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txnwatcher.go
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txnwatcher.go
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// Copyright 2012, 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package watcher
import (
"time"
"github.com/juju/errors"
"github.com/juju/mgo/v3"
"github.com/juju/mgo/v3/bson"
"github.com/juju/worker/v4"
"gopkg.in/tomb.v2"
"github.com/juju/juju/core/logger"
internallogger "github.com/juju/juju/internal/logger"
"github.com/juju/juju/internal/wrench"
)
// Hub represents a pubsub hub. The TxnWatcher only ever publishes
// events to the hub.
type Hub interface {
Publish(topic string, data interface{}) func()
}
// Clock represents the time methods used.
type Clock interface {
Now() time.Time
After(time.Duration) <-chan time.Time
}
const (
// TxnWatcherSyncErr is published to the TxnWatcher's hub if there's a
// sync error (e.g., an error iterating through the collection's rows).
TxnWatcherSyncErr = "sync err"
// TxnWatcherCollection is published to the TxnWatcher's hub for each
// change (data is the Change instance).
TxnWatcherCollection = "collection"
// txnWatcherErrorWait is the delay after an error before trying to resume
// the change stream by a call to aggregate changeStream.
txnWatcherErrorWait = 5 * time.Second
)
// RunCmdFunc allows tests to override calls to mongo db.Run.
type RunCmdFunc func(db *mgo.Database, cmd any, resp any) error
// A TxnWatcher watches a mongo change stream and publishes all change events
// to the hub.
type TxnWatcher struct {
hub Hub
clock Clock
logger logger.Logger
tomb tomb.Tomb
session *mgo.Session
jujuDBName string
reportRequest chan chan map[string]interface{}
// syncEvents contain the events to be
// dispatched to the watcher channels. They're queued during
// processing and flushed at the end to simplify the algorithm.
// The two queues are separated because events from sync are
// handled in reverse order due to the way the algorithm works.
syncEvents []Change
// iteratorStepCount tracks how many documents we've read from the database
iteratorStepCount uint64
// changesCount tracks all sync events that we have processed
changesCount uint64
// syncEventsLastLen was the length of syncEvents when we did our last flush()
syncEventsLastLen int
// averageSyncLen tracks a filtered average of how long the sync event queue gets before we flush
averageSyncLen float64
// resumeToken is passed back by the aggregate changeStream call so that a change stream may
// be resumed if the cursor dies for some reason.
resumeToken bson.Raw
// cursorId is the id of the current cursor used for paging results from the change stream.
cursorId int64
// pollInterval is the duration of the long polling getMore call on the cursor.
pollInterval time.Duration
// readyChan is closed when the watcher has started the change stream, used for tests.
readyChan chan any
// runCmd can be used to override the db.Run function, used for tests.
runCmd RunCmdFunc
// ignoreCollections when set the watcher will ignore all changes for these collections.
ignoreCollections []string
}
// TxnWatcherConfig contains the configuration parameters required
// for a NewTxnWatcher.
type TxnWatcherConfig struct {
// Session is used exclusively fot this TxnWatcher.
Session *mgo.Session
// JujuDBName is the Juju database name, usually "juju".
JujuDBName string
// Hub is where the changes are published to.
Hub Hub
// Clock allows tests to control the advancing of time.
Clock Clock
// Logger is used to control where the log messages for this watcher go.
Logger logger.Logger
// PollInterval is used to set how long mongo will wait before returning an
// empty result. It defaults to 1s.
PollInterval time.Duration
// RunCmd is called to run commands against an mgo.Database, used for
// testing.
RunCmd RunCmdFunc
// IgnoreCollections is optional, when provided the TxnWatcher will ignore changes
// to documents in these collections.
IgnoreCollections []string
}
// Validate ensures that all the values that have to be set are set.
func (config TxnWatcherConfig) Validate() error {
if config.Session == nil {
return errors.NotValidf("missing Session")
}
if config.JujuDBName == "" {
return errors.NotValidf("missing JujuDBName")
}
if config.Hub == nil {
return errors.NotValidf("missing Hub")
}
if config.Clock == nil {
return errors.NotValidf("missing Clock")
}
if config.PollInterval < 0 {
return errors.NotValidf("negative PollInterval")
}
return nil
}
// NewTxnWatcher returns a new Watcher observing the changelog collection.
