat responses has a bad
	// interaction with quiescence because the coalesced (delayed) heartbeat
	// response can unquiesce the leader. Consider:
	//
	// T+0: leader queues MsgHeartbeat
	// T+1: leader sends MsgHeartbeat
	//                                        follower receives MsgHeartbeat
	//                                        follower queues MsgHeartbeatResp
	// T+2: leader queues quiesce message
	//                                        follower sends MsgHeartbeatResp
	//      leader receives MsgHeartbeatResp
	// T+3: leader sends quiesce message
	//
	// Thus we want to make sure that heartbeats are responded to faster than
	// the quiesce cadence.
	CoalescedHeartbeatsInterval time.Duration

	// RaftHeartbeatIntervalTicks is the number of ticks that pass between heartbeats.
	RaftHeartbeatIntervalTicks int

	// ScanInterval is the default value for the scan interval
	ScanInterval time.Duration

	// ScanMinIdleTime is the minimum time the scanner will be idle between ranges.
	// If enabled (> 0), the scanner may complete in more than ScanInterval for
	// stores with many ranges.
	ScanMinIdleTime time.Duration

	// ScanMaxIdleTime is the maximum time the scanner will be idle between ranges.
	// If enabled (> 0), the scanner may complete in less than ScanInterval for small
	// stores.
	ScanMaxIdleTime time.Duration

	// If LogRangeEvents is true, major changes to ranges will be logged into
	// the range event log.
	LogRangeEvents bool

	// RaftEntryCacheSize is the size in bytes of the Raft log entry cache
	// shared by all Raft groups managed by the store.
	RaftEntryCacheSize uint64

	// IntentResolverTaskLimit is the maximum number of asynchronous tasks that
	// may be started by the intent resolver. -1 indicates no asynchronous tasks
	// are allowed. 0 uses the default value (defaultIntentResolverTaskLimit)
	// which is non-zero.
	IntentResolverTaskLimit int

	TestingKnobs StoreTestingKnobs

	// concurrentSnapshotApplyLimit specifies the maximum number of empty
	// snapshots and the maximum number of non-empty snapshots that are permitted
	// to be applied concurrently.
	concurrentSnapshotApplyLimit int

	// TimestampCachePageSize is (server.Config).TimestampCachePageSize
	TimestampCachePageSize uint32

	// HistogramWindowInterval is (server.Config).HistogramWindowInterval
	HistogramWindowInterval time.Duration

	// EnableEpochRangeLeases controls whether epoch-based range leases are used.
	EnableEpochRangeLeases bool

	// GossipWhenCapacityDeltaExceedsFraction specifies the fraction from the last
	// gossiped store capacity values which need be exceeded before the store will
	// gossip immediately without waiting for the periodic gossip interval.
	GossipWhenCapacityDeltaExceedsFraction float64

	// ExternalStorage creates ExternalStorage objects which allows access to external files
	ExternalStorage        cloud.ExternalStorageFactory
	ExternalStorageFromURI cloud.ExternalStorageFromURIFactory

	// ProtectedTimestampCache maintains the state of the protected timestamp
	// subsystem. It is queried during the GC process and in the handling of
	// AdminVerifyProtectedTimestampRequest.
	ProtectedTimestampCache protectedts.Cache
}

// ConsistencyTestingKnobs is a BatchEvalTestingKnobs struct used to control the
// behavior of the consistency checker for tests.
type ConsistencyTestingKnobs struct {
	// If non-nil, OnBadChecksumFatal is called by CheckConsistency() (instead of
	// calling log.Fatal) on a checksum mismatch.
	OnBadChecksumFatal func(roachpb.StoreIdent)
	// If non-nil, BadChecksumReportDiff is called by CheckConsistency() on a
	// checksum mismatch to report the diff between snapshots.
	BadChecksumReportDiff      func(roachpb.StoreIdent, ReplicaSnapshotDiffSlice)
	ConsistencyQueueResultHook func(response roachpb.CheckConsistencyResponse)
}

// Valid returns true if the StoreConfig is populated correctly.
// We don't check for Gossip and DB since some of our tests pass
// that as nil.
func (sc *StoreConfig) Valid() bool {
	return sc.Clock != nil && sc.Transport != nil &&
		sc.RaftTickInterval != 0 && sc.RaftHeartbeatIntervalTicks > 0 &&
		sc.RaftElectionTimeoutTicks > 0 && sc.ScanInterval >= 0 &&
		sc.AmbientCtx.Tracer != nil
}

// SetDefaults initializes unset fields in StoreConfig to values
// suitable for use on a local network.
// TODO(tschottdorf): see if this ought to be configurable via flags.
func (sc *StoreConfig) SetDefaults() {
	sc.RaftConfig.SetDefaults()

	if sc.CoalescedHeartbeatsInterval == 0 {
		sc.CoalescedHeartbeatsInterval = sc.RaftTickInterval / 2
	}
	if sc.RaftHeartbeatIntervalTicks == 0 {
		sc.RaftHeartbeatIntervalTicks = defaultRaftHeartbeatIntervalTicks
	}
	if sc.RaftEntryCacheSize == 0 {
		sc.RaftEntryCacheSize = defaultRaftEntryCacheSize
	}
	if sc.concurrentSnapshotApplyLimit == 0 {
		// NB: setting this value higher than 1 is likely to degrade client
		// throughput.
		sc.concurrentSnapshotApplyLimit =
			envutil.EnvOrDefaultInt("COCKROACH_CONCURRENT_SNAPSHOT_APPLY_LIMIT", 1)
	}

	if sc.GossipWhenCapacityDeltaExceedsFraction == 0 {
		sc.GossipWhenCapacityDeltaExceedsFraction = defaultGossipWhenCapacityDeltaExceedsFraction
	}
}

// GetStoreConfig exposes the config used for this store.
func (s *Store) GetStoreConfig() *StoreConfig {
	return &s.cfg
}

// LeaseExpiration returns an int64 to increment a manual clock with to
// make sure that all active range leases expire.
func (sc *StoreConfig) LeaseExpiration() int64 {
	// Due to lease extensions, the remaining interval can be longer than just
	// the sum of the offset (=length of stasis period) and the active
	// duration, but definitely not by 2x.
	maxOffset := sc.Clock.MaxOffset()
	return 2 * (sc.RangeLeaseActiveDuration() + maxOffset).Nanoseconds()
}

// NewStore returns a new instance of a store.
func NewStore(
	ctx context.Context, cfg StoreConfig, eng storage.Engine, nodeDesc *roachpb.NodeDescriptor,
) *Store {
	// TODO(tschottdorf): find better place to set these defaults.
	cfg.SetDefaults()

	if !cfg.Valid() {
		log.Fatalf(ctx, "invalid store configuration: %+v", &cfg)
	}
	s := &Store{
		cfg:      cfg,
		db:       cfg.DB, // TODO(tschottdorf): remove redundancy.
		engine:   eng,
		nodeDesc: nodeDesc,
		metrics:  newStoreMetrics(cfg.HistogramWindowInterval),
	}
	if cfg.RPCContext != nil {
		s.allocator = MakeAllocator(cfg.StorePool, cfg.RPCContext.RemoteClocks.Latency)
	} else {
		s.allocator = MakeAllocator(cfg.StorePool, func(string) (time.Duration, bool) {
			return 0, false
		})
	}
	s.replRankings = newReplicaRankings()

	s.draining.Store(false)
	s.scheduler = newRaftScheduler(s.metrics, s, storeSchedulerConcurrency)

	s.raftEntryCache = raftentry.NewCache(cfg.RaftEntryCacheSize)
	s.metrics.registry.AddMetricStruct(s.raftEntryCache.Metrics())

	s.coalescedMu.Lock()
	s.coalescedMu.heartbeats = map[roachpb.StoreIdent][]RaftHeartbeat{}
	s.coalescedMu.heartbeatResponses = map[roachpb.StoreIdent][]RaftHeartbeat{}
	s.coalescedMu.Unlock()

	s.mu.Lock()
	s.mu.replicaPlaceholders = map[roachpb.RangeID]*ReplicaPlaceholder{}
	s.mu.replicasByKey = btree.New(64 /* degree */)
	s.mu.uninitReplicas = map[roachpb.RangeID]*Replica{}
	s.mu.Unlock()

	s.unquiescedReplicas.Lock()
	s.unquiescedReplicas.m = map[roachpb.RangeID]struct{}{}
	s.unquiescedReplicas.Unlock()

	s.rangefeedReplicas.Lock()
	s.rangefeedReplicas.m = map[roachpb.RangeID]struct{}{}
	s.rangefeedReplicas.Unlock()

	s.tsCache = tscache.New(cfg.Clock, cfg.TimestampCachePageSize)
	s.metrics.registry.AddMetricStruct(s.tsCache.Metrics())

	s.txnWaitMetrics = txnwait.NewMetrics(cfg.HistogramWindowInterval)
	s.metrics.registry.AddMetricStruct(s.txnWaitMetrics)

	s.compactor = compactor.NewCompactor(
		s.cfg.Settings,
		s.engine,
		func() (roachpb.StoreCapacity, error) {
			return s.Capacity(false /* useCached */)
		},
		func(ctx context.Context) {
			s.asyncGossipStore(ctx, "compactor-initiated rocksdb compaction", false /* useCached */)
		},
	)
	s.metrics.registry.AddMetricStruct(s.compactor.Metrics)

	s.snapshotApplySem = make(chan struct{}, cfg.concurrentSnapshotApplyLimit)

	s.renewableLeasesSignal = make(chan struct{})

	s.limiters.BulkIOWriteRate = rate.NewLimiter(rate.Limit(bulkIOWriteLimit.Get(&cfg.Settings.SV)), bulkIOWriteBurst)
	bulkIOWriteLimit.SetOnChange(&cfg.Settings.SV, func() {
		s.limiters.BulkIOWriteRate.SetLimit(rate.Limit(bulkIOWriteLimit.Get(&cfg.Settings.SV)))
	})
	s.limiters.ConcurrentImportRequests = limit.MakeConcurrentRequestLimiter(
		"importRequestLimiter", int(importRequestsLimit.Get(&cfg.Settings.SV)),
	)
	importRequestsLimit.SetOnChange(&cfg.Settings.SV, func() {
		s.limiters.ConcurrentImportRequests.SetLimit(int(importRequestsLimit.Get(&cfg.Settings.SV)))
	})
	s.limiters.ConcurrentExportRequests = limit.MakeConcurrentRequestLimiter(
		"exportRequestLimiter", int(ExportRequestsLimit.Get(&cfg.Settings.SV)),
	)

