# Pointer-Like Index Property Extender

The Pointer-Like Index property extender makes it possible to use the value of an attribute from the target MIB table as the index into the source MIB table. Unlike the Index Split and Regex extenders, this extender class does not require the target and source MIB tables to share any index components.

## When to Use the Pointer-Like Index Property Extender

The Pointer-Like Index property extender is useful when the target MIB table contains a column whose value can be used as an index into the source MIB table. For example, the Cisco Process MIB’s `cpmCPUTotalTable` has its own index that is not shared with any other tables, but its `cpmCPUTotalPhysicalIndex` column contains an integer which can be used as an index into the `entPhysicalTable`.

``````cpmCPUTotalEntry OBJECT-TYPE
-- ...
DESCRIPTION
table come and go as CPUs are added and removed from the
system."
INDEX           { cpmCPUTotalIndex } (1)
-- ...

cpmCPUTotalPhysicalIndex OBJECT-TYPE (2)
-- ...
DESCRIPTION
"The entPhysicalIndex of the physical entity for which
the CPU statistics in this entry are maintained.
The physical entity can be a CPU chip, a group of CPUs,
a CPU card etc. The exact type of this entity is described by
its entPhysicalVendorType value. If the CPU statistics
in this entry correspond to more than one physical entity
(or to no physical entity), or if the entPhysicalTable is
not supported on the SNMP agent, the value of this object
must be zero."
-- ...

entPhysicalEntry       OBJECT-TYPE
-- ...
DESCRIPTION
"Information about a particular physical entity.

Each entry provides objects (entPhysicalDescr,
entPhysicalVendorType, and entPhysicalClass) to help an NMS
identify and characterize the entry, and objects
(entPhysicalContainedIn and entPhysicalParentRelPos) to help
an NMS relate the particular entry to other entries in this
table."
INDEX   { entPhysicalIndex } (3)
-- ...``````
 1 The `cpmCPUTotalTable` entry type is indexed on `cpmCPUTotalIndex`, which has no meaning outside this table. 2 The `cpmCPUTotalPhysicalIndex` column contains a value of `entPhysicalIndex` that corresponds to the CPU referenced in a given row. 3 The `entPhysicalTable` entry type is indexed on `entPhysicalIndex` and provides many useful textual columns.

By treating `cpmCPUTotalPhysicalIndex` somewhat like a pointer, it’s possible to import string properties from the `entPhysicalTable` for use in the resource label.

 Some combinations of Cisco hardware and software appear to use values of `cpmCPUTotalIndex` that are directly interchangeable with `entPhysicalIndex`. This relationship does not hold across all product lines or software revisions.

## Configure the Pointer-Like Index Property Extender

The Pointer-Like Index property extender expects three parameters, all of which are required:

Table 1. Pointer-Like Index Property Extender Parameters
Name Description

source-type

The name of the `resourceType` associated with the source MIB table.

source-attribute

The alias name of the string property to import from the source MIB table.

target-index-pointer-column

The alias name of the column in the target MIB table whose value may be used as an index into the source MIB table.

This example shows how to use `cpmCPUTotalPhysicalIndex` as a pointer-like index into the `entPhysicalTable`. The target resource gains a pair of string properties, which we will call `cpmCPUTotalName` and `cpmCPUTotalDescr`.

``````<resourceType name="entPhysicalEntry" label="Physical Entity" resourceLabel="${entPhysicalName} (${entPhysicalDescr}))">
<persistenceSelectorStrategy class="org.opennms.netmgt.collection.support.PersistAllSelectorStrategy"/>
<storageStrategy class="org.opennms.netmgt.collection.support.IndexStorageStrategy"/>
</resourceType>

<resourceType name="cpmCPUTotalEntry" label="Cisco CPU Total" resourceLabel="${cpmCPUTotalName} (${cpmCPUTotalDescr})">
<persistenceSelectorStrategy class="org.opennms.netmgt.collection.support.PersistAllSelectorStrategy" />
<storageStrategy class="org.opennms.netmgt.collection.support.IndexStorageStrategy" />
</resourceType>

<groups>
<group name="entity-physical-table" ifType="all">
<mibObj oid=".1.3.6.1.2.1.47.1.1.1.1.2" instance="entPhysicalEntry" alias="entPhysicalDescr" type="string"/> (1)
<mibObj oid=".1.3.6.1.2.1.47.1.1.1.1.7" instance="entPhysicalEntry" alias="entPhysicalName" type="string"/>
</group>

<group name="cpm-cpu-total" ifType="all">
<mibObj oid=".1.3.6.1.4.1.9.9.109.1.1.1.1.2"  instance="cpmCPUTotalEntry" alias="cpmCPUTotalPhysicalIndex" type="string" /> (2)
<mibObj oid=".1.3.6.1.4.1.9.9.109.1.1.1.1.8"  instance="cpmCPUTotalEntry" alias="cpmCPUTotal5minRev" type="gauge" />
<property instance="cpmCPUTotalEntry" alias="cpmCPUTotalName" class-name="org.opennms.netmgt.collectd.PointerLikeIndexPropertyExtender"> (3)
<parameter key="source-type" value="entPhysicalEntry"/>
<parameter key="source-attribute" value="entPhysicalName"/>
<parameter key="target-index-pointer-column" value="cpmCPUTotalPhysicalIndex"/>
</property>
<property instance="cpmCPUTotalEntry" alias="cpmCPUTotalDescr" class-name="org.opennms.netmgt.collectd.PointerLikeIndexPropertyExtender"> (4)
<parameter key="source-type" value="entPhysicalEntry"/>
<parameter key="source-attribute" value="entPhysicalDescr"/>
<parameter key="target-index-pointer-column" value="cpmCPUTotalPhysicalIndex"/>
</property>
</group>
</groups>``````
 1 First we collect `entPhysicalDescr` and `entPhysicalName` in the source group, which uses a resource type associated with the `entPhysicalTable`. 2 Then we collect the pointer-like `cpmCPUTotalPhysicalIndex` in the target group, whose resource type is associated with the `cpmCPUTotalTable`. 3 We derive `cpmCPUTotalName` in the target group, telling the extender to use the pointer-like property’s value as an index into the source table, and specifying that we want to use the source attribute `entPhysicalName`. 4 Deriving `cpmCPUTotalDescr` is almost identical, except that this time we use the value of `entPhysicalDescr`.