// maybeRejectClientLocked checks whether the (transactional) request is in a
// state that prevents it from continuing, such as the coordinator having
// considered the client abandoned, or a heartbeat having reported an error.
func (tc *TxnCoordSender) maybeRejectClientLocked(
	ctx context.Context, txn roachpb.Transaction,
) *roachpb.Error {

	if !txn.Writing {
		return nil
	}
	txnMeta, ok := tc.txns[*txn.ID]
	// Check whether the transaction is still tracked and has a chance of
	// completing. It's possible that the coordinator learns about the
	// transaction having terminated from a heartbeat, and GC queue correctness
	// (along with common sense) mandates that we don't let the client
	// continue.
	switch {
	case !ok:
		log.VEventf(ctx, 2, "rejecting unknown txn: %s", txn.ID)
		// TODO(spencerkimball): Could add coordinator node ID to the
		// transaction session so that we can definitively return the right
		// error between these possible errors. Or update the code to make an
		// educated guess based on the incoming transaction timestamp.
		return roachpb.NewError(errNoState)
	case txnMeta.txn.Status == roachpb.ABORTED:
		txn := txnMeta.txn.Clone()
		tc.cleanupTxnLocked(ctx, txn)
		return roachpb.NewErrorWithTxn(roachpb.NewTransactionAbortedError(),
			&txn)
	case txnMeta.txn.Status == roachpb.COMMITTED:
		txn := txnMeta.txn.Clone()
		tc.cleanupTxnLocked(ctx, txn)
		return roachpb.NewErrorWithTxn(roachpb.NewTransactionStatusError(
			"transaction is already committed"), &txn)
	default:
		return nil
	}
}

// TestEndWriteRestartReadOnlyTransaction verifies that if
// a transaction writes, then restarts and turns read-only,
// an explicit EndTransaction call is still sent if retry-
// able didn't, regardless of whether there is an error
// or not.
func TestEndWriteRestartReadOnlyTransaction(t *testing.T) {
	defer leaktest.AfterTest(t)()
	for _, success := range []bool{true, false} {
		expCalls := []roachpb.Method{roachpb.BeginTransaction, roachpb.Put, roachpb.EndTransaction}
		var calls []roachpb.Method
		db := NewDB(newTestSender(func(ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {
			calls = append(calls, ba.Methods()...)
			return ba.CreateReply(), nil
		}, nil))
		ok := false
		if err := db.Txn(context.TODO(), func(txn *Txn) error {
			if !ok {
				if err := txn.Put("consider", "phlebas"); err != nil {
					t.Fatal(err)
				}
				ok = true
				// Return an immediate txn retry error. We need to go through the pErr
				// and back to get a RetryableTxnError.
				return roachpb.NewErrorWithTxn(roachpb.NewTransactionRetryError(), &txn.Proto).GoError()
			}
			if !success {
				return errors.New("aborting on purpose")
			}
			return nil
		}); err == nil != success {
			t.Errorf("expected error: %t, got error: %v", !success, err)
		}
		if !reflect.DeepEqual(expCalls, calls) {
			t.Fatalf("expected %v, got %v", expCalls, calls)
		}
	}
}

// TestNonRetryableErrorOnCommit verifies that a non-retryable error from the
// execution of EndTransactionRequests is propagated to the client.
func TestNonRetryableErrorOnCommit(t *testing.T) {
	defer leaktest.AfterTest(t)()

	params, cmdFilters := createTestServerParams()
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()

	hitError := false
	cleanupFilter := cmdFilters.AppendFilter(
		func(args storagebase.FilterArgs) *roachpb.Error {
			if req, ok := args.Req.(*roachpb.EndTransactionRequest); ok {
				if bytes.Contains(req.Key, []byte(keys.DescIDGenerator)) {
					hitError = true
					return roachpb.NewErrorWithTxn(fmt.Errorf("testError"), args.Hdr.Txn)
				}
			}
			return nil
		}, false)
	defer cleanupFilter()

	if _, err := sqlDB.Exec("CREATE DATABASE t"); !testutils.IsError(err, "pq: testError") {
		t.Errorf("unexpected error %v", err)
	}
	if !hitError {
		t.Errorf("expected to hit error, but it didn't happen")
	}
}

// Tests that a retryable error for an inner txn doesn't cause the outer txn to
// be retried.
func TestWrongTxnRetry(t *testing.T) {
	defer leaktest.AfterTest(t)()
	db := NewDB(newTestSender(nil, nil))

	var retries int
	txnClosure := func(outerTxn *Txn) error {
		log.Infof(context.Background(), "outer retry")
		retries++
		// Ensure the KV transaction is created.
		if err := outerTxn.Put("a", "b"); err != nil {
			t.Fatal(err)
		}
		var execOpt TxnExecOptions
		execOpt.AutoRetry = false
		err := outerTxn.Exec(
			execOpt,
			func(innerTxn *Txn, opt *TxnExecOptions) error {
				// Ensure the KV transaction is created.
				if err := innerTxn.Put("x", "y"); err != nil {
					t.Fatal(err)
				}
				return roachpb.NewErrorWithTxn(&roachpb.TransactionPushError{
					PusheeTxn: outerTxn.Proto}, &innerTxn.Proto).GoError()
			})
		return err
	}

	if err := db.Txn(context.TODO(), txnClosure); !testutils.IsError(err, "failed to push") {
		t.Fatal(err)
	}
	if retries != 1 {
		t.Fatalf("unexpected retries: %d", retries)
	}
}

func TestAbortCountConflictingWrites(t *testing.T) {
	defer leaktest.AfterTest(t)()

	params, cmdFilters := createTestServerParams()
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()

	if _, err := sqlDB.Exec("CREATE DATABASE db"); err != nil {
		t.Fatal(err)
	}
	if _, err := sqlDB.Exec("CREATE TABLE db.t (k TEXT PRIMARY KEY, v TEXT)"); err != nil {
		t.Fatal(err)
	}

