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Classes, Instances, Counters

Performance Class

Performance class is a type of the system resource that can be monitored. This includes CPU, memory, disk, network, etc. A class is identified by its ID. You obtain the IDs of the available classes by retrieving them from the Agent vocabulary. Each performance class is represented by a category in the vocabulary. To distinguish the class categories from other categories, they all belong to another category named counters. Different server types (generic, Virtuozzo Containers) have their own sets of performance classes. The following are examples of performance class entries in a vocabulary.

Generic performance class (compatible with physical servers only):

<category>

  <id>counters_net</id>

  <category>generic</category>

  <category>counters</category>

  <short>Network usage</short>

  <long>Network usage related parameters</long>

</category>

Virtuozzo performance class (compatible with Virtuozzo Containers only):

<category>

  <id>counters_vz_net</id>

  <category>virtuozzo</category>

  <category>counters</category>

  <short>Network usage</short>

  <long>Container network-related counters</long>

</category>

The following table describes the properties of a performance class:

Property

Description

id

The unique class ID

category

The name of the parent vocabulary category.

The counters category indicates that this vocabulary entry is a performance class.

The generic category indicates that this class is compatible with generic servers (physical machines or virtual servers treated as real physical servers). Classes compatible with Virtuozzo Containers belong to the virtuozzo category.

short

Short description of the class.

long

Long description of the class.

Class Instance

While class identifies the type of the system resource, the term "instance" refers to a particular device when multiple devices of the same type exist in the system. For example, a network interface in general is a class, but each network card installed in the system is an instance of that class. Each class has at least one instance, but not all classes may have multiple instances.

Performance Counter

Counters are used to measure various aspects of a performance, such as the CPU times, network rates, disk usage, etc. Each class has its own set of counters. Counter data is comprised of the current, minimum, maximum, and average values. You retrieve the list of counters available for a particular class from the vocabulary by specifying the class name as the criteria. Performance counters are stored as parameters in a vocabulary. Each counter has a category property that contains the name of the performance class this counter belongs to. The following is an example of a performance counter entry in a vocabulary:

<parameter>

  <id>counter_cpu_system</id>

  <category>counters_vz_cpu</category>

  <type>int</type>

  <value_type>1</value_type>

  <counter_type>2</counter_type>

  <short>System</short>

  <long>System CPU time</long>

  <measure>seconds</measure>

</parameter>

The following table describes the properties of a performance counter:

Property

Description

id

A string containing the unique counter identifier.

category

A string containing the name of the parent performance class (in general, the name of the parent vocabulary category).

type

A string specifying the data type of the counter values. The possible values are:

int -- integer.

float -- floating point.

value_type

A numeric representation of the counter data type (used internally by Agent).

counter_type

An integer representing the counter type. Depending on the type, the values of the counter can be interpreted differently:

0 -- Periodic counter. Contains the minimum, maximum, and average values for the given time period.

1 -- Incremental counter. The value of an incremental counter is always higher or equals to the previous value. A good example is a network counter that counts the number of bytes the interface has sent or received. The minimum, maximum, and average values are the same and represent the difference between the current value and the value from the previous report.

2 -- Cumulative counter. The minimum, maximum, and average values are the same and represent the total accumulated value since the server was started. On server restart, counter values are reset to zero.

short

Short counter description.

long

Long counter description.

measure

Units of measure (seconds, percent).

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