[KUDU-792] Investigate "optimization" where LMP mismatch is handled in two places

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: Private Beta
• Component/s: consensus
• Assignee: Unassigned
• Reporter: Todd Lipcon
• Created: 28/May/15 13:47
• Updated: 16/Feb/18 15:26

Description

We have a bit of code when handling the LMP mismatch that says:

  // If the terms mismatch we abort down to the index before the leader's preceding,
  // since we know that is the last opid that has a chance of not being overwritten.
  // Aborting preemptively here avoids us reporting a last received index that is
  // possibly higher than the leader's causing an avoidable cache miss on the leader's
  // queue.
  if (term_mismatch) {
    return state_->AbortOpsAfterUnlocked(req.preceding_opid->index() - 1);
  }

The code looks like it's somewhat redundant (since we also abort operations elsewhere on the replica side), and it claims to be an optimization, but if we remove it, a bunch of correctness tests fail. We should understand better why this code is here and at least update the comment.