	// Inject errors on the INSERT below.
	restarted := false
	cmdFilters.AppendFilter(func(args storagebase.FilterArgs) *roachpb.Error {
		switch req := args.Req.(type) {
		// SQL INSERT generates ConditionalPuts for unique indexes (such as the PK).
		case *roachpb.ConditionalPutRequest:
			if bytes.Contains(req.Value.RawBytes, []byte("marker")) && !restarted {
				restarted = true
				return roachpb.NewErrorWithTxn(
					roachpb.NewTransactionAbortedError(), args.Hdr.Txn)
			}
		}
		return nil
	}, false)

	txn, err := sqlDB.Begin()
	if err != nil {
		t.Fatal(err)
	}
	_, err = txn.Exec("INSERT INTO db.t VALUES ('key', 'marker')")
	if !testutils.IsError(err, "aborted") {
		t.Fatal(err)
	}

	if err = txn.Rollback(); err != nil {
		t.Fatal(err)
	}

	if err := checkCounterEQ(s, sql.MetaTxnAbort, 1); err != nil {
		t.Error(err)
	}
	if err := checkCounterEQ(s, sql.MetaTxnBegin, 1); err != nil {
		t.Error(err)
	}
	if err := checkCounterEQ(s, sql.MetaTxnRollback, 0); err != nil {
		t.Error(err)
	}
	if err := checkCounterEQ(s, sql.MetaTxnCommit, 0); err != nil {
		t.Error(err)
	}
	if err := checkCounterEQ(s, sql.MetaInsert, 1); err != nil {
		t.Error(err)
	}
}

// TestRunTransactionRetryOnErrors verifies that the transaction
// is retried on the correct errors.
func TestRunTransactionRetryOnErrors(t *testing.T) {
	defer leaktest.AfterTest(t)()
	testCases := []struct {
		err   error
		retry bool // Expect retry?
	}{
		{roachpb.NewReadWithinUncertaintyIntervalError(hlc.ZeroTimestamp, hlc.ZeroTimestamp), true},
		{&roachpb.TransactionAbortedError{}, true},
		{&roachpb.TransactionPushError{}, true},
		{&roachpb.TransactionRetryError{}, true},
		{&roachpb.WriteTooOldError{}, true},
		{&roachpb.RangeNotFoundError{}, false},
		{&roachpb.RangeKeyMismatchError{}, false},
		{&roachpb.TransactionStatusError{}, false},
	}

	for i, test := range testCases {
		count := 0
		dbCtx := DefaultDBContext()
		dbCtx.TxnRetryOptions.InitialBackoff = 1 * time.Millisecond
		db := NewDBWithContext(newTestSender(
			func(ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {

				if _, ok := ba.GetArg(roachpb.Put); ok {
					count++
					if count == 1 {
						return nil, roachpb.NewErrorWithTxn(test.err, ba.Txn)
					}
				}
				return ba.CreateReply(), nil
			}, nil), dbCtx)
		err := db.Txn(context.TODO(), func(txn *Txn) error {
			return txn.Put("a", "b")
		})
		if test.retry {
			if count != 2 {
				t.Errorf("%d: expected one retry; got %d", i, count-1)
			}
			if err != nil {
				t.Errorf("%d: expected success on retry; got %s", i, err)
			}
		} else {
			if count != 1 {
				t.Errorf("%d: expected no retries; got %d", i, count)
			}
			if reflect.TypeOf(err) != reflect.TypeOf(test.err) {
				t.Errorf("%d: expected error of type %T; got %T", i, test.err, err)
			}
		}
	}
}

// TestTxnResetTxnOnAbort verifies transaction is reset on abort.
func TestTxnResetTxnOnAbort(t *testing.T) {
	defer leaktest.AfterTest(t)()
	db := NewDB(newTestSender(func(ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {
		return nil, roachpb.NewErrorWithTxn(&roachpb.TransactionAbortedError{}, ba.Txn)
	}, nil))

	txn := NewTxn(context.Background(), *db)
	_, pErr := txn.sendInternal(testPut())
	if _, ok := pErr.GetDetail().(*roachpb.TransactionAbortedError); !ok {
		t.Fatalf("expected TransactionAbortedError, got %v", pErr)
	}

	if txn.Proto.ID != nil {
		t.Errorf("expected txn to be cleared")
	}
}

// TestTransactionKeyNotChangedInRestart verifies that if the transaction already has a key (we're
// in a restart), the key in the begin transaction request is not changed.
func TestTransactionKeyNotChangedInRestart(t *testing.T) {
	defer leaktest.AfterTest(t)()
	tries := 0
	db := NewDB(newTestSender(nil, func(ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {
		var bt *roachpb.BeginTransactionRequest
		if args, ok := ba.GetArg(roachpb.BeginTransaction); ok {
			bt = args.(*roachpb.BeginTransactionRequest)
		} else {
			t.Fatal("failed to find a begin transaction request")
		}

