GeorgeMacRorie

Where we're going, we don't need consistency.

Back to the future revision.

mvcc: required revision is a future revision

If My Calculations Are Correct

// STM is an interface for software transactional memory.
type STM interface {
	// Get returns the value for a key and inserts the key in the txn's read set.
	// If Get fails, it aborts the transaction with an error, never returning.
	Get(key ...string) string
	// Put adds a value for a key to the write set.
	Put(key, val string, opts ...v3.OpOption)
	// Rev returns the revision of a key in the read set.
	Rev(key string) int64
	// Del deletes a key.
	Del(key string)

	// commit attempts to apply the txn's changes to the server.
	commit() *v3.TxnResponse
	reset()
}

	// SerializableSnapshot provides serializable isolation and also checks
	// for write conflicts.
	SerializableSnapshot Isolation = iota

		var out stmResponse
		for {
			s.reset()
			if out.err = apply(s); out.err != nil {
				break
			}
			if out.resp = s.commit(); out.resp != nil {
				break
			}
		}
		outc <- out

Your function is called in a retry loop

func getSomeKeys(client *etcdv3.Client) error {
    var valOne, valTwo string
    _, err := concurrency.NewSTM(client, func(s STM) error {
        valOne = s.Get("keyOne")
        valTwo = s.Get("keyTwo")
        return nil
    })

    fmt.Println(valOne, valTwo)

    return err
}

this happens to be all you need to tickle the bug we observed in production

if firstRead {
	// txn's base revision is defined by the first read
	s.getOpts = []v3.OpOption{
		v3.WithRev(resp.Header.Revision),
		v3.WithSerializable(),
	}
}

Sneaky little optimization

BEGIN
GET "keyOne"              // --> goes to replica ONE (returns rev 1)
GET "keyTwo" (with rev 1) // --> goes to replica ONE
END

BEGIN
GET "keyOne"              // --> goes to replica ONE (returns rev 1)
GET "keyTwo" (with rev 1) // --> goes to replica TWO
END

Whoa. This is Heavy.

Better get used to these bars, Kid.

But the only correct way to read from a Raft cluster is to pass the read through the log replication too.

It Works! It Works!