Database Reference
In-Depth Information
JDBC fetchlet
: This is similar to the URL Timing fetchlet because it collects the timing
information for running a specified SQL statement against any database supporting JDBC
connectivity. It collects such metrics as request status, total time, number of rows retrieved,
and other, more fine-grained timings such as separate connect time and fetch time.
Unfortunately, this JDBC fetchlet does not return the values retrieved as the result of the
SELECT
command. It would be more appropriate to call it the JDBC Timing fetchlet to reflect
its purpose better, but that's not how the Oracle Extensibility documentation names it.
Web Services and JMX fetchlets
: These provide mechanisms for retrieving data by
using Web Services or Java Management Extensions (JMX). Both are widely adopted
industry standards. While Web Services are a generic distributed messaging and remote
execution standard, JMX is a standard that's designed specifically for Java applications
manageability. While each Java virtual machine (JVM) implementation normally supports
JMX, applications need to be instrumented to report their metrics to the JVM so that
they are accessible to the monitoring tools. Oracle's application servers support JMX as
well as many other software products such as IBM WebSphere and Red Hat JBoss. Many
Apache projects are supporting JMX as well—for example, Apache Tomcat or Apache
ZooKeeper from the Hadoop ecosystem. In fact, Hadoop's core NameNode and JobTracker
components are instrumented to expose their runtime metrics via JMX. Chapter 20 of the
Extensibility Programmer's Reference
has a detailed walk-through for creating a new target
type based on Web Services and JMX.
WBEM fetchlet
: This is the collector to retrieve metrics from components supporting the
Web-Based Enterprise Management (WBEM) standard. This standard is widely adopted
by the industry and is supported by a lot of open source and proprietary software. The
WBEM standard is much more advanced than the outdated SNMP protocol, as it includes
all the metadata, is more secure, and is much more compatible among different vendors.
The WBEM fetchlet is basically a Common Information Model (CIM) client that connects
to CIM Object Manager (CIMOM), often called a CIM Server. Windows Management
Interface (WMI) is Microsoft's implementation of WBEM/CIM. CIMOM servers can be
embedded on the devices or servers (such as some Cisco devices or Windows or HP-UX).
There is also a WS-Management fetchlet that's similar to the WBEM fetchlet but is based
on WS-Management standards. Microsoft Windows Remote Management (WinRM) is one
example of a WS-Management implementation.
DMS Fetchlet
: This collector allows using the Dynamic Monitoring Service (implemented,
for example, in Oracle Application Server and Fusion Middleware). It allows applications
to be instrumented to exhibit runtime metrics via DMS, and then an agent can use very
effective collection mechanisms. Unlike using shell script-based metrics, DMS fetchlet
collectors don't fork any processes, so it's very effective in terms of resource consumption.
The DMS API was submitted to the Java Community Process in 2001 as Java Specification
Request 138: Performance Metric Instrumentation. However, it wasn't widely adopted in
the industry and was withdrawn in 2010.
Not
■
You can find a full description of fetchlets in Chapter 20 of the
Extensibility Programmer's Reference.
In addition, several fetchlets are not documented (and thus, are not guaranteed to work in the future or even
current releases). For example, the JDBCSQL fetchlet, unlike the JDBC Timing fetchlet, allows collection of values
returned by SQL via a JDBC connection to any database with JDBC drivers, and not just Oracle. However, be careful
relying on undocumented fetchlets, as any EM12c patch set or patch might affect functionality or availability of these
fetchlets even if they seem to work well at the moment.
