szetszwo commented on code in PR #643:
URL: https://github.com/apache/ratis/pull/643#discussion_r869195343
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ratis-server/src/main/java/org/apache/ratis/server/impl/SnapshotInstallationHandler.java:
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@@ -206,16 +209,16 @@ private InstallSnapshotReplyProto
notifyStateMachineToInstallSnapshot(
state.setLeader(leaderId, "installSnapshot");
server.updateLastRpcTime(FollowerState.UpdateType.INSTALL_SNAPSHOT_NOTIFICATION);
- if (inProgressInstallSnapshotIndex.compareAndSet(0,
firstAvailableLogIndex)) {
+ if (inProgressInstallSnapshotIndex.compareAndSet(INVALID_LOG_INDEX,
firstAvailableLogIndex)) {
LOG.info("{}: Received notification to install snapshot at index {}",
getMemberId(), firstAvailableLogIndex);
// Check if snapshot index is already at par or ahead of the first
// available log index of the Leader.
final long snapshotIndex = state.getLog().getSnapshotIndex();
- if (snapshotIndex + 1 >= firstAvailableLogIndex &&
firstAvailableLogIndex > 0) {
+ if (snapshotIndex >= firstAvailableLogIndex && firstAvailableLogIndex
> INVALID_LOG_INDEX) {
Review Comment:
Yes, ALREADY_INSTALLED is correct.
Leader tells firstAvailableLogIndex (=10) to a follower. The follower
checks if it needs to install a snapshot -- if its snapshotIndex < 9, say
snapshotIndex == 8, there is a gap between snapshotIndex and
firstAvailableLogIndex so that it needs to install a snapshot with index >= 9.
The leader is not able to send the index 9 log entry to the follower because
firstAvailableLogIndex is 10.
If the follower's snapshotIndex == 9, there is no gap so that it can tell
the leader to send log entires starting at index 10 without installing a
snapshot.
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