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queue.go
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// Copyright 2014 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
//
// Author: Spencer Kimball (spencer.kimball@gmail.com)
package storage
import (
"container/heap"
"sync"
"time"
"github.com/pkg/errors"
"golang.org/x/net/context"
"github.com/cockroachdb/cockroach/pkg/config"
"github.com/cockroachdb/cockroach/pkg/gossip"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/util/hlc"
"github.com/cockroachdb/cockroach/pkg/util/log"
"github.com/cockroachdb/cockroach/pkg/util/metric"
"github.com/cockroachdb/cockroach/pkg/util/stop"
"github.com/cockroachdb/cockroach/pkg/util/syncutil"
"github.com/cockroachdb/cockroach/pkg/util/timeutil"
)
const (
// purgatoryReportInterval is the duration between reports on
// purgatory status.
purgatoryReportInterval = 10 * time.Minute
// defaultProcessTimeout is the timeout when processing a replica.
// The timeout prevents a queue from getting stuck on a replica.
// For example, a replica whose range is not reachable for quorum.
defaultProcessTimeout = 1 * time.Minute
// defaultQueueMaxSize is the default max size for a queue.
defaultQueueMaxSize = 10000
)
// a purgatoryError indicates a replica processing failure which indicates
// the replica can be placed into purgatory for faster retries when the
// failure condition changes.
type purgatoryError interface {
error
purgatoryErrorMarker() // dummy method for unique interface
}
// A replicaItem holds a replica and its priority for use with a priority queue.
type replicaItem struct {
value roachpb.RangeID
priority float64
// The index is needed by update and is maintained by the heap.Interface methods.
index int // The index of the item in the heap.
}
// A priorityQueue implements heap.Interface and holds replicaItems.
type priorityQueue []*replicaItem
func (pq priorityQueue) Len() int { return len(pq) }
func (pq priorityQueue) Less(i, j int) bool {
// We want Pop to give us the highest, not lowest, priority so we use greater than here.
return pq[i].priority > pq[j].priority
}
func (pq priorityQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].index, pq[j].index = i, j
}
func (pq *priorityQueue) Push(x interface{}) {
n := len(*pq)
item := x.(*replicaItem)
item.index = n
*pq = append(*pq, item)
}
func (pq *priorityQueue) Pop() interface{} {
old := *pq
n := len(old)
item := old[n-1]
item.index = -1 // for safety
old[n-1] = nil // for gc
*pq = old[0 : n-1]
return item
}
// update modifies the priority of a replicaItem in the queue.
func (pq *priorityQueue) update(item *replicaItem, priority float64) {
item.priority = priority
heap.Fix(pq, item.index)
}
var (
errQueueDisabled = errors.New("queue disabled")
errQueueStopped = errors.New("queue stopped")
errReplicaNotAddable = errors.New("replica shouldn't be added to queue")
)
func isExpectedQueueError(err error) bool {
cause := errors.Cause(err)
return err == nil || cause == errQueueDisabled || cause == errReplicaNotAddable
}
// shouldQueueAgain is a helper function to determine whether the
// replica should be queued according to the current time, the last
// time the replica was processed, and the minimum interval between
// successive processing. Specifying minInterval=0 queues all replicas.
// Returns a bool for whether to queue as well as a priority based
// on how long it's been since last processed.
func shouldQueueAgain(now, last hlc.Timestamp, minInterval time.Duration) (bool, float64) {
if minInterval == 0 || last == (hlc.Timestamp{}) {
return true, 0
}
if diff := now.GoTime().Sub(last.GoTime()); diff >= minInterval {
priority := float64(1)
// If there's a non-zero last processed timestamp, adjust the
// priority by a multiple of how long it's been since the last
// time this replica was processed.
if last != (hlc.Timestamp{}) {
priority = float64(diff.Nanoseconds()) / float64(minInterval.Nanoseconds())
}
return true, priority
}
return false, 0
}
type queueImpl interface {
// shouldQueue accepts current time, a replica, and the system config
// and returns whether it should be queued and if so, at what priority.
