// startStats blocks and periodically logs transaction statistics (throughput,
// success rates, durations, ...). Note that this only captures write txns,
// since read-only txns are stateless as far as TxnCoordSender is concerned.
// stats).
func (tc *TxnCoordSender) startStats() {
	res := time.Millisecond // for duration logging resolution
	var statusLogTimer util.Timer
	defer statusLogTimer.Stop()
	scale := metric.Scale1M
	for {
		statusLogTimer.Reset(statusLogInterval)
		select {
		case <-statusLogTimer.C:
			statusLogTimer.Read = true
			if !log.V(1) {
				continue
			}

			// Take a snapshot of metrics. There's some chance of skew, since the snapshots are
			// not done atomically, but that should be fine for these debug stats.
			metrics := tc.metrics
			durations := metrics.Durations[scale].Current()
			restarts := metrics.Restarts.Current()
			commitRate := metrics.Commits.Rates[scale].Value()
			commit1PCRate := metrics.Commits1PC.Rates[scale].Value()
			abortRate := metrics.Aborts.Rates[scale].Value()
			abandonRate := metrics.Abandons.Rates[scale].Value()

			// Show transaction stats over the last minute. Maybe this should be shorter in the future.
			// We'll revisit if we get sufficient feedback.
			totalRate := commitRate + abortRate + abandonRate
			var pCommitted, pCommitted1PC, pAbandoned, pAborted float64
			if totalRate > 0 {
				pCommitted = 100 * (commitRate / totalRate)
				pCommitted1PC = 100 * (commit1PCRate / totalRate)
				pAborted = 100 * (abortRate / totalRate)
				pAbandoned = 100 * (abandonRate / totalRate)
			}

			dMean := durations.Mean()
			dDev := durations.StdDev()
			dMax := durations.Max()
			rMean := restarts.Mean()
			rDev := restarts.StdDev()
			rMax := restarts.Max()
			num := durations.TotalCount()

			log.Infof(
				"txn coordinator: %.2f txn/sec, %.2f/%.2f/%.2f/%.2f %%cmmt/cmmt1pc/abrt/abnd, %s/%s/%s avg/σ/max duration, %.1f/%.1f/%d avg/σ/max restarts (%d samples)",
				totalRate, pCommitted, pCommitted1PC, pAborted, pAbandoned,
				util.TruncateDuration(time.Duration(dMean), res),
				util.TruncateDuration(time.Duration(dDev), res),
				util.TruncateDuration(time.Duration(dMax), res),
				rMean, rDev, rMax, num,
			)

		case <-tc.stopper.ShouldStop():
			return
		}
	}
}

// startStats blocks and periodically logs transaction statistics (throughput,
// success rates, durations, ...).
// TODO(tschottdorf): Use a proper metrics subsystem for this (+the store-level
// stats).
// TODO(mrtracy): Add this to TimeSeries.
func (tc *TxnCoordSender) startStats() {
	res := time.Millisecond // for duration logging resolution
	lastNow := tc.clock.PhysicalNow()
	for {
		select {
		case <-time.After(statusLogInterval):
			if !log.V(1) {
				continue
			}

			tc.Lock()
			curStats := tc.txnStats
			tc.txnStats = txnCoordStats{}
			tc.Unlock()

			now := tc.clock.PhysicalNow()

			// Tests have weird clocks.
			if now-lastNow <= 0 {
				continue
			}

			num := len(curStats.durations)
			dMax := time.Duration(stats.Max(curStats.durations))
			dMean := time.Duration(stats.Mean(curStats.durations))
			dDev := time.Duration(stats.StdDevP(curStats.durations))
			rMax := stats.Max(curStats.restarts)
			rMean := stats.Mean(curStats.restarts)
			rDev := stats.StdDevP(curStats.restarts)

			rate := float64(int64(num)*int64(time.Second)) / float64(now-lastNow)
			var pCommitted, pAbandoned, pAborted float32
			if num > 0 {
				pCommitted = 100 * float32(curStats.committed) / float32(num)
				pAbandoned = 100 * float32(curStats.abandoned) / float32(num)
				pAborted = 100 * float32(curStats.aborted) / float32(num)
			}
			log.Infof("txn coordinator: %.2f txn/sec, %.2f/%.2f/%.2f %%cmmt/abrt/abnd, %s/%s/%s avg/σ/max duration, %.1f/%.1f/%.1f avg/σ/max restarts (%d samples)",
				rate, pCommitted, pAborted, pAbandoned, util.TruncateDuration(dMean, res),
				util.TruncateDuration(dDev, res), util.TruncateDuration(dMax, res),
				rMean, rDev, rMax, num)
			lastNow = now
		case <-tc.stopper.ShouldStop():
			return
		}
	}
}

