High Availability

Enabling high availability for HiveServer2

In order to enable high availability for HiveServer2, the user should take the following two steps:

• set the environment variable MR3_SHARED_SESSION_ID in env.sh
• configure high availability by updating hive-site.xml

First, set MR3_SHARED_SESSION_ID to a unique string before starting HiveServer2 instances, e.g.:

vi env.sh

export MR3_SHARED_SESSION_ID=d7b52f74-7349-405c-88a2-d0d1cbb5a918

The environment variable (whose value internally serves as the MR3 session ID in HiveServer2) can be set to any string, but should remain the same across all HiveServer2 instances so that they share the same staging directory on HDFS.

Next, configure HiveServer2 by updating hive-site.xml. The following table shows configuration keys relevant to high availability of HiveServer2. In particular, setting hive.server2.active.passive.ha.enable to true enables high availability and allows all HiveServer2 instances to share a common MR3 DAGAppMaster. Note that high availability requires service discovery (specified by hive.server2.support.dynamic.service.discovery) so that all HiveServer2 instances can be registered to ZooKeeper.

Name	Default value	Example to enable high availability
hive.server2.active.passive.ha.enable	false	true
hive.server2.support.dynamic.service.discovery	false	true
hive.mr3.zookeeper.appid.namespace	mr3AppId	(default value)
hive.server2.active.passive.ha.registry.namespace	hs2ActivePassiveHA	(default value)
hive.server2.zookeeper.namespace	hiveserver2	hiveserver2-mr3
hive.zookeeper.quorum		blue0:2181
hive.zookeeper.client.port	2181	2181

Since high availability of HiveServer2 uses service discovery, a Beeline connection selects a HiveServer2 instance randomly. In order to take advantage of service discovery, the user should specify the ZooKeeper server and a namespace when running Beeline. For example, with a ZooKeeper server running at blue0:2181 and a namespace hiveserver2-mr3, the user can set the environment variable HIVE_SERVER2_JDBC_OPTS in env.sh as follows.

vi env.sh

HIVE_SERVER2_JDBC_OPTS="ssl=false;serviceDiscoveryMode=zooKeeper;zooKeeperNamespace=hiveserver2-mr3"

Running multiple HiveServer2 instances on the same node

If multiple HiveServer2 instances are to be run on the same node, the user should assign different ports by setting the environment variable HIVE_SERVER2_PORT in env.sh to a unique value for each HiveServer2 instance. In addition, the following two configuration keys should be set in hive-site.xml.

• set hive.server2.webui.port to 0 so that no conflict arises
• set hive.server2.logging.operation.log.location appropriately, e.g., /tmp/hive/operation_logs/${hive.server2.port}

Using ZooKeeper

If HiveServer2 establishes connections to ZooKeeper at its launch, the user should make sure that the Curator module (org.apache.curator) used in HiveServer2 should be compatible with the ZooKeeper service. If not, the user should manually run ZooKeeper of an appropriate version and set the configuration key hive.zookeeper.quorum in hive-site.xml.