// The Replica is guaranteed to be initialized.
shouldQueue(
context.Context, hlc.Timestamp, *Replica, config.SystemConfig,
) (shouldQueue bool, priority float64)
// process accepts lease status, a replica, and the system config
// and executes queue-specific work on it. The Replica is guaranteed
// to be initialized.
process(context.Context, *Replica, config.SystemConfig) error
// timer returns a duration to wait between processing the next item
// from the queue. The duration of the last processing of a replica
// is supplied as an argument.
timer(time.Duration) time.Duration
// purgatoryChan returns a channel that is signaled when it's time
// to retry replicas which have been relegated to purgatory due to
// failures. If purgatoryChan returns nil, failing replicas are not
// sent to purgatory.
purgatoryChan() <-chan struct{}
}
type queueConfig struct {
// maxSize is the maximum number of replicas to queue.
maxSize int
// needsLease controls whether this queue requires the range lease to
// operate on a replica.
needsLease bool
// needsSystemConfig controls whether this queue requires a valid copy of the
// system config to operate on a replica. Not all queues require it, and it's
// unsafe for certain queues to wait on it. For example, a raft snapshot may
// be needed in order to make it possible for the system config to become
// available (as observed in #16268), so the raft snapshot queue can't
// require the system config to already be available.
needsSystemConfig bool
// acceptsUnsplitRanges controls whether this queue can process ranges that
// need to be split due to zone config settings. Ranges are checked before
// calling queueImpl.shouldQueue and queueImpl.process.
// This is to avoid giving the queue a replica that spans multiple config
// zones (which might make the action of the queue ambiguous - e.g. we don't
// want to try to replicate a range until we know which zone it is in and
// therefore how many replicas are required).
acceptsUnsplitRanges bool
// processTimeout is the timeout for processing a replica.
processTimeout time.Duration
// successes is a counter of replicas processed successfully.
successes *metric.Counter
// failures is a counter of replicas which failed processing.
failures *metric.Counter
// pending is a gauge measuring current replica count pending.
pending *metric.Gauge
// processingNanos is a counter measuring total nanoseconds spent processing replicas.
processingNanos *metric.Counter
// purgatory is a gauge measuring current replica count in purgatory.
purgatory *metric.Gauge
}
// baseQueue is the base implementation of the replicaQueue interface.
// Queue implementations should embed a baseQueue and implement queueImpl.
//
// In addition to normal processing of replicas via the replica
// scanner, queues have an optional notion of purgatory, where
// replicas which fail queue processing with a retryable error may be
// sent such that they will be quickly retried when the failure
// condition changes. Queue implementations opt in for purgatory by
// implementing the purgatoryChan method of queueImpl such that it
// returns a non-nil channel.
type baseQueue struct {
log.AmbientContext
name string
// The constructor of the queueImpl structure MUST return a pointer.
// This is because assigning queueImpl to a function-local, then
// passing a pointer to it to `makeBaseQueue`, and then returning it
// from the constructor function will return a queueImpl containing
// a pointer to a structure which is a copy of the one within which
// it is contained. DANGER.
impl queueImpl
store *Store
gossip *gossip.Gossip
queueConfig
incoming chan struct{} // Channel signaled when a new replica is added to the queue.
mu struct {
sync.Locker // Protects all variables in the mu struct
priorityQ priorityQueue // The priority queue
replicas map[roachpb.RangeID]*replicaItem // Map from RangeID to replicaItem (for updating priority)
purgatory map[roachpb.RangeID]error // Map of replicas to processing errors
stopped bool
// Some tests in this package disable queues.
disabled bool
}
// processMu synchronizes execution of processing for a single queue,
// ensuring that we never process more than a single replica at a time. This
// is needed because both the main processing loop and the purgatory loop can
// process replicas.
processMu sync.Locker
}
// newBaseQueue returns a new instance of baseQueue with the specified
// shouldQueue function to determine which replicas to queue and maxSize to
// limit the growth of the queue. Note that maxSize doesn't prevent new
// replicas from being added, it just limits the total size. Higher priority
// replicas can still be added; their addition simply removes the lowest
// priority replica.
func newBaseQueue(
name string, impl queueImpl, store *Store, gossip *gossip.Gossip, cfg queueConfig,
) *baseQueue {
// Use the default process timeout if none specified.
