Replicated Logs

Lagging Follower

A lagging follower is missing a leader suffix but has no conflicting term.

highlighted = computed this step

A lagging follower

A lagging follower has a correct prefix but is missing recent leader entries. Missing entries are not a conflict. Note: the repair row shows what catch-up would append.

lagging follower\text{lagging follower}

Matching prefix

The lagging follower matchIndex is 2 while the leader has 3 entries. Note: the gap is visible as blank cells.

matchIndex=2,leader entries=3\text{matchIndex}=2,\quad \text{leader entries}=3

a simplified leader-based log replication; quorum commit + log repair are exact on these tiny clusters; full Raft safety, leader election (next book), and network partitions/timing are beyond these traces - no product claims.

Lagging follower - quorum 2; committedIndex 2; divergent: F2nodeidx 1idx 2idx 3Lt1:at2:bt2:cF1t1:at2:bF1 repairt1:at2:bt2:cF2t1:at1:xF2 repairt1:at2:bt2:c

Summary

Lagging is a prefix problem, not a conflicting-term problem. Note: this is simplified leader-based replication; full Raft safety and leader election are the next book, while partitions and timing are beyond these traces.

prefix lag\text{prefix lag}