	// The snapshot storage is usually empty at this point since it is cleared
	// after each snapshot application, except when the node crashed right before
	// it can clean it up. If this fails it's not a correctness issue since the
	// storage is also cleared before receiving a snapshot.
	s.sstSnapshotStorage = NewSSTSnapshotStorage(s.engine, s.limiters.BulkIOWriteRate)
	if err := s.sstSnapshotStorage.Clear(); err != nil {
		log.Warningf(ctx, "failed to clear snapshot storage: %v", err)
	}
	s.protectedtsCache = cfg.ProtectedTimestampCache

	// On low-CPU instances, a default limit value may still allow ExportRequests
	// to tie up all cores so cap limiter at cores-1 when setting value is higher.
	exportCores := runtime.NumCPU() - 1
	if exportCores < 1 {
		exportCores = 1
	}
	ExportRequestsLimit.SetOnChange(&cfg.Settings.SV, func() {
		limit := int(ExportRequestsLimit.Get(&cfg.Settings.SV))
		if limit > exportCores {
			limit = exportCores
		}
		s.limiters.ConcurrentExportRequests.SetLimit(limit)
	})
	s.limiters.ConcurrentAddSSTableRequests = limit.MakeConcurrentRequestLimiter(
		"addSSTableRequestLimiter", int(addSSTableRequestLimit.Get(&cfg.Settings.SV)),
	)
	addSSTableRequestLimit.SetOnChange(&cfg.Settings.SV, func() {
		s.limiters.ConcurrentAddSSTableRequests.SetLimit(int(addSSTableRequestLimit.Get(&cfg.Settings.SV)))
	})
	s.limiters.ConcurrentRangefeedIters = limit.MakeConcurrentRequestLimiter(
		"rangefeedIterLimiter", int(concurrentRangefeedItersLimit.Get(&cfg.Settings.SV)),
	)
	concurrentRangefeedItersLimit.SetOnChange(&cfg.Settings.SV, func() {
		s.limiters.ConcurrentRangefeedIters.SetLimit(
			int(concurrentRangefeedItersLimit.Get(&cfg.Settings.SV)))
	})

	if s.cfg.Gossip != nil {
		// Add range scanner and configure with queues.
		s.scanner = newReplicaScanner(
			s.cfg.AmbientCtx, s.cfg.Clock, cfg.ScanInterval,
			cfg.ScanMinIdleTime, cfg.ScanMaxIdleTime, newStoreReplicaVisitor(s),
		)
		s.gcQueue = newGCQueue(s, s.cfg.Gossip)
		s.mergeQueue = newMergeQueue(s, s.db, s.cfg.Gossip)
		s.splitQueue = newSplitQueue(s, s.db, s.cfg.Gossip)
		s.replicateQueue = newReplicateQueue(s, s.cfg.Gossip, s.allocator)
		s.replicaGCQueue = newReplicaGCQueue(s, s.db, s.cfg.Gossip)
		s.raftLogQueue = newRaftLogQueue(s, s.db, s.cfg.Gossip)
		s.raftSnapshotQueue = newRaftSnapshotQueue(s, s.cfg.Gossip)
		s.consistencyQueue = newConsistencyQueue(s, s.cfg.Gossip)
		// NOTE: If more queue types are added, please also add them to the list of
		// queues on the EnqueueRange debug page as defined in
		// pkg/ui/src/views/reports/containers/enqueueRange/index.tsx
		s.scanner.AddQueues(
			s.gcQueue, s.mergeQueue, s.splitQueue, s.replicateQueue, s.replicaGCQueue,
			s.raftLogQueue, s.raftSnapshotQueue, s.consistencyQueue)

		if s.cfg.TimeSeriesDataStore != nil {
			s.tsMaintenanceQueue = newTimeSeriesMaintenanceQueue(
				s, s.db, s.cfg.Gossip, s.cfg.TimeSeriesDataStore,
			)
			s.scanner.AddQueues(s.tsMaintenanceQueue)
		}
	}

	if cfg.TestingKnobs.DisableGCQueue {
		s.setGCQueueActive(false)
	}
	if cfg.TestingKnobs.DisableMergeQueue {
		s.setMergeQueueActive(false)
	}
	if cfg.TestingKnobs.DisableRaftLogQueue {
		s.setRaftLogQueueActive(false)
	}
	if cfg.TestingKnobs.DisableReplicaGCQueue {
		s.setReplicaGCQueueActive(false)
	}
	if cfg.TestingKnobs.DisableReplicateQueue {
		s.SetReplicateQueueActive(false)
	}
	if cfg.TestingKnobs.DisableSplitQueue {
		s.setSplitQueueActive(false)
	}
	if cfg.TestingKnobs.DisableTimeSeriesMaintenanceQueue {
		s.setTimeSeriesMaintenanceQueueActive(false)
	}
	if cfg.TestingKnobs.DisableRaftSnapshotQueue {
		s.setRaftSnapshotQueueActive(false)
	}
	if cfg.TestingKnobs.DisableConsistencyQueue {
		s.setConsistencyQueueActive(false)
	}
	if cfg.TestingKnobs.DisableScanner {
		s.setScannerActive(false)
	}

	return s
}

// String formats a store for debug output.
func (s *Store) String() string {
	return fmt.Sprintf("[n%d,s%d]", s.Ident.NodeID, s.Ident.StoreID)
}

// ClusterSettings returns the node's ClusterSettings.
func (s *Store) ClusterSettings() *cluster.Settings {
	return s.cfg.Settings
}

// AnnotateCtx is a convenience wrapper; see AmbientContext.
func (s *Store) AnnotateCtx(ctx context.Context) context.Context {
	return s.cfg.AmbientCtx.AnnotateCtx(ctx)
}

// SetDraining (when called with 'true') causes incoming lease transfers to be
// rejected, prevents all of the Store's Replicas from acquiring or extending
// range leases, and attempts to transfer away any leases owned.
// When called with 'false', returns to the normal mode of operation.
//
// The reporter callback, if non-nil, is called on a best effort basis
// to report work that needed to be done and which may or may not have
// been done by the time this call returns. See the explanation in
// pkg/server/drain.go for details.
func (s *Store) SetDraining(drain bool, reporter func(int, string)) {
	s.draining.Store(drain)
	if !drain {
		newStoreReplicaVisitor(s).Visit(func(r *Replica) bool {
			r.mu.Lock()
			r.mu.draining = false
			r.mu.Unlock()
			return true
		})
		return
	}

	var wg sync.WaitGroup

	ctx := logtags.AddTag(context.Background(), "drain", nil)
	transferAllAway := func(transferCtx context.Context) int {
		// Limit the number of concurrent lease transfers.
		const leaseTransferConcurrency = 100
		sem := quotapool.NewIntPool("Store.SetDraining", leaseTransferConcurrency)

		// Incremented for every lease or Raft leadership transfer
		// attempted. We try to send both the lease and the Raft leaders
		// away, but this may not reliably work. Instead, we run the
		// surrounding retry loop until there are no leaders/leases left
		// (ignoring single-replica or uninitialized Raft groups).
		var numTransfersAttempted int32
		newStoreReplicaVisitor(s).Visit(func(r *Replica) bool {
			//
			// We need to be careful about the case where the ctx has been canceled
			// prior to the call to (*Stopper).RunLimitedAsyncTask(). In that case,
			// the goroutine is not even spawned. However, we don't want to
			// mis-count the missing goroutine as the lack of transfer attempted.
			// So what we do here is immediately increase numTransfersAttempted
			// to count this replica, and then decrease it when it is known
			// below that there is nothing to transfer (not lease holder and
			// not raft leader).
			atomic.AddInt32(&numTransfersAttempted, 1)
			wg.Add(1)
			if err := s.stopper.RunLimitedAsyncTask(
				r.AnnotateCtx(ctx), "storage.Store: draining replica", sem, true, /* wait */
				func(ctx context.Context) {
					defer wg.Done()

					select {
					case <-transferCtx.Done():
						// Context canceled: the timeout loop has decided we've
						// done enough draining
						// (server.shutdown.lease_transfer_wait).
						//
						// We need this check here because each call of
						// transferAllAway() traverses all stores/replicas without
						// checking for the timeout otherwise.
						if log.V(1) {
							log.Infof(ctx, "lease transfer aborted due to exceeded timeout")
						}
						return
					default:
					}

					r.mu.Lock()
					r.mu.draining = true
					status := r.raftStatusRLocked()
					// needsRaftTransfer is true when we can reasonably hope to transfer
					// this replica's lease and/or Raft leadership away.
					needsRaftTransfer := status != nil &&
						len(status.Progress) > 1 &&
						!(status.RaftState == raft.StateFollower && status.Lead != 0)
					r.mu.Unlock()

					var drainingLease roachpb.Lease
					for {
						var llHandle *leaseRequestHandle
						r.mu.Lock()
						lease, nextLease := r.getLeaseRLocked()
						if nextLease != (roachpb.Lease{}) && nextLease.OwnedBy(s.StoreID()) {
							llHandle = r.mu.pendingLeaseRequest.JoinRequest()
						}
						r.mu.Unlock()

						if llHandle != nil {
							<-llHandle.C()
							continue
						}
						drainingLease = lease
						break
					}