func NewTxnWatcher(config TxnWatcherConfig) (*TxnWatcher, error) {
if err := config.Validate(); err != nil {
return nil, errors.Annotate(err, "new TxnWatcher invalid config")
}
w := &TxnWatcher{
hub: config.Hub,
clock: config.Clock,
logger: config.Logger,
session: config.Session,
jujuDBName: config.JujuDBName,
reportRequest: make(chan chan map[string]interface{}),
readyChan: make(chan any),
pollInterval: config.PollInterval,
runCmd: config.RunCmd,
ignoreCollections: config.IgnoreCollections,
}
if w.logger == nil {
w.logger = internallogger.Noop()
}
if w.pollInterval == 0 {
w.pollInterval = 1 * time.Second
}
if w.runCmd == nil {
w.runCmd = w.runCmdImpl
}
w.tomb.Go(func() error {
err := w.loop()
// tomb expects ErrDying or ErrStillAlive as
// exact values, so we need to log and unwrap
// the error first.
cause := errors.Cause(err)
switch cause {
case tomb.ErrDying:
return tomb.ErrDying
case tomb.ErrStillAlive:
return tomb.ErrStillAlive
}
if err != nil {
w.logger.Infof("watcher loop failed: %v", err)
}
return err
})
return w, nil
}
// Kill is part of the worker.Worker interface.
func (w *TxnWatcher) Kill() {
w.tomb.Kill(nil)
}
// Wait is part of the worker.Worker interface.
func (w *TxnWatcher) Wait() error {
return w.tomb.Wait()
}
// Stop stops all the watcher activities.
func (w *TxnWatcher) Stop() error {
return worker.Stop(w)
}
// Dead returns a channel that is closed when the watcher has stopped.
func (w *TxnWatcher) Dead() <-chan struct{} {
return w.tomb.Dead()
}
// Err returns the error with which the watcher stopped.
// It returns nil if the watcher stopped cleanly, tomb.ErrStillAlive
// if the watcher is still running properly, or the respective error
// if the watcher is terminating or has terminated with an error.
func (w *TxnWatcher) Err() error {
return w.tomb.Err()
}
// Report is part of the watcher/runner Reporting interface, to expose runtime details of the watcher.
func (w *TxnWatcher) Report() map[string]interface{} {
// TODO: (jam) do we need to synchronize with the loop?
resCh := make(chan map[string]interface{})
select {
case <-w.tomb.Dying():
return nil
case w.reportRequest <- resCh:
break
}
select {
case <-w.tomb.Dying():
return nil
case res := <-resCh:
return res
}
}
// Ready waits for the watcher to have started the change stream against mongo or return an error.
// Useful for testing.
func (w *TxnWatcher) Ready() error {
select {
case <-w.tomb.Dying():
return w.tomb.Err()
case <-w.readyChan:
return nil
}
}
// loop implements the main watcher loop.
// period is the delay between each sync.
func (w *TxnWatcher) loop() error {
w.logger.Tracef("loop started")
defer w.logger.Tracef("loop finished")
// Change Stream specification can be found here:
// https://github.com/mongodb/specifications/blob/master/source/change-streams/change-streams.rst
w.resumeToken = bson.Raw{}
errorOccurred := false
immediate := make(chan time.Time)
close(immediate)
var next <-chan time.Time = immediate
first := true
for {
select {
case <-w.tomb.Dying():
return errors.Trace(tomb.ErrDying)
case <-next:
next = immediate
case resCh := <-w.reportRequest:
report := map[string]interface{}{
// How long was sync-events in our last flush
"sync-events-last-len": w.syncEventsLastLen,
// How long is sync-events on average
"sync-events-avg": int(w.averageSyncLen + 0.5),
// How long is the queue right now? (probably should always be 0 if we are at this point in the loop)
"sync-events-len": len(w.syncEvents),
// How big is our buffer
"sync-events-cap": cap(w.syncEvents),
// How many events have we actually generated
"total-changes": w.changesCount,
// How many database records have we read. note: because we have to iterate until we get to lastId,
// this is often a bit bigger than total-sync-events
"iterator-step-count": w.iteratorStepCount,
}
select {
case <-w.tomb.Dying():
return errors.Trace(tomb.ErrDying)
case resCh <- report:
}
// This doesn't indicate we need to perform a sync
continue
}
var err error
if errorOccurred || first {
if !first {
w.killCursor()
}
err = w.init()
if err != nil {
err = errors.Wrap(FatalChangeStreamError, err)
}
if first {
defer w.killCursor()
w.logger.Infof("txn watcher started")
close(w.readyChan)
first = false
}
} else {
err = w.sync()
}
if w.logger.IsLevelEnabled(logger.TRACE) && wrench.IsActive("txnwatcher", "sync-error") {
err = errors.New("test sync watcher error")
}
if err == nil {
if errorOccurred {
w.logger.Infof("txn sync watcher resumed after failure")
}
errorOccurred = false
w.flush()
} else {
w.logger.Warningf("txn watcher sync error: %v", err)
// If didn't get a resumable error and either we have already had one error resuming
// or received a fatal error, then exit the watcher and report failure.