		// In the first try, the transaction key is the key of the first write command. Before the
		// second try, the transaction key is set to txnKey by the test sender. In the second try, the
		// transaction key is txnKey.
		var expectedKey roachpb.Key
		if tries == 1 {
			expectedKey = testKey
		} else {
			expectedKey = txnKey
		}
		if !bt.Key.Equal(expectedKey) {
			t.Fatalf("expected transaction key %v, got %v", expectedKey, bt.Key)
		}

		return ba.CreateReply(), nil
	}))

	if err := db.Txn(context.TODO(), func(txn *Txn) error {
		tries++
		b := txn.NewBatch()
		b.Put("a", "b")
		if err := txn.Run(b); err != nil {
			t.Fatal(err)
		}
		if tries == 1 {
			return roachpb.NewErrorWithTxn(roachpb.NewTransactionRetryError(), &txn.Proto).GoError()
		}
		return nil
	}); err != nil {
		t.Errorf("unexpected error on commit: %s", err)
	}
	minimumTries := 2
	if tries < minimumTries {
		t.Errorf("expected try count >= %d, got %d", minimumTries, tries)
	}
}

// TestNonRetryableError verifies that a non-retryable error is propagated to the client.
func TestNonRetryableError(t *testing.T) {
	defer leaktest.AfterTest(t)()

	params, cmdFilters := createTestServerParams()
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()

	testKey := []byte("test_key")
	hitError := false
	cleanupFilter := cmdFilters.AppendFilter(
		func(args storagebase.FilterArgs) *roachpb.Error {
			if req, ok := args.Req.(*roachpb.ScanRequest); ok {
				if bytes.Contains(req.Key, testKey) {
					hitError = true
					return roachpb.NewErrorWithTxn(fmt.Errorf("testError"), args.Hdr.Txn)
				}
			}
			return nil
		}, false)
	defer cleanupFilter()

	// We need to do everything on one connection as we'll want to observe the
	// connection state after a COMMIT.
	sqlDB.SetMaxOpenConns(1)
	if _, err := sqlDB.Exec(`
CREATE DATABASE t;
CREATE TABLE t.test (k TEXT PRIMARY KEY, v TEXT);
INSERT INTO t.test (k, v) VALUES ('test_key', 'test_val');
SELECT * from t.test WHERE k = 'test_key';
`); !testutils.IsError(err, "pq: testError") {
		t.Errorf("unexpected error %v", err)
	}
	if !hitError {
		t.Errorf("expected to hit error, but it didn't happen")
	}
}

// TestPropagateTxnOnError verifies that DistSender.sendBatch properly
// propagates the txn data to a next iteration. Use txn.Writing field to
// verify that.
func TestPropagateTxnOnError(t *testing.T) {
	defer leaktest.AfterTest(t)()

	var storeKnobs storage.StoreTestingKnobs
	// Set up a filter to so that the first CPut operation will
	// get a ReadWithinUncertaintyIntervalError.
	targetKey := roachpb.Key("b")
	var numGets int32
	storeKnobs.TestingCommandFilter =
		func(fArgs storagebase.FilterArgs) *roachpb.Error {
			_, ok := fArgs.Req.(*roachpb.ConditionalPutRequest)
			if ok && fArgs.Req.Header().Key.Equal(targetKey) {
				if atomic.AddInt32(&numGets, 1) == 1 {
					z := hlc.ZeroTimestamp
					pErr := roachpb.NewReadWithinUncertaintyIntervalError(z, z)
					return roachpb.NewErrorWithTxn(pErr, fArgs.Hdr.Txn)
				}
			}
			return nil
		}
	s, _, _ := serverutils.StartServer(t,
		base.TestServerArgs{Knobs: base.TestingKnobs{Store: &storeKnobs}})
	defer s.Stopper().Stop()

	db := setupMultipleRanges(t, s, "b")

	// Set the initial value on the target key "b".
	origVal := "val"
	if err := db.Put(context.TODO(), targetKey, origVal); err != nil {
		t.Fatal(err)
	}

	// The following txn creates a batch request that is split
	// into two requests: Put and CPut. The CPut operation will
	// get a ReadWithinUncertaintyIntervalError and the txn will be
	// retried.
	epoch := 0
	if err := db.Txn(context.TODO(), func(txn *client.Txn) error {
		epoch++
		if epoch >= 2 {
			// Writing must be true since we ran the BeginTransaction command.
			if !txn.Proto.Writing {
				t.Errorf("unexpected non-writing txn")
			}
		} else {
			// Writing must be false since we haven't run any write command.
			if txn.Proto.Writing {
				t.Errorf("unexpected writing txn")
			}
		}

		b := txn.NewBatch()
		b.Put("a", "val")
		b.CPut(targetKey, "new_val", origVal)
		err := txn.CommitInBatch(b)
		if epoch == 1 {
			if retErr, ok := err.(*roachpb.RetryableTxnError); ok {
				if _, ok := retErr.Cause.(*roachpb.ReadWithinUncertaintyIntervalError); ok {
					if !retErr.Transaction.Writing {
						t.Errorf("unexpected non-writing txn on error")
					}
				} else {
					t.Errorf("expected ReadWithinUncertaintyIntervalError, but got: %s", retErr.Cause)
				}
			} else {
				t.Errorf("expected a retryable error, but got: %s", err)
			}
		}
		return err
	}); err != nil {
		t.Errorf("unexpected error on transactional Puts: %s", err)
	}

	if epoch != 2 {
		t.Errorf("unexpected epoch; the txn must be retried exactly once, but got %d", epoch)
	}
}