					// Learner replicas aren't allowed to become the leaseholder or raft
					// leader, so only consider the `Voters` replicas.
					needsLeaseTransfer := len(r.Desc().Replicas().Voters()) > 1 &&
						drainingLease.OwnedBy(s.StoreID()) &&
						r.IsLeaseValid(drainingLease, s.Clock().Now())

					if !needsLeaseTransfer && !needsRaftTransfer {
						if log.V(1) {
							// This logging is useful to troubleshoot incomplete drains.
							log.Info(ctx, "not moving out")
						}
						atomic.AddInt32(&numTransfersAttempted, -1)
						return
					}
					if log.V(1) {
						// This logging is useful to troubleshoot incomplete drains.
						log.Infof(ctx, "trying to move replica out: lease transfer = %v, raft transfer = %v", needsLeaseTransfer, needsRaftTransfer)
					}

					if needsLeaseTransfer {
						desc, zone := r.DescAndZone()
						leaseTransferred, err := s.replicateQueue.findTargetAndTransferLease(
							ctx,
							r,
							desc,
							zone,
							transferLeaseOptions{},
						)
						if log.V(1) && !leaseTransferred {
							// Note that a nil error means that there were no suitable
							// candidates.
							log.Errorf(
								ctx,
								"did not transfer lease %s for replica %s when draining: %v",
								drainingLease,
								desc,
								err,
							)
						}
						if err == nil && leaseTransferred {
							// If we just transferred the lease away, Raft leadership will
							// usually transfer with it. Invoking a separate Raft leadership
							// transfer would only obstruct this.
							needsRaftTransfer = false
						}
					}

					if needsRaftTransfer {
						r.raftMu.Lock()
						r.maybeTransferRaftLeadership(ctx)
						r.raftMu.Unlock()
					}
				}); err != nil {
				if log.V(1) {
					log.Errorf(ctx, "error running draining task: %+v", err)
				}
				wg.Done()
				return false
			}
			return true
		})
		wg.Wait()
		return int(numTransfersAttempted)
	}

	// Give all replicas at least one chance to transfer.
	// If we don't do that, then it's possible that a configured
	// value for raftLeadershipTransferWait is too low to iterate
	// through all the replicas at least once, and the drain
	// condition on the remaining value will never be reached.
	if numRemaining := transferAllAway(ctx); numRemaining > 0 {
		// Report progress to the Drain RPC.
		if reporter != nil {
			reporter(numRemaining, "range lease iterations")
		}
	} else {
		// No more work to do.
		return
	}

	// We've seen all the replicas once. Now we're going to iterate
	// until they're all gone, up to the configured timeout.
	transferTimeout := raftLeadershipTransferWait.Get(&s.cfg.Settings.SV)

	if err := contextutil.RunWithTimeout(ctx, "wait for raft leadership transfer", transferTimeout,
		func(ctx context.Context) error {
			opts := retry.Options{
				InitialBackoff: 10 * time.Millisecond,
				MaxBackoff:     time.Second,
				Multiplier:     2,
			}
			everySecond := log.Every(time.Second)
			var err error
			// Avoid retry.ForDuration because of https://github.com/cockroachdb/cockroach/issues/25091.
			for r := retry.StartWithCtx(ctx, opts); r.Next(); {
				err = nil
				if numRemaining := transferAllAway(ctx); numRemaining > 0 {
					// Report progress to the Drain RPC.
					if reporter != nil {
						reporter(numRemaining, "range lease iterations")
					}
					err = errors.Errorf("waiting for %d replicas to transfer their lease away", numRemaining)
					if everySecond.ShouldLog() {
						log.Info(ctx, err)
					}
				}
				if err == nil {
					// All leases transferred. We can stop retrying.
					break
				}
			}
			// If there's an error in the context but not yet detected in
			// err, take it into account here.
			return errors.CombineErrors(err, ctx.Err())
		}); err != nil {
		// You expect this message when shutting down a server in an unhealthy
		// cluster. If we see it on healthy ones, there's likely something to fix.
		log.Warningf(ctx, "unable to drain cleanly within %s, service might briefly deteriorate: %+v", transferTimeout, err)
	}
}

// IsStarted returns true if the Store has been started.
func (s *Store) IsStarted() bool {
	return atomic.LoadInt32(&s.started) == 1
}

// IterateIDPrefixKeys helps visit system keys that use RangeID prefixing (such
// as RaftHardStateKey, RangeTombstoneKey, and many others). Such keys could in
// principle exist at any RangeID, and this helper efficiently discovers all the
// keys of the desired type (as specified by the supplied `keyFn`) and, for each
// key-value pair discovered, unmarshals it into `msg` and then invokes `f`.
//
// Iteration stops on the first error (and will pass through that error).
func IterateIDPrefixKeys(
	ctx context.Context,
	reader storage.Reader,
	keyFn func(roachpb.RangeID) roachpb.Key,
	msg protoutil.Message,
	f func(_ roachpb.RangeID) (more bool, _ error),
) error {
	rangeID := roachpb.RangeID(1)
	iter := reader.NewIterator(storage.IterOptions{
		UpperBound: keys.LocalRangeIDPrefix.PrefixEnd().AsRawKey(),
	})
	defer iter.Close()

	for {
		bumped := false
		mvccKey := storage.MakeMVCCMetadataKey(keyFn(rangeID))
		iter.SeekGE(mvccKey)

		if ok, err := iter.Valid(); !ok {
			return err
		}

		unsafeKey := iter.UnsafeKey()

		if !bytes.HasPrefix(unsafeKey.Key, keys.LocalRangeIDPrefix) {
			// Left the local keyspace, so we're done.
			return nil
		}

		curRangeID, _, _, _, err := keys.DecodeRangeIDKey(unsafeKey.Key)
		if err != nil {
			return err
		}

		if curRangeID > rangeID {
			// `bumped` is always `false` here, but let's be explicit.
			if !bumped {
				rangeID = curRangeID
				bumped = true
			}
			mvccKey = storage.MakeMVCCMetadataKey(keyFn(rangeID))
		}

		if !unsafeKey.Key.Equal(mvccKey.Key) {
			if !bumped {
				// Don't increment the rangeID if it has already been incremented
				// above, or we could skip past a value we ought to see.
				rangeID++
				bumped = true // for completeness' sake; continuing below anyway
			}
			continue
		}

		ok, err := storage.MVCCGetProto(
			ctx, reader, unsafeKey.Key, hlc.Timestamp{}, msg, storage.MVCCGetOptions{})
		if err != nil {
			return err
		}
		if !ok {
			return errors.Errorf("unable to unmarshal %s into %T", unsafeKey.Key, msg)
		}

		more, err := f(rangeID)
		if !more || err != nil {
			return err
		}
		rangeID++
	}
}

// IterateRangeDescriptors calls the provided function with each descriptor
// from the provided Engine. The return values of this method and fn have
// semantics similar to engine.MVCCIterate.
func IterateRangeDescriptors(
	ctx context.Context,
	reader storage.Reader,
	fn func(desc roachpb.RangeDescriptor) (done bool, err error),
) error {
	log.Event(ctx, "beginning range descriptor iteration")
	// Iterator over all range-local key-based data.
	start := keys.RangeDescriptorKey(roachpb.RKeyMin)
	end := keys.RangeDescriptorKey(roachpb.RKeyMax)

	allCount := 0
	matchCount := 0
	bySuffix := make(map[string]int)
	kvToDesc := func(kv roachpb.KeyValue) (bool, error) {
		allCount++
		// Only consider range metadata entries; ignore others.
		_, suffix, _, err := keys.DecodeRangeKey(kv.Key)
		if err != nil {
			return false, err
		}
		bySuffix[string(suffix)]++
		if !bytes.Equal(suffix, keys.LocalRangeDescriptorSuffix) {
			return false, nil
		}
		var desc roachpb.RangeDescriptor
		if err := kv.Value.GetProto(&desc); err != nil {
			return false, err
		}
		matchCount++
		return fn(desc)
	}

	_, err := storage.MVCCIterate(ctx, reader, start, end, hlc.MaxTimestamp,
		storage.MVCCScanOptions{Inconsistent: true}, kvToDesc)
	log.Eventf(ctx, "iterated over %d keys to find %d range descriptors (by suffix: %v)",
		allCount, matchCount, bySuffix)
	return err
}

// ReadStoreIdent reads the StoreIdent from the store.
// It returns *NotBootstrappedError if the ident is missing (meaning that the
// store needs to be bootstrapped).
func ReadStoreIdent(ctx context.Context, eng storage.Engine) (roachpb.StoreIdent, error) {
	var ident roachpb.StoreIdent
	ok, err := storage.MVCCGetProto(
		ctx, eng, keys.StoreIdentKey(), hlc.Timestamp{}, &ident, storage.MVCCGetOptions{})
	if err != nil {
		return roachpb.StoreIdent{}, err
	} else if !ok {
		return roachpb.StoreIdent{}, &NotBootstrappedError{}
	}
	return ident, err
}

// Start the engine, set the GC and read the StoreIdent.
func (s *Store) Start(ctx context.Context, stopper *stop.Stopper) error {
	s.stopper = stopper

	// Populate the store ident. If not bootstrapped, ReadStoreIntent will
	// return an error.
	ident, err := ReadStoreIdent(ctx, s.engine)
	if err != nil {
		return err
	}
	s.Ident = &ident

	// Set the store ID for logging.
	s.cfg.AmbientCtx.AddLogTag("s", s.StoreID())
	ctx = s.AnnotateCtx(ctx)
	log.Event(ctx, "read store identity")