if !errors.Is(err, ResumableChangeStreamError) &&
(errors.Is(err, FatalChangeStreamError) || errorOccurred) {
_ = w.hub.Publish(TxnWatcherSyncErr, err)
return errors.Trace(err)
}
w.logger.Warningf("txn watcher resume queued")
errorOccurred = true
next = w.clock.After(txnWatcherErrorWait)
}
}
}
func (w *TxnWatcher) killCursor() {
if w.cursorId == 0 {
return
}
db := w.session.DB(w.jujuDBName)
var err error
for i := 0; i < 2; i++ {
err = w.runCmd(db, bson.D{
{"killCursors", "$cmd.aggregate"},
{"cursors", []int64{w.cursorId}},
}, nil)
if isCursorNotFoundError(err) {
break
} else if err == nil {
break
}
w.logger.Warningf("failed to kill cursor %d: %s", w.cursorId, err.Error())
}
w.cursorId = 0
}
func (w *TxnWatcher) init() error {
db := w.session.DB(w.jujuDBName)
cs := bson.M{
"fullDocument": "updateLookup",
}
if len(w.resumeToken.Data) > 0 {
cs["resumeAfter"] = w.resumeToken
}
match := bson.D{
{"$or", []bson.D{
{{"operationType", "insert"}},
{{"operationType", "update"}},
{{"operationType", "replace"}},
{{"operationType", "delete"}},
}},
}
if len(w.ignoreCollections) > 0 {
match = append(match, bson.DocElem{"ns.coll", bson.D{{"$not", bson.D{{"$in", w.ignoreCollections}}}}})
}
cmd := bson.D{
{"aggregate", 1},
{"pipeline", []bson.D{
{{"$changeStream", cs}},
{{"$match", match}},
}},
{"cursor", bson.D{{"batchSize", 10}}},
{"readConcern", bson.D{{"level", "majority"}}},
}
resp := aggregateResponse{}
err := w.runCmd(db, cmd, &resp)
if err != nil {
return errors.Annotate(err, "starting change stream")
}
w.cursorId = resp.Cursor.Id
err = w.process(resp.Cursor.FirstBatch)
if err != nil {
return errors.Annotate(err, "processing first change stream batch")
}
w.resumeToken = resp.Cursor.PostBatchResumeToken
return nil
}
func (w *TxnWatcher) process(changes []bson.Raw) error {
for i := len(changes) - 1; i >= 0; i-- {
changeRaw := changes[i]
change := changeStreamDocument{}
err := bson.Unmarshal(changeRaw.Data, &change)
if err != nil {
return errors.Trace(err)
}
if len(change.Id.Data) == 0 {
return errors.Annotate(FatalChangeStreamError, "missing change id in change")
}
revno := int64(0)
switch change.OperationType {
case "insert", "replace":
// We read the revno from the committed document as reported by the change stream.
revno = change.FullDocument.Revno
case "update":
// For updates we read the revno from the updated fields so that it isn't newer as
// FullDocument on an update is only guaranteed to be the state of the document after
// the update, not the state of the document as a result of the update, so the reported
// revno could be greater.
revno = change.UpdateDescription.UpdatedFields.Revno
if revno == 0 && change.TxnNumber == 0 {
a := bson.M{}
err := bson.Unmarshal(changeRaw.Data, &a)
if err != nil {
return errors.Trace(err)
}
j, err := bson.MarshalJSON(a)
if err != nil {
return errors.Trace(err)
}
// If you get this message then a document was updated outside a mongo multi-doc transaction
// and wasn't involved in a jujutxn (incrementing txn-revno).
// If you were trying to modify a document from the mongo cli, you need to start a transaction
// then modify the document while also incrementing its txn-revno field. Then commit the transaction.
// This will correctly trigger the watcher.
// If you are seeing this otherwise, maybe the collection should not have been watched, so go update
// the watcherIgnoreList in state/allcollections.go
// If you want to receive watch notifications on your collection and get here, you need to make sure
// all mutations are done inside a jujutxn otherwise you have a programming error and the change will
// get skipped.
w.logger.Criticalf("update %s %v without revno %s", change.Ns.Collection, change.DocumentKey.Id, j)
w.resumeToken = change.Id
continue
} else if revno == 0 && change.TxnNumber != 0 {
// Skip update because the revno "$set" was elided.
w.resumeToken = change.Id
continue
}
case "delete":
// Revno of -1 indicates a deleted document.
revno = -1
default:
// If we have a bad change, then we can just skip it, making sure to update the resumption token
// to resume after this event.
