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## System Log File Monitoring

The Oracle NoSQL Database is composed of the following components, and each component produces log files that can be monitored:

- Replication Nodes (RN) – Service read and write requests from API calls. Replication Nodes for a particular shard are laid out on different Storage Nodes (physical servers) by the topology manager, so the log files for the nodes in each shard are spread across multiple machines.

- Storage Node Agents (SNA) – Manage the Replication Nodes that are running on each Storage Node (SN). The Storage Node Agent maintains its own log regarding the state of each replication node it is managing. You can think of the Storage Node Agent log as a high level log of the Replication Node activity on a particular Storage Node.

- Administration (Admin) Nodes – Administrative Nodes handle the execution of commands from the administrative command line interface. Long running plans are also staged from the administrative nodes. Administrative Nodes also maintain a consolidated log of all the other logs in the Oracle NoSQL cluster.

All of the above mentioned log files can be found in the following directory structure `KVROOT/kvstore/log` on the machine where the component is running. It is possible to compress these log files to accommodate more files in the given disk space. For more details, see Log File Compression.

The following steps can be used to find the machines that are running the components of the cluster:

1. `java -Xmx64m -Xms64m -jar kvstore.jar ping -host <any machine in the cluster> -port <the port number used to initialize the KVStore>`

2. Each Storage Node (snXX) is listed in the output of the ping command, along with a list of Replication nodes (rgXX-rnXX) running on the host listed in the ping output. XX denotes the unique number assigned to that component by NoSQL Database. For Replication Nodes, rg denotes the shard number and stands for replication group, while rn denotes the Replication Node number within that shard.

3. Administration (Admin) Nodes – Identifying the nodes in the cluster that are running administrative services is a bit more challenging. To identify these nodes, a script would run ps axww on every host in the cluster and grep for kvstore.jar and -class Admin.

The Oracle NoSQL Database maintains a single consolidated log of every node in the cluster, and this can be found on any of the nodes running an administrative service. While this is a convenient and easy single place to monitor for errors, it is not 100% guaranteed. The single consolidated view is aggregated by getting log messages over the network, and transient network failures, packet loss, and high network utilization can cause this consolidated log to either be out of date, or have missing entries. Therefore, we recommend monitoring each host in the cluster as well as monitoring each type of log file on each host in the cluster.

Generally speaking, any log message with a level of SEVERE should be considered a potentially critical event and worthy of generating a systems management notification. The sections in the later part of this document illustrate how to correlate specific SEVERE exceptions with hardware component failure.

### Java Management Extensions (JMX) Monitoring

Oracle NoSQL Database is also monitored through JMX based system management tools. For more information on JMX, see Standardized Monitoring Interfaces.