vitess.io/vitess@v0.16.2/go/vt/vttablet/tabletserver/tx_pool.go

/*
Copyright 2019 The Vitess 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.
*/

package tabletserver

import (
	"context"
	"strings"
	"sync"
	"time"

	"vitess.io/vitess/go/pools"
	"vitess.io/vitess/go/timer"
	"vitess.io/vitess/go/trace"
	"vitess.io/vitess/go/vt/callerid"
	"vitess.io/vitess/go/vt/dbconfigs"
	"vitess.io/vitess/go/vt/log"
	"vitess.io/vitess/go/vt/servenv"
	"vitess.io/vitess/go/vt/sqlparser"
	"vitess.io/vitess/go/vt/vterrors"
	"vitess.io/vitess/go/vt/vttablet/tabletserver/tabletenv"
	"vitess.io/vitess/go/vt/vttablet/tabletserver/tx"
	"vitess.io/vitess/go/vt/vttablet/tabletserver/txlimiter"

	querypb "vitess.io/vitess/go/vt/proto/query"
	vtrpcpb "vitess.io/vitess/go/vt/proto/vtrpc"
)

const (
	txLogInterval  = 1 * time.Minute
	beginWithCSRO  = "start transaction with consistent snapshot, read only"
	trackGtidQuery = "set session session_track_gtids = START_GTID"
)

var txIsolations = map[querypb.ExecuteOptions_TransactionIsolation]string{
	querypb.ExecuteOptions_DEFAULT:                       "",
	querypb.ExecuteOptions_REPEATABLE_READ:               "repeatable read",
	querypb.ExecuteOptions_READ_COMMITTED:                "read committed",
	querypb.ExecuteOptions_READ_UNCOMMITTED:              "read uncommitted",
	querypb.ExecuteOptions_SERIALIZABLE:                  "serializable",
	querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY: "repeatable read",
}

var txAccessMode = map[querypb.ExecuteOptions_TransactionAccessMode]string{
	querypb.ExecuteOptions_CONSISTENT_SNAPSHOT: sqlparser.WithConsistentSnapshotStr,
	querypb.ExecuteOptions_READ_WRITE:          sqlparser.ReadWriteStr,
	querypb.ExecuteOptions_READ_ONLY:           sqlparser.ReadOnlyStr,
}

type (
	// TxPool does a lot of the transactional operations on StatefulConnections. It does not, with two exceptions,
	// concern itself with a connections life cycle. The two exceptions are Begin, which creates a new StatefulConnection,
	// and RollbackAndRelease, which does a Release after doing the rollback.
	TxPool struct {
		env     tabletenv.Env
		scp     *StatefulConnectionPool
		ticks   *timer.Timer
		limiter txlimiter.TxLimiter

		logMu   sync.Mutex
		lastLog time.Time
		txStats *servenv.TimingsWrapper
	}
)

// NewTxPool creates a new TxPool. It's not operational until it's Open'd.
func NewTxPool(env tabletenv.Env, limiter txlimiter.TxLimiter) *TxPool {
	config := env.Config()
	axp := &TxPool{
		env:     env,
		scp:     NewStatefulConnPool(env),
		ticks:   timer.NewTimer(txKillerTimeoutInterval(config)),
		limiter: limiter,
		txStats: env.Exporter().NewTimings("Transactions", "Transaction stats", "operation"),
	}
	// Careful: conns also exports name+"xxx" vars,
	// but we know it doesn't export Timeout.
	env.Exporter().NewGaugeDurationFunc("OlapTransactionTimeout", "OLAP transaction timeout", func() time.Duration {
		return config.TxTimeoutForWorkload(querypb.ExecuteOptions_OLAP)
	})
	env.Exporter().NewGaugeDurationFunc("TransactionTimeout", "Transaction timeout", func() time.Duration {
		return config.TxTimeoutForWorkload(querypb.ExecuteOptions_OLTP)
	})
	return axp
}

// Open makes the TxPool operational. This also starts the transaction killer
// that will kill long-running transactions.
func (tp *TxPool) Open(appParams, dbaParams, appDebugParams dbconfigs.Connector) {
	tp.scp.Open(appParams, dbaParams, appDebugParams)
	if tp.ticks.Interval() > 0 {
		tp.ticks.Start(func() { tp.transactionKiller() })
	}
}

// Close closes the TxPool. A closed pool can be reopened.
func (tp *TxPool) Close() {
	tp.ticks.Stop()
	tp.scp.Close()
}

// AdjustLastID adjusts the last transaction id to be at least
// as large as the input value. This will ensure that there are
// no dtid collisions with future transactions.
func (tp *TxPool) AdjustLastID(id int64) {
	tp.scp.AdjustLastID(id)
}