if cfg.processTimeout == 0 {
cfg.processTimeout = defaultProcessTimeout
}
ambient := store.cfg.AmbientCtx
ambient.AddLogTag(name, nil)
if !cfg.acceptsUnsplitRanges && !cfg.needsSystemConfig {
log.Fatalf(ambient.AnnotateCtx(context.Background()),
"misconfigured queue: acceptsUnsplitRanges=false requires needsSystemConfig=true; got %+v", cfg)
}
bq := baseQueue{
AmbientContext: ambient,
name: name,
impl: impl,
store: store,
gossip: gossip,
queueConfig: cfg,
incoming: make(chan struct{}, 1),
}
bq.mu.Locker = new(syncutil.Mutex)
bq.mu.replicas = map[roachpb.RangeID]*replicaItem{}
bq.processMu = new(syncutil.Mutex)
return &bq
}
// Length returns the current size of the queue.
func (bq *baseQueue) Length() int {
bq.mu.Lock()
defer bq.mu.Unlock()
return bq.mu.priorityQ.Len()
}
// PurgatoryLength returns the current size of purgatory.
func (bq *baseQueue) PurgatoryLength() int {
bq.mu.Lock()
defer bq.mu.Unlock()
return len(bq.mu.purgatory)
}
// SetDisabled turns queue processing off or on as directed.
func (bq *baseQueue) SetDisabled(disabled bool) {
bq.mu.Lock()
bq.mu.disabled = disabled
bq.mu.Unlock()
}
// Disabled returns true is the queue is currently disabled.
func (bq *baseQueue) Disabled() bool {
bq.mu.Lock()
defer bq.mu.Unlock()
return bq.mu.disabled
}
// Start launches a goroutine to process entries in the queue. The
// provided stopper is used to finish processing.
func (bq *baseQueue) Start(clock *hlc.Clock, stopper *stop.Stopper) {
bq.processLoop(clock, stopper)
}
// Add adds the specified replica to the queue, regardless of the
// return value of bq.shouldQueue. The replica is added with specified
// priority. If the queue is too full, the replica may not be added,
// as the replica with the lowest priority will be dropped. Returns
// (true, nil) if the replica was added, (false, nil) if the replica
// was already present, and (false, err) if the replica could not be
// added for any other reason.
func (bq *baseQueue) Add(repl *Replica, priority float64) (bool, error) {
bq.mu.Lock()
defer bq.mu.Unlock()
ctx := repl.AnnotateCtx(bq.AnnotateCtx(context.TODO()))
return bq.addInternal(ctx, repl.Desc(), true, priority)
}
// MaybeAdd adds the specified replica if bq.shouldQueue specifies it
// should be queued. Replicas are added to the queue using the priority
// returned by bq.shouldQueue. If the queue is too full, the replica may
// not be added, as the replica with the lowest priority will be
// dropped.
func (bq *baseQueue) MaybeAdd(repl *Replica, now hlc.Timestamp) {
ctx := repl.AnnotateCtx(bq.AnnotateCtx(context.TODO()))
// Load the system config if it's needed.
var cfg config.SystemConfig
var cfgOk bool
if bq.needsSystemConfig {
cfg, cfgOk = bq.gossip.GetSystemConfig()
if !cfgOk {
if log.V(1) {
log.Infof(ctx, "no system config available. skipping")
}
return
}
}
bq.mu.Lock()
defer bq.mu.Unlock()
if bq.mu.stopped || bq.mu.disabled {
return
}
if !repl.IsInitialized() {
return
}
if cfgOk && bq.requiresSplit(cfg, repl) {
// Range needs to be split due to zone configs, but queue does
// not accept unsplit ranges.
if log.V(1) {
log.Infof(ctx, "split needed; not adding")
}
return
}
if bq.needsLease {
// Check to see if either we own the lease or do not know who the lease
// holder is.
if lease, _ := repl.getLease(); repl.IsLeaseValid(lease, now) &&
!lease.OwnedBy(repl.store.StoreID()) {
if log.V(1) {
log.Infof(ctx, "needs lease; not adding: %+v", lease)
}
return
}
}
should, priority := bq.impl.shouldQueue(ctx, now, repl, cfg)
if _, err := bq.addInternal(ctx, repl.Desc(), should, priority); !isExpectedQueueError(err) {
log.Errorf(ctx, "unable to add: %s", err)
}
}
func (bq *baseQueue) requiresSplit(cfg config.SystemConfig, repl *Replica) bool {
if bq.acceptsUnsplitRanges {
return false
}
// If there's no store (as is the case in some narrow unit tests),
// the "required" split will never come. In that case, pretend we
// don't require the split.
