Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/157#discussion_r98734336
--- Diff: src/java/main/org/apache/zookeeper/server/ZooKeeperServer.java ---
@@ -507,9 +507,12 @@ public synchronized void shutdown() {
if (firstProcessor != null) {
firstProcessor.shutdown();
}
- if (zkDb != null) {
- zkDb.clear();
- }
+
+ // There is no need to clear the database
+ // * When a new quorum is established we can still apply the diff
+ // on top of the same zkDb data
+ // * If we fetch a new snapshot from leader, the zkDb will be
+ // cleared anyway before loading the snapshot
--- End diff --
There is one case we may still want to clear db here - when one of the
ZooKeeper critical threads (such as * processors, session trackers) fail,
ZooKeeper server will shutdown (see runFromConfig) and consequently invoke
ZooKeeper#shutdown. In this case, I don't see a particular reason not to clear
the db, though not doing it might be fine (as one could argue the server will
be dead anyway), but I tend to lean towards the safe side on cleaning the db.
One way to conditionally do that is to add a Boolean parameter to
ZooKeeper#shutdown so we can have fine grained control over when to clear db in
what code path.
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