// TestTxnCoordSenderTxnUpdatedOnError verifies that errors adjust the
// response transaction's timestamp and priority as appropriate.
func TestTxnCoordSenderTxnUpdatedOnError(t *testing.T) {
	defer leaktest.AfterTest(t)()
	origTS := makeTS(123, 0)
	plus10 := origTS.Add(10, 10)
	plus20 := plus10.Add(10, 0)
	testCases := []struct {
		pErr             *roachpb.Error
		expEpoch         uint32
		expPri           int32
		expTS, expOrigTS hlc.Timestamp
		nodeSeen         bool
	}{
		{
			// No error, so nothing interesting either.
			pErr:      nil,
			expEpoch:  0,
			expPri:    1,
			expTS:     origTS,
			expOrigTS: origTS,
		},
		{
			// On uncertainty error, new epoch begins and node is seen.
			// Timestamp moves ahead of the existing write.
			pErr: func() *roachpb.Error {
				pErr := roachpb.NewErrorWithTxn(
					roachpb.NewReadWithinUncertaintyIntervalError(hlc.ZeroTimestamp, hlc.ZeroTimestamp),
					&roachpb.Transaction{})
				const nodeID = 1
				pErr.GetTxn().UpdateObservedTimestamp(nodeID, plus10)
				pErr.OriginNode = nodeID
				return pErr
			}(),
			expEpoch:  1,
			expPri:    1,
			expTS:     plus10,
			expOrigTS: plus10,
			nodeSeen:  true,
		},
		{
			// On abort, nothing changes but we get a new priority to use for
			// the next attempt.
			pErr: roachpb.NewErrorWithTxn(&roachpb.TransactionAbortedError{},
				&roachpb.Transaction{
					TxnMeta: enginepb.TxnMeta{Timestamp: plus20, Priority: 10},
				}),
			expPri: 10,
		},
		{
			// On failed push, new epoch begins just past the pushed timestamp.
			// Additionally, priority ratchets up to just below the pusher's.
			pErr: roachpb.NewErrorWithTxn(&roachpb.TransactionPushError{
				PusheeTxn: roachpb.Transaction{
					TxnMeta: enginepb.TxnMeta{Timestamp: plus10, Priority: int32(10)},
				},
			},
				&roachpb.Transaction{}),
			expEpoch:  1,
			expPri:    9,
			expTS:     plus10,
			expOrigTS: plus10,
		},
		{
			// On retry, restart with new epoch, timestamp and priority.
			pErr: roachpb.NewErrorWithTxn(&roachpb.TransactionRetryError{},
				&roachpb.Transaction{
					TxnMeta: enginepb.TxnMeta{Timestamp: plus10, Priority: int32(10)},
				},
			),
			expEpoch:  1,
			expPri:    10,
			expTS:     plus10,
			expOrigTS: plus10,
		},
	}

	for i, test := range testCases {
		stopper := stop.NewStopper()

		manual := hlc.NewManualClock(origTS.WallTime)
		clock := hlc.NewClock(manual.UnixNano, 20*time.Nanosecond)

		senderFunc := func(_ context.Context, ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {
			var reply *roachpb.BatchResponse
			if test.pErr == nil {
				reply = ba.CreateReply()
			}
			return reply, test.pErr
		}
		ambient := log.AmbientContext{Tracer: tracing.NewTracer()}
		ts := NewTxnCoordSender(
			ambient,
			senderFn(senderFunc),
			clock,
			false,
			stopper,
			MakeTxnMetrics(metric.TestSampleInterval),
		)
		db := client.NewDB(ts)
//.........这里部分代码省略.........

// TestTxnPutOutOfOrder tests a case where a put operation of an older
// timestamp comes after a put operation of a newer timestamp in a
// txn. The test ensures such an out-of-order put succeeds and
// overrides an old value. The test uses a "Writer" and a "Reader"
// to reproduce an out-of-order put.
//
// 1) The Writer executes a put operation and writes a write intent with
//    time T in a txn.
// 2) Before the Writer's txn is committed, the Reader sends a high priority
//    get operation with time T+100. This pushes the Writer txn timestamp to
//    T+100 and triggers the restart of the Writer's txn. The original
//    write intent timestamp is also updated to T+100.
// 3) The Writer starts a new epoch of the txn, but before it writes, the
//    Reader sends another high priority get operation with time T+200. This
//    pushes the Writer txn timestamp to T+200 to trigger a restart of the
//    Writer txn. The Writer will not actually restart until it tries to commit
//    the current epoch of the transaction. The Reader updates the timestamp of
//    the write intent to T+200. The test deliberately fails the Reader get
//    operation, and cockroach doesn't update its read timestamp cache.
// 4) The Writer executes the put operation again. This put operation comes
//    out-of-order since its timestamp is T+100, while the intent timestamp
//    updated at Step 3 is T+200.
// 5) The put operation overrides the old value using timestamp T+100.
// 6) When the Writer attempts to commit its txn, the txn will be restarted
//    again at a new epoch timestamp T+200, which will finally succeed.
func TestTxnPutOutOfOrder(t *testing.T) {
	defer leaktest.AfterTest(t)()

	const key = "key"
	// Set up a filter to so that the get operation at Step 3 will return an error.
	var numGets int32

