I've been working on adding a TCPResponderThread to the leader election
process so that if a deployment needs to be TCP only, it can be and still
use all election types. Testing this has exposed what might be a race
condition in the leader election code that prevents a leader from being
Here's the behaviour I see in LETest occasionally. With three nodes (reduced
from 30 for ease of debugging), node 3 gets elected before either node 1 or
node 2 finish their election (there is one round where each node that 3 has
the highest id, and then 3 completes its second round by receiving votes for
itself from 1 and 2, but 1 and 2 do not receive votes from 3).
Now 3 is killed by the test harness. 1 and 2 are still voting for it, but
every time they try, the vote tally excludes 3 since it hasn't been heard
from. They then spin round the voting process, unable to reset their vote. I
expect that the heartbeat mechanism in a running QuorumPeer takes care of
this when the leader is lost, but the associated QuorumPeers aren't running.
If this is the case, then there is a simple fix to reset the nodes vote to
themselves if they are voting for a node that hasn't been heard from. I
don't know why using TCP instead of UDP for the responder thread is
exacerbating this (and we can't rule out my introducing a bug :)); but as
it's a race condition the different timings associated with waiting on a TCP
socket might just be enough to expose the issue.
Can someone verify this might be possible / figure out what I missed?