//.........这里部分代码省略.........
					trace.Event("coordinator spawns")
					txnMeta = &txnMetadata{
						txn:              *txn,
						keys:             cache.NewIntervalCache(cache.Config{Policy: cache.CacheNone}),
						firstUpdateNanos: tc.clock.PhysicalNow(),
						lastUpdateNanos:  tc.clock.PhysicalNow(),
						timeoutDuration:  tc.clientTimeout,
						txnEnd:           make(chan struct{}),
					}
					tc.txns[id] = txnMeta
					if !tc.stopper.RunAsyncTask(func() {
						tc.heartbeatLoop(id)
					}) {
						// The system is already draining and we can't start the
						// heartbeat. We refuse new transactions for now because
						// they're likely not going to have all intents committed.
						// In principle, we can relax this as needed though.
						call.Reply.Header().SetGoError(&proto.NodeUnavailableError{})
						tc.Unlock()
						tc.unregisterTxn(id)
						return
					}
				}
				txnMeta.addKeyRange(header.Key, header.EndKey)
			}
			// Update our record of this transaction.
			if txnMeta != nil {
				txnMeta.txn = *txn
				txnMeta.setLastUpdate(tc.clock.PhysicalNow())
			}
		}
		tc.Unlock()
	}

	// Cleanup intents and transaction map if end of transaction.
	switch t := call.Reply.Header().GoError().(type) {
	case *proto.TransactionStatusError:
		// Likely already committed or more obscure errors such as epoch or
		// timestamp regressions; consider it dead.
		tc.cleanupTxn(trace, t.Txn)
	case *proto.TransactionAbortedError:
		// If already aborted, cleanup the txn on this TxnCoordSender.
		tc.cleanupTxn(trace, t.Txn)
	case *proto.OpRequiresTxnError:
		// Run a one-off transaction with that single command.
		if log.V(1) {
			log.Infof("%s: auto-wrapping in txn and re-executing", call.Method())
		}
		// TODO(tschottdorf): this part is awkward. Consider resending here
		// without starting a new call, which is hard to trace. Plus, the
		// below depends on default configuration.
		tmpDB, err := client.Open(
			fmt.Sprintf("//%s?priority=%d",
				call.Args.Header().User, call.Args.Header().GetUserPriority()),
			client.SenderOpt(tc))
		if err != nil {
			log.Warning(err)
			return
		}
		call.Reply.Reset()
		if err := tmpDB.Txn(func(txn *client.Txn) error {
			txn.SetDebugName("auto-wrap", 0)
			b := &client.Batch{}
			b.InternalAddCall(call)
			return txn.CommitInBatch(b)
		}); err != nil {
			log.Warning(err)
		}
	case nil:
		if txn := call.Reply.Header().Txn; txn != nil {
			if _, ok := call.Args.(*proto.EndTransactionRequest); ok {
				// If the --linearizable flag is set, we want to make sure that
				// all the clocks in the system are past the commit timestamp
				// of the transaction. This is guaranteed if either
				// - the commit timestamp is MaxOffset behind startNS
				// - MaxOffset ns were spent in this function
				// when returning to the client. Below we choose the option
				// that involves less waiting, which is likely the first one
				// unless a transaction commits with an odd timestamp.
				if tsNS := txn.Timestamp.WallTime; startNS > tsNS {
					startNS = tsNS
				}
				sleepNS := tc.clock.MaxOffset() -
					time.Duration(tc.clock.PhysicalNow()-startNS)
				if tc.linearizable && sleepNS > 0 {
					defer func() {
						if log.V(1) {
							log.Infof("%v: waiting %s on EndTransaction for linearizability", txn.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
						}
						time.Sleep(sleepNS)
					}()
				}
				if txn.Status != proto.PENDING {
					tc.cleanupTxn(trace, *txn)
				}