w.logger.Warningf("received bad change type %s", change.OperationType)
w.resumeToken = change.Id
continue
}
w.logger.Debugf("txn watcher: %s %v #%d", change.Ns.Collection, change.DocumentKey.Id, revno)
w.syncEvents = append(w.syncEvents, Change{
C: change.Ns.Collection,
Id: change.DocumentKey.Id,
Revno: revno,
})
w.changesCount++
w.resumeToken = change.Id
}
return nil
}
// flush sends all pending events to their respective channels.
func (w *TxnWatcher) flush() {
// refreshEvents are stored newest first.
for i := len(w.syncEvents) - 1; i >= 0; i-- {
e := w.syncEvents[i]
_ = w.hub.Publish(TxnWatcherCollection, e)
}
w.averageSyncLen = (filterFactor * float64(len(w.syncEvents))) + ((1.0 - filterFactor) * w.averageSyncLen)
w.syncEventsLastLen = len(w.syncEvents)
w.syncEvents = w.syncEvents[:0]
// TODO(jam): 2018-11-07 Consider if averageSyncLen << cap(syncEvents) we should reallocate the buffer, so that it
// doesn't grow to the size of the largest-ever change and never shrink
}
// sync updates the watcher knowledge from the database, and
// queues events to observing channels.
func (w *TxnWatcher) sync() error {
w.logger.Tracef("txn watcher %p starting sync", w)
db := w.session.DB(w.jujuDBName)
resp := aggregateResponse{}
var err error
for i := 0; i < 2; i++ {
select {
case <-w.tomb.Dying():
return tomb.ErrDying
default:
}
err = w.runCmd(db, bson.D{
{"getMore", w.cursorId},
{"collection", "$cmd.aggregate"},
{"batchSize", 10},
{"maxTimeMS", w.pollInterval.Milliseconds()},
{"readConcern", bson.D{{"level", "majority"}}},
}, &resp)
if isCursorNotFoundError(err) {
return errors.Wrap(ResumableChangeStreamError, err)
} else if isFatalGetMoreError(err) {
return errors.Wrap(FatalChangeStreamError, err)
} else if err == nil {
break
}
}
if err != nil {
return errors.Wrap(ResumableChangeStreamError, err)
}
err = w.process(resp.Cursor.NextBatch)
if err != nil {
return errors.Trace(err)
}
w.resumeToken = resp.Cursor.PostBatchResumeToken
return nil
}
func (w *TxnWatcher) runCmdImpl(db *mgo.Database, cmd any, resp any) error {
return db.Run(cmd, resp)
}
type changeStreamDocument struct {
Id bson.Raw `bson:"_id"`
OperationType string `bson:"operationType"`
Ns nsRef `bson:"ns"`
DocumentKey *docKey `bson:"documentKey"`
ClusterTime bson.MongoTimestamp `bson:"clusterTime"`
FullDocument *txnDoc `bson:"fullDocument"`
UpdateDescription *updateDescription `bson:"updateDescription"`
TxnNumber int64 `bson:"txnNumber"`
}
type updateDescription struct {
UpdatedFields txnDoc `bson:"updatedFields"`
}
type nsRef struct {
Database string `bson:"db"`
Collection string `bson:"coll"`
}
type docKey struct {
Id any `bson:"_id"`
}
type txnDoc struct {
Revno int64 `bson:"txn-revno"`
}
type cursorData struct {
FirstBatch []bson.Raw `bson:"firstBatch"`
NextBatch []bson.Raw `bson:"nextBatch"`
Ns string `bson:"ns"`
Id int64 `bson:"id"`
PostBatchResumeToken bson.Raw `bson:"postBatchResumeToken"`
}
type aggregateResponse struct {
Ok bool
Cursor cursorData
}
func isCursorNotFoundError(err error) bool {
code := 0
switch e := err.(type) {
case *mgo.LastError:
code = e.Code
case *mgo.QueryError:
code = e.Code
}
switch code {
case 43: // CursorNotFound
return true
}
return false
}
func isFatalGetMoreError(err error) bool {
code := 0
switch e := err.(type) {
case *mgo.LastError:
code = e.Code
case *mgo.QueryError:
code = e.Code
}
switch code {
case
6, // HostUnreachable
7, // HostNotFound
89, // NetworkTimeout
91, // ShutdownInProgress
189, // PrimarySteppedDown
262, // ExceededTimeLimit
9001, // SocketException
10107, // NotWritablePrimary
11600, // InterruptedAtShutdown
11602, // InterruptedDueToReplStateChange
13435, // NotPrimaryNoSecondaryOk
13436, // NotPrimaryOrSecondary
63, // StaleShardVersion
150, // StaleEpoch
13388, // StaleConfig
234, // RetryChangeStream
133: // FailedToSatisfyReadPreference
return true
}
return false
}
const (
FatalChangeStreamError errors.ConstError = "fatal change stream error"
ResumableChangeStreamError errors.ConstError = "resumable change stream error"
)