Understanding SQL*Net
Using Oracle SNMP Support
Following are things you must do before using Oracle SNMP Support:
Start the Master Agent, Encapsulator, and Native SNMP Agent
This varies depending on the platform. See your operating system-specific documentation for the actual command names and instructions.
Controlling the Oracle Database Subagent
The SNMP subagent is a separate executable from the database, and it is not started automatically when the database is started.
To start, stop, and check to see if the database subagent is running or not, use the following commands from LSNRCTL:
LSNRCTL> dbsnmp_start
LSNRCTL> dbsnmp_stop
LSNRCTL> dbsnmp_status
You must run these commands on the machine where the SNMP subagent is running--there is no remote support.
Attention: The Master Agent must be running before starting the subagent.
Controlling SNMP Support for Network Services
The subagents for the listener, MultiProtocol Interchange, and Oracle Names Server are started when the listener, MultiProtocol Interchange, are Oracle Names Server are started. They are not separate executables, as with SNMP support for the Oracle database.
Polling Database MIB Variables
In using, tuning, and understanding applications that poll the SNMP-managed applications, some skill is required in taking the proper measurements at the proper times, accurately interpreting the data, and making sure that the very act of managing a process does not impose undue performance demands on that process.
Attention: Measuring performance should not negatively impact the performance.
As inherent components of the applications, the subagents for the listener, Interchange and Oracle Names always have access to the current value for any MIB variable. However, as a separate process from the database, there is some cost associated with the database subagent's querying a value. To reduce the impact of its queries against the database, the database subagent maintains a cache of values that it has retrieved from the database. The length of time that each variable is considered "fresh" may have one of two values: FAST or SLOW.
All variables retrieved by the database subagent, whether in the standard or Oracle Database MIB, are labeled as either FAST or SLOW. Only variables in the two database MIBs have this classification. Networking product subagents have access to internal data structures that are updated continuously; they do not cache values like the database Agent.
Polling Intervals
The polling times are hardcoded and cannot be configured. If polling times could be configured, problems in developing applications would result. Graphical elements would exhibit a false value, depending upon the frequency of polling and cache intervals. If various machines and services on a network had different polling intervals, significant problems might result.
FAST Variables
FAST variables are retrieved every 30 seconds or more. If a new query comes in and the subagent sees that the cached value is less than 30 seconds, it returns that value AGAIN. If the cached value is older than 30 seconds, it obtains the new value and returns it, as well as caches the new value.
SLOW Variables
SLOW variables are retrieved once every 5 minutes or more.