	// Add the store ID to the scanner's AmbientContext before starting it, since
	// the AmbientContext provided during construction did not include it.
	// Note that this is just a hacky way of getting around that without
	// refactoring the scanner/queue construction/start logic more broadly, and
	// depends on the scanner not having added its own log tag.
	if s.scanner != nil {
		s.scanner.AmbientContext.AddLogTag("s", s.StoreID())
	}

	// If the nodeID is 0, it has not be assigned yet.
	if s.nodeDesc.NodeID != 0 && s.Ident.NodeID != s.nodeDesc.NodeID {
		return errors.Errorf("node id:%d does not equal the one in node descriptor:%d", s.Ident.NodeID, s.nodeDesc.NodeID)
	}
	// Always set gossip NodeID before gossiping any info.
	if s.cfg.Gossip != nil {
		s.cfg.Gossip.NodeID.Set(ctx, s.Ident.NodeID)
	}

	// Create ID allocators.
	idAlloc, err := idalloc.NewAllocator(idalloc.Options{
		AmbientCtx:  s.cfg.AmbientCtx,
		Key:         keys.RangeIDGenerator,
		Incrementer: idalloc.DBIncrementer(s.db),
		BlockSize:   rangeIDAllocCount,
		Stopper:     s.stopper,
	})
	if err != nil {
		return err
	}

	// Create the intent resolver.
	s.intentResolver = intentresolver.New(intentresolver.Config{
		Clock:                s.cfg.Clock,
		DB:                   s.db,
		Stopper:              stopper,
		TaskLimit:            s.cfg.IntentResolverTaskLimit,
		AmbientCtx:           s.cfg.AmbientCtx,
		TestingKnobs:         s.cfg.TestingKnobs.IntentResolverKnobs,
		RangeDescriptorCache: s.cfg.RangeDescriptorCache,
	})
	s.metrics.registry.AddMetricStruct(s.intentResolver.Metrics)

	// Create the recovery manager.
	s.recoveryMgr = txnrecovery.NewManager(
		s.cfg.AmbientCtx, s.cfg.Clock, s.db, stopper,
	)
	s.metrics.registry.AddMetricStruct(s.recoveryMgr.Metrics())

	s.rangeIDAlloc = idAlloc

	now := s.cfg.Clock.Now()
	s.startedAt = now.WallTime

	// Iterate over all range descriptors, ignoring uncommitted versions
	// (consistent=false). Uncommitted intents which have been abandoned
	// due to a split crashing halfway will simply be resolved on the
	// next split attempt. They can otherwise be ignored.

	// TODO(peter): While we have to iterate to find the replica descriptors
	// serially, we can perform the migrations and replica creation
	// concurrently. Note that while we can perform this initialization
	// concurrently, all of the initialization must be performed before we start
	// listening for Raft messages and starting the process Raft loop.
	err = IterateRangeDescriptors(ctx, s.engine,
		func(desc roachpb.RangeDescriptor) (bool, error) {
			if !desc.IsInitialized() {
				return false, errors.Errorf("found uninitialized RangeDescriptor: %+v", desc)
			}
			replicaDesc, found := desc.GetReplicaDescriptor(s.StoreID())
			if !found {
				// This is a pre-emptive snapshot. It's also possible that this is a
				// range which has processed a raft command to remove itself (which is
				// possible prior to 19.2 or if the DisableEagerReplicaRemoval is
				// enabled) and has not yet been removed by the replica gc queue.
				// We treat both cases the same way.
				//
				// TODO(ajwerner): Remove this migration in 20.2. It exists in 20.1 to
				// find and remove any pre-emptive snapshots which may have been sent by
				// a 19.1 or older node to this node while it was running 19.2.
				return false /* done */, removePreemptiveSnapshot(ctx, s, &desc)
			}

			rep, err := newReplica(ctx, &desc, s, replicaDesc.ReplicaID)
			if err != nil {
				return false, err
			}

			// We can't lock s.mu across NewReplica due to the lock ordering
			// constraint (*Replica).raftMu < (*Store).mu. See the comment on
			// (Store).mu.
			s.mu.Lock()
			err = s.addReplicaInternalLocked(rep)
			s.mu.Unlock()
			if err != nil {
				return false, err
			}

			// Add this range and its stats to our counter.
			s.metrics.ReplicaCount.Inc(1)
			s.metrics.addMVCCStats(rep.GetMVCCStats())

			if _, ok := desc.GetReplicaDescriptor(s.StoreID()); !ok {
				// We are no longer a member of the range, but we didn't GC the replica
				// before shutting down. Add the replica to the GC queue.
				s.replicaGCQueue.AddAsync(ctx, rep, replicaGCPriorityRemoved)
			}

			// Note that we do not create raft groups at this time; they will be created
			// on-demand the first time they are needed. This helps reduce the amount of
			// election-related traffic in a cold start.
			// Raft initialization occurs when we propose a command on this range or
			// receive a raft message addressed to it.
			// TODO(bdarnell): Also initialize raft groups when read leases are needed.
			// TODO(bdarnell): Scan all ranges at startup for unapplied log entries
			// and initialize those groups.
			return false, nil
		})
	if err != nil {
		return err
	}

	// Start Raft processing goroutines.
	s.cfg.Transport.Listen(s.StoreID(), s)
	s.processRaft(ctx)

	// Register a callback to unquiesce any ranges with replicas on a
	// node transitioning from non-live to live.
	if s.cfg.NodeLiveness != nil {
		s.cfg.NodeLiveness.RegisterCallback(s.nodeIsLiveCallback)
	}

	// Gossip is only ever nil while bootstrapping a cluster and
	// in unittests.
	if s.cfg.Gossip != nil {
		// Register update channel for any changes to the system config.
		// This may trigger splits along structured boundaries,
		// and update max range bytes.
		gossipUpdateC := s.cfg.Gossip.RegisterSystemConfigChannel()
		s.stopper.RunWorker(ctx, func(context.Context) {
			for {
				select {
				case <-gossipUpdateC:
					cfg := s.cfg.Gossip.GetSystemConfig()
					s.systemGossipUpdate(cfg)
				case <-s.stopper.ShouldStop():
					return
				}
			}
		})

		// Start a single goroutine in charge of periodically gossiping the
		// sentinel and first range metadata if we have a first range.
		// This may wake up ranges and requires everything to be set up and
		// running.
		s.startGossip()

		// Start the scanner. The construction here makes sure that the scanner
		// only starts after Gossip has connected, and that it does not block Start
		// from returning (as doing so might prevent Gossip from ever connecting).
		s.stopper.RunWorker(ctx, func(context.Context) {
			select {
			case <-s.cfg.Gossip.Connected:
				s.scanner.Start(s.stopper)
			case <-s.stopper.ShouldStop():
				return
			}
		})
	}

	if !s.cfg.TestingKnobs.DisableAutomaticLeaseRenewal {
		s.startLeaseRenewer(ctx)
	}

	// Connect rangefeeds to closed timestamp updates.
	s.startClosedTimestampRangefeedSubscriber(ctx)

	if s.replicateQueue != nil {
		s.storeRebalancer = NewStoreRebalancer(
			s.cfg.AmbientCtx, s.cfg.Settings, s.replicateQueue, s.replRankings)
		s.storeRebalancer.Start(ctx, s.stopper)
	}

	// Start the storage engine compactor.
	if envutil.EnvOrDefaultBool("COCKROACH_ENABLE_COMPACTOR", true) {
		s.compactor.Start(s.AnnotateCtx(context.Background()), s.stopper)
	}

	// Set the started flag (for unittests).
	atomic.StoreInt32(&s.started, 1)

	return nil
}

// WaitForInit waits for any asynchronous processes begun in Start()
// to complete their initialization. In particular, this includes
// gossiping. In some cases this may block until the range GC queue
// has completed its scan. Only for testing.
func (s *Store) WaitForInit() {
	s.initComplete.Wait()
}

var errPeriodicGossipsDisabled = errors.New("periodic gossip is disabled")

// startGossip runs an infinite loop in a goroutine which regularly checks
// whether the store has a first range or config replica and asks those ranges
// to gossip accordingly.
func (s *Store) startGossip() {
	wakeReplica := func(ctx context.Context, repl *Replica) error {
		// Acquire the range lease, which in turn triggers system data gossip
		// functions (e.g. MaybeGossipSystemConfig or MaybeGossipNodeLiveness).
		_, pErr := repl.getLeaseForGossip(ctx)
		return pErr.GoError()
	}

	if s.cfg.TestingKnobs.DisablePeriodicGossips {
		wakeReplica = func(context.Context, *Replica) error {
			return errPeriodicGossipsDisabled
		}
	}

	gossipFns := []struct {
		key         roachpb.Key
		fn          func(context.Context, *Replica) error
		description string
		interval    time.Duration
	}{
		{
			key: roachpb.KeyMin,
			fn: func(ctx context.Context, repl *Replica) error {
				// The first range is gossiped by all replicas, not just the lease
				// holder, so wakeReplica is not used here.
				return repl.maybeGossipFirstRange(ctx).GoError()
			},
			description: "first range descriptor",
			interval:    s.cfg.SentinelGossipTTL() / 2,
		},
		{
			key:         keys.SystemConfigSpan.Key,
			fn:          wakeReplica,
			description: "system config",
			interval:    systemDataGossipInterval,
		},
		{
			key:         keys.NodeLivenessSpan.Key,
			fn:          wakeReplica,
			description: "node liveness",
			interval:    systemDataGossipInterval,
		},
	}

