[jira] [Commented] (ZOOKEEPER-1559) Learner should not snapshot uncommitted state

["Flavio Junqueira (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-1559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13471015#comment-13471015 ] 

Flavio Junqueira commented on ZOOKEEPER-1559:
---------------------------------------------

This is the main bit of code I've been looking at and I believe we need to fix:

{code}
boolean snapshotTaken = false;
            // we are now going to start getting transactions to apply followed by an UPTODATE
            outerLoop:
            while (self.isRunning()) {
                readPacket(qp);
                switch(qp.getType()) {
                case Leader.PROPOSAL:
                    PacketInFlight pif = new PacketInFlight();
                    pif.hdr = new TxnHeader();
                    pif.rec = SerializeUtils.deserializeTxn(qp.getData(), pif.hdr);
                    if (pif.hdr.getZxid() != lastQueued + 1) {
                    LOG.warn("Got zxid 0x"
                            + Long.toHexString(pif.hdr.getZxid())
                            + " expected 0x"
                            + Long.toHexString(lastQueued + 1));
                    }
                    lastQueued = pif.hdr.getZxid();
                    packetsNotCommitted.add(pif);
                    break;
                case Leader.COMMIT:
                    if (!snapshotTaken) {
                        pif = packetsNotCommitted.peekFirst();
                        if (pif.hdr.getZxid() != qp.getZxid()) {
                            LOG.warn("Committing " + qp.getZxid() + ", but next proposal is " + pif.hdr.getZxid());
                        } else {
                            zk.processTxn(pif.hdr, pif.rec);
                            packetsNotCommitted.remove();
                        }
                    } else {
                        packetsCommitted.add(qp.getZxid());
                    }
                    break;
                case Leader.INFORM:
                    TxnHeader hdr = new TxnHeader();
                    Record txn = SerializeUtils.deserializeTxn(qp.getData(), hdr);
                    zk.processTxn(hdr, txn);
                    break;
                case Leader.UPTODATE:
                    if (!snapshotTaken) { // true for the pre v1.0 case
                        zk.takeSnapshot();
                        self.setCurrentEpoch(newEpoch);
                    }
                    self.cnxnFactory.setZooKeeperServer(zk);                
                    break outerLoop;
                case Leader.NEWLEADER: // it will be NEWLEADER in v1.0
                    zk.takeSnapshot();
                    self.setCurrentEpoch(newEpoch);
                    snapshotTaken = true;
                    writePacket(new QuorumPacket(Leader.ACK, newLeaderZxid, null, null), true);
                    break;
                }
            }
{code}
                
> Learner should not snapshot uncommitted state
> ---------------------------------------------
>
>                 Key: ZOOKEEPER-1559
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1559
>             Project: ZooKeeper
>          Issue Type: Sub-task
>          Components: quorum
>            Reporter: Flavio Junqueira
>
> The code in Learner.java is a bit entangled for backward compatibility reasons. We need to make sure that we can remove the calls to take a snapshot without breaking it. 

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