			}
		}
	}
}

// startStats blocks and periodically logs transaction statistics (throughput,
// success rates, durations, ...). Note that this only captures write txns,
// since read-only txns are stateless as far as TxnCoordSender is concerned.
// stats).
// TODO(mrtracy): Add this to TimeSeries.
func (tc *TxnCoordSender) startStats() {
	res := time.Millisecond // for duration logging resolution
	lastNow := tc.clock.PhysicalNow()
	for {
		select {
		case <-time.After(statusLogInterval):
			if !log.V(1) {
				continue
			}

			tc.Lock()
			curStats := tc.txnStats
			tc.txnStats = txnCoordStats{}
			tc.Unlock()

			now := tc.clock.PhysicalNow()

			// Tests have weird clocks.
			if now-lastNow <= 0 {
				continue
			}

			num := len(curStats.durations)
			// Only compute when non-empty input.
			var dMax, dMean, dDev, rMax, rMean, rDev float64
			var err error
			if num > 0 {
				// There should never be an error in the below
				// computations.
				dMax, err = stats.Max(curStats.durations)
				if err != nil {
					panic(err)
				}
				dMean, err = stats.Mean(curStats.durations)
				if err != nil {
					panic(err)
				}
				dDev, err = stats.StdDevP(curStats.durations)
				if err != nil {
					panic(err)
				}
				rMax, err = stats.Max(curStats.restarts)
				if err != nil {
					panic(err)
				}
				rMean, err = stats.Mean(curStats.restarts)
				if err != nil {
					panic(err)
				}
				rDev, err = stats.StdDevP(curStats.restarts)
				if err != nil {
					panic(err)
				}
			}

			rate := float64(int64(num)*int64(time.Second)) / float64(now-lastNow)
			var pCommitted, pAbandoned, pAborted float32

			if fNum := float32(num); fNum > 0 {
				pCommitted = 100 * float32(curStats.committed) / fNum
				pAbandoned = 100 * float32(curStats.abandoned) / fNum
				pAborted = 100 * float32(curStats.aborted) / fNum
			}
			log.Infof(
				"txn coordinator: %.2f txn/sec, %.2f/%.2f/%.2f %%cmmt/abrt/abnd, %s/%s/%s avg/σ/max duration, %.1f/%.1f/%.1f avg/σ/max restarts (%d samples)",
				rate, pCommitted, pAborted, pAbandoned,
				util.TruncateDuration(time.Duration(dMean), res),
				util.TruncateDuration(time.Duration(dDev), res),
				util.TruncateDuration(time.Duration(dMax), res),
				rMean, rDev, rMax, num,
			)
			lastNow = now
		case <-tc.stopper.ShouldStop():
			return
		}
	}
}

//.........这里部分代码省略.........
			et.Key = ba.Txn.Key
			// Remember when EndTransaction started in case we want to
			// be linearizable.
			startNS = tc.clock.PhysicalNow()
			if len(et.Intents) > 0 {
				// TODO(tschottdorf): it may be useful to allow this later.
				// That would be part of a possible plan to allow txns which
				// write on multiple coordinators.
				return nil, roachpb.NewError(util.Errorf("client must not pass intents to EndTransaction"))
			}
			tc.Lock()
			txnMeta, metaOK := tc.txns[id]
			if id != "" && metaOK {
				et.Intents = txnMeta.intents()
			}
			tc.Unlock()

			if intents := ba.GetIntents(); len(intents) > 0 {
				// Writes in Batch, so EndTransaction is fine. Should add
				// outstanding intents to EndTransaction, though.
				// TODO(tschottdorf): possible issues when the batch fails,
				// but the intents have been added anyways.
				// TODO(tschottdorf): some of these intents may be covered
				// by others, for example {[a,b), a}). This can lead to
				// some extra requests when those are non-local to the txn
				// record. But it doesn't seem worth optimizing now.
				et.Intents = append(et.Intents, intents...)
			} else if !metaOK {
				// If we don't have the transaction, then this must be a retry
				// by the client. We can no longer reconstruct a correct
				// request so we must fail.
				//
				// TODO(bdarnell): if we had a GetTransactionStatus API then
				// we could lookup the transaction and return either nil or
				// TransactionAbortedError instead of this ambivalent error.
				return nil, roachpb.NewError(util.Errorf("transaction is already committed or aborted"))
			}
			if len(et.Intents) == 0 {
				// If there aren't any intents, then there's factually no
				// transaction to end. Read-only txns have all of their state in
				// the client.
				return nil, roachpb.NewError(util.Errorf("cannot commit a read-only transaction"))
			}
			if log.V(1) {
				for _, intent := range et.Intents {
					trace.Event(fmt.Sprintf("intent: [%s,%s)", intent.Key, intent.EndKey))
				}
			}
		}
	}

