Net-SNMP / 8.0-RELEASE - where did my Cached memory go?

R

roscoe

I use Cacti with FreeBSD 8.0 to monitor available memory among other things. I am using the built-in Cacti templates for

ucd/net - Memory - Buffers
ucd/net - Memory - Cache
ucd/net - Memory - Free

which polls the following SNMP MIBs:

UCD-SNMP-MIB::memShared.0 = INTEGER: 41928 kB
UCD-SNMP-MIB::memBuffer.0 = INTEGER: 113488 kB
UCD-SNMP-MIB::memCached.0 = INTEGER: 0 kB

Since upgrading to 8.0-RELEASE I've noticed the memCached always reads zero when polled. I never had this issue under 7.2.

Is this is a bug? "top" still shows a non-zero value for cached so I know it's not exhausted.

Thanks.
 
Do you have a value if you fire this command on your 8.x host
$ snmpwalk -v2c -c $YourSNMPComunity localhost .1.3.6.1.4.1.2021.4
$ snmpwalk -v2c -c $YourSNMPComunity localhost .1.3.6.1.4.1.2021.4.15

This is the OID .1.3.6.1.4.1.2021.4.15 Cacti use to query your missing Value.
To cross check fire the command with parameter -On and compare the OID.
 
Hi ohauer,

I tried the commands and here is the resulting output:

Code: 
# snmpwalk -v 2c -c 88VXR013 localhost .1.3.6.1.4.1.2021.4
UCD-SNMP-MIB::memIndex.0 = INTEGER: 0
UCD-SNMP-MIB::memErrorName.0 = STRING: swap
UCD-SNMP-MIB::memTotalSwap.0 = INTEGER: 1014576 kB
UCD-SNMP-MIB::memAvailSwap.0 = INTEGER: 1013812 kB
UCD-SNMP-MIB::memTotalReal.0 = INTEGER: 1035616 kB
UCD-SNMP-MIB::memAvailReal.0 = INTEGER: 224744 kB
UCD-SNMP-MIB::memTotalFree.0 = INTEGER: 398812 kB
UCD-SNMP-MIB::memMinimumSwap.0 = INTEGER: 16000 kB
UCD-SNMP-MIB::memShared.0 = INTEGER: 51156 kB
UCD-SNMP-MIB::memBuffer.0 = INTEGER: 113488 kB
[B]UCD-SNMP-MIB::memCached.0 = INTEGER: -12582912 kB[/B]
UCD-SNMP-MIB::memSwapError.0 = INTEGER: noError(0)
UCD-SNMP-MIB::memSwapErrorMsg.0 = STRING:

So that seems to be the offending value. It's odd how the value is sometimes negative, other times it's zero.

I always had valid values under 7.2. Restarting snmpd didn't seem to make a difference either.

I've decided to abandon SNMP and take the sysctl hardware counters route to plot the FreeBSD memory information for Cacti.

Thanks,
Roscoe
 
Just curious, is anyone else able to replicate this issue under 8.0? How about under 7.2?

Try ohauer's command and see if you get a negative value for memCached.

Code: 
$ snmpwalk -v2c -c $YourSNMPComunity localhost .1.3.6.1.4.1.2021.4

Thanks,
Roscoe
 
I've just tested 8.0 (amd64) in a VM with 512MB ram and my actual 7.2 (i386) machine.
net-snmp for the 8.0 machine was installed via pkg_add -r (version is net-snmp-5.4.2.1_6).

Maybe it is an overflow, can you file a PR?

7.2-RELEASE-p6 (i386, net-snmp-5.4.2.1_6)
Code: 
# snmpwalk -v2c -c $COMMUNITY localhost .1.3.6.1.4.1.2021.4
UCD-SNMP-MIB::memIndex.0 = INTEGER: 0
UCD-SNMP-MIB::memErrorName.0 = STRING: swap
UCD-SNMP-MIB::memTotalSwap.0 = INTEGER: 4194176 kB
UCD-SNMP-MIB::memAvailSwap.0 = INTEGER: 4194176 kB
UCD-SNMP-MIB::memTotalReal.0 = INTEGER: 2611604 kB
UCD-SNMP-MIB::memAvailReal.0 = INTEGER: 119416 kB
UCD-SNMP-MIB::memTotalFree.0 = INTEGER: 637840 kB
UCD-SNMP-MIB::memMinimumSwap.0 = INTEGER: 16000 kB
UCD-SNMP-MIB::memShared.0 = INTEGER: 49044 kB
UCD-SNMP-MIB::memBuffer.0 = INTEGER: 114880 kB
UCD-SNMP-MIB::memCached.0 = INTEGER: 42808 kB
UCD-SNMP-MIB::memSwapError.0 = INTEGER: noError(0)
UCD-SNMP-MIB::memSwapErrorMsg.0 = STRING:

8.0-RELEASE-p2 (amd64, net-snmp-5.4.2.1_6 after a 'find /')
Code: 
# snmpwalk -v2c -c $COMMUNITY 10.6.16.251 .1.3.6.1.4.1.2021.4
UCD-SNMP-MIB::memIndex.0 = INTEGER: 0
UCD-SNMP-MIB::memErrorName.0 = STRING: swap
UCD-SNMP-MIB::memTotalSwap.0 = INTEGER: 1008544 kB
UCD-SNMP-MIB::memAvailSwap.0 = INTEGER: 1008544 kB
UCD-SNMP-MIB::memTotalReal.0 = INTEGER: 510220 kB
UCD-SNMP-MIB::memAvailReal.0 = INTEGER: 444096 kB
UCD-SNMP-MIB::memTotalFree.0 = INTEGER: 208024 kB
UCD-SNMP-MIB::memMinimumSwap.0 = INTEGER: 16000 kB
UCD-SNMP-MIB::memShared.0 = INTEGER: 5524 kB
UCD-SNMP-MIB::memBuffer.0 = INTEGER: 31440 kB
UCD-SNMP-MIB::memCached.0 = INTEGER: 925822976 kB
UCD-SNMP-MIB::memSwapError.0 = INTEGER: noError(0)
UCD-SNMP-MIB::memSwapErrorMsg.0 = STRING:
 
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