How radonDB implement Snapshot Isolation

[louishust]

Is there some design doc for implementation of Snapshot Isolation ?

Queue commit action?

// CommitLock used to acquire the commit.
func (mgr *TxnManager) CommitLock() {
	mgr.commitLock.Lock()
}

[BohuTANG]

Hi @louishust,

radon has a commit lock to make snapshot isolation:
1, when 'xa commit' is in committing phase, it acquires a commit-lock at:

radon/src/backend/txn.go

Line 573 in a81a767

txn.mgr.CommitLock()

2, At the same time, if a read query executing, it will try to acquire the same lock at:

radon/src/backend/txn.go

Line 363 in a81a767

txn.mgr.CommitRLock()

So, he must wait the committing done.

This is the key to support snapshot isolation.
And, the backend MySQL must be in REPEATABLE-READ isolation level.

[louishust]

Thanks for your reply.

So the performance is like one thread?

If deploy two radondb in one cluster, how to maintain the lock?

[BohuTANG]

1, As the case we talked above,, its YES.
2, The lock only works for one node, otherwise we cannot guaranteec the snapshot isolation.