net-snmp System Memory Stats graph seems to be incorrect

While reviewing performance statistics on some of our servers, we noticed an anomaly with the System Memory Stats.  The "Used (Other)" value is showing as a negative value.

[cid:[email protected]]


I'm wondering if this is because the definition of "usedBytes" is not quite correct, as it does not take into consideration the swap.

usedBytes is currently defined as:

CDEF:usedBytes=memtotalrealBytes,membufferBytes,-,memcachedBytes,-,memsharedBytes,-,memavailrealBytes,- \


I thought maybe it should be the following, however, I'm starting to wonder now, if the issue is the memsharedBytes value is throwing the calculation out?

CDEF:usedBytes=memtotalrealBytes,memavailswapBytes,+,membufferBytes,-,memcachedBytes,-,memsharedBytes,-,memavailrealBytes,- \

All servers with graphs showing negative memory are running Oracle Linux 7.2, and net-snmp-5.7.2-24.  They are also Oracle Database servers


This is using the standard graph definition that comes with OpenNMS.  From netsnmp-graph.properties:


report.netsnmp.memStats.name=System Memory Stats
report.netsnmp.memStats.columns=memAvailSwap,memTotalReal,memAvailReal,memBuffer,memCached,memShared
report.netsnmp.memStats.type=nodeSnmp
report.netsnmp.memStats.suppress=netsnmp.memStatsNoShared
report.netsnmp.memStats.width=565
report.netsnmp.memStats.height=200
report.netsnmp.memStats.command=--title="System Memory Stats" \
--width 565 \
--height 200 \
--lower-limit 0 \
--base=1024 \
--vertical-label="Bytes" \
DEF:memavailswap={rrd1}:memAvailSwap:AVERAGE \
DEF:memtotalreal={rrd2}:memTotalReal:AVERAGE \
DEF:memavailreal={rrd3}:memAvailReal:AVERAGE \
DEF:membuffer={rrd4}:memBuffer:AVERAGE \
DEF:memcached={rrd5}:memCached:AVERAGE \
DEF:memshared={rrd6}:memShared:AVERAGE \
CDEF:memavailswapBytes=memavailswap,1024,* \
CDEF:memtotalrealBytes=memtotalreal,1024,* \
CDEF:memavailrealBytes=memavailreal,1024,* \
CDEF:membufferBytes=membuffer,1024,* \
CDEF:memcachedBytes=memcached,1024,* \
CDEF:memsharedBytes=memshared,UN,0,memshared,IF,1024,* \
CDEF:usedBytes=memtotalrealBytes,membufferBytes,-,memcachedBytes,-,memsharedBytes,-,memavailrealBytes,- \
AREA:usedBytes#c17d11:"Used (Other)" \
GPRINT:usedBytes:AVERAGE:"    Avg  \\: %8.2lf %s" \
GPRINT:usedBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:usedBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:membufferBytes#edd400:"IO Buff Ram " \
GPRINT:membufferBytes:AVERAGE:"    Avg  \\: %8.2lf %s" \
GPRINT:membufferBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:membufferBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:memsharedBytes#000a44:"Shared Mem    " \
GPRINT:memsharedBytes:AVERAGE:"  Avg  \\: %8.2lf %s" \
GPRINT:membufferBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:membufferBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:memsharedBytes#000a44:"Shared Mem    " \
GPRINT:memsharedBytes:AVERAGE:"  Avg  \\: %8.2lf %s" \
GPRINT:memsharedBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:memsharedBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:memcachedBytes#4e9a06:"Filesystem Cache" \
GPRINT:memcachedBytes:AVERAGE:"Avg  \\: %8.2lf %s" \
GPRINT:memcachedBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:memcachedBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:memavailrealBytes#8ae234:"Avail Real Mem" \
GPRINT:memavailrealBytes:AVERAGE:"  Avg  \\: %8.2lf %s" \
GPRINT:memavailrealBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:memavailrealBytes:MAX:"Max  \\: %8.2lf %s\\n" \
STACK:memavailswapBytes#cc0000:"Total Swap    " \
GPRINT:memavailswapBytes:AVERAGE:"  Avg  \\: %8.2lf %s" \
GPRINT:memavailswapBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:memavailswapBytes:MAX:"Max  \\: %8.2lf %s\\n" \
LINE2:memtotalrealBytes#204a87:"Total Real Mem" \
GPRINT:memtotalrealBytes:AVERAGE:"  Avg  \\: %8.2lf %s" \
GPRINT:memtotalrealBytes:MIN:"Min  \\: %8.2lf %s" \
GPRINT:memtotalrealBytes:MAX:"Max  \\: %8.2lf %s\\n"







Regards,

John Blackburn.

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