	stopper := stop.NewStopper()
	defer stopper.Stop()
	manual := hlc.NewManualClock(123)
	cfg := storage.TestStoreConfig(hlc.NewClock(manual.UnixNano, time.Nanosecond))
	cfg.TestingKnobs.TestingCommandFilter =
		func(filterArgs storagebase.FilterArgs) *roachpb.Error {
			if _, ok := filterArgs.Req.(*roachpb.GetRequest); ok &&
				filterArgs.Req.Header().Key.Equal(roachpb.Key(key)) &&
				filterArgs.Hdr.Txn == nil {
				// The Reader executes two get operations, each of which triggers two get requests
				// (the first request fails and triggers txn push, and then the second request
				// succeeds). Returns an error for the fourth get request to avoid timestamp cache
				// update after the third get operation pushes the txn timestamp.
				if atomic.AddInt32(&numGets, 1) == 4 {
					return roachpb.NewErrorWithTxn(errors.Errorf("Test"), filterArgs.Hdr.Txn)
				}
			}
			return nil
		}
	eng := engine.NewInMem(roachpb.Attributes{}, 10<<20)
	stopper.AddCloser(eng)
	store := createTestStoreWithEngine(t,
		eng,
		true,
		cfg,
		stopper,
	)

	// Put an initial value.
	initVal := []byte("initVal")
	err := store.DB().Put(context.TODO(), key, initVal)
	if err != nil {
		t.Fatalf("failed to put: %s", err)
	}

	waitPut := make(chan struct{})
	waitFirstGet := make(chan struct{})
	waitTxnRestart := make(chan struct{})
	waitSecondGet := make(chan struct{})
	waitTxnComplete := make(chan struct{})

	// Start the Writer.
	go func() {
		epoch := -1
		// Start a txn that does read-after-write.
		// The txn will be restarted twice, and the out-of-order put
		// will happen in the second epoch.
		if err := store.DB().Txn(context.TODO(), func(txn *client.Txn) error {
			epoch++

			if epoch == 1 {
				// Wait until the second get operation is issued.
				close(waitTxnRestart)
				<-waitSecondGet
			}

			updatedVal := []byte("updatedVal")
			if err := txn.Put(key, updatedVal); err != nil {
				return err
			}

			// Make sure a get will return the value that was just written.
			actual, err := txn.Get(key)
			if err != nil {
				return err
			}
			if !bytes.Equal(actual.ValueBytes(), updatedVal) {
				t.Fatalf("unexpected get result: %s", actual)
//.........这里部分代码省略.........

// send runs the specified calls synchronously in a single batch and
// returns any errors. If the transaction is read-only or has already
// been successfully committed or aborted, a potential trailing
// EndTransaction call is silently dropped, allowing the caller to
// always commit or clean-up explicitly even when that may not be
// required (or even erroneous). Returns (nil, nil) for an empty batch.
func (txn *Txn) send(ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error) {

	if txn.Proto.Status != roachpb.PENDING || txn.IsFinalized() {
		return nil, roachpb.NewErrorf(
			"attempting to use transaction with wrong status or finalized: %s", txn.Proto.Status)
	}

	// It doesn't make sense to use inconsistent reads in a transaction. However,
	// we still need to accept it as a parameter for this to compile.
	if ba.ReadConsistency != roachpb.CONSISTENT {
		return nil, roachpb.NewErrorf("cannot use %s ReadConsistency in txn",
			ba.ReadConsistency)
	}

	lastIndex := len(ba.Requests) - 1
	if lastIndex < 0 {
		return nil, nil
	}

	// firstWriteIndex is set to the index of the first command which is
	// a transactional write. If != -1, this indicates an intention to
	// write. This is in contrast to txn.Proto.Writing, which is set by
	// the coordinator when the first intent has been created, and which
	// lives for the life of the transaction.
	firstWriteIndex := -1
	var firstWriteKey roachpb.Key

	for i, ru := range ba.Requests {
		args := ru.GetInner()
		if i < lastIndex {
			if _, ok := args.(*roachpb.EndTransactionRequest); ok {
				return nil, roachpb.NewErrorf("%s sent as non-terminal call", args.Method())
			}
		}
		if roachpb.IsTransactionWrite(args) && firstWriteIndex == -1 {
			firstWriteKey = args.Header().Key
			firstWriteIndex = i
		}
	}

	haveTxnWrite := firstWriteIndex != -1
	endTxnRequest, haveEndTxn := ba.Requests[lastIndex].GetInner().(*roachpb.EndTransactionRequest)
	needBeginTxn := !txn.Proto.Writing && haveTxnWrite
	needEndTxn := txn.Proto.Writing || haveTxnWrite
	elideEndTxn := haveEndTxn && !needEndTxn

	// If we're not yet writing in this txn, but intend to, insert a
	// begin transaction request before the first write command.
	if needBeginTxn {
		// If the transaction already has a key (we're in a restart), make
		// sure we set the key in the begin transaction request to the original.
		bt := &roachpb.BeginTransactionRequest{
			Span: roachpb.Span{
				Key: firstWriteKey,
			},
		}
		if txn.Proto.Key != nil {
			bt.Key = txn.Proto.Key
		}
		// Inject the new request before position firstWriteIndex, taking
		// care to avoid unnecessary allocations.
		oldRequests := ba.Requests
		ba.Requests = make([]roachpb.RequestUnion, len(ba.Requests)+1)
		copy(ba.Requests, oldRequests[:firstWriteIndex])
		ba.Requests[firstWriteIndex].MustSetInner(bt)
		copy(ba.Requests[firstWriteIndex+1:], oldRequests[firstWriteIndex:])
	}