	// Periodic updates run in a goroutine and signal a WaitGroup upon completion
	// of their first iteration.
	s.initComplete.Add(len(gossipFns))
	for _, gossipFn := range gossipFns {
		gossipFn := gossipFn // per-iteration copy
		s.stopper.RunWorker(context.Background(), func(ctx context.Context) {
			ticker := time.NewTicker(gossipFn.interval)
			defer ticker.Stop()
			for first := true; ; {
				// Retry in a backoff loop until gossipFn succeeds. The gossipFn might
				// temporarily fail (e.g. because node liveness hasn't initialized yet
				// making it impossible to get an epoch-based range lease), in which
				// case we want to retry quickly.
				retryOptions := base.DefaultRetryOptions()
				retryOptions.Closer = s.stopper.ShouldStop()
				for r := retry.Start(retryOptions); r.Next(); {
					if repl := s.LookupReplica(roachpb.RKey(gossipFn.key)); repl != nil {
						annotatedCtx := repl.AnnotateCtx(ctx)
						if err := gossipFn.fn(annotatedCtx, repl); err != nil {
							log.Warningf(annotatedCtx, "could not gossip %s: %+v", gossipFn.description, err)
							if err != errPeriodicGossipsDisabled {
								continue
							}
						}
					}
					break
				}
				if first {
					first = false
					s.initComplete.Done()
				}
				select {
				case <-ticker.C:
				case <-s.stopper.ShouldStop():
					return
				}
			}
		})
	}
}

// startLeaseRenewer runs an infinite loop in a goroutine which regularly
// checks whether the store has any expiration-based leases that should be
// proactively renewed and attempts to continue renewing them.
//
// This reduces user-visible latency when range lookups are needed to serve a
// request and reduces ping-ponging of r1's lease to different replicas as
// maybeGossipFirstRange is called on each (e.g.  #24753).
func (s *Store) startLeaseRenewer(ctx context.Context) {
	// Start a goroutine that watches and proactively renews certain
	// expiration-based leases.
	s.stopper.RunWorker(ctx, func(ctx context.Context) {
		repls := make(map[*Replica]struct{})
		timer := timeutil.NewTimer()
		defer timer.Stop()

		// Determine how frequently to attempt to ensure that we have each lease.
		// The divisor used here is somewhat arbitrary, but needs to be large
		// enough to ensure we'll attempt to renew the lease reasonably early
		// within the RangeLeaseRenewalDuration time window. This means we'll wake
		// up more often that strictly necessary, but it's more maintainable than
		// attempting to accurately determine exactly when each iteration of a
		// lease expires and when we should attempt to renew it as a result.
		renewalDuration := s.cfg.RangeLeaseActiveDuration() / 5
		for {
			s.renewableLeases.Range(func(k int64, v unsafe.Pointer) bool {
				repl := (*Replica)(v)
				annotatedCtx := repl.AnnotateCtx(ctx)
				if _, pErr := repl.redirectOnOrAcquireLease(annotatedCtx); pErr != nil {
					if _, ok := pErr.GetDetail().(*roachpb.NotLeaseHolderError); !ok {
						log.Warningf(annotatedCtx, "failed to proactively renew lease: %s", pErr)
					}
					s.renewableLeases.Delete(k)
				}
				return true
			})

			if len(repls) > 0 {
				timer.Reset(renewalDuration)
			}
			select {
			case <-s.renewableLeasesSignal:
			case <-timer.C:
				timer.Read = true
			case <-s.stopper.ShouldStop():
				return
			}
		}
	})
}

// startClosedTimestampRangefeedSubscriber establishes a new ClosedTimestamp
// subscription and runs an infinite loop to listen for closed timestamp updates
// and inform Replicas with active Rangefeeds about them.
func (s *Store) startClosedTimestampRangefeedSubscriber(ctx context.Context) {
	// NB: We can't use Stopper.RunWorker because doing so would race with
	// calling Stopper.Stop. We give the subscription channel a small capacity
	// to avoid blocking the closed timestamp goroutine.
	ch := make(chan ctpb.Entry, 8)
	const name = "closedts-rangefeed-subscriber"
	if err := s.stopper.RunAsyncTask(ctx, name, func(ctx context.Context) {
		s.cfg.ClosedTimestamp.Provider.Subscribe(ctx, ch)
	}); err != nil {
		return
	}

	s.stopper.RunWorker(ctx, func(ctx context.Context) {
		var replIDs []roachpb.RangeID
		for {
			select {
			case <-ch:
				// Drain all notifications from the channel.
			loop:
				for {
					select {
					case _, ok := <-ch:
						if !ok {
							break loop
						}
					default:
						break loop
					}
				}

				// Gather replicas to notify under lock.
				s.rangefeedReplicas.Lock()
				for replID := range s.rangefeedReplicas.m {
					replIDs = append(replIDs, replID)
				}
				s.rangefeedReplicas.Unlock()

				// Notify each replica with an active rangefeed to
				// check for an updated closed timestamp.
				for _, replID := range replIDs {
					repl, err := s.GetReplica(replID)
					if err != nil {
						continue
					}
					repl.handleClosedTimestampUpdate(ctx)
				}
				replIDs = replIDs[:0]
			case <-s.stopper.ShouldQuiesce():
				return
			}
		}
	})
}

func (s *Store) addReplicaWithRangefeed(rangeID roachpb.RangeID) {
	s.rangefeedReplicas.Lock()
	s.rangefeedReplicas.m[rangeID] = struct{}{}
	s.rangefeedReplicas.Unlock()
}

func (s *Store) removeReplicaWithRangefeed(rangeID roachpb.RangeID) {
	s.rangefeedReplicas.Lock()
	delete(s.rangefeedReplicas.m, rangeID)
	s.rangefeedReplicas.Unlock()
}

// systemGossipUpdate is a callback for gossip updates to
// the system config which affect range split boundaries.
func (s *Store) systemGossipUpdate(sysCfg *config.SystemConfig) {
	ctx := s.AnnotateCtx(context.Background())
	s.computeInitialMetrics.Do(func() {
		// Metrics depend in part on the system config. Compute them as soon as we
		// get the first system config, then periodically in the background
		// (managed by the Node).
		if err := s.ComputeMetrics(ctx, -1); err != nil {
			log.Infof(ctx, "%s: failed initial metrics computation: %s", s, err)
		}
		log.Event(ctx, "computed initial metrics")
	})

	// We'll want to offer all replicas to the split and merge queues. Be a little
	// careful about not spawning too many individual goroutines.

	// For every range, update its zone config and check if it needs to
	// be split or merged.
	now := s.cfg.Clock.Now()
	newStoreReplicaVisitor(s).Visit(func(repl *Replica) bool {
		key := repl.Desc().StartKey
		zone, err := sysCfg.GetZoneConfigForKey(key)
		if err != nil {
			if log.V(1) {
				log.Infof(context.TODO(), "failed to get zone config for key %s", key)
			}
			zone = s.cfg.DefaultZoneConfig
		}
		repl.SetZoneConfig(zone)
		s.splitQueue.Async(ctx, "gossip update", true /* wait */, func(ctx context.Context, h queueHelper) {
			h.MaybeAdd(ctx, repl, now)
		})
		s.mergeQueue.Async(ctx, "gossip update", true /* wait */, func(ctx context.Context, h queueHelper) {
			h.MaybeAdd(ctx, repl, now)
		})
		return true // more
	})
}

func (s *Store) asyncGossipStore(ctx context.Context, reason string, useCached bool) {
	if err := s.stopper.RunAsyncTask(
		ctx, fmt.Sprintf("storage.Store: gossip on %s", reason),
		func(ctx context.Context) {
			if err := s.GossipStore(ctx, useCached); err != nil {
				log.Warningf(ctx, "error gossiping on %s: %+v", reason, err)
			}
		}); err != nil {
		log.Warningf(ctx, "unable to gossip on %s: %+v", reason, err)
	}
}

// GossipStore broadcasts the store on the gossip network.
func (s *Store) GossipStore(ctx context.Context, useCached bool) error {
	select {
	case <-s.cfg.Gossip.Connected:
	default:
		// Nothing to do if gossip is not connected.
		return nil
	}

	// Temporarily indicate that we're gossiping the store capacity to avoid
	// recursively triggering a gossip of the store capacity.
	syncutil.StoreFloat64(&s.gossipQueriesPerSecondVal, -1)
	syncutil.StoreFloat64(&s.gossipWritesPerSecondVal, -1)

	storeDesc, err := s.Descriptor(useCached)
	if err != nil {
		return errors.Wrapf(err, "problem getting store descriptor for store %+v", s.Ident)
	}

	// Set countdown target for re-gossiping capacity earlier than
	// the usual periodic interval. Re-gossip more rapidly for RangeCount
	// changes because allocators with stale information are much more
	// likely to make bad decisions.
	rangeCountdown := float64(storeDesc.Capacity.RangeCount) * s.cfg.GossipWhenCapacityDeltaExceedsFraction
	atomic.StoreInt32(&s.gossipRangeCountdown, int32(math.Ceil(math.Min(rangeCountdown, 3))))
	leaseCountdown := float64(storeDesc.Capacity.LeaseCount) * s.cfg.GossipWhenCapacityDeltaExceedsFraction
	atomic.StoreInt32(&s.gossipLeaseCountdown, int32(math.Ceil(math.Max(leaseCountdown, 1))))
	syncutil.StoreFloat64(&s.gossipQueriesPerSecondVal, storeDesc.Capacity.QueriesPerSecond)
	syncutil.StoreFloat64(&s.gossipWritesPerSecondVal, storeDesc.Capacity.WritesPerSecond)

	// Unique gossip key per store.
	gossipStoreKey := gossip.MakeStoreKey(storeDesc.StoreID)
	// Gossip store descriptor.
	return s.cfg.Gossip.AddInfoProto(gossipStoreKey, storeDesc, gossip.StoreTTL)
}

type capacityChangeEvent int

const (
	rangeAddEvent capacityChangeEvent = iota
	rangeRemoveEvent
	leaseAddEvent
	leaseRemoveEvent
)

