[kudu-CR] KUDU-1365. Add leader pre-elections

["Todd Lipcon (Code Review)" <ge...@cloudera.org>]

Hello Kudu Jenkins,

I'd like you to reexamine a change.  Please visit

    http://gerrit.cloudera.org:8080/4694

to look at the new patch set (#3).

Change subject: KUDU-1365. Add leader pre-elections
......................................................................

KUDU-1365. Add leader pre-elections

This implements the "pre-election" extension to the Raft algorithm.
The idea is that, before calling a leader election, a candidate first
sends a pre-election vote request to all voters. The voters respond
as they would have in a real vote, except they don't actually record
their vote.

Cluster tests verify that this substantially reduces the election storms
after a node has a temporarily slow disk or otherwise freezes.

A new experimental flag 'raft_enable_pre_election' is introduced which
defaults the feature to on, but provides a safety valve to disable this
in case we find some bug after release.

Change-Id: Ifcfabd8c9ffe31f17ab768542a046426f656db43
---
M src/kudu/consensus/consensus.h
M src/kudu/consensus/consensus.proto
M src/kudu/consensus/leader_election-test.cc
M src/kudu/consensus/leader_election.cc
M src/kudu/consensus/leader_election.h
M src/kudu/consensus/raft_consensus.cc
M src/kudu/consensus/raft_consensus.h
M src/kudu/consensus/raft_consensus_quorum-test.cc
M src/kudu/integration-tests/raft_consensus-itest.cc
M src/kudu/tserver/tablet_service.cc
10 files changed, 261 insertions(+), 109 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/94/4694/3
-- 
To view, visit http://gerrit.cloudera.org:8080/4694
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ifcfabd8c9ffe31f17ab768542a046426f656db43
Gerrit-PatchSet: 3
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: Todd Lipcon <to...@apache.org>
Gerrit-Reviewer: David Ribeiro Alves <dr...@apache.org>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mike Percy <mp...@apache.org>
Gerrit-Reviewer: Tidy Bot
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>