if store := repl.store; store == nil {
return false
}
desc := repl.Desc()
return cfg.NeedsSplit(desc.StartKey, desc.EndKey)
}
// addInternal adds the replica the queue with specified priority. If
// the replica is already queued, updates the existing
// priority. Expects the queue lock to be held by caller.
func (bq *baseQueue) addInternal(
ctx context.Context, desc *roachpb.RangeDescriptor, should bool, priority float64,
) (bool, error) {
if bq.mu.stopped {
return false, errQueueStopped
}
if bq.mu.disabled {
if log.V(3) {
log.Infof(ctx, "queue disabled")
}
return false, errQueueDisabled
}
if !desc.IsInitialized() {
// We checked this above in MaybeAdd(), but we need to check it
// again for Add().
return false, errors.New("replica not initialized")
}
// If the replica is currently in purgatory, don't re-add it.
if _, ok := bq.mu.purgatory[desc.RangeID]; ok {
return false, nil
}
item, ok := bq.mu.replicas[desc.RangeID]
if !should {
if ok {
if log.V(1) {
log.Infof(ctx, "%s: removing from queue", item.value)
}
bq.remove(item)
}
return false, errReplicaNotAddable
} else if ok {
if item.priority != priority {
if log.V(1) {
log.Infof(ctx, "updating priority: %0.3f -> %0.3f", item.priority, priority)
}
}
// Replica has already been added; update priority.
bq.mu.priorityQ.update(item, priority)
return false, nil
}
if log.V(3) {
log.Infof(ctx, "adding: priority=%0.3f", priority)
}
item = &replicaItem{value: desc.RangeID, priority: priority}
bq.add(item)
// If adding this replica has pushed the queue past its maximum size,
// remove the lowest priority element.
if pqLen := bq.mu.priorityQ.Len(); pqLen > bq.maxSize {
bq.remove(bq.mu.priorityQ[pqLen-1])
}
// Signal the processLoop that a replica has been added.
select {
case bq.incoming <- struct{}{}:
default:
// No need to signal again.
}
return true, nil
}
// MaybeRemove removes the specified replica from the queue if enqueued.
func (bq *baseQueue) MaybeRemove(rangeID roachpb.RangeID) {
bq.mu.Lock()
defer bq.mu.Unlock()
if bq.mu.stopped {
return
}
if item, ok := bq.mu.replicas[rangeID]; ok {
ctx := bq.AnnotateCtx(context.TODO())
if log.V(3) {
log.Infof(ctx, "%s: removing", item.value)
}
bq.remove(item)
}
}
// processLoop processes the entries in the queue until the provided
// stopper signals exit.
func (bq *baseQueue) processLoop(clock *hlc.Clock, stopper *stop.Stopper) {
ctx := bq.AnnotateCtx(context.Background())
stopper.RunWorker(ctx, func(ctx context.Context) {
defer func() {
bq.mu.Lock()
bq.mu.stopped = true
bq.mu.Unlock()
}()
// nextTime is initially nil; we don't start any timers until the queue
// becomes non-empty.
var nextTime <-chan time.Time
immediately := make(chan time.Time)
close(immediately)
for {
select {
// Exit on stopper.
case <-stopper.ShouldStop():
return
// Incoming signal sets the next time to process if there were previously
// no replicas in the queue.
case <-bq.incoming:
if nextTime == nil {
// When a replica is added, wake up immediately. This is mainly
// to facilitate testing without unnecessary sleeps.
nextTime = immediately
// In case we're in a test, still block on the impl.
bq.impl.timer(0)
}
// Process replicas as the timer expires.
case <-nextTime:
repl := bq.pop()
var duration time.Duration
if repl != nil {
annotatedCtx := repl.AnnotateCtx(ctx)
if stopper.RunTask(annotatedCtx, func(annotatedCtx context.Context) {
start := timeutil.Now()
if err := bq.processReplica(annotatedCtx, repl, clock); err != nil {
// Maybe add failing replica to purgatory if the queue supports it.
bq.maybeAddToPurgatory(annotatedCtx, repl, err, clock, stopper)
}
duration = timeutil.Since(start)
if log.V(2) {
log.Infof(annotatedCtx, "done %s", duration)
}
bq.processingNanos.Inc(duration.Nanoseconds())
}) != nil {
return
}
}
if bq.Length() == 0 {
nextTime = nil
} else {
nextTime = time.After(bq.impl.timer(duration))
}
}
}
})
}
// processReplica processes a single replica. This should not be
// called externally to the queue. bq.mu.Lock must not be held
// while calling this method.