// maybeGossipOnCapacityChange decrements the countdown on range
// and leaseholder counts. If it reaches 0, then we trigger an
// immediate gossip of this store's descriptor, to include updated
// capacity information.
func (s *Store) maybeGossipOnCapacityChange(ctx context.Context, cce capacityChangeEvent) {
	if s.cfg.TestingKnobs.DisableLeaseCapacityGossip && (cce == leaseAddEvent || cce == leaseRemoveEvent) {
		return
	}

	// Incrementally adjust stats to keep them up to date even if the
	// capacity is gossiped, but isn't due yet to be recomputed from scratch.
	s.cachedCapacity.Lock()
	switch cce {
	case rangeAddEvent:
		s.cachedCapacity.RangeCount++
	case rangeRemoveEvent:
		s.cachedCapacity.RangeCount--
	case leaseAddEvent:
		s.cachedCapacity.LeaseCount++
	case leaseRemoveEvent:
		s.cachedCapacity.LeaseCount--
	}
	s.cachedCapacity.Unlock()

	if ((cce == rangeAddEvent || cce == rangeRemoveEvent) && atomic.AddInt32(&s.gossipRangeCountdown, -1) == 0) ||
		((cce == leaseAddEvent || cce == leaseRemoveEvent) && atomic.AddInt32(&s.gossipLeaseCountdown, -1) == 0) {
		// Reset countdowns to avoid unnecessary gossiping.
		atomic.StoreInt32(&s.gossipRangeCountdown, 0)
		atomic.StoreInt32(&s.gossipLeaseCountdown, 0)
		s.asyncGossipStore(ctx, "capacity change", true /* useCached */)
	}
}

// recordNewPerSecondStats takes recently calculated values for the number of
// queries and key writes the store is handling and decides whether either has
// changed enough to justify re-gossiping the store's capacity.
func (s *Store) recordNewPerSecondStats(newQPS, newWPS float64) {
	oldQPS := syncutil.LoadFloat64(&s.gossipQueriesPerSecondVal)
	oldWPS := syncutil.LoadFloat64(&s.gossipWritesPerSecondVal)
	if oldQPS == -1 || oldWPS == -1 {
		// Gossiping of store capacity is already ongoing.
		return
	}

	const minAbsoluteChange = 100
	updateForQPS := (newQPS < oldQPS*.5 || newQPS > oldQPS*1.5) && math.Abs(newQPS-oldQPS) > minAbsoluteChange
	updateForWPS := (newWPS < oldWPS*.5 || newWPS > oldWPS*1.5) && math.Abs(newWPS-oldWPS) > minAbsoluteChange

	if !updateForQPS && !updateForWPS {
		return
	}

	var message string
	if updateForQPS && updateForWPS {
		message = "queries-per-second and writes-per-second change"
	} else if updateForQPS {
		message = "queries-per-second change"
	} else {
		message = "writes-per-second change"
	}
	// TODO(a-robinson): Use the provided values to avoid having to recalculate
	// them in GossipStore.
	s.asyncGossipStore(context.TODO(), message, false /* useCached */)
}

// VisitReplicas invokes the visitor on the Store's Replicas until the visitor returns false.
// Replicas which are added to the Store after iteration begins may or may not be observed.
func (s *Store) VisitReplicas(visitor func(*Replica) bool) {
	v := newStoreReplicaVisitor(s)
	v.Visit(visitor)
}

// WriteLastUpTimestamp records the supplied timestamp into the "last up" key
// on this store. This value should be refreshed whenever this store's node
// updates its own liveness record; it is used by a restarting store to
// determine the approximate time that it stopped.
func (s *Store) WriteLastUpTimestamp(ctx context.Context, time hlc.Timestamp) error {
	ctx = s.AnnotateCtx(ctx)
	return storage.MVCCPutProto(
		ctx,
		s.engine,
		nil,
		keys.StoreLastUpKey(),
		hlc.Timestamp{},
		nil,
		&time,
	)
}

// ReadLastUpTimestamp returns the "last up" timestamp recorded in this store.
// This value can be used to approximate the last time the engine was was being
// served as a store by a running node. If the store does not contain a "last
// up" timestamp (for example, on a newly bootstrapped store), the zero
// timestamp is returned instead.
func (s *Store) ReadLastUpTimestamp(ctx context.Context) (hlc.Timestamp, error) {
	var timestamp hlc.Timestamp
	ok, err := storage.MVCCGetProto(ctx, s.Engine(), keys.StoreLastUpKey(), hlc.Timestamp{},
		&timestamp, storage.MVCCGetOptions{})
	if err != nil {
		return hlc.Timestamp{}, err
	} else if !ok {
		return hlc.Timestamp{}, nil
	}
	return timestamp, nil
}

// WriteHLCUpperBound records an upper bound to the wall time of the HLC
func (s *Store) WriteHLCUpperBound(ctx context.Context, time int64) error {
	ctx = s.AnnotateCtx(ctx)
	ts := hlc.Timestamp{WallTime: time}
	batch := s.Engine().NewBatch()
	// Write has to sync to disk to ensure HLC monotonicity across restarts
	defer batch.Close()
	if err := storage.MVCCPutProto(
		ctx,
		batch,
		nil,
		keys.StoreHLCUpperBoundKey(),
		hlc.Timestamp{},
		nil,
		&ts,
	); err != nil {
		return err
	}

	if err := batch.Commit(true /* sync */); err != nil {
		return err
	}
	return nil
}

// ReadHLCUpperBound returns the upper bound to the wall time of the HLC
// If this value does not exist 0 is returned
func ReadHLCUpperBound(ctx context.Context, e storage.Engine) (int64, error) {
	var timestamp hlc.Timestamp
	ok, err := storage.MVCCGetProto(ctx, e, keys.StoreHLCUpperBoundKey(), hlc.Timestamp{},
		&timestamp, storage.MVCCGetOptions{})
	if err != nil {
		return 0, err
	} else if !ok {
		return 0, nil
	}
	return timestamp.WallTime, nil
}

// ReadMaxHLCUpperBound returns the maximum of the stored hlc upper bounds
// among all the engines. This value is optionally persisted by the server and
// it is guaranteed to be higher than any wall time used by the HLC. If this
// value is persisted, HLC wall clock monotonicity is guaranteed across server
// restarts
func ReadMaxHLCUpperBound(ctx context.Context, engines []storage.Engine) (int64, error) {
	var hlcUpperBound int64
	for _, e := range engines {
		engineHLCUpperBound, err := ReadHLCUpperBound(ctx, e)
		if err != nil {
			return 0, err
		}
		if engineHLCUpperBound > hlcUpperBound {
			hlcUpperBound = engineHLCUpperBound
		}
	}
	return hlcUpperBound, nil
}

func checkEngineEmpty(ctx context.Context, eng storage.Engine) error {
	kvs, err := storage.Scan(eng, roachpb.KeyMin, roachpb.KeyMax, 10)
	if err != nil {
		return err
	}
	if len(kvs) > 0 {
		// See if this is an already-bootstrapped store.
		ident, err := ReadStoreIdent(ctx, eng)
		if err != nil {
			return errors.Wrap(err, "unable to read store ident")
		}
		keyVals := make([]string, len(kvs))
		for i, kv := range kvs {
			keyVals[i] = fmt.Sprintf("%s: %q", kv.Key, kv.Value)
		}
		return errors.Errorf("engine belongs to store %s, contains %s", ident.String(), keyVals)
	}
	return nil
}

// GetReplica fetches a replica by Range ID. Returns an error if no replica is found.
func (s *Store) GetReplica(rangeID roachpb.RangeID) (*Replica, error) {
	if value, ok := s.mu.replicas.Load(int64(rangeID)); ok {
		return (*Replica)(value), nil
	}
	return nil, roachpb.NewRangeNotFoundError(rangeID, s.StoreID())
}

// LookupReplica looks up the replica that contains the specified key. It
// returns nil if no such replica exists.
func (s *Store) LookupReplica(key roachpb.RKey) *Replica {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var repl *Replica
	s.mu.replicasByKey.DescendLessOrEqual(rangeBTreeKey(key), func(item btree.Item) bool {
		repl, _ = item.(*Replica)
		// Stop iterating immediately. The first item we see is the only one that
		// can possibly contain key.
		return false
	})
	if repl == nil || !repl.Desc().ContainsKey(key) {
		return nil
	}
	return repl
}

// lookupPrecedingReplica finds the replica in this store that immediately
// precedes the specified key without containing it. It returns nil if no such
// replica exists. It ignores replica placeholders.
//
// Concretely, when key represents a key within replica R,
// lookupPrecedingReplica returns the replica that immediately precedes R in
// replicasByKey.
func (s *Store) lookupPrecedingReplica(key roachpb.RKey) *Replica {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var repl *Replica
	s.mu.replicasByKey.DescendLessOrEqual(rangeBTreeKey(key), func(item btree.Item) bool {
		if r, ok := item.(*Replica); ok && !r.ContainsKey(key.AsRawKey()) {
			repl = r
			return false // stop iterating
		}
		return true // keep iterating
	})
	return repl
}

// getOverlappingKeyRangeLocked returns a KeyRange from the Store overlapping the given
// descriptor (or nil if no such KeyRange exists).
func (s *Store) getOverlappingKeyRangeLocked(rngDesc *roachpb.RangeDescriptor) KeyRange {
	var kr KeyRange
	s.mu.replicasByKey.DescendLessOrEqual(rangeBTreeKey(rngDesc.EndKey),
		func(item btree.Item) bool {
			if kr0 := item.(KeyRange); kr0.startKey().Less(rngDesc.EndKey) {
				kr = kr0
				return false // stop iterating
			}
			return true // keep iterating
		})
	if kr != nil && rngDesc.StartKey.Less(kr.Desc().EndKey) {
		return kr
	}
	return nil
}