	// Send the command through wrapped sender, taking appropriate measures
	// on error.
	var br *roachpb.BatchResponse
	{
		var pErr *roachpb.Error
		br, pErr = tc.wrapped.Send(ctx, ba)

		if _, ok := pErr.GoError().(*roachpb.OpRequiresTxnError); ok {
			br, pErr = tc.resendWithTxn(ba)
		}

		if pErr := tc.updateState(ctx, ba, br, pErr); pErr != nil {
			return nil, pErr
		}
	}

	if br.Txn == nil {
		return br, nil
	}

	if _, ok := ba.GetArg(roachpb.EndTransaction); !ok {
		return br, nil
	}
	// If the --linearizable flag is set, we want to make sure that
	// all the clocks in the system are past the commit timestamp
	// of the transaction. This is guaranteed if either
	// - the commit timestamp is MaxOffset behind startNS
	// - MaxOffset ns were spent in this function
	// when returning to the client. Below we choose the option
	// that involves less waiting, which is likely the first one
	// unless a transaction commits with an odd timestamp.
	if tsNS := br.Txn.Timestamp.WallTime; startNS > tsNS {
		startNS = tsNS
	}
	sleepNS := tc.clock.MaxOffset() -
		time.Duration(tc.clock.PhysicalNow()-startNS)
	if tc.linearizable && sleepNS > 0 {
		defer func() {
			if log.V(1) {
				log.Infof("%v: waiting %s on EndTransaction for linearizability", br.Txn.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
			}
			time.Sleep(sleepNS)
		}()
	}
	if br.Txn.Status != roachpb.PENDING {
		tc.cleanupTxn(trace, *br.Txn)
	}
	return br, nil
}

//.........这里部分代码省略.........
				// That would be part of a possible plan to allow txns which
				// write on multiple coordinators.
				return nil, roachpb.NewErrorf("client must not pass intents to EndTransaction")
			}
			tc.Lock()
			txnMeta, metaOK := tc.txns[txnID]
			{
				// Populate et.IntentSpans, taking into account both existing
				// writes (if any) and new writes in this batch, and taking
				// care to perform proper deduplication.
				var keys interval.RangeGroup
				if metaOK {
					keys = txnMeta.keys
				} else {
					keys = interval.NewRangeTree()
				}
				ba.IntentSpanIterate(func(key, endKey roachpb.Key) {
					addKeyRange(keys, key, endKey)
				})
				et.IntentSpans = collectIntentSpans(keys)
			}
			tc.Unlock()

			if len(et.IntentSpans) > 0 {
				// All good, proceed.
			} else if !metaOK {
				// If we don't have the transaction, then this must be a retry
				// by the client. We can no longer reconstruct a correct
				// request so we must fail.
				//
				// TODO(bdarnell): if we had a GetTransactionStatus API then
				// we could lookup the transaction and return either nil or
				// TransactionAbortedError instead of this ambivalent error.
				return nil, roachpb.NewErrorf("transaction is already committed or aborted")
			}
			if len(et.IntentSpans) == 0 {
				// If there aren't any intents, then there's factually no
				// transaction to end. Read-only txns have all of their state in
				// the client.
				return nil, roachpb.NewErrorf("cannot commit a read-only transaction")
			}
			if log.V(1) {
				for _, intent := range et.IntentSpans {
					log.Trace(ctx, fmt.Sprintf("intent: [%s,%s)", intent.Key, intent.EndKey))
				}
			}
		}
	}

