Ejemplo n.º 1
0
// InternalPushTxn resolves conflicts between concurrent txns (or
// between a non-transactional reader or writer and a txn) in several
// ways depending on the statuses and priorities of the conflicting
// transactions. The InternalPushTxn operation is invoked by a
// "pusher" (the writer trying to abort a conflicting txn or the
// reader trying to push a conflicting txn's commit timestamp
// forward), who attempts to resolve a conflict with a "pushee"
// (args.PushTxn -- the pushee txn whose intent(s) caused the
// conflict).
//
// Txn already committed/aborted: If pushee txn is committed or
// aborted return success.
//
// Txn Timeout: If pushee txn entry isn't present or its LastHeartbeat
// timestamp isn't set, use PushTxn.Timestamp as LastHeartbeat. If
// current time - LastHeartbeat > 2 * DefaultHeartbeatInterval, then
// the pushee txn should be either pushed forward, aborted, or
// confirmed not pending, depending on value of Request.PushType.
//
// Old Txn Epoch: If persisted pushee txn entry has a newer Epoch than
// PushTxn.Epoch, return success, as older epoch may be removed.
//
// Lower Txn Priority: If pushee txn has a lower priority than pusher,
// adjust pushee's persisted txn depending on value of
// args.PushType. If args.PushType is ABORT_TXN, set txn.Status to
// ABORTED, and priority to one less than the pusher's priority and
// return success. If args.PushType is PUSH_TIMESTAMP, set
// txn.Timestamp to pusher's Timestamp + 1 (note that we use the
// pusher's Args.Timestamp, not Txn.Timestamp because the args
// timestamp can advance during the txn).
//
// Higher Txn Priority: If pushee txn has a higher priority than
// pusher, return TransactionPushError. Transaction will be retried
// with priority one less than the pushee's higher priority.
func (r *Range) InternalPushTxn(batch engine.Engine, ms *engine.MVCCStats, args *proto.InternalPushTxnRequest, reply *proto.InternalPushTxnResponse) {
	if !bytes.Equal(args.Key, args.PusheeTxn.Key) {
		reply.SetGoError(util.Errorf("request key %s should match pushee's txn key %s", args.Key, args.PusheeTxn.Key))
		return
	}
	key := keys.TransactionKey(args.PusheeTxn.Key, args.PusheeTxn.ID)

	// Fetch existing transaction if possible.
	existTxn := &proto.Transaction{}
	ok, err := engine.MVCCGetProto(batch, key, proto.ZeroTimestamp,
		true /* consistent */, nil /* txn */, existTxn)
	if err != nil {
		reply.SetGoError(err)
		return
	}
	if ok {
		// Start with the persisted transaction record as final transaction.
		reply.PusheeTxn = gogoproto.Clone(existTxn).(*proto.Transaction)
		// Upgrade the epoch, timestamp and priority as necessary.
		if reply.PusheeTxn.Epoch < args.PusheeTxn.Epoch {
			reply.PusheeTxn.Epoch = args.PusheeTxn.Epoch
		}
		reply.PusheeTxn.Timestamp.Forward(args.PusheeTxn.Timestamp)
		if reply.PusheeTxn.Priority < args.PusheeTxn.Priority {
			reply.PusheeTxn.Priority = args.PusheeTxn.Priority
		}
	} else {
		// Some sanity checks for case where we don't find a transaction record.
		if args.PusheeTxn.LastHeartbeat != nil {
			reply.SetGoError(proto.NewTransactionStatusError(&args.PusheeTxn,
				"no txn persisted, yet intent has heartbeat"))
			return
		} else if args.PusheeTxn.Status != proto.PENDING {
			reply.SetGoError(proto.NewTransactionStatusError(&args.PusheeTxn,
				fmt.Sprintf("no txn persisted, yet intent has status %s", args.PusheeTxn.Status)))
			return
		}
		// The transaction doesn't exist yet on disk; use the supplied version.
		reply.PusheeTxn = gogoproto.Clone(&args.PusheeTxn).(*proto.Transaction)
	}

	// If already committed or aborted, return success.
	if reply.PusheeTxn.Status != proto.PENDING {
		// Trivial noop.
		return
	}

	// If we're trying to move the timestamp forward, and it's already
	// far enough forward, return success.
	if args.PushType == proto.PUSH_TIMESTAMP && args.Timestamp.Less(reply.PusheeTxn.Timestamp) {
		// Trivial noop.
		return
	}

	// pusherWins bool is true in the event the pusher prevails.
	var pusherWins bool

