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After I upgraded a NodeJS server application from v6 to v14, I am facing with a strange memory behavior.

I noticed this issue (if it is) when I analyzed the memory usage using Dynatrace:

  1. the process gives no problems, nor restarts nor failure have been encountered: all is working fine

  2. the total memory usage increases constantly until it reaches about 5GB (we used --max-memory-restart 5G option when to run the application — who knows if it has something to do with it ...)

  3. the Heap size has its usual value and remains stable around 100~150MB

  4. the Resident Set grows constantly until it reaches 5GB and never broken this cap limit (furthermore: the restart security option features has been never triggered)

  5. I encounter this "issue" only in NodeJS v14, not in NodeJS v6, the application base-code is the same

Some details about memory usage here:

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I haven't a great knowledge about JS Engine V8 memory structure and usage, but I given a read to following lectures:

Despite these great lectures, I am not convinced at all what may causes this Resident Set memory growing int this way. Since it's not causing me any real problems, can I gloss over? Or should I deepen, if so, what do you advise me to do?

shogitai
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    If the heap size remains stable, then I wouldn't worry about the resident set if it's not causing you a problem. That's just an issue about when or if nodejs actually returns memory to the OS. As long as it isn't growing continually, then you have a stable situation without any long term leaks. – jfriend00 Dec 11 '20 at 19:19
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    When you mention V4 and V8, what version are you talking about? The nodejs version (which is now on v14/v15)? Or the internal Javascript interpreter version? The "V8" in your "A Tour of V8: Garbage Collection" is the name of the JS interpreter that Google builds and not really a version number. – jfriend00 Dec 11 '20 at 19:21
  • I may confused the versions of JS engines and NodeJS versions after the lectures: actually I was referring to the upgrade from NodeJS v6 to NodeJS v14. I have updated the answer, sorry and thanks for clarification. – shogitai Dec 13 '20 at 11:20

2 Answers2

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Within the v8 memory chart, Dynatrace does not only show the heap memory, it also compares it with the resident set size of the whole process. Some may find this confusing, but this helps tremendously to separate JS memory leaks from native memory leaks. In your case there seems to be a potential native memory leak that is caused by native modules.

You mentioned the --max-memory-restart parameter, so I guess you are using PM2. It's official documentation is not clear about whether the tool monitors just the memory used on the heap or overall memory usage. According to this article it seems that PM2 is not able to cover also native memory. Even more interesting are this bug report (closed but according to latest comments still not fixed) and the accepted answer to this question on Stack Overflow. It seems that even your version of PM2 may contain native memory leaks.

Here you can find more information on how to analyze a native memory leak in NodeJS. The accepted answer of the mentioned question from above lists also some links to alterntives for PM2.

By the way, Dynatrace will tell you if the increasing memory usage should have any measurable negtive effect on your services / applications or on end user experience.

rmunge
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I upgraded a NodeJS server application from V4 to V8. [...] I encounter this "issue" only in V8, not in V4

Clarification of terms: every version of Node has been built around the V8 JavaScript engine (which itself has versions which currently happen to be 8.x, but that's distinct from its name: earlier we had V8 v7.x, and soon we'll have V8 v9.x).

If you indeed mean that you just updated from Node version 4.x to Node version 8.x, then please just update further: at least to Node version 12.x, even better 14.x.

I'm not familiar with Dynatrace, but those graphs are a bit confusing. There is no such thing as "resident set size of the V8 heap memory": the overall process has a resident set size, and one part of what's in there is V8's heap memory. But since the latter apparently remains at ~150MB, it provides us no clue regarding the growth of the former. V8's garbage collection affects its heap, not the RSS. It's hard to guess what might be going on there, but...

Since it's not causing me any real problems, can I gloss over?

...sure. Let's use our collective time to fix problems that matter.

jmrk
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