Does not track swap memory

[zamiang]

I've been investigating a memory leak potentially related to #134 but stumbled on another issue.

Many comments on #134 note that memory 'levels out' after a certain time. By comparing our memory usage from newrelic with that of heroku, we have noticed that memory does not flatten out - newrelic-node just doesn't track swap memory. In the graph below, we compare newrelic's memory monitoring with heroku's at https://dashboard-next.heroku.com/apps/#{app-name}/metrics/web

Memory drops are from deploying / restarting the app.

For some context, this node app is running express 3.4.7 on Heroku. Our app places a significant number of external http(s) requests before rendering a page. We are https only and use 2 2x dynos with 1gb of ram each. Newrelic log level is 'info'.

Please let me know if I can add anymore info. Will followup with a graph w/o newrelic-node install in a day or so.

[txase]

@zamiang I believe the chart you are looking at is in the "instances" dashboard. For further context of others who may be interested in knowing where this dashboard exists, this is only available for Heroku customers due to some extra integration we have with them.

You're right that we don't report memory in the same way as Heroku does. We can only report what the Node.js runtime tells us: http://nodejs.org/api/process.html#process_process_memoryusage. We use the value of the "rss" size. The rss size refers to the amount of physical memory used by the process, but it does not include the amount of swap memory used by the process. The other available values, related to the V8 heap size, are useful in their own ways, but do not provide the total memory usage either.

In the end, we are hamstrung by what the Node.js runtime can tell us. However, we should be more clear in the title of the graph that the chart only refers to physical memory rather than total memory used by the process. We will open an internal issue to resolve this discrepancy.

As an aside, we also have a server monitoring product that provides much more detailed insight on the memory used by applications running on each server. This is what some customers on ticket #134 were using when providing screenshots. Unfortunately, this product is incompatible with Heroku, so you will need to rely on Heroku's own monitoring.

If you would like further help with this issue, please contact http://support.newrelic.com. We are winding down our Github issues support, and we can provide a better experience through our dedicated support channel. We thank you for your understanding as we undergo this transition.