	if elideEndTxn {
		ba.Requests = ba.Requests[:lastIndex]
	}

	br, pErr := txn.sendInternal(ba)
	if elideEndTxn && pErr == nil {
		// Check that read only transactions do not violate their deadline. This can NOT
		// happen since the txn deadline is normally updated when it is about to expire
		// or expired. We will just keep the code for safety (see TestReacquireLeaseOnRestart).
		if endTxnRequest.Deadline != nil {
			if endTxnRequest.Deadline.Less(txn.Proto.Timestamp) {
				return nil, roachpb.NewErrorWithTxn(roachpb.NewTransactionAbortedError(), &txn.Proto)
			}
		}
		// This normally happens on the server and sent back in response
		// headers, but this transaction was optimized away. The caller may
		// still inspect the transaction struct, so we manually update it
		// here to emulate a true transaction.
		if endTxnRequest.Commit {
			txn.Proto.Status = roachpb.COMMITTED
		} else {
			txn.Proto.Status = roachpb.ABORTED
		}
		txn.finalized = true
	}

//.........这里部分代码省略.........

// TestUserTxnRestart tests user-directed txn restarts.
// The test will inject and otherwise create retriable errors of various kinds
// and checks that we still manage to run a txn despite them.
func TestTxnUserRestart(t *testing.T) {
	defer leaktest.AfterTest(t)()

	aborter := NewTxnAborter()
	defer aborter.Close(t)
	params, cmdFilters := createTestServerParams()
	params.Knobs.SQLExecutor = aborter.executorKnobs()
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()
	{
		pgURL, cleanup := sqlutils.PGUrl(t, s.ServingAddr(), "TestTxnUserRestart", url.User(security.RootUser))
		defer cleanup()
		if err := aborter.Init(pgURL); err != nil {
			t.Fatal(err)
		}
	}

	if _, err := sqlDB.Exec(`
CREATE DATABASE t;
CREATE TABLE t.test (k INT PRIMARY KEY, v TEXT);
`); err != nil {
		t.Fatal(err)
	}

	// Set up error injection that causes retries.
	testCases := []struct {
		magicVals   *filterVals
		expectedErr string
	}{
		{
			magicVals: createFilterVals(
				map[string]int{"boulanger": 2}, // restartCounts
				nil),
			expectedErr: ".*encountered previous write with future timestamp.*",
		},
		{
			magicVals: createFilterVals(
				nil,
				map[string]int{"boulanger": 2}), // abortCounts
			expectedErr: ".*txn aborted.*",
		},
	}

	for _, tc := range testCases {
		for _, rs := range []rollbackStrategy{rollbackToSavepoint, declareSavepoint} {
			cleanupFilter := cmdFilters.AppendFilter(
				func(args storagebase.FilterArgs) *roachpb.Error {
					if err := injectErrors(args.Req, args.Hdr, tc.magicVals); err != nil {
						return roachpb.NewErrorWithTxn(err, args.Hdr.Txn)
					}
					return nil
				}, false)

			// Also inject an error at RELEASE time, besides the error injected by magicVals.
			const sentinelInsert = "INSERT INTO t.test(k, v) VALUES (0, 'sentinel')"
			if err := aborter.QueueStmtForAbortion(
				sentinelInsert, 1 /* abortCount */, true, /* willBeRetriedIbid */
			); err != nil {
				t.Fatal(err)
			}

			commitCount := s.MustGetSQLCounter(sql.MetaTxnCommit.Name)
			// This is the magic. Run the txn closure until all the retries are exhausted.
			retryExec(t, sqlDB, rs, func(tx *gosql.Tx) bool {
				return runTestTxn(t, tc.magicVals, tc.expectedErr, sqlDB, tx, sentinelInsert)
			})
			checkRestarts(t, tc.magicVals)

			// Check that we only wrote the sentinel row.
			rows, err := sqlDB.Query("SELECT * FROM t.test")
			if err != nil {
				t.Fatal(err)
			}
			for rows.Next() {
				var k int
				var v string
				err = rows.Scan(&k, &v)
				if err != nil {
					t.Fatal(err)
				}
				if k != 0 || v != "sentinel" {
					t.Fatalf("didn't find expected row: %d %s", k, v)
				}
			}
			// Check that the commit counter was incremented. It could have been
			// incremented by more than 1 because of the transactions we use to force
			// aborts, plus who knows what else the server is doing in the background.
			checkCounterGE(t, s, sql.MetaTxnCommit, commitCount+1)
			// Clean up the table for the next test iteration.
			_, err = sqlDB.Exec("DELETE FROM t.test WHERE true")
			if err != nil {
				t.Fatal(err)
			}
			rows.Close()
			cleanupFilter()
		}
	}
//.........这里部分代码省略.........

// Test the logic in the sql executor for automatically retrying txns in case of
// retriable errors.
func TestTxnAutoRetry(t *testing.T) {
	defer leaktest.AfterTest(t)()

	aborter := NewTxnAborter()
	defer aborter.Close(t)
	params, cmdFilters := createTestServerParams()
	params.Knobs.SQLExecutor = aborter.executorKnobs()
	// Disable one phase commits because they cannot be restarted.
	params.Knobs.Store.(*storage.StoreTestingKnobs).DisableOnePhaseCommits = true
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()
	{
		pgURL, cleanup := sqlutils.PGUrl(t, s.ServingAddr(), "TestTxnAutoRetry", url.User(security.RootUser))
		defer cleanup()
		if err := aborter.Init(pgURL); err != nil {
			t.Fatal(err)
		}
	}

