Hive: acquire explicit exclusive lock - hive

Question

Configuration (hortonworks)
hive: BUILD hive-1.2.1.2.3.0.0
Hadoop 2.7.1.2.3.0.0-2557
I'm trying to execute
lock table event_metadata EXCLUSIVE;
Hive response:
Error while processing statement: FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. Current transaction manager does not support explicit lock requests. Transaction manager: org.apache.hadoop.hive.ql.lockmgr.DbTxnManager
In the code there is obvious place where explicit locks are disabled:
http://grepcode.com/file/repo1.maven.org/maven2/org.apache.hive/hive-exec/1.2.0/org/apache/hadoop/hive/ql/lockmgr/DbTxnManager.java#DbTxnManager
321 #Override
322 public boolean supportsExplicitLock() {
323 return false;
324 }
Questions:
how can I make explicit locks work? In what version of hive do they appear?
Here is an example http://www.ericlin.me/how-table-locking-works-in-hive for cloudera that explicit locks work.

Answer 1

You may set the concurrency parameter on the fly:
set hive.support.concurrency=true;
After this you may try executing your command

Answer 2

Hive includes a locking feature that uses Apache Zookeeper for locking. Zookeeper implements highly reliable distributed coordination. Other than some additional setup and configuration steps, Zookeeper is invisible to Hive users.
In the $HIVE_HOME/hive-site.xml file, set the following properties:
<property>
<name>hive.zookeeper.quorum</name>
<value>zk1.site.pvt,zk1.site.pvt,zk1.site.pvt</value>
<description>The list of zookeeper servers to talk to.
This is only needed for read/write locks.
</description>
</property>
<property>
<name>hive.support.concurrency</name>
<value>true</value>
<description>Whether Hive supports concurrency or not.
A Zookeeper instance must be up and running for the default Hive lock manager to support read-write locks.</description>
</property>
After restarting hive, run the command
hive> lock table event_metadata EXCLUSIVE;
Reference: Programing Hive, O'REILLY
EDIT:
DummyTxnManager.java, which provides default Hive behavior, has
#Override
public boolean supportsExplicitLock() {
return true;
}
DummyTxnManager replicates pre Hive-0.13 behavior doesn't support transactions
where as
DbTxnManager.java,which stores the transactions in the metastore database, has:
#Override
public boolean supportsExplicitLock() {
return false;
}

Answer 3

Try the following:
set hive.txn.manager=org.apache.hadoop.hive.ql.lockmgr.DummyTxnManager;
unlock table tablename;