Cloudera Docs

Troubleshooting Hive ACID table replication policies

The troubleshooting scenarios in this topic help you to troubleshoot the Hive ACID table replication policies in Replication Manager.

In Cloudera Manager, the history of a schedule appears as FAILED and the status shows SKIPPED. Why are the SKIPPED runs listed as FAILED runs?

This scenario appears when there is no data to load during replication load on the target cluster.

FAILED with SKIPPED status might indicate an issue with the dump schedule on the source cluster. This can also appear when the dump completes after the load starts which might result in no data to load. Note that the first run (bootstrap) of the schedule takes a longer time than the subsequent (incremental) runs. Hence, the Hive query on the target side (load) might fail because the query runs at the same time as on source before the source completes the dumping operation.

How to recover a schedule from FAILED_ADMIN state?

When a non-recoverable error appears for a replication job and the status says FAILED_ADMIN, you can perform the following steps to recover a schedule from this state:
  1. Go to the error log path.
  2. Search for the file _non_recoverable.
  3. Search for the error stack in the _non_recoverable file.
  4. Fix the error.
  5. Delete the _non_recoverable.

Why are notification events missing in the metastore?

One of the possible errors that might appear with FAILED_ADMIN status is when the notification events’ TTL expires. This results in notifications being deleted in the metastore. In this scenario, the workaround is to start a fresh bootstrap phase of replication.

To re-bootstrap the database in the source cluster, perform the following steps:

  1. Use beeline to drop the target database.
  2. Remove the dump directory on HDFS for the required policy. The path of the _non_recoverable error file path has the dump directory path.

The policy schedule resumes automatically with the bootstrap phase.

How does Hive ACID table replication handle default and custom locations for databases and tables?

The following use cases show how the default location and custom locations for databases and tables are handled during Hive ACID table replication:

  • Use case 1 - Database location and managedlocation properties.
    • If the source database properties location and managedlocation are set to the default location (<dbname>.db.toLowerCase()), the target database properties location and managedlocation are also set to the default location after replication.
    • If the source database properties location and managedlocation are set to custom locations, the target database properties location and managedlocation retain the corresponding custom locations on the target cluster after replication.

    By default, the custom location is retained on the target cluster. You can disable this behaviour by configuring the hive.repl.retain.custom.db.locations.on.target policy-level configuration property to false. When you disable this property and run the Hive ACID table replication, the replicated database locations on the target cluster are set to default locations, irrespective of whether the database locations on the source are set to default or custom locations.

  • Use case 2: Table location and managedlocation properties.
    • After replication, a replicated managed table inherits the parent’s database managedlocation property irrespective of whether the managedlocation property of the parent’s database is set to the default location or custom location on the source cluster.
    • After replication, a replicated external table derives its location from the value of the hive.repl.replica.external.table.base.dir property and the external table location on the source cluster.

      For example, if an external table ext_tab1 is located at /ext_loc/ext_tab1/ on the source cluster and the hive.repl.replica.external.table.base.dir property is configured as /ext_base1 on the target, the location for ext_tab1 on the target cluster is /ext_base1/ext_loc/ext_tab1.

      The hive.repl.replica.external.table.base.dir property is derived from the value you set for the External Table Base Directory option in the Hive ACID table replication policy.

Which replication policy in Replication Manager replicates both the managed tables (ACID) and external tables in a database?

To replicate managed tables (ACID) and external tables in the database successfully, you must first replicate the ACID tables using Hive ACID table replication policy. After the replication policy run completes, create the Hive external table replication policy to replicate the external tables in the database.

To accomplish this task, perform the following steps:
  1. Create a Hive ACID table replication policy where you choose the required database. The replication policy replicates data and metadata of the ACID tables in the database.

    The first run of the replication policy performs a bootstrap replication. During bootstrap replication, the target database is created and all the ACID tables are replicated to the target database. The subsequent policy runs are incremental. During incremental replication, only the source database changes between the current run and previous run are replicated.

  2. Ensure that the first Hive ACID table replication policy run is complete in Replication Manager.
  3. Create a Hive external table replication policy for the database. After policy creation is complete, a full replication (bootstrap) of data and metadata of all the external tables from the source database to target database is initiated. After the bootstrap replication is complete, the next policy run jobs leverage the HDFS snapshots to perform incremental replication of external table data.

Subsequent replication job runs perform full metadata replication and incremental data replication.

What table types in Hive does Replication Manager support?

The following replication policies replicate the given table types in Hive:
  • Hive ACID table replication policies replicate data and metadata of the following table types in Hive:
    • Managed: CRUD transactional
    • Managed: Insert-only transactional
  • Hive external table replication policies replicate data and metadata of external tables.

After creating a Hive external table replication policy, the “Bootstrap REPL LOAD is not allowed on Database: sourceDB as it is not empty. One or more tables/functions exist.” error appears. How to resolve this issue?

This error appears if you create the Hive external table replication policy before you create the Hive ACID table external table policy.

To resolve this issue, the administrator must perform the following steps:
  1. Drop the database with the replicated data and metadata on the target cluster.
  2. Create a Hive ACID table replication policy.
  3. After the Hive ACID table replication policy run completes, create a Hive external table replication policy.