// RaftStatus returns the current raft status of the local replica of
// the given range.
func (s *Store) RaftStatus(rangeID roachpb.RangeID) *raft.Status {
	if value, ok := s.mu.replicas.Load(int64(rangeID)); ok {
		return (*Replica)(value).RaftStatus()
	}
	return nil
}

// ClusterID accessor.
func (s *Store) ClusterID() uuid.UUID { return s.Ident.ClusterID }

// StoreID accessor.
func (s *Store) StoreID() roachpb.StoreID { return s.Ident.StoreID }

// Clock accessor.
func (s *Store) Clock() *hlc.Clock { return s.cfg.Clock }

// Engine accessor.
func (s *Store) Engine() storage.Engine { return s.engine }

// DB accessor.
func (s *Store) DB() *kv.DB { return s.cfg.DB }

// Gossip accessor.
func (s *Store) Gossip() *gossip.Gossip { return s.cfg.Gossip }

// Compactor accessor.
func (s *Store) Compactor() *compactor.Compactor { return s.compactor }

// Stopper accessor.
func (s *Store) Stopper() *stop.Stopper { return s.stopper }

// TestingKnobs accessor.
func (s *Store) TestingKnobs() *StoreTestingKnobs { return &s.cfg.TestingKnobs }

// IsDraining accessor.
func (s *Store) IsDraining() bool {
	return s.draining.Load().(bool)
}

// AllocateRangeID allocates a new RangeID from the cluster-wide RangeID allocator.
func (s *Store) AllocateRangeID(ctx context.Context) (roachpb.RangeID, error) {
	id, err := s.rangeIDAlloc.Allocate(ctx)
	if err != nil {
		return 0, err
	}
	return roachpb.RangeID(id), nil
}

// Attrs returns the attributes of the underlying store.
func (s *Store) Attrs() roachpb.Attributes {
	return s.engine.Attrs()
}

// Capacity returns the capacity of the underlying storage engine. Note that
// this does not include reservations.
// Note that Capacity() has the side effect of updating some of the store's
// internal statistics about its replicas.
func (s *Store) Capacity(useCached bool) (roachpb.StoreCapacity, error) {
	if useCached {
		s.cachedCapacity.Lock()
		capacity := s.cachedCapacity.StoreCapacity
		s.cachedCapacity.Unlock()
		if capacity != (roachpb.StoreCapacity{}) {
			return capacity, nil
		}
	}

	capacity, err := s.engine.Capacity()
	if err != nil {
		return capacity, err
	}

	now := s.cfg.Clock.Now()
	var leaseCount int32
	var rangeCount int32
	var logicalBytes int64
	var totalQueriesPerSecond float64
	var totalWritesPerSecond float64
	replicaCount := s.metrics.ReplicaCount.Value()
	bytesPerReplica := make([]float64, 0, replicaCount)
	writesPerReplica := make([]float64, 0, replicaCount)
	rankingsAccumulator := s.replRankings.newAccumulator()
	newStoreReplicaVisitor(s).Visit(func(r *Replica) bool {
		rangeCount++
		if r.OwnsValidLease(now) {
			leaseCount++
		}
		mvccStats := r.GetMVCCStats()
		logicalBytes += mvccStats.Total()
		bytesPerReplica = append(bytesPerReplica, float64(mvccStats.Total()))
		// TODO(a-robinson): How dangerous is it that these numbers will be
		// incorrectly low the first time or two it gets gossiped when a store
		// starts? We can't easily have a countdown as its value changes like for
		// leases/replicas.
		var qps float64
		if avgQPS, dur := r.leaseholderStats.avgQPS(); dur >= MinStatsDuration {
			qps = avgQPS
			totalQueriesPerSecond += avgQPS
			// TODO(a-robinson): Calculate percentiles for qps? Get rid of other percentiles?
		}
		if wps, dur := r.writeStats.avgQPS(); dur >= MinStatsDuration {
			totalWritesPerSecond += wps
			writesPerReplica = append(writesPerReplica, wps)
		}
		rankingsAccumulator.addReplica(replicaWithStats{
			repl: r,
			qps:  qps,
		})
		return true
	})
	capacity.RangeCount = rangeCount
	capacity.LeaseCount = leaseCount
	capacity.LogicalBytes = logicalBytes
	capacity.QueriesPerSecond = totalQueriesPerSecond
	capacity.WritesPerSecond = totalWritesPerSecond
	capacity.BytesPerReplica = roachpb.PercentilesFromData(bytesPerReplica)
	capacity.WritesPerReplica = roachpb.PercentilesFromData(writesPerReplica)
	s.recordNewPerSecondStats(totalQueriesPerSecond, totalWritesPerSecond)
	s.replRankings.update(rankingsAccumulator)

	s.cachedCapacity.Lock()
	s.cachedCapacity.StoreCapacity = capacity
	s.cachedCapacity.Unlock()

	return capacity, nil
}

// ReplicaCount returns the number of replicas contained by this store. This
// method is O(n) in the number of replicas and should not be called from
// performance critical code.
func (s *Store) ReplicaCount() int {
	var count int
	s.mu.replicas.Range(func(_ int64, _ unsafe.Pointer) bool {
		count++
		return true
	})
	return count
}

// Registry returns the store registry.
func (s *Store) Registry() *metric.Registry {
	return s.metrics.registry
}

// Metrics returns the store's metric struct.
func (s *Store) Metrics() *StoreMetrics {
	return s.metrics
}

// Descriptor returns a StoreDescriptor including current store
// capacity information.
func (s *Store) Descriptor(useCached bool) (*roachpb.StoreDescriptor, error) {
	capacity, err := s.Capacity(useCached)
	if err != nil {
		return nil, err
	}

	// Initialize the store descriptor.
	return &roachpb.StoreDescriptor{
		StoreID:  s.Ident.StoreID,
		Attrs:    s.Attrs(),
		Node:     *s.nodeDesc,
		Capacity: capacity,
	}, nil
}

// RangeFeed registers a rangefeed over the specified span. It sends updates to
// the provided stream and returns with an optional error when the rangefeed is
// complete.
func (s *Store) RangeFeed(
	args *roachpb.RangeFeedRequest, stream roachpb.Internal_RangeFeedServer,
) *roachpb.Error {
	if err := verifyKeys(args.Span.Key, args.Span.EndKey, true); err != nil {
		return roachpb.NewError(err)
	}

	// Get range and add command to the range for execution.
	repl, err := s.GetReplica(args.RangeID)
	if err != nil {
		return roachpb.NewError(err)
	}
	if !repl.IsInitialized() {
		// (*Store).Send has an optimization for uninitialized replicas to send back
		// a NotLeaseHolderError with a hint of where an initialized replica might
		// be found. RangeFeeds can always be served from followers and so don't
		// otherwise return NotLeaseHolderError. For simplicity we also don't return
		// one here.
		return roachpb.NewError(roachpb.NewRangeNotFoundError(args.RangeID, s.StoreID()))
	}
	return repl.RangeFeed(args, stream)
}

// updateReplicationGauges counts a number of simple replication statistics for
// the ranges in this store.
// TODO(bram): #4564 It may be appropriate to compute these statistics while
// scanning ranges. An ideal solution would be to create incremental events
// whenever availability changes.
func (s *Store) updateReplicationGauges(ctx context.Context) error {
	// Load the system config.
	cfg := s.Gossip().GetSystemConfig()
	if cfg == nil {
		return errors.Errorf("%s: system config not yet available", s)
	}

	var (
		raftLeaderCount               int64
		leaseHolderCount              int64
		leaseExpirationCount          int64
		leaseEpochCount               int64
		raftLeaderNotLeaseHolderCount int64
		quiescentCount                int64
		averageQueriesPerSecond       float64
		averageWritesPerSecond        float64

		rangeCount                int64
		unavailableRangeCount     int64
		underreplicatedRangeCount int64
		overreplicatedRangeCount  int64
		behindCount               int64
	)

	timestamp := s.cfg.Clock.Now()
	var livenessMap IsLiveMap
	if s.cfg.NodeLiveness != nil {
		livenessMap = s.cfg.NodeLiveness.GetIsLiveMap()
	}
	clusterNodes := s.ClusterNodeCount()

	var minMaxClosedTS hlc.Timestamp
	newStoreReplicaVisitor(s).Visit(func(rep *Replica) bool {
		metrics := rep.Metrics(ctx, timestamp, livenessMap, clusterNodes)
		if metrics.Leader {
			raftLeaderCount++
			if metrics.LeaseValid && !metrics.Leaseholder {
				raftLeaderNotLeaseHolderCount++
			}
		}
		if metrics.Leaseholder {
			leaseHolderCount++
			switch metrics.LeaseType {
			case roachpb.LeaseNone:
			case roachpb.LeaseExpiration:
				leaseExpirationCount++
			case roachpb.LeaseEpoch:
				leaseEpochCount++
			}
		}
		if metrics.Quiescent {
			quiescentCount++
		}
		if metrics.RangeCounter {
			rangeCount++
			if metrics.Unavailable {
				unavailableRangeCount++
			}
			if metrics.Underreplicated {
				underreplicatedRangeCount++
			}
			if metrics.Overreplicated {
				overreplicatedRangeCount++
			}
		}
		behindCount += metrics.BehindCount
		if qps, dur := rep.leaseholderStats.avgQPS(); dur >= MinStatsDuration {
			averageQueriesPerSecond += qps
		}
		if wps, dur := rep.writeStats.avgQPS(); dur >= MinStatsDuration {
			averageWritesPerSecond += wps
		}
		mc, ok := rep.maxClosed(ctx)
		if ok && (minMaxClosedTS.IsEmpty() || mc.Less(minMaxClosedTS)) {
			minMaxClosedTS = mc
		}
		return true // more
	})

