Bharath Vissapragada created HBASE-24603:
--------------------------------------------
Summary: Zookeeper sync() call is async
Key: HBASE-24603
URL: https://issues.apache.org/jira/browse/HBASE-24603
Project: HBase
Issue Type: Improvement
Components: master, regionserver
Affects Versions: 3.0.0-alpha-1, 2.3.0, 1.7.0
Reporter: Bharath Vissapragada
Assignee: Bharath Vissapragada
Here is the method that does as sync() of lagging followers with leaders in the
quorum. We rely on this to see a consistent snapshot of ZK data from multiple
clients. However the problem is that the underlying sync() call is actually
async() since are passing a 'null' call back. See the ZK API
[doc|https://zookeeper.apache.org/doc/r3.5.7/apidocs/zookeeper-server/index.html]
for details. The end-result is that sync() doesn't guarantee that it has
happened by the time it returns.
{noformat}
/**
* Forces a synchronization of this ZooKeeper client connection.
* <p>
* Executing this method before running other methods will ensure that the
* subsequent operations are up-to-date and consistent as of the time that
* the sync is complete.
* <p>
* This is used for compareAndSwap type operations where we need to read the
* data of an existing node and delete or transition that node, utilizing the
* previously read version and data. We want to ensure that the version read
* is up-to-date from when we begin the operation.
*/
public void sync(String path) throws KeeperException {
this.recoverableZooKeeper.sync(path, null, null);
}
{noformat}
We rely on this heavily (at least in the older branches that do ZK based region
assignment). In branch-1 we saw weird "BadVersionException" exceptions in RITs
because of the inconsistent view of the ZK snapshot. It could manifest
differently in other branches. Either way, this is something we need to fix.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