	// If there's no incoming transaction, the pusher is non-transactional.
	// We make a random priority, biased by specified
	// args.Header().UserPriority in this case.
	var priority int32
	if args.Txn != nil {
		priority = args.Txn.Priority
	} else {
		// Make sure we have a deterministic random number when generating
		// a priority for this txn-less request, so all replicas see same priority.
		randGen := rand.New(rand.NewSource(int64(reply.PusheeTxn.Priority) ^ args.Timestamp.WallTime))
		priority = proto.MakePriority(randGen, args.GetUserPriority())
	}

	// Check for txn timeout.
	if reply.PusheeTxn.LastHeartbeat == nil {
		reply.PusheeTxn.LastHeartbeat = &reply.PusheeTxn.Timestamp
	}
	if args.Now.Equal(proto.ZeroTimestamp) {
		reply.SetGoError(util.Error("the field Now must be provided"))
		return
	}
	// Compute heartbeat expiration (all replicas must see the same result).
	expiry := args.Now
	expiry.Forward(args.Timestamp) // if Timestamp is ahead, use that
	expiry.WallTime -= 2 * DefaultHeartbeatInterval.Nanoseconds()

	if reply.PusheeTxn.LastHeartbeat.Less(expiry) {
		if log.V(1) {
			log.Infof("pushing expired txn %s", reply.PusheeTxn)
		}
		pusherWins = true
	} else if reply.PusheeTxn.Isolation == proto.SNAPSHOT && args.PushType == proto.PUSH_TIMESTAMP {
		if log.V(1) {
			log.Infof("pushing timestamp for snapshot isolation txn")
		}
		pusherWins = true
	} else if args.PushType == proto.CLEANUP_TXN {
		// If just attempting to cleanup old or already-committed txns, don't push.
		pusherWins = false
	} else if reply.PusheeTxn.Priority < priority ||
		(reply.PusheeTxn.Priority == priority && args.Txn != nil &&
			args.Txn.Timestamp.Less(reply.PusheeTxn.Timestamp)) {
		// Pusher wins based on priority; if priorities are equal, order
		// by lower txn timestamp.
		if log.V(1) {
			log.Infof("pushing intent from txn with lower priority %s vs %d", reply.PusheeTxn, priority)
		}
		pusherWins = true
	}

	if !pusherWins {
		err := proto.NewTransactionPushError(args.Txn, reply.PusheeTxn)
		if log.V(1) {
			log.Info(err)
		}
		reply.SetGoError(err)
		return
	}

	// Upgrade priority of pushed transaction to one less than pusher's.
	reply.PusheeTxn.UpgradePriority(priority - 1)

	// If aborting transaction, set new status and return success.
	if args.PushType == proto.ABORT_TXN {
		reply.PusheeTxn.Status = proto.ABORTED
	} else if args.PushType == proto.PUSH_TIMESTAMP {
		// Otherwise, update timestamp to be one greater than the request's timestamp.
		reply.PusheeTxn.Timestamp = args.Timestamp
		reply.PusheeTxn.Timestamp.Logical++
	}

	// Persist the pushed transaction using zero timestamp for inline value.
	if err := engine.MVCCPutProto(batch, ms, key, proto.ZeroTimestamp, nil, reply.PusheeTxn); err != nil {
		reply.SetGoError(err)
		return
	}
}
Ejemplo n.º 2
0
// InternalPushTxn resolves conflicts between concurrent txns (or
// between a non-transactional reader or writer and a txn) in several
// ways depending on the statuses and priorities of the conflicting
// transactions. The InternalPushTxn operation is invoked by a
// "pusher" (the writer trying to abort a conflicting txn or the
// reader trying to push a conflicting txn's commit timestamp
// forward), who attempts to resolve a conflict with a "pushee"
// (args.PushTxn -- the pushee txn whose intent(s) caused the
// conflict).
//
// Txn already committed/aborted: If pushee txn is committed or
// aborted return success.
//
// Txn Timeout: If pushee txn entry isn't present or its LastHeartbeat
// timestamp isn't set, use PushTxn.Timestamp as LastHeartbeat. If
// current time - LastHeartbeat > 2 * DefaultHeartbeatInterval, then
// the pushee txn should be either pushed forward or aborted,
// depending on value of Request.Abort.
//
// Old Txn Epoch: If persisted pushee txn entry has a newer Epoch than
// PushTxn.Epoch, return success, as older epoch may be removed.
//
// Lower Txn Priority: If pushee txn has a lower priority than pusher,
// adjust pushee's persisted txn depending on value of args.Abort. If
// args.Abort is true, set txn.Status to ABORTED, and priority to one
// less than the pusher's priority and return success. If args.Abort
// is false, set txn.Timestamp to pusher's txn.Timestamp + 1.
//
// Higher Txn Priority: If pushee txn has a higher priority than
// pusher, return TransactionRetryError. Transaction will be retried
// with priority one less than the pushee's higher priority.
func (r *Range) InternalPushTxn(args *proto.InternalPushTxnRequest, reply *proto.InternalPushTxnResponse) {
	if !bytes.Equal(args.Key, args.PusheeTxn.ID) {
		reply.SetGoError(util.Errorf("request key %q should match pushee's txn ID %q", args.Key, args.PusheeTxn.ID))
		return
	}
	// Create the actual key to the system-local transaction table.
	key := engine.MakeKey(engine.KeyLocalTransactionPrefix, args.Key)

