// NewTransaction creates a new transaction. The transaction key is
// composed using the specified baseKey (for locality with data
// affected by the transaction) and a random UUID to guarantee
// uniqueness. The specified user-level priority is combined with
// a randomly chosen value to yield a final priority, used to settle
// write conflicts in a way that avoids starvation of long-running
// transactions (see Range.InternalPushTxn).
func NewTransaction(baseKey engine.Key, userPriority int32,
isolation proto.IsolationType, clock *hlc.Clock) *proto.Transaction {
// Compute priority by adjusting based on userPriority factor.
if userPriority < 1 {
userPriority = 1
}
priority := math.MaxInt32 - util.CachedRand.Int31n(math.MaxInt32/userPriority)
// Compute timestamp and max timestamp.
now := clock.Now()
max := now
max.WallTime += clock.MaxDrift().Nanoseconds()
return &proto.Transaction{
ID: append(baseKey, []byte(uuid.New())...),
Priority: priority,
Isolation: isolation,
Timestamp: now,
MaxTimestamp: max,
}
}
// Clear clears the cache and resets the high water mark to the
// current time plus the maximum clock skew.
func (tc *TimestampCache) Clear(clock *hlc.Clock) {
tc.cache.Clear()
tc.highWater = clock.Now()
tc.highWater.WallTime += clock.MaxDrift().Nanoseconds()
tc.latest = tc.highWater
}