func (bq *baseQueue) processReplica(
queueCtx context.Context, repl *Replica, clock *hlc.Clock,
) error {
bq.processMu.Lock()
defer bq.processMu.Unlock()
// Load the system config if it's needed.
var cfg config.SystemConfig
var cfgOk bool
if bq.needsSystemConfig {
cfg, cfgOk = bq.gossip.GetSystemConfig()
if !cfgOk {
if log.V(1) {
log.Infof(queueCtx, "no system config available. skipping")
}
return nil
}
}
if cfgOk && bq.requiresSplit(cfg, repl) {
// Range needs to be split due to zone configs, but queue does
// not accept unsplit ranges.
if log.V(3) {
log.Infof(queueCtx, "split needed; skipping")
}
return nil
}
// Putting a span in a context means that events will no longer go to the
// event log. Use queueCtx for events that are intended for the event log.
ctx, span := bq.AnnotateCtxWithSpan(queueCtx, bq.name)
defer span.Finish()
// Also add the Replica annotations to ctx.
ctx = repl.AnnotateCtx(ctx)
ctx, cancel := context.WithTimeout(ctx, bq.processTimeout)
defer cancel()
if log.V(1) {
log.Infof(ctx, "processing replica")
}
if !repl.IsInitialized() {
// We checked this when adding the replica, but we need to check it again
// in case this is a different replica with the same range ID (see #14193).
return errors.New("cannot process uninitialized replica")
}
if err := repl.IsDestroyed(); err != nil {
if log.V(3) {
log.Infof(queueCtx, "replica destroyed (%s); skipping", err)
}
return nil
}
// If the queue requires a replica to have the range lease in
// order to be processed, check whether this replica has range lease
// and renew or acquire if necessary.
if bq.needsLease {
if _, pErr := repl.redirectOnOrAcquireLease(ctx); pErr != nil {
switch v := pErr.GetDetail().(type) {
case *roachpb.NotLeaseHolderError, *roachpb.RangeNotFoundError:
if log.V(3) {
log.Infof(queueCtx, "%s; skipping", v)
}
log.Eventf(ctx, "%s; skipping", v)
return nil
default:
log.ErrEventf(ctx, "could not obtain lease: %s", pErr)
return errors.Wrapf(pErr.GoError(), "%s: could not obtain lease", repl)
}
}
}
if log.V(3) {
log.Infof(queueCtx, "processing")
}
if err := bq.impl.process(ctx, repl, cfg); err != nil {
return err
}
if log.V(3) {
log.Infof(ctx, "done")
}
bq.successes.Inc(1)
return nil
}
// maybeAddToPurgatory possibly adds the specified replica to the
// purgatory queue, which holds replicas which have failed
// processing. To be added, the failing error must implement
// purgatoryError and the queue implementation must have its own
// mechanism for signaling re-processing of replicas held in
// purgatory.
func (bq *baseQueue) maybeAddToPurgatory(
ctx context.Context, repl *Replica, triggeringErr error, clock *hlc.Clock, stopper *stop.Stopper,
) {
// Increment failures metric here to capture all error returns from
// process().
bq.failures.Inc(1)
// Check whether the failure is a purgatory error and whether the queue supports it.
if _, ok := triggeringErr.(purgatoryError); !ok || bq.impl.purgatoryChan() == nil {
log.Error(ctx, triggeringErr)
return
}
bq.mu.Lock()
defer bq.mu.Unlock()
// First, check whether the replica has already been re-added to queue.
if _, ok := bq.mu.replicas[repl.RangeID]; ok {
return
}
if log.V(1) {
log.Info(ctx, errors.Wrap(triggeringErr, "purgatory"))
}
item := &replicaItem{value: repl.RangeID}
bq.mu.replicas[repl.RangeID] = item
defer func() {
bq.purgatory.Update(int64(len(bq.mu.purgatory)))
}()
// If purgatory already exists, just add to the map and we're done.
if bq.mu.purgatory != nil {
bq.mu.purgatory[repl.RangeID] = triggeringErr
return
}
// Otherwise, create purgatory and start processing.