// Shutdown immediately rolls back all transactions that are not in use.
// In-use connections will be closed when they are unlocked (not in use).
func (tp *TxPool) Shutdown(ctx context.Context) {
	for _, v := range tp.scp.ShutdownAll() {
		tp.RollbackAndRelease(ctx, v)
	}
}

func (tp *TxPool) transactionKiller() {
	defer tp.env.LogError()
	for _, conn := range tp.scp.GetElapsedTimeout(vterrors.TxKillerRollback) {
		log.Warningf("killing transaction (exceeded timeout: %v): %s", conn.timeout, conn.String(tp.env.Config().SanitizeLogMessages))
		switch {
		case conn.IsTainted():
			conn.Close()
			tp.env.Stats().KillCounters.Add("ReservedConnection", 1)
		case conn.IsInTransaction():
			_, err := conn.Exec(context.Background(), "rollback", 1, false)
			if err != nil {
				conn.Close()
			}
			tp.env.Stats().KillCounters.Add("Transactions", 1)
		}
		// For logging, as transaction is killed as the connection is closed.
		if conn.IsTainted() && conn.IsInTransaction() {
			tp.env.Stats().KillCounters.Add("Transactions", 1)
		}
		if conn.IsInTransaction() {
			tp.txComplete(conn, tx.TxKill)
		}
		conn.Releasef("exceeded timeout: %v", conn.timeout)
	}
}

// WaitForEmpty waits until all active transactions are completed.
func (tp *TxPool) WaitForEmpty() {
	tp.scp.WaitForEmpty()
}

// NewTxProps creates a new TxProperties struct
func (tp *TxPool) NewTxProps(immediateCaller *querypb.VTGateCallerID, effectiveCaller *vtrpcpb.CallerID, autocommit bool) *tx.Properties {
	return &tx.Properties{
		StartTime:       time.Now(),
		EffectiveCaller: effectiveCaller,
		ImmediateCaller: immediateCaller,
		Autocommit:      autocommit,
		Stats:           tp.txStats,
	}
}

// GetAndLock fetches the connection associated to the connID and blocks it from concurrent use
// You must call Unlock on TxConnection once done.
func (tp *TxPool) GetAndLock(connID tx.ConnID, reason string) (*StatefulConnection, error) {
	conn, err := tp.scp.GetAndLock(connID, reason)
	if err != nil {
		return nil, vterrors.Errorf(vtrpcpb.Code_ABORTED, "transaction %d: %v", connID, err)
	}
	return conn, nil
}

// Commit commits the transaction on the connection.
func (tp *TxPool) Commit(ctx context.Context, txConn *StatefulConnection) (string, error) {
	if !txConn.IsInTransaction() {
		return "", vterrors.New(vtrpcpb.Code_INTERNAL, "not in a transaction")
	}
	span, ctx := trace.NewSpan(ctx, "TxPool.Commit")
	defer span.Finish()
	defer tp.txComplete(txConn, tx.TxCommit)
	if txConn.TxProperties().Autocommit {
		return "", nil
	}

	if _, err := txConn.Exec(ctx, "commit", 1, false); err != nil {
		txConn.Close()
		return "", err
	}
	return "commit", nil
}

// RollbackAndRelease rolls back the transaction on the specified connection, and releases the connection when done
func (tp *TxPool) RollbackAndRelease(ctx context.Context, txConn *StatefulConnection) {
	defer txConn.Release(tx.TxRollback)
	rollbackError := tp.Rollback(ctx, txConn)
	if rollbackError != nil {
		log.Errorf("tried to rollback, but failed with: %v", rollbackError.Error())
	}
}

// Rollback rolls back the transaction on the specified connection.
func (tp *TxPool) Rollback(ctx context.Context, txConn *StatefulConnection) error {
	span, ctx := trace.NewSpan(ctx, "TxPool.Rollback")
	defer span.Finish()
	if txConn.IsClosed() || !txConn.IsInTransaction() {
		return nil
	}
	if txConn.TxProperties().Autocommit {
		tp.txComplete(txConn, tx.TxCommit)
		return nil
	}
	defer tp.txComplete(txConn, tx.TxRollback)
	if _, err := txConn.Exec(ctx, "rollback", 1, false); err != nil {
		txConn.Close()
		return err
	}
	return nil
}