	s.metrics.RaftLeaderCount.Update(raftLeaderCount)
	s.metrics.RaftLeaderNotLeaseHolderCount.Update(raftLeaderNotLeaseHolderCount)
	s.metrics.LeaseHolderCount.Update(leaseHolderCount)
	s.metrics.LeaseExpirationCount.Update(leaseExpirationCount)
	s.metrics.LeaseEpochCount.Update(leaseEpochCount)
	s.metrics.QuiescentCount.Update(quiescentCount)
	s.metrics.AverageQueriesPerSecond.Update(averageQueriesPerSecond)
	s.metrics.AverageWritesPerSecond.Update(averageWritesPerSecond)
	s.recordNewPerSecondStats(averageQueriesPerSecond, averageWritesPerSecond)

	s.metrics.RangeCount.Update(rangeCount)
	s.metrics.UnavailableRangeCount.Update(unavailableRangeCount)
	s.metrics.UnderReplicatedRangeCount.Update(underreplicatedRangeCount)
	s.metrics.OverReplicatedRangeCount.Update(overreplicatedRangeCount)
	s.metrics.RaftLogFollowerBehindCount.Update(behindCount)

	if !minMaxClosedTS.IsEmpty() {
		nanos := timeutil.Since(minMaxClosedTS.GoTime()).Nanoseconds()
		s.metrics.ClosedTimestampMaxBehindNanos.Update(nanos)
	}

	return nil
}

// checkpoint creates a RocksDB checkpoint in the auxiliary directory with the
// provided tag used in the filepath. The filepath for the checkpoint directory
// is returned.
func (s *Store) checkpoint(ctx context.Context, tag string) (string, error) {
	checkpointBase := filepath.Join(s.engine.GetAuxiliaryDir(), "checkpoints")
	_ = os.MkdirAll(checkpointBase, 0700)

	checkpointDir := filepath.Join(checkpointBase, tag)
	if err := s.engine.CreateCheckpoint(checkpointDir); err != nil {
		return "", err
	}

	return checkpointDir, nil
}

// ComputeMetrics immediately computes the current value of store metrics which
// cannot be computed incrementally. This method should be invoked periodically
// by a higher-level system which records store metrics.
//
// The tick argument should increment across repeated calls to this
// method. It is used to compute some metrics less frequently than others.
func (s *Store) ComputeMetrics(ctx context.Context, tick int) error {
	ctx = s.AnnotateCtx(ctx)
	if err := s.updateCapacityGauges(); err != nil {
		return err
	}
	if err := s.updateReplicationGauges(ctx); err != nil {
		return err
	}

	// Get the latest RocksDB stats.
	stats, err := s.engine.GetStats()
	if err != nil {
		return err
	}
	s.metrics.updateRocksDBStats(*stats)

	// Get engine Env stats.
	envStats, err := s.engine.GetEnvStats()
	if err != nil {
		return err
	}
	s.metrics.updateEnvStats(*envStats)

	sstables := s.engine.GetSSTables()
	s.metrics.RdbNumSSTables.Update(int64(sstables.Len()))
	readAmp := sstables.ReadAmplification()
	s.metrics.RdbReadAmplification.Update(int64(readAmp))
	s.metrics.RdbPendingCompaction.Update(stats.PendingCompactionBytesEstimate)
	// Log this metric infrequently (with current configurations,
	// every 10 minutes). Trigger on tick 1 instead of tick 0 so that
	// non-periodic callers of this method don't trigger expensive
	// stats.
	if tick%logSSTInfoTicks == 1 /* every 10m */ {
		log.Infof(ctx, "sstables (read amplification = %d):\n%s", readAmp, sstables)
		log.Infof(ctx, "%s", s.engine.GetCompactionStats())
	}
	return nil
}

// ClusterNodeCount returns this store's view of the number of nodes in the
// cluster. This is the metric used for adapative zone configs; ranges will not
// be reported as underreplicated if it is low. Tests that wait for full
// replication by tracking the underreplicated metric must also check for the
// expected ClusterNodeCount to avoid catching the cluster while the first node
// is initialized but the other nodes are not.
func (s *Store) ClusterNodeCount() int {
	return s.cfg.StorePool.ClusterNodeCount()
}

// HotReplicaInfo contains a range descriptor and its QPS.
type HotReplicaInfo struct {
	Desc *roachpb.RangeDescriptor
	QPS  float64
}

// HottestReplicas returns the hottest replicas on a store, sorted by their
// QPS. Only contains ranges for which this store is the leaseholder.
//
// Note that this uses cached information, so it's cheap but may be slightly
// out of date.
func (s *Store) HottestReplicas() []HotReplicaInfo {
	topQPS := s.replRankings.topQPS()
	hotRepls := make([]HotReplicaInfo, len(topQPS))
	for i := range topQPS {
		hotRepls[i].Desc = topQPS[i].repl.Desc()
		hotRepls[i].QPS = topQPS[i].qps
	}
	return hotRepls
}

// StoreKeySpanStats carries the result of a stats computation over a key range.
type StoreKeySpanStats struct {
	ReplicaCount         int
	MVCC                 enginepb.MVCCStats
	ApproximateDiskBytes uint64
}

// ComputeStatsForKeySpan computes the aggregated MVCCStats for all replicas on
// this store which contain any keys in the supplied range.
func (s *Store) ComputeStatsForKeySpan(startKey, endKey roachpb.RKey) (StoreKeySpanStats, error) {
	var result StoreKeySpanStats

	newStoreReplicaVisitor(s).Visit(func(repl *Replica) bool {
		desc := repl.Desc()
		if bytes.Compare(startKey, desc.EndKey) >= 0 || bytes.Compare(desc.StartKey, endKey) >= 0 {
			return true // continue
		}
		result.MVCC.Add(repl.GetMVCCStats())
		result.ReplicaCount++
		return true
	})

	var err error
	result.ApproximateDiskBytes, err = s.engine.ApproximateDiskBytes(startKey.AsRawKey(), endKey.AsRawKey())
	return result, err
}

// AllocatorDryRun runs the given replica through the allocator without actually
// carrying out any changes, returning all trace messages collected along the way.
// Intended to help power a debug endpoint.
func (s *Store) AllocatorDryRun(ctx context.Context, repl *Replica) (tracing.Recording, error) {
	ctx, collect, cancel := tracing.ContextWithRecordingSpan(ctx, "allocator dry run")
	defer cancel()
	canTransferLease := func() bool { return true }
	_, err := s.replicateQueue.processOneChange(
		ctx, repl, canTransferLease, true /* dryRun */)
	if err != nil {
		log.Eventf(ctx, "error simulating allocator on replica %s: %s", repl, err)
	}
	return collect(), nil
}

// ManuallyEnqueue runs the given replica through the requested queue,
// returning all trace events collected along the way as well as the error
// message returned from the queue's process method, if any.  Intended to help
// power an admin debug endpoint.
func (s *Store) ManuallyEnqueue(
	ctx context.Context, queueName string, repl *Replica, skipShouldQueue bool,
) (tracing.Recording, string, error) {
	ctx = repl.AnnotateCtx(ctx)

	var queue queueImpl
	var needsLease bool
	for _, replicaQueue := range s.scanner.queues {
		if strings.EqualFold(replicaQueue.Name(), queueName) {
			queue = replicaQueue.(queueImpl)
			needsLease = replicaQueue.NeedsLease()
		}
	}
	if queue == nil {
		return nil, "", errors.Errorf("unknown queue type %q", queueName)
	}

	sysCfg := s.cfg.Gossip.GetSystemConfig()
	if sysCfg == nil {
		return nil, "", errors.New("cannot run queue without a valid system config; make sure the cluster " +
			"has been initialized and all nodes connected to it")
	}

	// Many queues are only meant to be run on leaseholder replicas, so attempt to
	// take the lease here or bail out early if a different replica has it.
	if needsLease {
		hasLease, pErr := repl.getLeaseForGossip(ctx)
		if pErr != nil {
			return nil, "", pErr.GoError()
		}
		if !hasLease {
			return nil, fmt.Sprintf("replica %v does not have the range lease", repl), nil
		}
	}

	ctx, collect, cancel := tracing.ContextWithRecordingSpan(
		ctx, fmt.Sprintf("manual %s queue run", queueName))
	defer cancel()

	if !skipShouldQueue {
		log.Eventf(ctx, "running %s.shouldQueue", queueName)
		shouldQueue, priority := queue.shouldQueue(ctx, s.cfg.Clock.Now(), repl, sysCfg)
		log.Eventf(ctx, "shouldQueue=%v, priority=%f", shouldQueue, priority)
		if !shouldQueue {
			return collect(), "", nil
		}
	}

	log.Eventf(ctx, "running %s.process", queueName)
	err := queue.process(ctx, repl, sysCfg)
	if err != nil {
		return collect(), err.Error(), nil
	}
	return collect(), "", nil
}

// GetClusterVersion reads the the cluster version from the store-local version
// key. Returns an empty version if the key is not found.
func (s *Store) GetClusterVersion(ctx context.Context) (clusterversion.ClusterVersion, error) {
	return ReadClusterVersion(ctx, s.engine)
}

// WriteClusterVersion writes the given cluster version to the store-local cluster version key.
func WriteClusterVersion(
	ctx context.Context, writer storage.ReadWriter, cv clusterversion.ClusterVersion,
) error {
	return storage.MVCCPutProto(ctx, writer, nil, keys.StoreClusterVersionKey(), hlc.Timestamp{}, nil, &cv)
}

// ReadClusterVersion reads the the cluster version from the store-local version key.
func ReadClusterVersion(
	ctx context.Context, reader storage.Reader,
) (clusterversion.ClusterVersion, error) {
	var cv clusterversion.ClusterVersion
	_, err := storage.MVCCGetProto(ctx, reader, keys.StoreClusterVersionKey(), hlc.Timestamp{},
		&cv, storage.MVCCGetOptions{})
	return cv, err
}

func init() {
	tracing.RegisterTagRemapping("s", "store")
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}