	// Send the command through wrapped sender, taking appropriate measures
	// on error.
	var br *roachpb.BatchResponse
	{
		var pErr *roachpb.Error
		br, pErr = tc.wrapped.Send(ctx, ba)

		if _, ok := pErr.GetDetail().(*roachpb.OpRequiresTxnError); ok {
			// TODO(tschottdorf): needs to keep the trace.
			br, pErr = tc.resendWithTxn(ba)
		}

		if pErr = tc.updateState(startNS, ctx, ba, br, pErr); pErr != nil {
			log.Trace(ctx, fmt.Sprintf("error: %s", pErr))
			return nil, pErr
		}
	}

	if br.Txn == nil {
		return br, nil
	}

	if _, ok := ba.GetArg(roachpb.EndTransaction); !ok {
		return br, nil
	}
	// If the --linearizable flag is set, we want to make sure that
	// all the clocks in the system are past the commit timestamp
	// of the transaction. This is guaranteed if either
	// - the commit timestamp is MaxOffset behind startNS
	// - MaxOffset ns were spent in this function
	// when returning to the client. Below we choose the option
	// that involves less waiting, which is likely the first one
	// unless a transaction commits with an odd timestamp.
	if tsNS := br.Txn.Timestamp.WallTime; startNS > tsNS {
		startNS = tsNS
	}
	sleepNS := tc.clock.MaxOffset() -
		time.Duration(tc.clock.PhysicalNow()-startNS)
	if tc.linearizable && sleepNS > 0 {
		defer func() {
			if log.V(1) {
				log.Infof("%v: waiting %s on EndTransaction for linearizability", br.Txn.ID.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
			}
			time.Sleep(sleepNS)
		}()
	}
	if br.Txn.Status != roachpb.PENDING {
		tc.cleanupTxn(ctx, *br.Txn)
	}
	return br, nil
}

//.........这里部分代码省略.........

			// Populate et.IntentSpans, taking into account both any existing
			// and new writes, and taking care to perform proper deduplication.
			txnMeta := tc.txns[*ba.Txn.ID]
			distinctSpans := true
			if txnMeta != nil {
				et.IntentSpans = txnMeta.keys
				// Defensively set distinctSpans to false if we had any previous
				// requests in this transaction. This effectively limits the distinct
				// spans optimization to 1pc transactions.
				distinctSpans = len(txnMeta.keys) == 0
			}
			ba.IntentSpanIterate(func(key, endKey roachpb.Key) {
				et.IntentSpans = append(et.IntentSpans, roachpb.Span{
					Key:    key,
					EndKey: endKey,
				})
			})
			// TODO(peter): Populate DistinctSpans on all batches, not just batches
			// which contain an EndTransactionRequest.
			var distinct bool
			// The request might already be used by an outgoing goroutine, so
			// we can't safely mutate anything in-place (as MergeSpans does).
			et.IntentSpans = append([]roachpb.Span(nil), et.IntentSpans...)
			et.IntentSpans, distinct = roachpb.MergeSpans(et.IntentSpans)
			ba.Header.DistinctSpans = distinct && distinctSpans
			if len(et.IntentSpans) == 0 {
				// If there aren't any intents, then there's factually no
				// transaction to end. Read-only txns have all of their state
				// in the client.
				return roachpb.NewErrorf("cannot commit a read-only transaction")
			}
			if txnMeta != nil {
				txnMeta.keys = et.IntentSpans
			}
			return nil
		}(); pErr != nil {
			return nil, pErr
		}

		if hasET && log.V(1) {
			for _, intent := range et.IntentSpans {
				log.Tracef(ctx, "intent: [%s,%s)", intent.Key, intent.EndKey)
			}
		}
	}

	// Send the command through wrapped sender, taking appropriate measures
	// on error.
	var br *roachpb.BatchResponse
	{
		var pErr *roachpb.Error
		br, pErr = tc.wrapped.Send(ctx, ba)

		if _, ok := pErr.GetDetail().(*roachpb.OpRequiresTxnError); ok {
			// TODO(tschottdorf): needs to keep the trace.
			br, pErr = tc.resendWithTxn(ba)
		}

		if pErr = tc.updateState(startNS, ctx, ba, br, pErr); pErr != nil {
			log.Tracef(ctx, "error: %s", pErr)
			return nil, pErr
		}
	}

