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https://issues.apache.org/jira/browse/ZOOKEEPER-2678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15847250#comment-15847250
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ASF GitHub Bot commented on ZOOKEEPER-2678:
-------------------------------------------
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.
> Large databases take a long time to regain a quorum
> ---------------------------------------------------
>
> Key: ZOOKEEPER-2678
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2678
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.9, 3.5.2
> Reporter: Robert Joseph Evans
> Assignee: Robert Joseph Evans
>
> I know this is long but please here me out.
> I recently inherited a massive zookeeper ensemble. The snapshot is 3.4 GB on
> disk. Because of its massive size we have been running into a number of
> issues. There are lots of problems that we hope to fix with tuning GC etc,
> but the big one right now that is blocking us making a lot of progress on the
> rest of them is that when we lose a quorum because the leader left, for what
> ever reason, it can take well over 5 mins for a new quorum to be established.
> So we cannot tune the leader without risking downtime.
> We traced down where the time was being spent and found that each server was
> clearing the database so it would be read back in again before leader
> election even started. Then as part of the sync phase each server will write
> out a snapshot to checkpoint the progress it made as part of the sync.
> I will be putting up a patch shortly with some proposed changes in it.
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