Replicating Data to Impala Clusters

Replicating Impala Metadata

Impala metadata replication is performed as a part of Hive replication. Impala replication is only supported between two CDH 5 clusters. The Impala and Hive services must be running on both clusters.

To enable Impala metadata replication, perform the following tasks:
  1. Schedule Hive replication as described in Configuring Replication of Hive/Impala Data.
  2. Confirm that the Replicate Impala Metadata option is set to Yes on the Advanced tab in the Create Hive Replication dialog.
When you set the Replicate Impala Metadata option to Yes, Impala UDFs (user-defined functions) will be available on the target cluster, just as on the source cluster. As part of replicating the UDFs, the binaries in which they are defined are also replicated.

Refreshing Impala Metadata

For Impala clusters that do not use LDAP authentication, you can configure an Advanced Configuration Snippet to automatically refresh Impala metadata with the INVALIDATE METADATA statement after Hive replication completes.

Alternatively, you can run the INVALIDATE METADATA statement manually for replicated tables. For more information about the statement, see INVALIDATE METADATA Statement.

To set the Advanced Configuration Snippet, perform the following steps:
  1. Navigate to the Configuration page for the Hive node you want to replicate.
  2. For the Category, select Advanced.
  3. In the Hive Replication Environment Advanced Configuration Snippet (Safety Valve) field, add the following parameter: RUN_INVALIDATE_METADATA=true.
  4. Save the changes.
The RUN_INVALIDATE_METADATA=true configuration causes the Hive replication job to run the Impala INVALIDATE METADATA statement on the destination cluster after completing the replication. The statement purges the metadata of the replicated tables and views within the destination cluster's Impala upon completion of replication, allowing other Impala clients at the destination to query these tables successfully with accurate results. However, this operation is potentially unsafe if DDL operations are being performed on any of the replicated tables or views while the replication is running. In general, directly modifying replicated data/metadata on the destination is not recommended. Ignoring this can lead to unexpected or incorrect behavior of applications and queries using these tables or views.