From 1ee34dd008c436499fc30b5d2e5a0f51a75a637c Mon Sep 17 00:00:00 2001
From: Doodle <13706157+critical27@users.noreply.github.com>
Date: Wed, 1 Jun 2022 16:29:21 +0800
Subject: [PATCH] fix learner's wal is not empty in rare cases (#4292)

* fix learner's wal is not empty

* fix lastLogTerm is not reset...

confrim with sophie.xie
---
 src/kvstore/raftex/RaftPart.cpp  | 9 +++++++++
 src/kvstore/wal/FileBasedWal.cpp | 1 +
 2 files changed, 10 insertions(+)

diff --git a/src/kvstore/raftex/RaftPart.cpp b/src/kvstore/raftex/RaftPart.cpp
index 0ab5d572601..ab57b775e1b 100644
--- a/src/kvstore/raftex/RaftPart.cpp
+++ b/src/kvstore/raftex/RaftPart.cpp
@@ -401,6 +401,15 @@ const char* RaftPart::roleStr(Role role) const {
 void RaftPart::start(std::vector<HostAddr>&& peers, bool asLearner) {
   std::lock_guard<std::mutex> g(raftLock_);
 
+  // There are some rare cases that the part start as learner, but wal is not empty. For example,
+  // the node is dead, and one partition is removed from raft group (majority still alive). However,
+  // the part is added back to raft group again as learner. So the wal may be not empty, what is
+  // worse, there could be case that commitLogId is 0, but wal's lastLogId is not 0, which is
+  // obviously not expected
+  if (asLearner) {
+    wal_->reset();
+  }
+
   lastLogId_ = wal_->lastLogId();
   lastLogTerm_ = wal_->lastLogTerm();
   term_ = lastLogTerm_;
diff --git a/src/kvstore/wal/FileBasedWal.cpp b/src/kvstore/wal/FileBasedWal.cpp
index 5b783b81d85..25a7a811b21 100644
--- a/src/kvstore/wal/FileBasedWal.cpp
+++ b/src/kvstore/wal/FileBasedWal.cpp
@@ -631,6 +631,7 @@ bool FileBasedWal::reset() {
     unlink(absFn.c_str());
   }
   lastLogId_ = firstLogId_ = 0;
+  lastLogTerm_ = 0;
   return true;
 }