Replicating data to Impala clusters

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

Replicating Impala metadata

To enable Impala metadata replication, set the Advanced > Replicate Impala Metadata option to Yes during Hive external table replication policy creation. After the replication job completes, you can view the Impala UDFs (user-defined functions) 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.

Invalidating Impala metadata

For Impala clusters that do not use LDAP authentication, configure Advanced > Invalidate Impala Metadata on Destination during Hive external table replication policy creation so that the replication job automatically invalidates Impala metadata after replication completes. If the clusters use Sentry, the Impala user should have permissions to run INVALIDATE METADATA.

The configuration causes the Hive/Impala replication job to run the Impala INVALIDATE METADATA statement per table 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.

Alternatively, you can run the INVALIDATE METADATA statement manually for replicated tables.