	if br.Txn == nil {
		return br, nil
	}

	if _, ok := ba.GetArg(roachpb.EndTransaction); !ok {
		return br, nil
	}
	// If the --linearizable flag is set, we want to make sure that
	// all the clocks in the system are past the commit timestamp
	// of the transaction. This is guaranteed if either
	// - the commit timestamp is MaxOffset behind startNS
	// - MaxOffset ns were spent in this function
	// when returning to the client. Below we choose the option
	// that involves less waiting, which is likely the first one
	// unless a transaction commits with an odd timestamp.
	if tsNS := br.Txn.Timestamp.WallTime; startNS > tsNS {
		startNS = tsNS
	}
	sleepNS := tc.clock.MaxOffset() -
		time.Duration(tc.clock.PhysicalNow()-startNS)
	if tc.linearizable && sleepNS > 0 {
		defer func() {
			if log.V(1) {
				log.Infof(ctx, "%v: waiting %s on EndTransaction for linearizability", br.Txn.ID.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
			}
			time.Sleep(sleepNS)
		}()
	}
	if br.Txn.Status != roachpb.PENDING {
		tc.Lock()
		tc.cleanupTxnLocked(ctx, *br.Txn)
		tc.Unlock()
	}
	return br, nil
}

//.........这里部分代码省略.........
		tc.updateResponseTxn(header, call.Reply.Header())
	}

	if txn := call.Reply.Header().Txn; txn != nil {
		tc.Lock()
		txnMeta := tc.txns[string(txn.ID)]
		// If this transactional command leaves transactional intents, add the key
		// or key range to the intents map. If the transaction metadata doesn't yet
		// exist, create it.
		if call.Reply.Header().GoError() == nil {
			if proto.IsTransactionWrite(call.Args) {
				if txnMeta == nil {
					txnMeta = &txnMetadata{
						txn:              *txn,
						keys:             cache.NewIntervalCache(cache.Config{Policy: cache.CacheNone}),
						firstUpdateNanos: tc.clock.PhysicalNow(),
						lastUpdateNanos:  tc.clock.PhysicalNow(),
						timeoutDuration:  tc.clientTimeout,
						txnEnd:           make(chan struct{}),
					}
					id := string(txn.ID)
					tc.txns[id] = txnMeta
					tc.heartbeat(id)
				}
				txnMeta.addKeyRange(header.Key, header.EndKey)
			}
			// Update our record of this transaction.
			if txnMeta != nil {
				txnMeta.txn = *txn
				txnMeta.setLastUpdate(tc.clock.PhysicalNow())
			}
		}
		tc.Unlock()
	}

	// Cleanup intents and transaction map if end of transaction.
	switch t := call.Reply.Header().GoError().(type) {
	case *proto.TransactionStatusError:
		// Likely already committed or more obscure errors such as epoch or
		// timestamp regressions; consider it dead.
		tc.cleanupTxn(t.Txn, nil)
	case *proto.TransactionAbortedError:
		// If already aborted, cleanup the txn on this TxnCoordSender.
		tc.cleanupTxn(t.Txn, nil)
	case *proto.OpRequiresTxnError:
		// Run a one-off transaction with that single command.
		if log.V(1) {
			log.Infof("%s: auto-wrapping in txn and re-executing", call.Method())
		}
		tmpDB, err := client.Open(
			fmt.Sprintf("//%s?priority=%d",
				call.Args.Header().User, call.Args.Header().GetUserPriority()),
			client.SenderOpt(tc))
		if err != nil {
			log.Warning(err)
			return
		}
		call.Reply.Reset()
		if err := tmpDB.Txn(func(txn *client.Txn) error {
			txn.SetDebugName("auto-wrap")
			b := &client.Batch{}
			b.InternalAddCall(call)
			return txn.Commit(b)
		}); err != nil {
			log.Warning(err)
		}
	case nil:
		var resolved []proto.Key
		if txn := call.Reply.Header().Txn; txn != nil {
			if _, ok := call.Args.(*proto.EndTransactionRequest); ok {
				// If the --linearizable flag is set, we want to make sure that
				// all the clocks in the system are past the commit timestamp
				// of the transaction. This is guaranteed if either
				// - the commit timestamp is MaxOffset behind startNS
				// - MaxOffset ns were spent in this function
				// when returning to the client. Below we choose the option
				// that involves less waiting, which is likely the first one
				// unless a transaction commits with an odd timestamp.
				if tsNS := txn.Timestamp.WallTime; startNS > tsNS {
					startNS = tsNS
				}
				sleepNS := tc.clock.MaxOffset() -
					time.Duration(tc.clock.PhysicalNow()-startNS)
				if tc.linearizable && sleepNS > 0 {
					defer func() {
						if log.V(1) {
							log.Infof("%v: waiting %s on EndTransaction for linearizability", txn.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
						}
						time.Sleep(sleepNS)
					}()
				}
				resolved = call.Reply.(*proto.EndTransactionResponse).Resolved
				if txn.Status != proto.PENDING {
					tc.cleanupTxn(*txn, resolved)
				}

