APMIA hostmonitoring extension reports two metrics which should have the same value:
However, their values differ and the Physical RAM:PercentUsed value is inconsistent with ratio of values of metrics Storage|Physical RAM:Used (MB) and Storage|Physical RAM:Size (MB).
The SystemEdge documentation does not explain the configuration sufficiently to determine exactly which SNMP OID values are collected to populate these metrics or how to deduce this from the various cf files.
Nor does the documentation explain whether some values are computed (such as these % metrics) or are simply collected from the operating system and reported as is. Thus it could be the error is in operating system, SystemEdge or hostmonitoring extensions processing of values collected.
The oid mapping is defined in the <hostmonitor-extension>/config/oid2metrics-linux.json. Seeing that the PercentUsed metric is retrieved directly from SNMP, not calculated by APMIA.
{
"oid": "1.3.6.1.2.1.25.2.3.1.8",
"groups": "storage",
"metricType": "IntAverage",
"metricName": "SystemEdge|{$HostName}|Storage|{TABLE:StorageName}:PercentUsed"
},
"Physical RAM" is listed as one of the storage devices is handled the same way as any other devices, so not controlled by APMIA.
As to why its value is different from the Memory usage metric, my guess is the usage in perspective of storage vs memory is probably not the same.
Q. Given that the OS must be providing incorrect value for Storage|Physical RAM:PercentUsed, can we the JSON OID mapping specified above to drop the metric?
A. It should be possible to remove an unwanted OID from the configuration. However seems this one is for all storage devices, not just "Physical RAM", so removing this OID will remove the corresponding metric for all other devices as well, which is not desired.