How to limit node application memory size, and how to verify current memory usage and capacity? - node.js

Question

I want to customize node application memory size, also I want to add some middleware to record realtime application memory usage and capacity.
I know memory limit can be raised by setting --max-old-space-size to a maximum of ~1gb (32-bit) and ~1.7gb (64-bit)
Example:
node --max-old-space-size=1024 app.js
But when I use v8, how to verify memory capacity and usage?
Update:
I have used another approach to raise memory for app with v8.
const v8 = require('v8');
v8.setFlagsFromString('--max_old_space_size=2048');
This is log for HeapSpaceStatistics
########## v8.getHeapSpaceStatistics() ################
[
{
"space_name": "new_space",
"space_size": 1048576,
"space_used_size": 781704,
"space_available_size": 249464,
"physical_space_size": 798416
},
{
"space_name": "old_space",
"space_size": 18874368,
"space_used_size": 16844024,
"space_available_size": 270840,
"physical_space_size": 18772464
},
{
"space_name": "code_space",
"space_size": 4718592,
"space_used_size": 4344800,
"space_available_size": 95424,
"physical_space_size": 4586176
},
{
"space_name": "map_space",
"space_size": 1572864,
"space_used_size": 962104,
"space_available_size": 584648,
"physical_space_size": 1187888
},
{
"space_name": "large_object_space",
"space_size": 1626112,
"space_used_size": 1603664,
"space_available_size": 1471614464,
"physical_space_size": 1626112
}
]
I have set memory limit for 2GB, base on log, how to verify that?

Answer 1

The --trace_gc V8 option and process.memoryUsage() should give you good overall numbers
node --trace_gc --max_old_space_size=4096 -e '
let a = []
for( let i=1; i>0; i++){
a.push({ a: "testing" })
if ( i % 1000000 === 0 ) console.log("%j", process.memoryUsage())
if ( i % 10000000 === 0 ) console.log(v8.getHeapSpaceStatistics())
}
'
Note that the node process won't start at the set max_old_space_size size, but that will allow node to grow to the value. I don't believe V8 has the concept of setting a minimum old space size like the Java VM does.
Also note that the other memory spaces, like "new" and possibly "external" memory, are used on top of the old space size, so what you set for max_old_space_size is not the actual OS process memory limit. The OS value will likely be higher again.