	// Make sure all the commands we send in this test are sent over the same connection.
	// This is a bit of a hack; in Go you're not supposed to have connection state
	// outside of using a db.Tx. But we can't use a db.Tx here, because we want
	// to control the batching of BEGIN/COMMIT statements.
	// This SetMaxOpenConns is pretty shady, it doesn't guarantee that you'll be using
	// the *same* one connection across calls. A proper solution would be to use a
	// lib/pq connection directly. As of Feb 2016, there's code in cli/sql_util.go to
	// do that.
	sqlDB.SetMaxOpenConns(1)

	if _, err := sqlDB.Exec(`
CREATE DATABASE t;
CREATE TABLE t.test (k INT PRIMARY KEY, v TEXT, t DECIMAL);
`); err != nil {
		t.Fatal(err)
	}

	// Set up error injection that causes retries.
	magicVals := createFilterVals(nil, nil)
	magicVals.restartCounts = map[string]int{
		"boulanger": 2,
		"dromedary": 2,
		"fajita":    2,
		"hooly":     2,
		"josephine": 2,
		"laureal":   2,
	}
	magicVals.abortCounts = map[string]int{
		"boulanger": 2,
	}
	cleanupFilter := cmdFilters.AppendFilter(
		func(args storagebase.FilterArgs) *roachpb.Error {
			if err := injectErrors(args.Req, args.Hdr, magicVals); err != nil {
				return roachpb.NewErrorWithTxn(err, args.Hdr.Txn)
			}
			return nil
		}, false)

	if err := aborter.QueueStmtForAbortion(
		"INSERT INTO t.test(k, v, t) VALUES (1, 'boulanger', cluster_logical_timestamp())", 2 /* abortCount */, true, /* willBeRetriedIbid */
	); err != nil {
		t.Fatal(err)
	}
	if err := aborter.QueueStmtForAbortion(
		"INSERT INTO t.test(k, v, t) VALUES (2, 'dromedary', cluster_logical_timestamp())", 2 /* abortCount */, true, /* willBeRetriedIbid */
	); err != nil {
		t.Fatal(err)
	}
	if err := aborter.QueueStmtForAbortion(
		"INSERT INTO t.test(k, v, t) VALUES (3, 'fajita', cluster_logical_timestamp())", 2 /* abortCount */, true, /* willBeRetriedIbid */
	); err != nil {
		t.Fatal(err)
	}
	if err := aborter.QueueStmtForAbortion(
		"INSERT INTO t.test(k, v, t) VALUES (4, 'hooly', cluster_logical_timestamp())", 2 /* abortCount */, true, /* willBeRetriedIbid */
	); err != nil {
		t.Fatal(err)
	}

	// Test that implicit txns - txns for which we see all the statements and prefixes
	// of txns (statements batched together with the BEGIN stmt) - are retried.
	// We also exercise the SQL cluster logical timestamp in here, because
	// this must be properly propagated across retries.
	//
	// The SELECT within the transaction also checks that discarded
	// intermediate result sets are properly released: the result set it
	// produces is accounted for by the session monitor, and if it is
	// not properly released upon a retry the monitor will cause the
	// server to panic (and thus the test to fail) when the connection
	// is closed.
	//
	// TODO(knz) This test can be made more robust by exposing the
	// current allocation count in monitor and checking that it has the
	// same value at the beginning of each retry.
	if _, err := sqlDB.Exec(`
INSERT INTO t.test(k, v, t) VALUES (1, 'boulanger', cluster_logical_timestamp());
BEGIN;
SELECT * FROM t.test;
INSERT INTO t.test(k, v, t) VALUES (2, 'dromedary', cluster_logical_timestamp());
//.........这里部分代码省略.........

// Test that a TransactionRetryError will retry the read until it succeeds. The
// test is designed so that if the proto timestamps are bumped during retry
// a failure will occur.
func TestAsOfRetry(t *testing.T) {
	defer leaktest.AfterTest(t)()

	params, cmdFilters := createTestServerParams()
	// Disable one phase commits because they cannot be restarted.
	params.Knobs.Store.(*storage.StoreTestingKnobs).DisableOnePhaseCommits = true
	s, sqlDB, _ := serverutils.StartServer(t, params)
	defer s.Stopper().Stop()

	const val1 = 1
	const val2 = 2
	const name = "boulanger"

	if _, err := sqlDB.Exec(`
			CREATE DATABASE d;
			CREATE TABLE d.t (s STRING PRIMARY KEY, a INT);
		`); err != nil {
		t.Fatal(err)
	}
	var tsStart string
	if err := sqlDB.QueryRow(`
			INSERT INTO d.t (s, a) VALUES ($1, $2)
			RETURNING cluster_logical_timestamp();
		`, name, val1).Scan(&tsStart); err != nil {
		t.Fatal(err)
	}

	var tsVal2 string
	if err := sqlDB.QueryRow("UPDATE d.t SET a = $1 RETURNING cluster_logical_timestamp()", val2).Scan(&tsVal2); err != nil {
		t.Fatal(err)
	}
	walltime := new(inf.Dec)
	if _, ok := walltime.SetString(tsVal2); !ok {
		t.Fatalf("couldn't set decimal: %s", tsVal2)
	}
	oneTick := inf.NewDec(1, 0)
	// Set tsVal1 to 1ns before tsVal2.
	tsVal1 := walltime.Sub(walltime, oneTick).String()