// Begin begins a transaction, and returns the associated connection and
// the statements (if any) executed to initiate the transaction. In autocommit
// mode the statement will be "".
// The connection returned is locked for the callee and its responsibility is to unlock the connection.
func (tp *TxPool) Begin(ctx context.Context, options *querypb.ExecuteOptions, readOnly bool, reservedID int64, savepointQueries []string, setting *pools.Setting) (*StatefulConnection, string, string, error) {
	span, ctx := trace.NewSpan(ctx, "TxPool.Begin")
	defer span.Finish()

	var conn *StatefulConnection
	var err error
	if reservedID != 0 {
		conn, err = tp.scp.GetAndLock(reservedID, "start transaction on reserve conn")
		if err != nil {
			return nil, "", "", vterrors.Errorf(vtrpcpb.Code_ABORTED, "transaction %d: %v", reservedID, err)
		}
		// Update conn timeout.
		timeout := tp.env.Config().TxTimeoutForWorkload(options.GetWorkload())
		conn.SetTimeout(timeout)
	} else {
		immediateCaller := callerid.ImmediateCallerIDFromContext(ctx)
		effectiveCaller := callerid.EffectiveCallerIDFromContext(ctx)
		if !tp.limiter.Get(immediateCaller, effectiveCaller) {
			return nil, "", "", vterrors.Errorf(vtrpcpb.Code_RESOURCE_EXHAUSTED, "per-user transaction pool connection limit exceeded")
		}
		conn, err = tp.createConn(ctx, options, setting)
		defer func() {
			if err != nil {
				// The transaction limiter frees transactions on rollback or commit. If we fail to create the transaction,
				// release immediately since there will be no rollback or commit.
				tp.limiter.Release(immediateCaller, effectiveCaller)
			}
		}()
	}
	if err != nil {
		return nil, "", "", err
	}
	sql, sessionStateChanges, err := tp.begin(ctx, options, readOnly, conn, savepointQueries)
	if err != nil {
		conn.Close()
		conn.Release(tx.ConnInitFail)
		return nil, "", "", err
	}
	return conn, sql, sessionStateChanges, nil
}

func (tp *TxPool) begin(ctx context.Context, options *querypb.ExecuteOptions, readOnly bool, conn *StatefulConnection, savepointQueries []string) (string, string, error) {
	immediateCaller := callerid.ImmediateCallerIDFromContext(ctx)
	effectiveCaller := callerid.EffectiveCallerIDFromContext(ctx)
	beginQueries, autocommit, sessionStateChanges, err := createTransaction(ctx, options, conn, readOnly, savepointQueries)
	if err != nil {
		return "", "", err
	}

	conn.txProps = tp.NewTxProps(immediateCaller, effectiveCaller, autocommit)

	return beginQueries, sessionStateChanges, nil
}

func (tp *TxPool) createConn(ctx context.Context, options *querypb.ExecuteOptions, setting *pools.Setting) (*StatefulConnection, error) {
	conn, err := tp.scp.NewConn(ctx, options, setting)
	if err != nil {
		errCode := vterrors.Code(err)
		switch err {
		case pools.ErrCtxTimeout:
			tp.LogActive()
			err = vterrors.Errorf(errCode, "transaction pool aborting request due to already expired context")
		case pools.ErrTimeout:
			tp.LogActive()
			err = vterrors.Errorf(errCode, "transaction pool connection limit exceeded")
		}
		return nil, err
	}
	return conn, nil
}

func createTransaction(
	ctx context.Context,
	options *querypb.ExecuteOptions,
	conn *StatefulConnection,
	readOnly bool,
	savepointQueries []string,
) (beginQueries string, autocommitTransaction bool, sessionStateChanges string, err error) {
	switch options.GetTransactionIsolation() {
	case querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY:
		beginQueries, sessionStateChanges, err = handleConsistentSnapshotCase(ctx, conn)
		if err != nil {
			return "", false, "", err
		}
	case querypb.ExecuteOptions_AUTOCOMMIT:
		autocommitTransaction = true
	case querypb.ExecuteOptions_REPEATABLE_READ, querypb.ExecuteOptions_READ_COMMITTED, querypb.ExecuteOptions_READ_UNCOMMITTED,
		querypb.ExecuteOptions_SERIALIZABLE, querypb.ExecuteOptions_DEFAULT:
		isolationLevel := txIsolations[options.GetTransactionIsolation()]
		var execSQL string
		if isolationLevel != "" {
			execSQL, err = setIsolationLevel(ctx, conn, isolationLevel)
			if err != nil {
				return
			}
			beginQueries += execSQL
		}

		var beginSQL string
		beginSQL, err = createStartTxStmt(options, readOnly)
		if err != nil {
			return "", false, "", err
		}

		execSQL, sessionStateChanges, err = startTransaction(ctx, conn, beginSQL)
		if err != nil {
			return "", false, "", err
		}

