// IsVersionSkip 检测是否发生了版本跳跃
func IsVersionSkip(tm tm.TransactionManager, t *transaction, e *entry) bool {
xmax := e.XMAX()
if t.Level == 0 { // readCommitted 不判断版本跳跃, 直接返回false
return false
} else {
return tm.IsCommited(xmax) && (xmax > t.XID || t.InSnapShot(xmax))
}
}
/*
Repeatable Read:
(XMIN == Ti and // created by Ti itself and
(XMAX == NULL or // not deleted now or
))
or // or
(XMIN is commited and // created by a commited treansaction and
XMIN < XID and // the transaction begin before Ti and
XMIN is not in SP(Ti) and // the transaction commited before Ti begin and
(XMAX == NULL or // not deleted now or
(XMAX != Ti and // deleted by another transaction but
(XMAX is not commited or // the transaction is not commtied now or
XMAX > Ti or // begain after Ti or
XMAX is in SP(Ti) // not commited when Ti begain
))))
*/
func repeatableRead(tm tm.TransactionManager, t *transaction, e *entry) bool {
xid := t.XID
xmin := e.XMIN()
xmax := e.XMAX()
if xmin == xid && xmax == 0 {
return true
}
isCommitted := tm.IsCommited(xmin)
if isCommitted && xmin < xid && t.InSnapShot(xmin) == false {
if xmax == 0 {
return true
}
if xmax != xid {
isCommitted = tm.IsCommited(xmax)
if isCommitted == false || xmax > xid || t.InSnapShot(xmax) {
return true
}
}
}
return false
}
/*
Read Committed:
(XMIN == Ti and // created by Ti itself and
XMAX == NULL // not deleted now
)
or // or
(XMIN is commited and // created by a commited transaction and
(XMAX == NULL or // not deleted now or
(XMAX != Ti and XMAX is not commited) // deleted by a uncommited transaction
))
*/
func readCommitted(tm tm.TransactionManager, t *transaction, e *entry) bool {
xid := t.XID
xmin := e.XMIN()
xmax := e.XMAX()
if xmin == xid && xmax == 0 {
return true
}
isCommitted := tm.IsCommited(xmin)
if isCommitted {
if xmax == 0 {
return true
}
if xmax != xid {
isCommitted = tm.IsCommited(xmax)
if isCommitted == false {
return true
}
}
}
return false
}
