Logging Options

In a MapR cluster, the logging option that you configure defines how the logs are stored and accessed.

Centralized logging. The logs are written to local volumes on the MapR filesystem.
YARN log aggregation. The logs are written to the local filesystem and then the container logs from each node are aggregated and stored on the MapR filesystem.
Local logging. The log files for each job or application are written to the local filesystem. This is the default behavior for MapReduce version 2 (MRv2) applications and non-MapReduce applications.
- For MRv2 or other applications that run on YARN, the logs are written to the following directory on the local filesystem: /opt/mapr/hadoop/hadoop-2.x.x/logs/userlogs/

The logging options that you can choose from are determined by the type of jobs or applications that you run:

Type of Job or Application	Available Logging Options
MRv2	Centralized logging YARN log aggregation Local logging (default)
YARN applications (non- MapReduce)	YARN log aggregation Local logging (default)

If you enable centralized logging for MRv2, the MapReduce applications will use centralized logging, while the other YARN applications in the cluster will use local logging.

Note: Select a logging option that stores the logs on the MapR filesystem for the following reasons:

Prevent job or application failures due to a lack of space on the local filesystem for logs.
Prevent the loss or inaccessibility of logs due to node failure. Logs stored in a local volume are two-way replicated.