	// Fetch existing transaction if possible.
	existTxn := &proto.Transaction{}
	ok, err := engine.GetProto(r.engine, key, existTxn)
	if err != nil {
		reply.SetGoError(err)
		return
	}
	if ok {
		// Start with the persisted transaction record as final transaction.
		reply.PusheeTxn = gogoproto.Clone(existTxn).(*proto.Transaction)
		// Upgrade the epoch and timestamp as necessary.
		if reply.PusheeTxn.Epoch < args.PusheeTxn.Epoch {
			reply.PusheeTxn.Epoch = args.PusheeTxn.Epoch
		}
		if reply.PusheeTxn.Timestamp.Less(args.PusheeTxn.Timestamp) {
			reply.PusheeTxn.Timestamp = args.PusheeTxn.Timestamp
		}
	} else {
		// Some sanity checks for case where we don't find a transaction record.
		if args.PusheeTxn.LastHeartbeat != nil {
			reply.SetGoError(proto.NewTransactionStatusError(&args.PusheeTxn,
				"no txn persisted, yet intent has heartbeat"))
			return
		} else if args.PusheeTxn.Status != proto.PENDING {
			reply.SetGoError(proto.NewTransactionStatusError(&args.PusheeTxn,
				fmt.Sprintf("no txn persisted, yet intent has status %s", args.PusheeTxn.Status)))
			return
		}
		// The transaction doesn't exist yet on disk; use the supplied version.
		reply.PusheeTxn = gogoproto.Clone(&args.PusheeTxn).(*proto.Transaction)
	}

	// If already committed or aborted, return success.
	if reply.PusheeTxn.Status != proto.PENDING {
		// Trivial noop.
		return
	}
	// If we're trying to move the timestamp forward, and it's already
	// far enough forward, return success.
	if !args.Abort && args.Timestamp.Less(reply.PusheeTxn.Timestamp) {
		// Trivial noop.
		return
	}

	// pusherWins bool is true in the event the pusher prevails.
	var pusherWins bool

	// Check for txn timeout.
	if reply.PusheeTxn.LastHeartbeat == nil {
		reply.PusheeTxn.LastHeartbeat = &reply.PusheeTxn.Timestamp
	}
	// Compute heartbeat expiration.
	expiry := r.clock.Now()
	expiry.WallTime -= 2 * DefaultHeartbeatInterval.Nanoseconds()
	if reply.PusheeTxn.LastHeartbeat.Less(expiry) {
		log.V(1).Infof("pushing expired txn %+v", reply.PusheeTxn)
		pusherWins = true
	} else if args.PusheeTxn.Epoch < reply.PusheeTxn.Epoch {
		// Check for an intent from a prior epoch.
		log.V(1).Infof("pushing intent from previous epoch for txn %+v", reply.PusheeTxn)
		pusherWins = true
	} else if reply.PusheeTxn.Priority < args.Txn.Priority ||
		(reply.PusheeTxn.Priority == args.Txn.Priority && args.Txn.Timestamp.Less(reply.PusheeTxn.Timestamp)) {
		// Finally, choose based on priority; if priorities are equal, order by lower txn timestamp.
		log.V(1).Infof("pushing intent from txn with lower priority %+v vs %+v", reply.PusheeTxn, args.Txn)
		pusherWins = true
	}

	if !pusherWins {
		log.V(1).Infof("failed to push intent %+v vs %+v", reply.PusheeTxn, args.Txn)
		reply.SetGoError(proto.NewTransactionRetryError(reply.PusheeTxn))
		return
	}

	// If aborting transaction, set new status and return success.
	if args.Abort {
		reply.PusheeTxn.Status = proto.ABORTED
	} else {
		// Otherwise, update timestamp to be one greater than the request's timestamp.
		reply.PusheeTxn.Timestamp = args.Timestamp
		reply.PusheeTxn.Timestamp.Logical++
	}
	// Persist the pushed transaction.
	if err := engine.PutProto(r.engine, key, reply.PusheeTxn); err != nil {
		reply.SetGoError(err)
		return
	}
}