		// Add the begin statement to the list of queries.
		beginQueries += execSQL
	default:
		return "", false, "", vterrors.Errorf(vtrpcpb.Code_INTERNAL, "[BUG] don't know how to open a transaction of this type: %v", options.GetTransactionIsolation())
	}

	for _, savepoint := range savepointQueries {
		if _, err = conn.Exec(ctx, savepoint, 1, false); err != nil {
			return "", false, "", err
		}
	}
	return
}

// createStartTxStmt - this method return the start transaction statement based on the TransactionAccessMode in options
// and the readOnly flag passed in.
// When readOnly is true, ReadWrite option should not have been passed, that will result in an error.
// If no option is passed, the default on the connection will be used by just execution "begin" statement.
func createStartTxStmt(options *querypb.ExecuteOptions, readOnly bool) (string, error) {
	// default statement.
	beginSQL := "begin"

	// generate the access mode string
	var modesStr strings.Builder
	// to know if read only is already added to modeStr
	// so that explicit addition of read only is not required in case of readOnly parameter is true.
	var readOnlyAdded bool
	for idx, accessMode := range options.GetTransactionAccessMode() {
		txMode, ok := txAccessMode[accessMode]
		if !ok {
			return "", vterrors.Errorf(vtrpcpb.Code_INTERNAL, "[BUG] transaction access mode not known of this type: %v", accessMode)
		}
		if readOnly && accessMode == querypb.ExecuteOptions_READ_WRITE {
			return "", vterrors.Errorf(vtrpcpb.Code_FAILED_PRECONDITION, "cannot start read write transaction on a read only tablet")
		}
		if accessMode == querypb.ExecuteOptions_READ_ONLY {
			readOnlyAdded = true
		}
		if idx == 0 {
			modesStr.WriteString(txMode)
			continue
		}
		modesStr.WriteString(", " + txMode)
	}

	if readOnly && !readOnlyAdded {
		if modesStr.Len() != 0 {
			modesStr.WriteString(", read only")
		} else {
			modesStr.WriteString("read only")
		}
	}
	if modesStr.Len() != 0 {
		beginSQL = "start transaction " + modesStr.String()
	}
	return beginSQL, nil
}

func handleConsistentSnapshotCase(ctx context.Context, conn *StatefulConnection) (beginSQL string, sessionStateChanges string, err error) {
	_, err = conn.execWithRetry(ctx, trackGtidQuery, 1, false)
	// We allow this to fail since this is a custom MySQL extension, but we return
	// then if this query was executed or not.
	//
	// Callers also can know because the sessionStateChanges will be empty for a snapshot
	// transaction and get GTID information in another (less efficient) way.
	if err == nil {
		beginSQL = trackGtidQuery + "; "
	}

	isolationLevel := txIsolations[querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY]

	execSQL, err := setIsolationLevel(ctx, conn, isolationLevel)
	if err != nil {
		return
	}
	beginSQL += execSQL

	execSQL, sessionStateChanges, err = startTransaction(ctx, conn, beginWithCSRO)
	if err != nil {
		return
	}
	beginSQL += execSQL
	return
}

func startTransaction(ctx context.Context, conn *StatefulConnection, transaction string) (string, string, error) {
	sessionStateChanges, err := conn.execWithRetry(ctx, transaction, 1, false)
	if err != nil {
		return "", "", err
	}
	return transaction, sessionStateChanges, nil
}

func setIsolationLevel(ctx context.Context, conn *StatefulConnection, level string) (string, error) {
	txQuery := "set transaction isolation level " + level
	if _, err := conn.execWithRetry(ctx, txQuery, 1, false); err != nil {
		return "", err
	}
	return txQuery + "; ", nil
}

// LogActive causes all existing transactions to be logged when they complete.
// The logging is throttled to no more than once every txLogInterval.
func (tp *TxPool) LogActive() {
	tp.logMu.Lock()
	defer tp.logMu.Unlock()
	if time.Since(tp.lastLog) < txLogInterval {
		return
	}
	tp.lastLog = time.Now()
	tp.scp.ForAllTxProperties(func(props *tx.Properties) {
		props.LogToFile = true
	})
}

func (tp *TxPool) txComplete(conn *StatefulConnection, reason tx.ReleaseReason) {
	conn.LogTransaction(reason)
	tp.limiter.Release(conn.TxProperties().ImmediateCaller, conn.TxProperties().EffectiveCaller)
	conn.CleanTxState()
}

func txKillerTimeoutInterval(config *tabletenv.TabletConfig) time.Duration {
	return smallerTimeout(
		config.TxTimeoutForWorkload(querypb.ExecuteOptions_OLAP),
		config.TxTimeoutForWorkload(querypb.ExecuteOptions_OLTP),
	) / 10
}