kezhuw commented on code in PR #2152:
URL: https://github.com/apache/zookeeper/pull/2152#discussion_r1731040660
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zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Learner.java:
##########
@@ -753,29 +752,60 @@ protected void syncWithLeader(long newLeaderZxid) throws
Exception {
isPreZAB1_0 = false;
// ZOOKEEPER-3911: make sure sync the uncommitted logs
before commit them (ACK NEWLEADER).
- sock.setSoTimeout(self.tickTime * self.syncLimit);
- self.setSyncMode(QuorumPeer.SyncMode.NONE);
- zk.startupWithoutServing();
- if (zk instanceof FollowerZooKeeperServer) {
+ if (zk instanceof FollowerZooKeeperServer &&
!packetsCommitted.isEmpty()) {
long startTime = Time.currentElapsedTime();
FollowerZooKeeperServer fzk =
(FollowerZooKeeperServer) zk;
- for (PacketInFlight p : packetsNotCommitted) {
- final Request request = fzk.appendRequest(p.hdr,
p.rec, p.digest);
- requestsToAck.add(request);
+
+ /*
+ * @see https://github.com/apache/zookeeper/pull/1848
+ * Persist and process the committed txns in
"packetsNotLogged"
+ * according to "packetsCommitted", which have been
committed by
+ * the leader. For these committed proposals, there is
no need to
+ * reply ack.
+ *
+ * @see
https://issues.apache.org/jira/browse/ZOOKEEPER-4394
+ * Keep the outstanding proposals in
"packetsNotLogged" to avoid
+ * NullPointerException when the follower receives
COMMIT packet(s)
+ * right after replying NEWLEADER ack.
+ */
+ while (!packetsCommitted.isEmpty()) {
+ long zxid = packetsCommitted.removeFirst();
+ pif = packetsNotLogged.peekFirst();
+ if (pif == null) {
+ LOG.warn("Committing 0x{}, but got no
proposal", Long.toHexString(zxid));
+ continue;
+ } else if (pif.hdr.getZxid() != zxid) {
+ LOG.warn("Committing 0x{}, but next proposal
is 0x{}",
+ Long.toHexString(zxid),
Long.toHexString(pif.hdr.getZxid()));
+ continue;
+ }
+ packetsNotLogged.removeFirst();
+ fzk.appendRequest(pif.hdr, pif.rec, pif.digest);
+ fzk.processTxn(pif.hdr, pif.rec);
}
- // persist the txns to disk
+ // @see
https://issues.apache.org/jira/browse/ZOOKEEPER-4646
+ // Make sure to persist the txns to disk before
replying NEWLEADER ack.
fzk.getZKDatabase().commit();
- LOG.info("{} txns have been persisted and it took
{}ms",
- packetsNotCommitted.size(), Time.currentElapsedTime()
- startTime);
- packetsNotCommitted.clear();
+ LOG.info("It took {}ms to persist and commit txns in
packetsCommitted. "
+ + "{} outstanding txns left in
packetsNotLogged",
+ Time.currentElapsedTime() - startTime,
packetsNotLogged.size());
}
- // set the current epoch after all the tnxs are persisted
+ // @see
https://issues.apache.org/jira/browse/ZOOKEEPER-4643
+ // @see
https://issues.apache.org/jira/browse/ZOOKEEPER-4785
+ // Update current epoch after the committed txns are
persisted
self.setCurrentEpoch(newEpoch);
LOG.info("Set the current epoch to {}", newEpoch);
- // send NEWLEADER ack after all the tnxs are persisted
+ // Now we almost complete the synchronization phase. Start
RequestProcessors
+ // to asynchronously process the pending txns in
"packetsNotLogged" and
+ // "packetsCommitted" later.
+ sock.setSoTimeout(self.tickTime * self.syncLimit);
+ self.setSyncMode(QuorumPeer.SyncMode.NONE);
+ zk.startupWithoutServing();
Review Comment:
I think we don't need this `startupWithoutServing` anymore. It was
introduced in #1445 to process asynchronous log process. And now we process log
synchronously.
This should solve problem @changruill raised in
https://github.com/apache/zookeeper/pull/2154#issuecomment-2167267712
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