bq.mu.purgatory = map[roachpb.RangeID]error{
repl.RangeID: triggeringErr,
}
workerCtx := bq.AnnotateCtx(context.Background())
stopper.RunWorker(workerCtx, func(ctx context.Context) {
ticker := time.NewTicker(purgatoryReportInterval)
for {
select {
case <-bq.impl.purgatoryChan():
// Remove all items from purgatory into a copied slice.
bq.mu.Lock()
ranges := make([]roachpb.RangeID, 0, len(bq.mu.purgatory))
for rangeID := range bq.mu.purgatory {
item := bq.mu.replicas[rangeID]
ranges = append(ranges, item.value)
bq.remove(item)
}
bq.mu.Unlock()
for _, id := range ranges {
repl, err := bq.store.GetReplica(id)
if err != nil {
log.Errorf(ctx, "range %s no longer exists on store: %s", id, err)
return
}
annotatedCtx := repl.AnnotateCtx(ctx)
if stopper.RunTask(annotatedCtx, func(annotatedCtx context.Context) {
if err := bq.processReplica(annotatedCtx, repl, clock); err != nil {
bq.maybeAddToPurgatory(annotatedCtx, repl, err, clock, stopper)
}
}) != nil {
return
}
}
bq.mu.Lock()
if len(bq.mu.purgatory) == 0 {
log.Infof(ctx, "purgatory is now empty")
bq.mu.purgatory = nil
bq.mu.Unlock()
return
}
bq.mu.Unlock()
case <-ticker.C:
// Report purgatory status.
bq.mu.Lock()
errMap := map[string]int{}
for _, err := range bq.mu.purgatory {
errMap[err.Error()]++
}
bq.mu.Unlock()
for errStr, count := range errMap {
log.Errorf(ctx, "%d replicas failing with %q", count, errStr)
}
case <-stopper.ShouldStop():
return
}
}
})
}
// pop dequeues the highest priority replica, if any, in the queue. Expects
// mutex to be locked.
func (bq *baseQueue) pop() *Replica {
var repl *Replica
for repl == nil {
bq.mu.Lock()
if bq.mu.priorityQ.Len() == 0 {
bq.mu.Unlock()
return nil
}
item := heap.Pop(&bq.mu.priorityQ).(*replicaItem)
bq.pending.Update(int64(bq.mu.priorityQ.Len()))
delete(bq.mu.replicas, item.value)
bq.mu.Unlock()
repl, _ = bq.store.GetReplica(item.value)
}
return repl
}
// add adds an element to the priority queue. Caller must hold mutex.
func (bq *baseQueue) add(item *replicaItem) {
heap.Push(&bq.mu.priorityQ, item)
bq.pending.Update(int64(bq.mu.priorityQ.Len()))
bq.mu.replicas[item.value] = item
}
// remove removes an element from purgatory (if it's experienced an
// error) or from the priority queue by index. Caller must hold mutex.
func (bq *baseQueue) remove(item *replicaItem) {
if _, ok := bq.mu.purgatory[item.value]; ok {
delete(bq.mu.purgatory, item.value)
bq.purgatory.Update(int64(len(bq.mu.purgatory)))
} else {
heap.Remove(&bq.mu.priorityQ, item.index)
bq.pending.Update(int64(bq.mu.priorityQ.Len()))
}
delete(bq.mu.replicas, item.value)
}
// DrainQueue locks the queue and processes the remaining queued replicas. It
// processes the replicas in the order they're queued in, one at a time.
// Exposed for testing only.
//
// TODO(bdarnell): this method may race with the call to bq.pop() in
// the main loop, in which case it does not guarantee that all
// replicas have been processed by the time it returns. This is most
// noticeable with ForceReplicaGCScanAndProcess, since the replica GC
// queue has many event-driven triggers. This should synchronize
// somehow with processLoop so we wait for anything being handled
// there to finish too. When that's done, the SucceedsSoon at the end
// of TestRemoveRangeWithoutGC (and perhaps others) can be replaced
// with a one-time check.
func (bq *baseQueue) DrainQueue(clock *hlc.Clock) {
ctx := bq.AnnotateCtx(context.TODO())
for repl := bq.pop(); repl != nil; repl = bq.pop() {
annotatedCtx := repl.AnnotateCtx(ctx)
if err := bq.processReplica(annotatedCtx, repl, clock); err != nil {
bq.failures.Inc(1)
log.Error(annotatedCtx, err)
}
}
}