	// Set up error injection that causes retries.
	magicVals := createFilterVals(nil, nil)
	magicVals.restartCounts = map[string]int{
		name: 5,
	}
	cleanupFilter := cmdFilters.AppendFilter(
		func(args storagebase.FilterArgs) *roachpb.Error {
			magicVals.Lock()
			defer magicVals.Unlock()

			switch req := args.Req.(type) {
			case *roachpb.ScanRequest:
				for key, count := range magicVals.restartCounts {
					if err := checkCorrectTxn(string(req.Key), magicVals, args.Hdr.Txn); err != nil {
						return roachpb.NewError(err)
					}
					if count > 0 && bytes.Contains(req.Key, []byte(key)) {
						magicVals.restartCounts[key]--
						err := roachpb.NewTransactionRetryError()
						magicVals.failedValues[string(req.Key)] =
							failureRecord{err, args.Hdr.Txn}
						txn := args.Hdr.Txn.Clone()
						txn.Timestamp = txn.Timestamp.Add(0, 1)
						return roachpb.NewErrorWithTxn(err, &txn)
					}
				}
			}
			return nil
		}, false)

	var i int
	// Query with tsVal1 which should return the first value. Since tsVal1 is just
	// one nanosecond before tsVal2, any proto timestamp bumping will return val2
	// and error.
	// Must specify the WHERE here to trigger the injection errors.
	if err := sqlDB.QueryRow(fmt.Sprintf("SELECT a FROM d.t AS OF SYSTEM TIME %s WHERE s = '%s'", tsVal1, name)).Scan(&i); err != nil {
		t.Fatal(err)
	} else if i != val1 {
		t.Fatalf("unexpected val: %v", i)
	}

	cleanupFilter()
	// Verify that the retry errors were injected.
	checkRestarts(t, magicVals)

	// Query with tsVal2 to ensure val2 is indeed present.
	if err := sqlDB.QueryRow(fmt.Sprintf("SELECT a FROM d.t AS OF SYSTEM TIME %s", tsVal2)).Scan(&i); err != nil {
		t.Fatal(err)
	} else if i != val2 {
		t.Fatalf("unexpected val: %v", i)
	}
}

//.........这里部分代码省略.........
			status:     roachpb.COMMITTED,
			orig:       gcTxnAndAC - 1,
			newStatus:  -1,
			expResolve: true,
			expAbortGC: true,
		},
		// Same as the previous one, but we've rigged things so that the intent
		// resolution here will fail and consequently no GC is expected.
		"g": {
			status:      roachpb.COMMITTED,
			orig:        gcTxnAndAC - 1,
			newStatus:   roachpb.COMMITTED,
			failResolve: true,
			expResolve:  true,
			expAbortGC:  true,
		},
	}

	resolved := map[string][]roachpb.Span{}

	tc := testContext{}
	tsc := TestStoreConfig()
	tsc.TestingKnobs.TestingCommandFilter =
		func(filterArgs storagebase.FilterArgs) *roachpb.Error {
			if resArgs, ok := filterArgs.Req.(*roachpb.ResolveIntentRequest); ok {
				id := string(resArgs.IntentTxn.Key)
				resolved[id] = append(resolved[id], roachpb.Span{
					Key:    resArgs.Key,
					EndKey: resArgs.EndKey,
				})
				// We've special cased one test case. Note that the intent is still
				// counted in `resolved`.
				if testCases[id].failResolve {
					return roachpb.NewErrorWithTxn(errors.Errorf("boom"), filterArgs.Hdr.Txn)
				}
			}
			return nil
		}
	tc.StartWithStoreConfig(t, tsc)
	defer tc.Stop()
	tc.manualClock.Set(int64(now))

	outsideKey := tc.rng.Desc().EndKey.Next().AsRawKey()
	testIntents := []roachpb.Span{{Key: roachpb.Key("intent")}}

	txns := map[string]roachpb.Transaction{}
	for strKey, test := range testCases {
		baseKey := roachpb.Key(strKey)
		txnClock := hlc.NewClock(hlc.NewManualClock(int64(test.orig)).UnixNano)
		txn := newTransaction("txn1", baseKey, 1, enginepb.SERIALIZABLE, txnClock)
		txn.Status = test.status
		txn.Intents = testIntents
		if test.hb > 0 {
			txn.LastHeartbeat = &hlc.Timestamp{WallTime: int64(test.hb)}
		}
		// Set a high Timestamp to make sure it does not matter. Only
		// OrigTimestamp (and heartbeat) are used for GC decisions.
		txn.Timestamp.Forward(hlc.MaxTimestamp)
		txns[strKey] = *txn
		for _, addrKey := range []roachpb.Key{baseKey, outsideKey} {
			key := keys.TransactionKey(addrKey, txn.ID)
			if err := engine.MVCCPutProto(context.Background(), tc.engine, nil, key, hlc.ZeroTimestamp, nil, txn); err != nil {
				t.Fatal(err)
			}
		}
		entry := roachpb.AbortCacheEntry{Key: txn.Key, Timestamp: txn.LastActive()}

// Verifies that an expired lease is released and a new lease is acquired on transaction
// restart.
//
// This test triggers the above scenario by making ReadWithinUncertaintyIntervalError advance
// the clock, so that the transaction timestamp exceeds the deadline of the EndTransactionRequest.
func TestReacquireLeaseOnRestart(t *testing.T) {
	defer leaktest.AfterTest(t)()

	advancement := 2 * sql.LeaseDuration

	var cmdFilters CommandFilters
	cmdFilters.AppendFilter(checkEndTransactionTrigger, true)

	var clockUpdate int32
	testKey := []byte("test_key&qu