kezhuw commented on code in PR #2069:
URL: https://github.com/apache/zookeeper/pull/2069#discussion_r1342101080
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zookeeper-server/src/main/java/org/apache/zookeeper/server/quorum/Leader.java:
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@@ -915,22 +934,30 @@ private long getDesignatedLeader(Proposal
reconfigProposal, long zxid) {
* @return True if committed, otherwise false.
**/
public synchronized boolean tryToCommit(Proposal p, long zxid,
SocketAddress followerAddr) {
+ // in order to be committed, a proposal must be accepted by a quorum.
+ //
+ // getting a quorum from all necessary configurations.
+ if (!p.hasAllQuorums()) {
+ return false;
+ }
+
// make sure that ops are committed in order. With reconfigurations it
is now possible
// that different operations wait for different sets of acks, and we
still want to enforce
// that they are committed in order. Currently we only permit one
outstanding reconfiguration
// such that the reconfiguration and subsequent outstanding ops
proposed while the reconfig is
// pending all wait for a quorum of old and new config, so it's not
possible to get enough acks
// for an operation without getting enough acks for preceding ops. But
in the future if multiple
// concurrent reconfigs are allowed, this can happen.
- if (outstandingProposals.containsKey(zxid - 1)) {
- return false;
- }
-
- // in order to be committed, a proposal must be accepted by a quorum.
- //
- // getting a quorum from all necessary configurations.
- if (!p.hasAllQuorums()) {
- return false;
+ Proposal previous = outstandingProposals.get(zxid - 1);
Review Comment:
It is changed for:
1. Make sure `p` has majority acked.
2. Commit also preceding quorum read to guard against downgrading.
Previously, we return directly if there is preceding proposal, but now we
are committing it if preceding proposal is a quorum read. So the order becomes
matter.
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