			}
		}
	}
}

//.........这里部分代码省略.........
			// be linearizable.
			startNS = tc.clock.PhysicalNow()
			if len(et.IntentSpans) > 0 {
				// TODO(tschottdorf): it may be useful to allow this later.
				// That would be part of a possible plan to allow txns which
				// write on multiple coordinators.
				return nil, roachpb.NewErrorf("client must not pass intents to EndTransaction")
			}
			tc.Lock()
			txnMeta, metaOK := tc.txns[txnID]
			if metaOK {
				et.IntentSpans = txnMeta.intentSpans()
			}
			tc.Unlock()

			if intentSpans := ba.GetIntentSpans(); len(intentSpans) > 0 {
				// Writes in Batch, so EndTransaction is fine. Should add
				// outstanding intents to EndTransaction, though.
				// TODO(tschottdorf): possible issues when the batch fails,
				// but the intents have been added anyways.
				// TODO(tschottdorf): some of these intents may be covered
				// by others, for example {[a,b), a}). This can lead to
				// some extra requests when those are non-local to the txn
				// record. But it doesn't seem worth optimizing now.
				et.IntentSpans = append(et.IntentSpans, intentSpans...)
			} else if !metaOK {
				// If we don't have the transaction, then this must be a retry
				// by the client. We can no longer reconstruct a correct
				// request so we must fail.
				//
				// TODO(bdarnell): if we had a GetTransactionStatus API then
				// we could lookup the transaction and return either nil or
				// TransactionAbortedError instead of this ambivalent error.
				return nil, roachpb.NewErrorf("transaction is already committed or aborted")
			}
			if len(et.IntentSpans) == 0 {
				// If there aren't any intents, then there's factually no
				// transaction to end. Read-only txns have all of their state in
				// the client.
				return nil, roachpb.NewErrorf("cannot commit a read-only transaction")
			}
			if log.V(1) {
				for _, intent := range et.IntentSpans {
					sp.LogEvent(fmt.Sprintf("intent: [%s,%s)", intent.Key, intent.EndKey))
				}
			}
		}
	}

	// Send the command through wrapped sender, taking appropriate measures
	// on error.
	var br *roachpb.BatchResponse
	{
		var pErr *roachpb.Error
		br, pErr = tc.wrapped.Send(ctx, ba)

		if _, ok := pErr.GetDetail().(*roachpb.OpRequiresTxnError); ok {
			// TODO(tschottdorf): needs to keep the trace.
			br, pErr = tc.resendWithTxn(ba)
		}

		if pErr = tc.updateState(ctx, ba, br, pErr); pErr != nil {
			sp.LogEvent(fmt.Sprintf("error: %s", pErr))
			return nil, pErr
		}
	}

	if br.Txn == nil {
		return br, nil
	}

	if _, ok := ba.GetArg(roachpb.EndTransaction); !ok {
		return br, nil
	}
	// If the --linearizable flag is set, we want to make sure that
	// all the clocks in the system are past the commit timestamp
	// of the transaction. This is guaranteed if either
	// - the commit timestamp is MaxOffset behind startNS
	// - MaxOffset ns were spent in this function
	// when returning to the client. Below we choose the option
	// that involves less waiting, which is likely the first one
	// unless a transaction commits with an odd timestamp.
	if tsNS := br.Txn.Timestamp.WallTime; startNS > tsNS {
		startNS = tsNS
	}
	sleepNS := tc.clock.MaxOffset() -
		time.Duration(tc.clock.PhysicalNow()-startNS)
	if tc.linearizable && sleepNS > 0 {
		defer func() {
			if log.V(1) {
				log.Infof("%v: waiting %s on EndTransaction for linearizability", br.Txn.Short(), util.TruncateDuration(sleepNS, time.Millisecond))
			}
			time.Sleep(sleepNS)
		}()
	}
	if br.Txn.Status != roachpb.PENDING {
		tc.cleanupTxn(sp, *br.Txn)
	}
	return br, nil
}