Memory check against resident memory is wrong

[Sirtea]

Hi,

According to m202 course, in memory model section, resident memory is not a good metric for memory usage, because is not freed, although it's not used.

db.serverStatus().mem
{
"bits" : 32,
"resident" : 31,
"virtual" : 211,
"supported" : true,
"mapped" : 80
}

Please consider looking at workingSet pages to get a more real approximation

db.serverStatus({workingSet:1}).workingSet
{
"note" : "thisIsAnEstimate",
"pagesInMemory" : 5,
"computationTimeMicros" : 15064,
"overSeconds" : 417
}

This means that this empty instance is consuming 5 pages of memory (4kb each, for a 20kb total memory usage), but memory check is reporting 31mb. The numbers are more dramatic in our production systems.

Regards